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SYNTHESIS OF AMPHIPHILIC BLOCK COPOLYMERS

AND THE GENERATION OF NANOPARTICLES OF Au

& Ag IN THEIR MICELLAR COMPARTMENTS

IMAD UD-DIN

DEPARTMENT OF CHEMISTRY HAZARA

UNIVERSITY MANSEHRA 2015

SYNTHESIS OF AMPHIPHILIC BLOCK COPOLYMERS

AND THE GENERATION OF NANOPARTICLES OF Au

& Ag IN THEIR MICELLAR COMPARTMENTS

By

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IMAD UD-DIN

A dissertation submitted in Partial fulfillment of the

requirement for the degree of

Doctor of Philosophy

in

Chemistry

DEPARTMENT OF CHEMISTRY HAZARA

UNIVERSITY MANSEHRA 2015

SYNTHESIS OF AMPHIPHILIC BLOCK COPOLYMERS

AND THE GENERATION OF NANOPARTICLES OF Au

& Ag IN THEIR MICELLAR COMPARTMENTS

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CERTIFICATE

Certified that the work contained in this dissertation is carried out by Mr. Imadud Din under our

supervision from the Department of Chemistry, Hazara University Mansehra, Pakistan and

approved as to style and content.

_______________________ ________________________

Dr. Mohsan Nawaz Dr. Musa Kaleem Baloch

Supervisor Co-Supervisor

Department of Chemistry Department of Chemistry

Hazara University Gomal University

Mansehra, KPK, Pakistan D.I. Khan, KPK, Pakistan

________________________

Dr. Mohsan Nawaz

Head,

Department of Chemistry

Hazara University,

Mansehra, KPK, Pakistan

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Declaration

I declare that any material in this thesis which is not my own work has been identified and that no

material has previously been submitted and approved for the award of a degree by this or any other

university.

Signature:___________________

Author’s Name: Imad Ud Din

It is certified that the work in this thesis is carried out and completed under our supervision.

Supervisor

Prof. Dr. Mohsan Nawaz

Department of Chemistry

Hazara University, Mansehra

Co-Supervisor:

Prof. Dr. Musa Kaleem Baloch

Department of Chemistry, Gomal

University, D.I. Khan

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Dedication

This dissertation is dedicated to my Parents and my respectable Supervisor Dr.

Mohsan Nawaz, great admirers of higher education.

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LIST OF PUBLICATIONS

1.Mohsan Nawaz, ImadUd-Din, Gareth Price and Musa KaleemBaloch. “Preparation of gold

nanoparticles in polystyrene–PEO block copolymers: the role of ultrasound” Journal of Polymer

Research (2014) 21:495.DOI 10.1007/s10965-014-0495-3.

2.Muhammad Siddiq, Imad-Ud-Din, Mohsan Nawaz*, WajidRehman**, IramBibi, Abbas Khan

and Bakhtiar Muhammad. “Self Assemble Behavior of Poly (Oxybutylene-Oxyethylene)

(BmEnBm) Triblock Copolymer in Solution” Journal of Chemical Society Pakistan. Vol. 36, No.

2,(2014).

3.MohsanNawaz , Musa KaleemBaloch, Gareth James Price, ImadUd-Din, El-Sayed ElBadawey

and El-Mossalamy. “Synthesis, association and surface morphology of poly (ethylene oxide)-

polystyrene block copolymer” Journal of Polymer Research (2013) 20:180. DOI

10.1007/s10965-013-0180-y.

4.Muhammad Waseem, SajidaMunsif, Umer Rashid and Imad-ud-Din, “Physical properties of aFe2O3

nanoparticles fabricated by modified hydrolysis technique” Journal of applied science(2013).DOI

10.1007/s13204-013-0240-y.

5. Imad-Ud-Din1, Mohsan Nawaz1, Rukhsana BiBi1, Gareth James Price2, Musa Kaleem Baloch3

and Rasheed Ahmad4 “Self Assembly and Thermal Behavior of Amphiphilic Di-block Copolymers of

Poly(methyl methacrylate)-block-Poly(Ethylene Oxide) (PMMA-b-PEO)”.Journalof Polymer

Research (Under review 2014).

6. Imad-Ud-Din1, Mohsan Nawaz1, Rukhsana BiBi1, Gareth James Price2, Musa Kaleem Baloch3

and Rasheed Ahmad4 “Self Assembly and Thermal Behavior of Amphiphilic Di-block Copolymers of

Poly(styrene)-block-Poly(Ethylene Oxide) (PS-b-PEO)”.Journalof Polymer Research (Under review

2014).

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PREFACE

Amphiphilic block copolymers polystyrene-block-polyethylene oxide and polymethyl methacrylate-block-

polyethylene oxide has attracted the focus of many researchers because of the lower cost, easy

availability, high hydrophilicity and higher thermal stability. Block copolymer of polyethylene oxide (PEO)

corona with hydrophobic and biodegradable polystyrene is very attractive due to its bio compatibility.

Amphiphilic block copolymers having hydrophilic and hydrophobic blocks have a wide range of

applications in different fields’ e.g pharmaceutical, environmental, cosmetics, agricultural and detergent

formulations. Polystyrene-blockpolyethylene oxide has its applications as emulsion stabilizers,

In the present work, synthesis of amphiphilic blocks copolymers and the generation of nanoparticles of

Au & Ag in their micellar compartments have been carried out. The main emphases were on the

preparation of Macroinitiator, Polymerization of styrene The whole research work has been demarcated

into three chapters. Chapter 1 provides a overview of polymers, amphiphilic block copolymers, block

copolymers, Atom transfer free radicals (ATRP) polymerizations and their applications and a review about

them. Chapter 2 represents details of the materials, characterization, processing and synthesis of block

copolymers, preparation of macroinitiator and synthesis of gold and silver nanoparticles. The sequence

used for the structural, morphological, electrical and thermal characterization is also included. While

chapter 3, comprises of results and discussion for the synthesis of polystyrene-block-polyethylene oxide

and polymethyl methacrylate-block-polyethylene oxide. Detail analysis of the developed material was

carried out using various analytical techniques.

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ACKNOWLEDGEMENT

First of all, I would like to pay my deepest gratitude to Almighty ALLAH, WHO blessed me with

motivation and strength for completing my PhD research. Peace and blessings of Allah be upon the Holy

Prophet Muhammad (Peace be upon Him) and his virtuous progeny, who is a source of guidance and

knowledge for humanity.

After that, it would be a great honor for me to offer profound and cordial gratitude to my supervisor Dr.

Mohsan Nawaz and co-supervisor Prof. Dr. Musa Kaleem Baloch for their kind and encouraging

behavior throughout my PhD. They were always there for any advice, guidance, and recommendation. I

am very grateful to them for their privileges, which were awarded to me during the project.

I would like to extend my gratitude to Prof. Dr. Gareth James Price who provided me the opportunity

to work at the Laboratory in 1 South Chemistry Research lab 0.50, Department of Chemistry University of

Bath, UK. Appreciation is extended to Dr. John Lowe and Orsella Potter for their help and support

during my work at University of Bath, UK.

My appreciation also goes to Prof. Dr. Bakhtiar Muhammad registrar Hazara University, Prof. Dr.

Khalid Mehmood, Chairman Department of Chemistry and Prof. Dr. Habib Ahmad Dean faculty of

Science Hazara University for their helpful discussions and technical advice.

I am also thankful to my valuable friends, Dr. Sahib Gul Afridi, Muhammad Tariq, Amjad Ali,

Shakeel, Zafar Iqbal, Shah Faisal, Rahat Ali and Irfan Saif for their all-time support and

encouragement. Thanks also go to my all friends of past and present. I express my sincere gratitude to

colleagues at University of Bath UK, Emily, Cecelia, Judith Brown and Jamie.

I would like to thank my family for their love and cooperation, especially to my father Shah

Hosh Khan and my brother Muhammad Ismail Khan being a great admirer of Higher Education. He

always encourage me and provide full support to pursue my doctoral studies. Last but not least very

special thanks go to my parents, brothers and Sisters for their love and support all times.

I acknowledge management of Hazara University Mansehra, for facilitating me to pursue doctoral

studies. I am also very much thankful to the Higher education commission (HEC) of Pakistan. This

research would not have been possible without the financial support provided by the Higher Education

Commission (HEC), Pakistan, under the National Research Programme for Universities (NRPU) and

International Research Support Initiative Program (IRSIP). Imad Ud Din

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ABSTRACT Synthesis of block copolymers is of great interest due to their abilities to self-assemble into a variety of

structured, ordered, or partially ordered morphologies, and variety of applications. Three samples of

poly(styrene)-block-poly(ethylene oxide) (PS-b-PEO) and three samples of poly(methylmethacryolate)-

block-poly(ethylene oxide) (PMMA-b-PEO) were synthesized by atom transfer radical polymerization

(ATRP) technique using monofunctional PEO macroinitiator (mPEO-F) as starting material. The

composition of the copolymer was obtained through NMR spectroscopy, whereas the molecular mass

and degree of dispersity from light scattering and GPC/SEC. The CMC was obtained from the dependence

of hydrodynamic radius (RH) over the concentration and found that it was decreased with contents of

polystyrene and temperature. The dependence of hydrodynamic radius on the concentration also

indicated that shape of micelles change after a particular concentration of the block copolymer. The

reduced viscosity data plotted against concentration did not show a simple straight line as expected in

the case of polymers; rather, its slope was changed at a particular concentration, indicating sudden

variation in the self-assembling behavior of the copolymers. The transmission electron microscopic

results of the material indicated the morphology pattern of two-dimensional arrays of hexagons with

holes.

This work reports the preparation of ordered arrays of gold and silver nanoparticles by sonochemically

enhanced borohydride reduction of precursor lithium tetrachloroaurate (LiAuCl4) and (AgNO3)

incorporated into the core of polymeric micelles formed from amphiphilic block copolymers of

polystyrene (PS) and poly(ethylene oxide) (PEO) and (PMMA). The copolymers were prepared with

varying styrene and methylmethacryolate block lengths from a PEO macroinitiator by atom transfer

radical polymerization (ATRP). UV/visible spectroscopy were used to confirm the formation of elemental

gold and silver. The effect of sonication time on the appearance of the gold and silver nanoparticles was

determined and showed that the absorbance first increased as the nanoparticles formed but decreased

at longer times, presumably as a result of a degree of agglomeration. Transmission electron microscopy

and Scanning electronic microscopy revealed the morphology of the nanocomposites which confirmed

that micellar polystyrene-block-polyethylene oxide and polymethylmethacryolateblock-polyethylene

oxide is an excellent vehicle for the formation of well-defined films containing nanoparticulate gold and

silver. However, we report for the first time that care must be taken to optimize the preparation time to

obtain the desired particle sizes because this parameter is very sensitive to the duration over which

sonication is carried out.

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LIST OF FIGURES

Page No Figure.1.1: General Structure of polymer 2

Figure 1.2: Simplest amphiphilic molecule. 6

Figure 1.3: Biological materials 15

Figure 1.3: Scheme of the formation of nanoparticles in a block copolymer micelle. 22

Figure 3.1: 1H NMR spectrum of polystyrene88-block-polyethylene oxide113 35

Figure 3.2: 1HNMR Spectrum of polymethylmethacrylate50-block-polyethylene

oxide113 37

Figure 3.3: FT-IR spectra of PS and PEO homopolymer standards. 38

Figure 3.4: FT-IR Curve of Amphiphilic Diblock copolymer PS61-b-PEO113 39

Figure 3.5: FT-IR spectra of PMMA homopolymer standard. 39

Figure 3.6: FT-IR spectra of amphiphilic block copolymer PMMA50-b-PEO113. 40

Figure 3.7: A typical Zimm plot of PS61-b-PEO113 block copolymer dissolved in

THF and measured at 25 °C. 41

Figure 3.8: A typical autocorrelation functions obtained for PS61-b-PEO113

copolymer. 42

Figure 3.9: Hydrodynamic radius as a function of concentration of copolymer and

contents of polystyrene in the copolymer. The insertion shows the same data

for dilute concentration. 43

Figure 3.10: CMC of block copolymers as a function of temperature. 43

Figure 3.11: A typical autocorrelation functions obtained for PMMA50-b-PEO113

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Copolymer in water. 44

Figure 3.12: Apparent hydrodynamic radius (RH) as a function of Temperature (K)

for PMMA-b-PEO of amphiphilic diblock copolymer. 45

Figure 3.13: GPC traces of samples of block copolymers PS-b-PEO. 46

Figure 3.14: GPC traces of samples of PMMA-b-PEO diblock copolymer.

Figure 3.15: Variation of relative viscosity with concentration of amphiphilic

block copolymers PS-b-PEO having different PS block length

46

and measured at 30°C.

Figure 3.16: Slopes of plots of relative viscosity versus concentration as

47

a function of temperature for PS-b-PEO block copolymers.

Figure 3.17: Reduced viscosities of block copolymers as a function

48

of concentration measured at 20 °C for PS-b-PEO. 49

Figure 3.18: Intrinsic viscosities of copolymers as a function of temperature. 49

Figure 3.19: Variation in relative viscosity with concentration of block copolymers

at 30 oC.

Figure 3.20: Variation in reduced viscosity with concentration of block copolymers

51

at 20 oC. 51

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Figure 3.21: Plots of Huggins’s constant values of three block copolymer PMMA-b-PEO

versus temperature. 52

Figure 3.22: Plots of Intrinsic viscosity values of three block copolymer PMMA-b-PEO

versus temperatures. 52

Figure 3.23: TEM micrographs of PEO61-b-PS113 di-block copolymer casted from

1-wt.% toluene solution onto carbon coated copper grids and stained with osmium

tetraoxide (a) at low magnification (b) at high magnification. 53

Figure 3.24: TEM micrographs of mixture of PS and PEO (50:50) stained with osmium

tetraoxide. 54

Figure 3.25: TEM micrographs of mixture of PS and PEO (50:50) stained with

phosphotungstic acid. 55

Figure 3.26: DSC heat scans of diblock copolymer PS61-b-PEO113 56

Figure 3.27: DSC heat scans of diblock copolymer PS72-b-PEO113. 56

Figure 3.28: DSC heat scans of diblock copolymer PS88-b-PEO113. 57

Figure 3.29: DSC heat scans of diblock copolymer PMMA7-b-PEO113. 57

Figure 3.30: DSC heat scans of diblock copolymer PMMA20-b-PEO113. 58

Figure 3.31: DSC heat scans of diblock copolymer PMMA50-b-PEO113. 58

Figure 3.32: TGA and DTA thermograms of amphiphilic block copolymer PS-b-PEO. 60

Figure 3.33: TGA and DTA thermograms of amphiphilic block copolymer

PMMA-b-PEO. 60

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Figure 3.34: Master curves of G' and G" as a function of frequency for the diblock copolymer

(A) PS88-b-PEO113 (B) PS72-b-PEO113 (C) PS61-b-PEO113. 62

Figure 3.35: Master curves of G' and G" as a function of frequency for diblock copolymer

(A) PMMA50-b-PEO113 (B) PMMA20-b-PEO113

(C) PMMA7-b-PEO113. 62

Figure 3.36: 600 MHz 2D DOSY NMR spectra obtained at 298 K for the standard PEO solution in

CDCl3. 65

Figure 3.37: 600 MHz 2D DOSY NMR spectra obtained at 298 K for the standard PS

solution in CDCl3. 66

Figure 3.38: 600 MHz 2D DOSY NMR spectra obtained at 298 K for the copolymer

PS61-b-PEO113 solution in CDCl3. 67

Figure 3.39: 600 MHz 2D DOSY NMR spectra obtained at 298 K for standard PMMA

solution in CDCl3. 68

Figure 3.40: 600 MHz 2D DOSY NMR spectra obtained at 298 K for copolymer

PMMA50-b-PEO113 solution in CDCl3. 69

Figure 3.41: Determination of the CMC for PS61-b-PEO113 from DOSY NMR

Measurements. 70

Figure 3.42: Determination of the CMC for PMMA50-b-PEO113 from DOSY NMR

Measurements. 71

Figure 3.43: Fluorescence emission spectra of diblock copolymer PS61-b-PEO113 at

indicated concentrations in aqueous solutions using pyrene (6*10-7 M) as

hydrophobic fluorescent probe. 72

Figure 3.44: Fluorescence emission spectra of diblock copolymer PMMA50-b-PEO113

at indicated concentrations in aqueous solutions using pyrene (6*10-7 M) as

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hydrophobic fluorescent probe. 73

Figure 3.45: Fluorescence emission spectra of pyrene (6*10-7 M) in aqueous solutions

1.1g/L (concentrated) and 0.3 g/L (Dilute) concentration of diblock

copolymer. 73

Figure 3.46: Determination of the CMC by fluorimetry measurements of the block

copolymer PS61-b-PEO113. 74

Figure 3.47: Determination of the CMC by fluorimetry measurements of the block

copolymer PMMA50-b-PEO113. 74

Figure 3.48: Plots of Surface tension as a function of concentration for PS61-b-PEO113

at different temperatures (♦) 293K, (■) 303K, (▲) 313, (x) 323K. 76 Figure 3.49:

Plots of Surface tension as a function of concentration for PMMA50-b-PEO113 at

different temperatures (♦) 293K,(■)303K, (▲)313K, (x)323K. 76

Figure 3.50: Plots of lnCMC of both block copolymers (▲) PS61-b-PEO113 and

(♦) PMMA50-b-PEO113 as a function of inverse temperature according

to Arrhenius equation for the determination of thermodynamic and surface

parameters. 77

Figure 3.51: Absorbance spectra for gold nanoparticles in PS61-b-PEO113 during

sonochemical borohydride reduction. 81

Figure 3.52: Colour of the samples at different sonication times before and after the

formation of gold nanoparticles. 82

Figure 3.53: Absorbance spectra for gold nanoparticles in PS61-b-PEO113 at different

times after sonication; the inset shows the absorbance just after the formation

of nanoparticles at two different loading ratios of gold: ethylene oxide. 83

Figure 3.54: Absorbance spectra for gold nanoparticles in PS72-b-PEO113 at different

times after sonication; the inset shows the absorbance just after the formation

of nanoparticles at two different loading ratios of gold: ethylene oxide. 83

Figure 3.55: Absorbance spectra for gold nanoparticles in PS88-b-PEO113 at different

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times after sonication; the inset shows the absorbance just after the formation

of nanoparticles at two different loading ratios of gold: ethylene oxide. 84

Figure 3.56: Absorbance spectra for gold nanoparticles in PMMA-b-PEO at different

times after sonication. 84

Figure 3.57: Absorbance spectra for gold nanoparticles in PVP at different times after

Sonication. 85

Figure 3.58: TEM image for Au nanoparticles in block copolymers (a) PS61-b-PEO113,

(b) PS72-b-PEO113, (c) PS88-b-PEO113. 86

Figure 3.59: TEM images for Au nanoparticles in block copolymers

(a) PMMA7-b-PEO113 (b) PMM20-b-PEO113 (c) PMMA50-b-PEO113. 86

Figure 3.60: TEM image for Au nanoparticles in PEO. 87

Figure 3.61: SEM image for Au nanoparticles in a block copolymers (a) PS61-b-PEO113,

(b) PS72-b-PEO113, (c) PS88-b-PEO113. 88

Figure 3.62: SEM image for Au nanoparticles in a block copolymers

(a)PMMA7-b-PEO17(b)PMM20-b-PEO45(c)PMMA50-b-PEO113. 88

Figure 3.63: Absorbance spectra for silver nanoparticles in PS61-b-PEO113 after 1h

sonication before the addition of sodium borohydride reduction the inset

shows the colour just after the 1h sonication. 89

Figure 3.64: Absorbance spectra for silver nanoparticles in PS61-b-PEO113 for 1h

sonication after addition of sodium borohydride, the inset shows the colour

of the solution just after the 1h sonication. 90

Figure 3.65: Colour of the samples at different sonication times before and after the

formation of silver nanoparticles. 91

Figure 3.66: Absorbance spectra for silver nanoparticles at different sonication times

of PS-b-PEO diblock copolymer. 92

Figure 3.67: Absorbance spectra for silver nanoparticles at different sonication times

of PMMA-b-PEO diblock copolymer. 92

Figure 3.68: TEM image for Ag nanoparticles in a block copolymers (a) PS61-b-PEO113

(b) PS72-b-PEO113(c) PS88-b-PEO113. 93

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Figure 3.69: SEM image for Ag nanoparticles in a block copolymers

(a) PMMA7-b-PEO17 (b) PMM20-b-PEO45 (c) PMMA50-b-PEO113. 94

Figure 3.70: SEM image for Ag nanoparticles in a block copolymers (a) PS61-b-PEO113,

(b) PS72-b-PEO113, (c) PS88-b-PEO113. 94

Figure 3.71: SEM image for Ag nanoparticles in a block copolymers

(a) PMMA7-b-PEO17 (b) PMM20-b-PEO45 (c) PMMA50-b-PEO113. 95

LIST OF TABLES

Page No Table 3.1: Molecular weight, degree of dispersity of the samples of the copolymers. 47

Table 3.2: Tg and ∆H values of all polymer samples of PS-b-PEO and PMMA-b-PEO

Determine from DSC measurements. 59

Table 3.3: Diffusion analysis of PS61-b-PEO113 block copolymer 67

Table 3.4: Diffusion analysis of PMMA50-b-PEO113 block copolymer 70

Table 3.5: The critical micelle concentration (CMC) and thermodynamic parameters of

micellization, interfacial area per molecule, surface excess concentration and Gibbs free

energy of adsorption at various temperatures for of PS61-b-PEO113 in

toluene. 79

Table 3.6: The critical micelle concentration (CMC) and thermodynamic parameters of

micellization, interfacial area per molecule, surface excess concentration and Gibbs free

energy of adsorption at various temperatures for of PMMA50-b-PEO113

in toluene. 79

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LIST OF ABBREVIATION

PEO Polyethylene Oxide

MePEO Macroinitiators of Polyethylene Oxide

PMMA Polymethyl methacrylate

ATRP Atom Transfer free Radical Polymerization

1H NMR Proton Nuclear Magnetic Resonance

GPC Gel Permeation Chromatography

SEC Size Exclusion Chromatography

TGA Thermal gravimetric Analysis

DTA Differential Thermal Analysis

DSC Differential Scanning Calariometry

Tg Glass Transition Temperature

CMC Critical Micelle Concentration

LLS Laser Light Scattering

DLS Dynamic Light Scattering

SLS Static Light Scattering

DOSY Diffusion Ordered Spectroscopy

FTIR Fourier Transform Infra Red Spectroscopy

UV Ultra Violet

TEM Transmission Electronic Microscopy

Bipy Bipyredine

PS-b-PEO Polystyrene-block-polyethylene

PMMA-b-PEO Polymethyl methacrylate-block-Polyethylene Oxide

RI Refractive Index

THF Tetra Hydrofurane

G' Storage modulus

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G'' Loss modulus MMA Methyl methacrylate

RH,app Apparent Hydrodynamic Radius PDI Polydispersity Index ω*

Characteristic Frequency

ΔGmic Gibbs free energy of Micellization

ΔHmic Enthalpy of micellization

ΔSmic Entropy of micellization

Ao Area per molecule Ґ

Surface Excess Concentration

ΔGads Gibbs free energy of adsorption

KH Huggins Constant

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CHAPTER-1 INTRODUCTION

1.1 Polymer Polymers, just try to imagine modern life without them. No clothes, no cars, no

computers, no glue, no television, the list is endless. But there’s more than that. Try to

imagine life itself without polymers. In fact, without polymers Earth would be just

another lump of bare, dead rock flying through the universe. DNA, the database of life,

and proteins, the compounds that regulate all the chemical processes in a living being,

are natural polymers. Wood, fur, cotton, all these materials are composed of natural

polymers. Ever since man has discovered the fascinating properties of polymers, even

without having the slightest idea of what they exactly where, he used them in daily life.

Moreover, being as a brilliant creature, man made attempts to modify these materials

to improve their properties, and later on succeeded in passing by Mother Nature and

created fully synthetic polymers, although at that time the exact structure of these

compounds was still a mystery. The first completely synthetic polymer was

commercialized in 1910 under the trade name Bakelite. It took some ten years more

however, before Staudinger [1] postulated that natural and synthetic polymers are big

molecules which composed of small, covalently bonded molecules, and that polymers

differ from “ordinary” molecules primarily only in size. This is also where the name

polymer stems from, which is derived from Greek and literally means many parts. Since

then, synthetic polymer chemistry and polymer technology has taken on a high flight,

and polymers evolved from the poor man’s cheap replacement for natural fibers etc, to

a high-tech material with properties far beyond the reach of traditional materials like

metals, wood and ceramics [2].

A polymer is a large but a single chain-like molecule in which the repeating units are

derived from small molecules called monomers. These monomers are bound together to

form polymers. The process by which monomers are transformed in to a polymer is

called polymerization. The number of monomers which are joined together in a polymer

is called the degree of polymerization [3].

A polymer always has a repeating structure or a monomer while a

macromolecule may or may not have such a unit

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There are many natural polymers often called biopolymers, such as

carbohydrates and proteins.

Most synthetic polymers are long chain organic molecules and contain

thousands of monomer units; such molecules have very high molecular mass

and often called macromolecules

All polymers are macromolecules but all macromolecules are not polymers.

For example, hemoglobin and chlorophyll are macromolecules but not

polymers.

A polymer is analogous to necklace made of small beads. Usually a biggest difference in

properties of polymers is how the atoms and chains are linked together in space.1-D

structure of polymers have different properties in comparison to 2-D and 3-D structure.

Figure.1.1: General Structure of polymer

Polymers are compounds that composed of several units of monomers which are in

repetitive manner [4] and held together by covalent bond. The polymer is often refers

to plastics, which consist of variety of natural and synthetic materials with different

properties. The polymers play an important role in our daily life because the polymers

have an extra ordinary range of their properties [5, 6]. Their role varies from synthetic

plastics and elastomers to natural biopolymers i.e proteins and nucleic acids.

Polymers are produced through a polymerization process where monomer react

together chemically to form either linear chains, branched or three dimensional

networks of polymers chains. The main characteristic of the chains is that the bonding is

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directional and strong along the chains, but on the sideways they are bonded by

secondary Vander Waal forces with hydrogen-bonding [7].

1.2 History of Polymers Polymer Science is a relatively young discipline which developed rapidly following the

recognition 30 or 40 years ago that polymers are made up of long molecules. Although it

is now widely accepted that these materials contain macromolecules it was only with

the pioneering work of people like Staudinger, Carothers and others that chemical

aspects of polymer science were established on a firm scientific footing. Polymers have

been around us in a natural form since life began and naturally occurring biological

polymers, such as shellac, tortoise, shell, tar and horns. So these polymers are used in

useful articles like hair ornaments and jewelry etc.

In 1800s the chemical modification of many polymers takes place for the production of

new materials. These materials were modified to vulcanize rubber, gun cotton and

celluloid. In 1909 the first semi-synthetic polymer was produced and the first synthetic

fiber Rayon was developed in 1911.

Even with such progress it was not until World War II that significant changes occurred

in polymer industry. Natural substances were available prior to World War II, so the

developments of synthetic materials were not necessary. After the World War II, the

natural sources of many materials like silk, wool, latex and other materials were finished

which makes the use of synthetic materials critical. The use of synthetics materials such

as nylon, neoprene, SBR, polyethylene and many other polymers takes the place of

natural materials which was no longer available during this period of time. Since, then

significant changes takes place in the polymer industry and has continued to grow as

fastest growing industries in the United States and in the world.

1.3 Copolymer Copolymer can be made not just from two different monomers but from three, four, or

even more. They can be made not only by free radical chain reactions, but by any of the

polymerization methods we shall take up: ionic, coordination or step reaction. The

monomer units may be distributed in various ways, depending on the technique used.

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1.4 Types of Copolymer Copolymers are found in different forms on the base of monomer arrangement.

Copolymer varies along the chain depending on mechanism and method of synthesis

used [8]. It consists of at least two kinds of constitutionals units. Copolymers are

classified according to the arrangement of monomer in the main chain [9].

These are;

A. Alternating copolymers

When the two monomers are arranged in a regular pattern is called

alternating copolymers.

(M1M2 M1M2)n

B. Graft copolymers

In graft copolymers a branches of monomers is grafted to the backbone of

the main chain. The main chain of polymer and the other monomer irradiate

forming active sites to which second monomer is attached [10].

C. Random copolymers

As the name applies, there is no pattern to the arrangement of monomer

units in a random copolymer. These copolymers follow a statistical rule for

the arrangement of monomer along the chain. When the probability of

finding a given monomer residue at a particular point chain is equal to the

mole fraction of that monomer residue in the chain, then the polymer may

be referred to as a truly random copolymer [11].

(M1 M1 M1 M1 M1)n

(M2 M2 M2 M2)

D. Block copolymer

Block copolymers composed of two or more subunits of homopolymer, linked

together by covalent bond. The block copolymer composed of two different

blocks of monomers are called diblock copolymers and block copolymer

composed of different monomeric blocks are called tri-block copolymers

[12].

(M1 M1 M1 M1 M1 - M2 M2 M2 M2 M2 )n

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1.5 Block Copolymers Block copolymers consists of long chain of few or more types of monomer units [13].

Block copolymer consists of different arrangement of the monomeric units held

together by covalent bond in a fashion like M1M1 M1M1M2 M2 M2 M2 (in this M1 and M2

represent different types of monomers in the parent chain). Block copolymer are further

classified on the basis of number and arrangements of blocks in a polymer. For example

• Diblock: A block copolymer in which two different blocks are joined

together at the ends.

• Triblock: A block copolymer in which three different blocks are joined

together at the ends.

• Multiblock: A block copolymer having more than three different blocks.

Block copolymers can also be classified on the basis of arrangement which includes

linear, star arrangement and end-to-end arrangement, in which one polymer provides

the base for other different branches [14-15]. Star di-block copolymer of PS and PEO at

the air-water interface was studied by Jennifer L. Logan et al, [16]. The investigated

polymers at the air-water interface have variations in their composition and

architectures. Block copolymers are made of different blocks of monomer, which have

fascinating tendency to achieved, through block segregation and micro phase

separation, diverse ordered structured such as spheres, cylinders and lamellae. These

structures of block copolymers are due to the self assembly of right component (block

copolymers) of different morphologies and block lengths, solvent conditions (such as

pressure, temperature, and composition) [17-18]. Amphiphilic block copolymer were

synthesized by Richard, D.H et.al, [19] using hydrophobic PS as a middle block. The

anionic polymerization methods were used by him and difunctional Polystyrene was

extended to tri-block copolymer. The preparation of copolymers firstly needs the

formation of living homopolymer and termination prevention from impurities like water

(H2O), oxygen (O2) followed by the addition of the second monomer in the system to

form block copolymer [20]. The order of monomer addition can have a significant effect

e.g styrene-methacrylate block copolymers can be formed by addition of styrene to a

living polymer of MMA. Block copolymer can also be synthesized by many other

methods [21] without living polymers. Zhuo Yuang, Michael Crothers carried out

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research on styrene oxide and synthesized them by sequential oxyanionic

polymerization. These block copolymers were characterized by calorimeter, Surface

Tensiometry, light scattering, tube inversion and coquette rheometry. Critical micelle

concentration and standard enthalpies of micellization were found out by surface

tension method. Calorimetry and isothermal titrations were used for confirmation of

enthalpies of micellization. For the determination of miceller association numbers and

hydrodynamic radii, light scattering technique was used. Tube inversion and couette

rheometry [22] were used for the determination of phase diagrams defining regions of

hard and soft gel.

1.6 Amphiphilic block copolymers Amphiphilic block copolymers are formed by the chemical linkage of two different

repeating units in which one of the blocks is hydrophobic and other block is hydrophilic

[23]. Amphiphilic molecules are a special class of molecules, which have dual affinity or

affinity for two or more different kind of environments. A simplest amphiphilic molecule

is shown in Figure 1.2, which has a distinct hydrophobic tail and hydrophilic head. So the

dual affiliation is for hydrophilic and hydrophobic environments.

Hydrophilic Head Hydrophobic Tail

Figure 1.2: Simplest amphiphilic molecule.

1.7 Methods used for the synthesis of block copolymer.

The synthesis of block copolymers having well defined molecular weight, narrow

molecular weight distribution and tailored structure has major contribution to polymer

chemistry [24]. Chih-Feng Huang “et al”. [33] demonstrated dual simultaneous

polymerization for a single step approach. This method is used for the synthesis of

different block copolymers having combination of two different systems of

polymerization. Di-block copolymers are representing an important class of compounds

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having two different polymer blocks of unique characteristics [25]. PEO, PS and PMMA

are best choice for the selection of amphiphilic di-block copolymer because PEO is a bio

consistent and PS is an inexpensive polymer that can be easily synthesized [26]. PMMA

is a thermoplastic, but is hydrophobic and in its glassy state (Tg=398K for atactic PMMA)

has a high resistance to wear and chemical attack and possesses excellent optical

properties. The pot synthesis method were used for the synthesis of amphiphilic block

copolymers in which second monomer is added to the reaction medium, after the first

monomer [27] consumption is nearly to complete.

Anionic polymerization [28] technique is used for the synthesis of monofunctional

initiator diblock copolymers of PS-b-PEO and these acts as polymeric stabilizers in

emulsion polymerization. Adriana Boschetti-de-fierro et. al used sequential living anionic

polymerization [29] for the preparation of ter-polymers of polybutadiene-b-polystyrene

-b-poly (ethylene oxide). Catalytic hydrogenation led to PE-b-PS-b-PEO, in these Tri-

block terpolymers the two blocks are crystallizable and PS is glassy one. The

composition, morphologies and thermal properties of tri-block terpolymers are

characterized by SAXS, TEM and Differential Scanning Calorimetry. The process of living

polymerization generally begins by initiation step; followed by propagation and remain

active without termination [30-32].

1.8 Atom Transfer Radical Polymerization (ATRP) Atom Transfer Radical Polymerization is a type of controlled radical or transfer radical

polymerization. In ATRP, carbon-carbon bond is formed by the use of transition metal

catalyst and the transfer of atom is the major phase in ATRP which is responsible for the

growth of polymer chain. In 1995 ATRP were discovered by Prof Krzystof Matyjaszewski

[33] and Prof Mitsuo Sawamoto [34].

B. Reining, Helmut Keul et, al carried out research on ATRP of methyl methacrylate and

styrene substituted model and macro initiators and evaluates the structural aspects

quantitively and it affects the efficiency of initiation step. Uniformed polymer chain

growth is due to transition metal based catalyst which leads to a low polydispersity,

because catalyst provides equilibrium between active (propagating form) and inactive

form (dormant) of the polymers. Side reactions are suppressed due to the polymers

dormant state which is usually preferred in equilibrium. Unintentional termination,

molecular weight and the concentration of propagating radicals is controlled in

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equilibrium state. The functional groups such as allyl, epoxy, amino, hydroxy and vinyl

groups [35] favor ATRP reactions. ATRP is a useful [36] and easy method along with

other characteristics like commercial availability and cheap catalyst like pyridine based

ligands and initiators.

1.9 Applications of Amphiphilic Block Copolymers Amphiphilic block copolymers have a wide range of applications in different fields.

Especially Amphiphilic block and graft polymer can be used as stabilizers for dispersion

and emulsions, while it can also be used in photo electronics, biomedical material, etc

[37]. Diblock copolymers are used for information storage, drug delivery and photonic

crystals [38]. Amphiphilic block copolymer is also used in polymeric blends as

compatibilizers. The bio-stable polymer can be used in artificial organs, blood vessel

prostheses, blood pumps and heart vessels [39].

Block copolymer of PEO corona with hydrophobic and biodegradable polystyrene is very

attractive due to its bio compatibility [40]. Amphiphilic block copolymers having

hydrophilic and hydrophobic blocks are used in biological membrane application [41-45]

as well. In general amphiphilic block copolymers have a wide range of applications in

different fields e.g pharmaceutical, environmental, cosmetics, agricultural adjutant and

detergent formulations [46,47]. Polystyrene-block-polyethylene oxide has its

applications as emulsion stabilizers, demulsifies, deformers [48], and foam stabilizers.

1.10 Characterization of Amphiphilic block

copolymer

The amphiphilic block copolymers under observation during the present investigation

can be characterized by various techniques some of which are discussed below;

1.10.1 Nuclear magnetic resonance (NMR) The potential of NMR spectroscopy as a promising tool for the analysis and

characterization of block copolymer properties have attracted much attention, owing to

important advantages as compared with other analytical methods [49]. NMR

spectroscopy is non-destructive, does not require samples pre-treatment and the optical

transparency of the sample is not a prerequisite for the analysis unlike other analytical

methods such as DLS. The NMR techniques can provide information about sample

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composition and spatial distribution of the components and determination of molecular

weight of block copolymer [50].

1.10.2 GPC (Gel Permeation Chromatography) Gel Permeation Chromatography is an extremely powerful technique for fractioning a

polymer and determining its molar mass distribution. It has only been used for synthetic

polymers since the early 1960s, but now it is a routine technique of polymer

characterization. GPC is the type of size exclusion chromatography (SEC), and was

developed by Lathe and Ruthven [51] in 1955. GPC is now widely used both for analysis

of molecular mass distribution and the preparations of sharp fractions of many

polymers. Polymers can be also be characterized by different method for molecular

weight which include the number average molecular weight (Mn) , the weight average

molecular weight (Mw), or the size average molecular weight (Mz) and PDI (poly

dispersity index) [52].

a) Number average molecular weight Mn

Mn=Σ Nx Mx

(1.1)

Nx stands for mole fraction and Mx stand for the weight of molecule

b) Weight average molecular weight Mw

Mw=Σ Wx Mx

(1.2)

Wx stands for weight fraction

So for different average molecular weight of polymer molecule exact PDI [53]

determination is an important factor.

PDI = Mw /Mn

(1.3)

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1.10.3 Viscosity Huggins’s constant showing the association between the different chains of the block

copolymers and intrinsic viscosity are the two important parameters that can be

determined from the viscosity measurements by using the following equations; [54].

Huggins’s equation

ηspec / C = [η] + KH [η]2C

(1.4)

Intrinsic viscosity

spec

limc 0

(1.5) C

The intrinsic viscosity can also be used to calculate the molecular weight of the

polymers by a well known Mark Houwink equation

[η] = K Ma

(1.6) The associative behavior of block copolymers was studied by Jose R.

Quintana et. al with the help of Lauda automatic, viscometer and the data were noted to

get intrinsic viscosity [55].

1.10.4 Surface Tension Surface tension of block copolymer is an important physical characteristic that can be

used to calculate many surface parameters. (i) Area Per Molecule (A°)

The area per molecule is calculated from the surface excess concentration by using the

following relationship;

A = 1 / NA Γ

(1.7)

Where NA is Avogadro’s number and ‘‘Γ’’ is surface excess concentration [56].

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(ii) Surface Excess Concentration (Γ) Interfacial properties of block copolymers provide useful information about solute-

solvent and solute-solute interactions. Surface excess concentration for surface-active

solutes can be assumed to be equal to the actual surface concentration without any

error. The concentration of diblock copolymer solutions at the interface may therefore

be calculated from surface or interfacial tension data by use of the appropriate Gibb’s

equation [57]. The surface concentration can be obtained from the slope of a plot of γ

versus log C at constant temperature.

Γ2= - 1 / 2.303 R T (∂γ / ∂ log C2)T

(1.8)

Where T is the absolute temperature in Kelvin, R is the gas constant (∂γ / ∂ log C2 is the

linear portion of the slope of the γ versus log C plots) [58].

(iii) Critical Micelle Concentration (CMC) Micelle formation or Micellization is an important phenomenon not only because a

number of important interfacial phenomena, such as detergency and solubilization,

depend on the existence of micelles in solution, but because it affects other interfacial

phenomena such as surface tension or interfacial tension reduction that do not directly

involve micelles [59]. The surface tension is a function of polymer concentration which

indicates that there is an inflection point at some specific concentration which is

associated with the formation of supramolecular aggregates known as critical micelle

concentration [60]. We determine CMC from various techniques that is Surface tension,

Conductance, PH, Density, fluorescence and Diffusion order spectroscopy (DOSY).

(iv)Free Energy of Micellization (ΔG°mic) For the calculation of free energy of micellization of pure di-block copolymer solution

the following equation is used;

(1.9)

R=gas constant having value 8.314J mol-1 K-1

T =absolute temperature and

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X cmc=mole fraction

If solution is prepared in molarity or molality then Xcmc can be calculated by the

equation.

CMC

(1.10)

55.55

As

(1.11)

In case of g/L of solution we convert Xcmc by the equation

(1.12)

(v) Free Energy of Adsorption (ΔG°ads)

The free energy of adsorption ΔG°ads of pure di-block copolymer solution is calculated by

the following equation;

(1.13)

πCMC is the surface pressure at critical concentration and is equal to

(1.14)

Where γο is the value of surface tension of any pure solvent (toluene) and γ cmc is the

critical concentration.

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(vi) Enthalpy of Micellization (ΔHmic) The enthalpy of micellization (ΔHmic) for pure diblock coplymer system can be calculated

as;

(1.15)

In this equation R is the gas constant ant T is the absolute temperature, plotting graph

between In

CMC gives us a straight line with slope equal to .

(vii) Entropy of Micellization (ΔSmic)

The entropy of micellization (ΔSmic)for pure di-block copolymer is given by the following

equation

(1.16)

1.10.5 Laser Light Scattering (LLS)

Light scattering occurs when polarizable particles in a sample are bathed in the

oscillating electric fields of a beam of light. The varying field induces oscillating dipoles in

the particle, and this radiate light in all direction [61]. In 1869 John Tyndall found that

different sized particles scattered light in different ways. Two years later, Lord Rayleigh

described the first theory of light scattering based on the theory of electromagnetic

waves.

Laser light scattering (LLS) is a highly informative method, and the combination of quasi-

elastic LS and integrated scattering intensity measurements in the same experimental

set up increases the amount of information for the system studied [62]. For studying

structural information’s in systems containing proteins, enzymes, polymers and other

macromolecular components, Photon correlation spectroscopy (PCS) has become a

popular technique [63-65]. LLS is the most versatile method for the determination of

molecular size and molar mass of macromolecules [66].

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1.10.6 Types of LLS 1.10.7 Static Light Scattering Static light scattering (SLS) is a technique used for the characterization of particles in the

solution according their mass, size, and shape. This method is based on the polarizability

generated within the molecules when an electromagnetic wave interacts with their

electrons, inducing a dipole moment. The intensity of elastically scattered light is

measured as a function of scattering angle [67].

Static light scattering is potentially a powerful technique for polymer characterization

as, in principle, it determine the shape and size of the molecules in solution and also

gives the information about molecular mass (Mw), second viral coefficient (A2), radius of

gyration (Rg), of the polymers or polymer complexes [68, 69].

1.10.8 Dynamic Laser Scattering One of the most popular techniques in colloid and polymer analysis is Dynamic Light

Scattering (DLS). This method enables the determination of the hydrodynamic radii and

polydispersity of a colloidal system.

This technique is based on the principle of Photon Correlation Spectroscopy and now a

day it is used as a routine analysis for the particle size in the sub micrometer range. It

also provides information about polymer average size and its distribution during

measuring time within few minutes [70].

1.10.9 Thermal Analysis (TGA/DTA) There are two main thermal analyses one is TGA (Thermogravimetric analysis) which

records automatically the change in weight of a sample as a function of either

temperature or time and the second one is the DTA (Differential Thermal Analysis)

which determine the change in temperature; so DTA can measure change in heat

content. In DTA methods the flow of heat to the reference and sample remains same as

compared to the temperature. On heating the reference and sample; phase and other

thermal changes takes place due to the difference of temperature between the

reference and sample [71].

Thermal analysis is used in block copolymers determination of the degree of crystillinity,

glass transition, processing conditions, curing/crosslinking, oxidative stability, isothermal

crystallizations, specific heat (Heat capacity), kinetics studies, Moistures/volatiles

content, composition analysis, combustion/decomposition analysis, material strength/

modulus, expansion/contraction [72].

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1.10.10 Differential Scanning Calorimetry (DSC)

DSC records automatically the temperature and heat flows which are due to the

transition in compound as a function of either time or temperature in a controlled

atmosphere. The measurements of DSC give us qualitative and quantitive information

about physical and chemical changes related to exothermic or endothermic process and

also the changes in glass transition temperature as well as heat capacity [73]. DSC is

mainly used as a quality instrument an industrial scale because of the applicability in

evaluating sample purity and also for the polymer characterization [74].

DSC can mainly be used to determine Glass Transition Temperature (Tg) of the

polymers. The effectiveness of a plasticizer may be judged by how much it reduces Tg or

affects the shape of the transition. Examination of the transitions in polymer blends

gives information as to their compatibility.

1.10.11 Rheological Measurements Rheology is the study of flow of matter under certain conditions; it applies to

compounds having complex structure, which includes sludge’s, mud’s, suspension,

bodily fluids, polymers, and other biological substances.

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Biopolymer

Figure 1.3: Biological materials having complex structures.

1.10.12 Diffusion Order Spectroscopy (DOSY NMR) Diffusion-ordered NMR spectroscopy (DOSY) has been introduced into NMR as a new

tool to analyze the composition of mixtures [75]. The two dimensional DOSY spectrum,

which represents chemical shifts and diffusion coefficients in two orthogonal directions,

effectively differentiates NMR signals from the individual components in the diffusion

dimension [76]. This method has been extensively employed for the characterization of

aggregates, studies of hydrogen bonding, supramolecular assemblies, etc. [77]. The

diffusion ordered spectroscopy (DOSY) [78] has been utilized as a non-invasive

technique which involves the separation of peaks corresponding to individual

components of mixtures on the basis of different molecular weights and diffusion

coefficients. Diffusion order spectroscopy (DOSY) may be used as a powerful tool for

characterizing amphiphilic block copolymers especially with reference to their critical

micelle concentration (CMC).

1.10.13 Fluorescence Fluorescence is the molecular absorption of light energy at one wavelength and its

nearly instantaneous re-emission at another, usually longer, wavelength. Some

molecules fluoresce naturally and others can be modified to make fluorescent

compounds [79]. Fluorescence is used for the determination of critical micelle

concentration (CMC) of block copolymer.

Fluorimetry is chosen for its extraordinary sensitivity, high specificity, simplicity, and low

cost as compared to other analytical techniques [80]. Fluorimetry is ordinarily 1000-fold

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more sensitive than absorbance measurements. It is a widely accepted and powerful

technique that is used for a variety of environmental, industrial, and biotechnology

applications. It is a valuable analytical tool for both quantitative and qualitative analysis

[81].

1.10.14 Fourier Transform Infra Red Spectroscopy (FTIR) Infrared spectroscopy has been a work horse technique for materials analysis in the

laboratory for over seventy years. An infrared spectrum represents a fingerprint of a

sample with absorption peaks which correspond to the frequencies of vibrations

between the bonds of the atoms making up the material. Because each different

material is a unique combination of atoms, no two compounds produce the exact same

infrared spectrum [82]. Therefore, infrared spectroscopy can result in a positive

identification (qualitative analysis) of every different kind of material. In addition, the

size of the peaks in the spectrum is a direct indication of the amount of material

present. With modern software algorithms, infrared is an excellent tool for quantitative

analysis [83].

1.11 Nanoparticles Nanometer-sized particles of metals and semiconductors have been investigated

intensively in recent years because of the influence which their dimensions have on

their electronic properties (structures such as quantum wires, quantum wells and

quantum dots) [84]. To fabricate electronic devices, it is necessary to develop

nanostructures arrays with small metal or semiconductor is lands separated by tunnel

barriers [85]. A periodical structure with two potential barriers in series, separated by a

potential well, can be considered as a man-made super lattice. However, most physical

nanofabrication techniques, for example, electron-beam and scanning probe

lithography, are costly and time consuming in producing large-scale devices. Many

alternative accesses to forming composite nanoparticles have been developed based on

chemical methods [86]. The general principle of such methods is to mix nanoscale metal

or semiconductor particles with processable matrixes, such as polymer micelles.

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1.12 Characterization of Nanoparticles

1.12.1 UV/Visible spectrophotometer Ultraviolet/Visible spectroscopy is a technique used to quantify the light that is

absorbed and scattered by a sample. In its simplest form, a sample is placed between a

light source and a photodetector, and the intensity of a beam of light is measured

before and after passing through the sample. These measurements are compared at

each wavelength to quantify the samples wavelength dependent extinction spectrum.

The data is typically plotted as extinction as a function of wavelength [87].

Nanoparticles have optical properties that are sensitive to size, shape, concentration,

agglomeration state, and refractive index near the nanoparticles surface, which makes

UV/Vis spectroscopy a valuable tool for identification, characterization, and studying

these materials. UV-visible spectroscopy is used for the confirmation of elemental gold

and silver nanoparticles [88].

1.12.2 Transmission Electronic Microscopy (TEM) Transmission electron microscopy (TEM) uses high energy electrons to penetrate

through a thin (≤100 nm) sample. This offers increased spatial resolution in imaging

(down to individual atoms) as well as the possibility of carrying out diffraction from

nano-sized volumes. When electrons are accelerated up to high energy levels (few

hundreds keV) and focused on a material, they can scatter or backscatter elastically or

inelastically, or produce many interactions, source of different signals such as X-rays,

Auger electrons or light [89]. Some of them are used in transmission electron

microscopy (TEM).

1.12.3 Scanning Electronic Microscopy (SEM) Scanning electron microscopy (SEM) uses a focused electron probe to extract structural

and chemical information point-by-point from a region of interest in the sample. The

high spatial resolution of an SEM makes it a powerful tool to characterize a wide range

of specimens at the nanometer to micrometer length scales [90].

1.13 LITERARURE REVIEW Deng-Xue Du et. al., [111] studied the concentration dependence of the reduced

viscosity sp/C and the translational diffusion coefficients (D°t) as well as the radius of

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gyration (Rg) of PS in toluene by Viscometry and LLS respectively. They also determine

the influence of the experimental error of the sp/C.

Brite Reining et al [91] synthesize MMA and styrene having different substitution and

macroinitiators to elucidate the qualitative structure which influence the initiation step,

and observed that the dissociation of halogen atom was enhanced by those

substituent’s which stabilize the radicals and the initiation efficiency of MMA and

styrene were increased.

Yung-Wei Yang et al studied the dissociation of di-block and tri-block copolymers in

water by LLS techniques. The CMC of diblock and tri block copolymer were compared

and the effects of architecture were also investigated [92].

Vaishali S. Shinde et al synthesis diblock copolymer using ATRP method. They also

studied that the amphiphilic behavior of diblock copolymer leads to phase separation

resulting in two glass transition temperature as detected by DSC. TGA was also studied

by them [93].

Daniel J. Siegwart, Nei Wu, et al synthesis tri block copolymer (PMMA-PEO-PMMA) using

ATRP [94]. DSC techniques were used for the determination of melting temperature and

glass transition temperature of the copolymer. Based on DSC techniques they studied

the melting temperature of PEO component in the block-copolymer and found it in good

agreement as compared to the homopolymer melting temperature.

Henrich Frielinghas, Walter Batsberg Pederson “et al” determine the molar masses of PS

in diblock copolymer of (PS-OH) by SEC technique, using THF as a solvent. By SEC

technique the molar mass distribution was determined [95]. Zhao Yang et al used the

GPC techniques for the characterization of tri-block copolymers. From the GPC profile

they obtained the ratio of mass average to number average (Mw: Mn) and the peak

molar mass [96]. GPC technique was also used by Zhuo Yang, M. Crothers for the

characterization of their di-block copolymer. The traces of GPC gave the molar mass

distribution of the copolymer in the ratio of Mw/Mn [97]. Katja Jankava et. al.,

determined the Mw/Mn of PEO-2000 and macroinitiators were characterized by GPC for

the synthesis of PS-b-PEG-b-PS [98] amphiphilic tri-block copolymers. GPC was also used

by Glader Cristobal [99] and Chirphon Chaibundit for their blocks copolymer for the

determination of molar mass distribution [100].

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Jain-Jun Yuan et al and Thomas W. Smith use the GPC technique for the characterization

of polystyrene / poly (4-vinyl pyridine) [101] tri-block copolymer and polystyrene / poly

[styreneb-(ethylene oxide) [102] respectively to find out the molecular weight and

molecular weight distribution of these copolymers. Henrich Frielinghas et al also

determine molar mass distributions of poly (styrene)/ poly (ethylene oxide) copolymer

by SEC techniques [103]. Stelle. C synthesized amphiphilic di-block copolymer which is

based on the nonionic, hydrophilic monomer (HEGMA) and the hydrophobic monomer

BzMA (benzyl methacrylate) of different composition and molecular weight by group

transfer polymerization. These copolymers were characterized by GPC and HNMR

spectroscopy for the determination of molecular weight and co-monomer composition

respectively. LLS of these copolymers show that all the copolymers form aggregate

whose size increased with w/w % of BzMA composition and also of molecular weight of

the linear chains [104].

The Qun Zhao and et al characterize di-block copolymers (PMMA and PDMAEMAZ)

through H1 NMR and the results showed that the obtained molecular weight is in good

agreement between monomer to initiator ratio [105]. GPC traces indicates that

homopolymer PDMAEMA and the above mentioned two blocks copolymer have a

molecular weight distribution block of polystyrene / poly [styrene-b-(ethylene oxide) in

the range of 1.15-1.34, and homopolymer PMMA molecular weight distribution were in

the range of 1.29-1.60.

Kashiwigi et. al [106] carried out the thermal degradation of PMMA polymerized by free

radical method in three steps. Manring and co-workers carried out a research on the

thermal degradation of PMMA component and also the different steps involve in this

process in 2011, he synthesized and characterized MMA which have styrene in different

composition. Viscosity measurements of the combined homo-polymer and the

copolymer in methyl benzene solutions were achieved at 40°C [107].

The Nirmalya Bag, et. al characterized Diffusion measurements and the subsequent FCS

diffusion law analyses at different temperatures show that the modulation in membrane

dynamics at high temperature (313 K) is a cumulative effect of domain melting and

rigidity relaxation [108].

Youssef and co-worker determine the critical micelle concentration (CMC) using DOSY

NMR experiments. The CMC value correlated with those obtained by fluorimetry and

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static light scattering. The CMC value was found to be 0.11 g L-1. All the results suggest

that DOSY NMR is a valuable analytical tool for the polymer community. [109]

Štˇepán Popelka and researchers studied the adsorption of amphiphilic poly(ethylene

oxide)– block–polylactide (mPEO–PLA) copolymers from a selective solvent onto a

polylactide surface as a method of polylactide surface modification and its effect on

nonspecific protein adsorption was evaluated. A series of well-defined mPEO–PLA

copolymers was prepared to investigate the effect of copolymer composition on the

resulting PEO chain density and on the surface resistance to protein adsorption. The

copolymers contained PEO blocks with molecular weights ranging between 5600 and

23,800 and with 16–47 wt% of PLA. The adsorption of both the copolymers and bovine

serum albumin was quantified by attenuated total reflection FTIR spectroscopy (ATR-

FTIR)[110].

M. Szyman´ ska-Chargot, et. al studied the synthesis of silver nanoparticles during

electrolysis of NaCl solutions and silver electrodes was controlled by using UV

absorption and massspectrometric methods. For mass-spectrometric measurements,

the laser desorption/ionization method and a time of flight (TOF) spectrometer were

employed. Results of investigations show the possibility of formation of small silver

nanoparticles [111].

M. Zimbone and co-worker studied Gold nanoparticles solution prepared in water by

laser ablation at 1064 nm of a gold metal plate and was characterized by dynamic light

scattering and UV–vis spectroscopy. Polarized dynamic scattering allows the

measurement of translational diffusivity of Au nanoparticles, while depolarized

scattering yields simultaneously the characterization of translational and rotational

diffusivities. From these measurements the size and shape of Au nanoparticles are

determined. Dynamic light scattering yields an average radius of 32nm for the spherical

nanoparticles. The same measurements performed in an aged solution reveal the

formation of ellipsoidal nanoparticles with minor and major semi-axis of 36nm and

69nm, respectively [112]. The measured values allow to fit the UV–vis spectra with the

MieGans model and to measure the concentration of Au nanoparticles obtaining a

complete characterization of their nanostructure.

From the detailed review of literature, it is quite clear that the di-block copolymers are

representing an important class of compounds having two different polymer blocks of

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unique characteristics. PEO, PS and PMMA are best choice for the selection of

amphiphilic di-block copolymer because PEO is a bio consistent and PS is an inexpensive

polymer that can be easily synthesized [113]. PMMA is a thermoplastic, but is

hydrophobic and in its glassy state, (Tg=398K for atactic PMMA), has a high resistance to

wear and chemical attack and possesses excellent optical properties.

Systems containing block copolymers are also of great interest due to their specific

multiphase morphology with interesting or useful self-assembly or phase separation

behavior and can offer some advantages compared to low molecular weight surfactants

with respect to the stability of the self-organized structures as well as film formation

[114]. Because the self-organization of block copolymers is sensitive to the presence of

low molecular weight compounds such as the solvent or the inorganic compound,

particle and film formation is usually accompanied by complex transformation of the

equilibrium structures. In order to avoid the entailed loss in structural control, an

approach was chosen where the kinetic stability of the micelles formed in dilute solution

is sufficient to prepare solvent-free films from the unaltered micelles [115]. By selecting

an appropriate solvent, a block copolymer with both polar and non-polar blocks tends to

form micelle which includes an insoluble core and a soluble shell. Because the polar

block is capable of binding metal salts or adsorbing at the surface of an inorganic

particle via various interactions, the precursor component can be introduced into the

core of the micelle and be conversed to nanoparticles [116].

1.14 Aims of Project:

Under nearly equilibrium conditions, block copolymers can self-organize into a variety of

nanosized microphase separation structures, depending on their block volume fractions,

FloryHuggins parameter and polymerization degree [117]. Block copolymers do not only

form micelles in solution but also assemble in solid films with a regular micro-domain

structure. Furthermore, the critical micelle concentration of block copolymers is

typically smaller and their kinetic stability is larger than that of low molecular weight

surfactants [118]. Under such conditions, the micelles not only become the nanoscale

reaction vessels where the size of metals or semiconductor particles are of controlled

charge but also build the potential barriers with homogeneous periods. Nanometer-

sized particles of metals and semiconductors have been investigated intensively in

recent years because of the influence which their dimensions have on their electronic

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properties. With these advantages, block copolymers can be one of the intriguing

candidates for syntheses of composite nanoparticles that can be applied prospectively in

nanolithography and nanofabrication [119].

Herein, with the aim to synthesize block copolymers of required structure and molecular

mass and construct nano-structured particles films. It was therefore, aimed to:

Synthesize the amphiphilic diblock copolymer of PS-b-PEO and PMMA-b-PEO by

varying the length of PS and PMMA block while keeping the PEO block constant.

Characterize these synthesized block copolymers with reference to their

molecular weight, structure & size (various techniques), flow and thermal

behavior.

Determine the optimum concentration for the micelle formation in the

synthesized block copolymers using various techniques ranging from very simple

to highly sophisticated one like surface tension, DOSY NMR etc.

Investigate the self-assembling of synthesized block copolymers.

Utilize these A-B diblock copolymers to form small compartments (micelles) in

which the nanoparticles can be generated and which may allow us to prepare

thin, coherent films as depicted in Figure 1.3.

Use these block copolymer micelles for the extraction of gold and silver

nanoparticles and cast films having the homogeneous dispersion of these

nanoparticles

Investigate the distribution of nanoparticles in the micelles of the block

copolymers by looking into the morphology through the electron microscopy

Establish the optimum conditions for having homogeneously dispersed particles

of uniform size in the required material.

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Figure 1.3: Scheme of the formation of nanoparticles in a block copolymer micelle:

I) Micelle formation in a selective solvent; II) Loading with the precursor component;

III) Transformation to a single gold particle.

1.15 Plane of work

The present work/dissertation is an effort to contribute a research segment to the

synthesis of amphiphilic block copolymers and the generation of nanoparticles of Au &

Ag in their micellar compartments. The following section will reveal the fundamental

strategies employed in the presented work/ dissertation. The scheme of work has been

planned to complete in five steps. Preparation of Macroinitiator, Polymerization of

styrene in bulk with macroinitiators, Polymerization of Methyl methacrylate in bulk with

macroinitiators, Preparation of Gold nanoparticles, Preparation of silver nanoparticles

will be achieved using following schemes.

Step 1:

Preparation of Poly(ethylene oxide) Macroinitiator PEO (MePEO, Mn = 5000) was dissolved in toluene and heated for 12 h and

refluxed on a water separator.

The dry solution of 7.06 mmol (35.3g) of MePEO in 100 cm3 toluene was treated

with

28.24 mmol (5.3385g) of the α-Chlorophenylacetylchloride and refluxed for 24 h.

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The solvents and volatiles were removed under high vacuum and the residue

dissolved in 150 cm3 methylene chloride, stirred over K2CO3, and filtered

following which the solvent was removed and the residue was dried.

For purification the macroinitiator was dissolved in100 ml toluene, reprecipitated

into 750 cm3 hexane, isolated by filtration, and dried to constant weight.

Step 2:

Bulk Polymerization of styrene with macroinitiator Into a Schlenk glass tube 0.181 mmol initiator, 0.181 mmol CuBr, 0.543 mmol bipy

and 34.76 mmol monomer (styrene) were filled.

The mixture was degassed three times under vacuum and filled with nitrogen

before immersion in an oil bath at 130oC.

The polymerization was terminated by cooling rapidly to room temperature after

20 h.

The product was dissolved in 40 cm3 dichloromethane and precipitated into

mixture of 30ml of 0.5% HCL in 450ml of methanol.

The polymer was isolated by filtration and dried to constant weight.

By varying the amount of styrene monomer and initiator, block copolymers (PS-

b-PEO) with different PS block length were synthesized.

Confirmation of block copolymer PS-b-PEO synthesis by NMR.

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Cl Ph Ph

PEO-b-PS

Step 3:

Bulk Polymerization of methyl methacrylate

(PMMA) with macroinitiators Into a Schlenk glass tube 0.181 mmol initiator, 0.181 mmol CuBr, 0.543 mmol

bipyredine and 34.76 mmol monomer (methyl methacrylate) were filled.

The mixture was degassed three times under vacuum and filled with nitrogen

before immersion in an oil bath at 130oC.

The polymerization was terminated by cooling rapidly at room temperature after

20 h.

The product was dissolved in 40 cm3 dichloromethane and precipitated into

mixture of 30ml of 0.5% HCL in 450ml of methanol.

[

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The polymer was isolated by filtration and dried to constant weight.

By varying the amount of methyl methacrylate monomer and initiator, block

copolymers (PMMA-b-PEO) with different PMMA block length were synthesized.

Confirmation of block copolymer PMMA-b-PEO synthesis by NMR.

Step 4:

Synthesis of gold Nanoparticles 1% (w/w) PS-b-PEO and PMMA-b-PEO solutions of both block copolymers were

prepared by dissolving the diblock copolymer in toluene.

Definite amount of LiAuCl4 (0.1 and 0.2 equivalents of LiAuCl4 bound per ethylene

oxide) was added to above solution.

The mixture was facilitated by means of ultrasound and a bright yellow solution

was obtained after 1 h.

Then sodium borohydride (NaBH4) powders were introduced into the system. The

yellow colour for gold solution turned into purple gradually after 1 h sonication.

The formation of elemental gold was confirmed by UV/Vis absorption spectrum

using UV/Vis spectrophotometer and transmission electronic microscopy.

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Step 5:

Synthesis of silver nanoparticles PMMA-b-PEO and PS-b-PEO solutions were prepared by dissolving the diblock

copolymer in toluene.

Definite amount of AgNO3 (0.1, 0.2 and 0.3 equivalents of AgNO3 bound per

ethylene oxide) was added to above solution.

The mixture was facilitated by means of ultrasound and a semi-transparent

solution was obtained after 1 h.

Then sodium borohydride (NaBH4) powders were introduced into the system. The

semitransparent for silver solution turned into purple gradually after 1 h.

The formation of silver nanoparticles was confirmed by UV/Vis absorption

spectrum using UV/Vis spectrophotometer and transmission electronic

microscopy.

Appendix: Mechanism for the preparation of gold and silver nanoparticles with block

copolymer.

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CHAPTER-2 EXPERIMENTAL

2.1 Materials α-Chlorophenylacetylchloride (95%, Aldrich) was distilled over a

Vigreux column. PEO monomethyl ether (MePEO) 5000, 2000 and 750 (Aldrich) was

dried by removing residual water by azeotropic distillation with toluene on a water

separator. Inhibitors in styrene (St) were removed by passing the monomer over an

aluminum oxide column. CuBr (98%, Aldrich) and 2,2-bipyridine (bipy) (Aldrich) were

used as received. Polymerization was carried out in nitrogen atmosphere. Solvents and

chemicals used were Toluene, Dichloromethane, Hexane, HCL, Methanol, Aluminum

oxid and K2CO3.

2.2 Preparation of Poly(ethylene oxide)

Macroinitiator PEO (MePEO, Mn = 5000) was dissolved in toluene, heated for 12 h and refluxed on a

water separator. The dry solution of 7.06 mmol (35.3g) of MePEO in 100 cm3 toluene

was treated with

28.24 mmol (5.3385g) of the α-Chlorophenylacetylchloride and refluxed for 24 h. The

solvents and volatiles were removed under high vacuum. The residue left behind was

dissolved in 150 cm3 methylene chloride, stirred over K2CO3, and filtered. Following

which the solvent was removed and the residue was dried. For purification the

macroinitiator was dissolved in 100cm3 toluene, reprecipitated into 750 cm3 hexane,

isolated by filtration, and dried to constant weight.

PEO (MePEO, Mn = 2000) was dissolved in toluene and heated for 12 hour at reflux on a

water separator. The dry solution of 7.06 mmol (14.12g) of MePEO in 100 cm3 toluene

was treated with 28.24 mmol (5.337g) of the α-Chlorophenylacetylchloride and refluxed

for 24 h. The solvents and volatiles were removed under high vacuum and the residue

was dissolved in 150 cm3 methylene chloride, stirred over K2CO3, and filtered following

which the solvent was removed and the residue was dried. For purification the

macroinitiator was dissolved in 100 cm3 toluene, reprecipitated into 750 cm3 hexane,

isolated by filtration, and dried to constant weight. PEO (MePEO, Mn = 750) was

dissolved in toluene and heated for 12 h and refluxed on a water separator. The dry

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solution of 7.06 mmol (5.295g) of MePEO in 100 cm3 toluene was treated with 28.24

mmol (5.337g) of the α-Chlorophenylacetylchloride and refluxed for 24 h. The solvents

and volatiles were removed under high vacuum and the residue dissolved in 150 cm3

methylene chloride, stirred over K2CO3, and filtered following which the solvent was

removed and the residue dried. For purification the macroinitiator was dissolved in

100cm3 toluene, reprecipitated into 750 cm3 hexane, isolated by filtration, and dried to

constant weight.

2.3 Bulk Polymerization of styrene with

macroinitiator Into a Schlenk glass tube 0.181 mmol initiator, 0.181 mmol CuBr, 0.543 mmol bipy and

34.76 mmol monomer (styrene) were filled. The mixture was degassed three times

under vaccuum and filled with nitrogen before immersion in an oil bath at 130oC. The

polymerization was terminated by cooling rapidly to room temperature. The product

was dissolved in 40 cm3 dichloromethane and precipitated into mixture of 30ml of 0.5%

HCL in 450ml of methanol. The polymer was isolated by filtration and dried to constant

weight. By varying the amount of styrene monomer and initiator, block copolymers (PS-

b-PEO) with different PS block length were synthesized.

2.4 Bulk Polymerization of methyl methacrylate (PMMA) with

macroinitiators Into a Schlenk glass tube 0.181 mmol initiator, 0.181 mmolCuBr, 0.543 mmolbipyredine

and 34.76 mmol monomer (methyl methacrylate) were filled. The mixture was degassed

three times under vacuum and filled with nitrogen before immersion in an oil bath at

130oC. The polymerization was terminated by cooling rapidly to room temperature. The

product was dissolved in 40 cm3 dichloromethane and precipitated into mixture of 30ml

of 0.5% HCL in 450ml of methanol. The polymer was isolated by filtration and dried to

constant weight. By varying the amount of methyl methacrylate monomer and initiator,

block copolymers (PMMA-bPEO) with different PMMA block length were synthesized.

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2.5 Characterization

2.5.1 NMR Measurements The macroinitiators and block copolymers were characterized by 1H NMR, using Bruker

250 and 300 MHz spectrometers with CDCl3 as solvent. The block copolymer

composition was determined by the ratio of the NMR signal intensities of the phenyl

peak region to that of the PEO region.

2.5.2 Fourier Transform Infra Red Spectroscopy

(FTIR) FT-IR spectra were recorded on a Perkin Elmer spectrum Express version 1.02.00 from

USA. Spectra were recorded at 4cm-1 resolution with 64 scans ranging (600cm-1 to

4000cm-1) recorded for each spectrum. All samples were analyzed in solution toluene at

a fix concentration of 5mg/mL.

2.5.3 Laser Light scattering Measurements Dynamic light scattering experiment was carried out by a commercial LLS spectrometer

BI200SM motor-driven goniometer. It is equipped with BI-9000AT digital

autocorrelator or the BI-9025AT photon counter. A cylindrical 22mW uniphase He–Ne

laser and BI-ISTW software was used. The spectrometer had a high coherence factor of

β ~ 0.95 because of a novel single- mode fiber optic coupled with an efficient avalanche-

photodiode.

Static Laser Light Scattering measurements were performed on DAWN EOS supplied by

Wyatt, USA, with helium–neon laser of 632.8-nm wavelength as light source. A

cylindrical cell (SV) of 2-cm diameter was used for the purpose. A simultaneous

extrapolation to zero angle and concentration yielded an intercept, which was the

inverse of the Mw. From the results the molecular mass of the copolymers was

determined. Before the measurements for the samples were made, the instrument was

calibrated using the polymer samples provided by the supplier. The instrument was very

sensitive to dust particle so as to avoid discrepancy, all the glassware were washed with

acetone before use and dried carefully in oven. Solutions analyzed contain fixed amount

of triblock copolymer, then filtered into quartz LLS cell (10 mm in diameters) to remove

dust by using PTFE 0.1 µm filter. The experiment duration was 5 min. Each experiment

was repeated two or more times. In the dynamic light scattering, the measurements

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were carried out at a scattering angle of 90º. Scattering intensities were measured at

different temperature from (20-40oC) for various concentrations.

2.5.4 Gel Permeation Chromatography (GPC)

measurements It is often necessary to separate polymers, both to analyze them as well as to purify the

desired product. When characterizing polymers, it is important to consider the

polydispersity index (PDI) as well the molecular weight.

The number average (Mn), and weight average (Mw) molecular weight and molecular

mass distribution of block copolymers under investigation were determined by GPC/SEC

instrument, provided by Perkin Elmer, using RI detector. The experiments were

performed in THF solvent at room temperature with 1mL/min flow and calibration

based upon polystyrene standards.

2.5.5 Viscosity Measurements Solution viscosity of each polymer sample was measured at 20, 30 and 40oC in toluene

by using dilution Ubbelohde viscometer. The viscometer was calibrated over the

required temperature range and the obtained data indicated that there was no need for

applying end correction to the length of the capillary and kinetic energy correction for

this particular viscometer. Measurements were made in a thermostat, manufactured by

F.G Bode and Co, laboratory equipment Hamburg Germany, and the temperature was

maintained within +0.01°C accuracy.

2.5.6 Differential Scanning Calorimetry (DSC)

Measurements Differential scanning calorimetry or DSC is a thermo analytical technique in which the

difference in the amount of heat required to increase the temperature of a sample and

reference is measured as a function of temperature. Both the sample and reference are

maintained at nearly the same temperature throughout the experiment. Generally, the

temperature program for a DSC analysis is designed such that the sample holder

temperature increases linearly as a function of time.

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DSC measurements were carried out by using power compensation designed Perkin-

Elmer DSC7, linked to a Perkin–Elmer TAC7/PC Instrumental Controller and a Dell PC

indium and zinc standards were used for calibration and a Perkin-Elmer Controlled

cooling. Accessory was used for low temperature work. The powdered polymer samples,

approximately 2mg for PS-bPEO block copolymer and 2.5mg for PMMA-b-PEO block

copolymer were sealed in aluminium sample pans, (Perkin Elmer Kit No 0219-0062), and

as a reference an empty sealed aluminium sample pans were used. For melting point

and glass transition temperature determination, the scanning rate was 10Co/min and

the DSC head was continuously purged using dry Nitrogen.

2.5.7 TGA/DTA Measurements The DTA/TGA is a powerful thermo analytical technique that combines a DTA and a TGA

into one instrument that performs both DTA and TGA on the same sample at the same

time. This instrument or testing technique is sometimes referred to as simultaneous

Thermal Analysis, or STA, or simply ST. The resulting DTA and TGA curves are

simultaneously plotted on a dual Yaxis graph so the DTA’s fingerprint and the TGA’s

weigh loss/gain characteristics are directly compared as the test sample is heated and

cooled.

TGA/DTA measurements of amphiphilic block copolymer of PS-b-PEO and PMMA-b-PEO

were performed on a TG/DTA Module. The powdered polymer samples, approximately

5mg were sealed in aluminum sample pans, (Perkin Elmer Kit No 0219-0062), and as a

reference an empty sealed aluminum pan was used. For melting point and glass

transition temperature determination, the scanning rate was10Co/min and the TG/DTA

head was continuously purged using dry Nitrogen.

2.5.8 Rheological Measurements A rheometer is a laboratory device used to measure the way in which a liquid,

suspension or slurry flows in response to applied forces. It is used for those fluids which

cannot be defined by a single value of viscosity and therefore require more parameters

to be set and measured. For rheological measurements the experiments were carried

out on an Advance Modules HAAK MARS II Rheometer. A cone-plate with a diameter of

35/2mm Pi platinum and an angle of 1° was applied. The complex viscosity was achieved

by the measurements of storage modulus and loss moduli as a function of frequency at

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a constant temperature. The experiments were performed in linear viscoelastic regime

of the samples. The complex viscosity ( ) was achieved from the storage (G') and loss

(G'') moduli as Viscosity = [(G'2+ G"2) / (2η f)2]1/2, where f is the frequency of

oscillation. From the crossover point of G' and G'' plots against frequency the sol-gel

transition temperature were obtained.

2.5.9 Diffusion Order spectroscopy (DOSY NMR) Diffusion-ordered NMR spectroscopy (DOSY) has been introduced into NMR as a new

tool to analyze the composition of mixtures. The application of DOSY to determine the

composition of mixtures is based on the differences in diffusion coefficients of the

individual components. DOSY is the two-dimensional (2D) version of the pulsed field

gradient (PFG) spin echo experiment used for measuring the diffusion coefficient. In

DOSY, the results are displayed as a 2D spectrum in which signals are dispersed

according to chemical shift in one dimension and diffusion constant in the other.

The block copolymers were characterized by Diffusion order NMR spectroscopy using

Bruker 250 and 300MHz spectrometers using CDCL3 as solvent.

2.5.10 Fluorescence Measurements Fluorescence is the molecular absorption of light energy at one wavelength and its

nearly instantaneous re-emission at another, usually longer, wavelength. The CMC of

the block copolymer was determined by fluorescence spectroscopy using pyrene as a

hydrophobic fluorescent probe. Briefly, an aliquot of pyrene solution (6 *10-6 M in

acetone, 1 mL) was added to different vials, and the solvent was evaporated.

Then, 10 mL of aqueous solutions containing different concentrations of copolymer

were added to the vials. The final concentration of pyrene in each vial was 6*10-7 M.

Fluorescence measurements were performed on LS55 perkin Elmer spectrofluorometer

made in USA. The emission and excitation slit widths is 5 nm, respectively. The samples

were excited at 330 nm and emission spectra were recorded from 340 to 600 nm and

scan speed is 300nm/min. The emission fluorescence values I372 and I393, at 372 and 393

nm, respectively, were used for subsequent calculations.

The CMC was determined by plotting the I372/I393 ratio against the polymer

concentration. The CMC was taken as the intersection of regression lines calculated

from the linear portions of the plot.

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2.5.11 Surface Tension Measurements For measurement of surface tension, stock solution for each amphiphilic diblock

copolymer was prepared by dissolving 0.022g in 15mL toluene i.e stock solution was

1.5g/L. Stock solutions of each copolymer were diluted by the addition of toluene for

each measurement of surface tension each time. Surface tension for these solutions of

each copolymer was measured at temperatures ranging from, 20-50oC with the

difference of 10oC. Torsion Balance (White Elec. Inst. Co. Ltd.) equipped with a platinum

ring (4 cm circumference) along with a temperature controlled thermostatic water bath

(Irmeco) was used to measure the Surface tension. A special homemade glass cell for

holding the sample was used. The Sample cell had hollow space, an inlet and outlet for

circulation of water that helps in maintaining the desired temperature. The sample was

taken in the cell around which water with required temperature, was made circulated in

the hollow portion of cell and thus desired temperature of the sample was achieved.

The Torsion Balance was placed on a smooth supporting surface in such a position that

the dial was viewed easily and accurately. The balance was leveled by means of two

leveling screws in the tripod base so that the bubble in the spirit level was exactly in the

center. The platinum ring (4cm circumference) was attached to the extension hook. The

instrument was kept free from vibrations. The torsion balance was checked for zero and

calibrated with water. The platinum wire of the ring must be circular in one plane and

free from bends. All glassware was washed thoroughly using chromic acid followed by

rinsing with deionized water and were dried in oven.

After calibration of the instrument, stock solution was taken in the measuring cell

(having water circulation through the hollow space around measuring sample) and

placed on the platform below the ring. The position of the cell on platform was adjusted

in such a way that the sample’s surface was about 10 mm below the platinum ring. Then

unclamped the beam and moved the cell on platform up with the help of special screw

at the base of platform so that the ring was dipped in sample.

2.6 Synthesis of Gold Nanoparticles Polymethamethylacrylate-block-polyethylene oxide (PMMA-b-PEO) and polystyrene-

blockpolyethylene oxide (PS-b-PEO) having different block lengths were first synthesized

and then employed as a micelle forming block copolymer. For the small particles to be

generated inside the micelles, gold was chosen. 1% (w/w) PMMA-b-PEO and PS-b-PEO

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solutions of both block copolymers were prepared by dissolving the diblock copolymer

in toluene. Definite amount of LiAuCl4 (0.1 and 0.2 equivalents of LiAuCl4 bound per

ethylene oxide) was added to above solution. The mixture was facilitated by means of

ultrasound and a bright yellow solution I was obtained after 1 h. Then sodium

borohydride (NaBH4) powder was introduced into the system. The yellow colour for gold

solution turned into purple gradually.

After ultrasonic vibration and centrifugation of surplus NaBH4, a clear and dark purple

solution II was obtained. Solution of lower concentration was obtained by diluting a

part of this stock solution with toluene. Three different samples of each block

copolymer varying in block length of PS and PMMA were employed for the experiments

described here. In addition to that, Poly vinyl pyrrolidone (PVP) has also been used for

the generation of gold nanoparticles to compare the results between homo and block

copolymers.

2.7 Synthesis of Silver Nanoparticles Polymethamethylacrylate-block-polyethylene oxide (PMMA-b-PEO) and polystyrene-

blockpolyethylene oxide were synthesized and then employed as a micelle forming

block copolymer. For the small particles to be generated inside the micelles, it was

decided to silver. Under the conditions employed, PMMA-b-PEO and PS-b-PEO

associates to form micelles in a non-polar solvent (toluene). 1% (w/w) PMMA-b-PEO and

PS-b-PEO solutions were prepared by dissolving the diblock copolymer in toluene.

Definite amount of AgNO3 (0.1, 0.2 and 0.3 equivalents of AgNO3 bound per ethylene

oxide) was added to above solution. The mixture was facilitated by means of ultrasound

and a semi-transparent solution I was obtained after 1 h. Then sodium borohydride

(NaBH4) powders were introduced into the system. The semi-transparent for silver

solution turned into purple gradually.

After ultrasonic vibration and centrifugalization of surplus NaBH4, a clear and dark

purple solution II was obtained. Solution of lower concentration was obtained by

diluting a part of this stock solution with toluene. Three different samples of each block

copolymer varying in block length of PS and PMMA were employed for the experiments

described here.

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2.8 Characterization of Nanoparticles

2.8.1 UV/visible Spectrophotometer Measurements The formation of elemental gold and silver was confirmed by UV/Vis absorption

spectrum using an Agilent 8453 UV-Visible Spectrophotometer with 1.0 cm path length

quartz cuvette, monitoring the presence of a peak around 520 nm of gold nanoparticles

and 410 nm of silver nanoparticles.

2.8.2 Transmission Electronic Microscopy (TEM)

Analysis A small drop of diluted solution of nanoparticles with a block copolymer concentration

of 0.1%, was put on a carbon-coated copper grid for casting. The liquid was immediately

removed by means of a soaking tissue. The films were studied by transmission electron

microscopy (JEOL JEM 1200, 80 kV). In order to minimize the destruction of the polymer

by the electron beam, the electron beam intensity was kept as low as possible. The

formation of micellar monolayers was controlled by the qualitative determination of the

electron absorption, which is sensitive to the layer thickness.

2.8.3 Scanning Electronic Microscopy (SEM)

Analysis

One drop of a diluted black purple solution with a block copolymer concentration of

0.1% in toluene was placed on a carbon-coated copper grid and the solvent allowed

evaporating. Scanning electronic microscope (SEM) micrographs (JEOL JSM.6480LV)

were recorded. In order to minimize charging and damage to the polymer, the electron

beam intensity was kept as low as possible.

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CHAPTER-3 RESULTS AND

DISCUSSION

3.1 1H NMR Characterization

The PEO macroinitiator was prepared by reaction of MePEO (Mn = 5000, Mn = 2000, Mn

= 750) with an α-Chlorophenylacetylchloride. This material was used in ATRP reactions

with varying amounts of styrene to synthesize three copolymers having structure as

PS61-b-PEO113, PS72-bPEO113 and PS88-b-PEO113 (Appendix 1). NMR results showed

essentially a quantitative reaction. Integration of the aromatic and aliphatic peak region

gave 56 wt.% PS, so the molecular mass (Mn) of PS was 6,300 g mol−1 (Fig. 3.1, Sample

spectra for PS61-b-PEO113) and for the rest of the two products was 7,500 g mol−1 and

9200 g mol−1.

Figure 3.1: 1H NMR spectrum of polystyrene88-block-polyethylene oxide113

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Appendix-1: Mechanism for the synthesis of PEO macro-initiator and block copolymer PS-b-

PEO.

Cl

Ph Ph

PEO-b-PS

The proton1H NMR spectra of polymer solutions of the diblock copolymer having

different block length (PMMA7-b-PEO17, PMMA20-b-PEO45, & PMMA50-b-PEO113) in CDCl3

using TMS as a reference were recorded and is shown in (figure 3.2, sample spectrum

for PMMA50-bPEO113). The mechanism for the reaction is shown in Appendix 2.

The block copolymer composition was determined by the ratio of the NMR signal

intensities of the methoxy peak region to that of the PEO region. All the spectra show

the same pattern of aliphatic proton peaks while the characteristic peak at 3.6 ppm

attributed to the methyl ester group of PMMA in Figure 3.2 as well as the multiplets at

[

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the regions 1.5–2.1 ppm, attributed to the methylene- and a-methyl-group of PMMA

[120]. Moreover, a small broad peak at 3.7 ppm and a shoulder at 1 ppm are observed,

corresponding to the methoxy- and a-methyl- groups of MMA units. This is also due to

the tendency of PMMA blocks to form aggregates.

Figure 3.2 : H1NMR Spectrum of polymethylmethacrylate50-block-polyethylene oxide113

Appendix-2: Mechanism for the synthesis of PEO macro-initator and block copolymer

PMMA-b-PEO.

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3.2 Fourier Transform Infra Red Spectroscopy

(FTIR) Measurements FTIR spectroscopy was applied to study the behavior of block copolymers consisting of

PEO,

MMA and styrene segments. The advantage of using infrared spectroscopy to

investigate PS-bPEO and PMMA-b-PEO diblock copolymers is evident that the several

bands in the spectra are sensitive to the structure and conformational change of

copolymers. The PS-b-PEO and PMMAb-PEO dependence of spectra features is

explained as the structure and conformational difference of PMMA50-b-PEO113 and PS61-

b-PEO113 diblock copolymers [121]. The block copolymers and homopolymer PEO, PS and

MMA shows in figures (3.3 to 3.6) the conformational changes along with the

temperature change. Above transition temperature, they all form the disorder structure

as the homopolymer MMA.

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Figure 3.3: FT-IR spectra of PS and PEO homopolymer standards

Figure 3.4: FT-IR Curve of Amphiphilic Diblock copolymer PS61-b-PEO113

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Figure 3.5: FT-IR spectra of PMMA homopolymer standard

Figure 3.6: FT-IR spectra of amphiphilic block copolymer PMMA50-b-PEO113.

The FT-IR spectrum for the amphiphilic block copolymer of PS61-b-PEO113 and PMMA50-

bPEO113 were shown in figure 3.4 and 3.6. The following absorption bands of block

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copolymer PS61-b-PEO113: at about 3388cm-1 and 3025.91 cm-1 –OH group vibration from

‒COOH is observed: 2886 cm-1 [ῡ (CH, CH2)]; at 1723cm-1 [ῡ(‒C=O)]; and 695.92cm-1

[ῡ(aromatic ring of styrene)]. PS has a strong absorption at 695.92 cm-1 due to the

asymmetric C‒H stretching, while the strongest absorption of PEO is the triplet at

1106.18 cm-1 due to the C‒O‒C asymmetric stretching. FT-IR spectra of PS61-b-PEO113 is

shown in Figure. 3.4. The following absorption bands of block copolymer PMMA50-b-

PEO113: at about 2996.26 cm-1‒OH group vibration from –COOH is observed: 2949.91 cm-

1 [ῡ (CH, CH2)]; at 1723cm-1 [ῡ(‒C=O)]. PMMA has a strong absorption at 750.04 cm-1

due to the asymmetric C‒H stretching, while the strongest absorption of PEO is the

triplet at 1143.33 cm-1 due to the C‒O‒C asymmetric stretching [122]. FT-IR spectra

verified that the carbonyl band ῡ(‒C=O group) at 1723 cm-1 in figure. 3.6.

3.3 Laser light scattering measurements Light scattering is of two types one is static laser light scattering and second is dynamic

laser light scattering. Static laser light scattering was employed to measure the weight-

average molecular weight (Mw) [123]. Before going into the measurements of static light

scattering, it was necessary to obtain the refractive index increment (dn/dc) which was

successfully done by digital Optilab Differential Refractrometer, supplied by Wyatt,

USA. The value of refractive index increment obtained were 17.81, 17.45 and17.24 dL/g

for the polymer samples PS61-b-

PEO113, PS72-b-PEO113and PS88-b-PEO113, respectively. A typical Zimm plot is displayed in

Figure. 3.7. The results obtained for molecular mass of three samples was 1.46×104,

1.51×104 and 1.68×104 g/mol.

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Figure 3.7: A typical Zimm plot of PS61-b-PEO113 block copolymer dissolved in THF and

measured at 25 °C

Hydrodynamics radius (RH,app) of block copolymers micelles was determined by dynamic

light Scattering method. A typical correlation curve is depicted in figure 3.8 obtained for

PS61-b-PEO113.

Figure 3.8: A typical autocorrelation functions obtained for PS61-b-PEO113 copolymer

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The results obtained for RH are displayed in figure. 3.9 and the insertion of the

figure displays only dilute range of concentration. The data show that RH increases slowly

and smoothly till the concentration of copolymer approached to about 0.095 g/dL.

However, if the concentration further increases the RH value increases sharply indicating

the formation of micelles [124]. Therefore, the concentration at which a sharp increase

in RH was observed, considered as CMC. The figure 3.9 also shows that if the

concentration increases beyond 0.5 g/dL, the rate of increase in RH with concentration

also decreases that is attributed to the change in shape of the micelles with the

concentration [125].

Figure 3.9: Hydrodynamic radius as a function of concentration of copolymer and contents of

polystyrene in the copolymer. The insertion shows the same data for dilute concentration

The results obtained for CMC of all the samples obtained through this method

are displayed in figure 3.10 as a function of temperature as well as polystyrene contents.

The data concluded that the CMC decreases with the increase in polystyrene contents as

well as temperature showing a thermodynamic deterioration of the solvent [126]. This

means that the solvent used was the selective solvent for PS block. Further the results

showed good agreement with the available values in the literature for similar sort of

copolymers [127].

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Figure 3.10: CMC of block copolymers as a function of temperature

Apparent hydrodynamics radius (RH,app) of micelles of diblock copolymers (PMMA-b-

PEO) having different block lengths of PMMA and PEO also determined by Dynamic Light

Scattering method. The measurements were carried out at 90° and at different

temperatures (20, 30, 40 and 50oC) keeping polymer concentration at 2 g/L. The values

of apparent hydrodynamic radii for each copolymer are given in the figure 3.12. It was

noted that the hydrodynamic radii of all the three diblock copolymers decreases as the

temperature increases. It was reported earlier [128] that the hydrodynamic value

depends on temperature and association number (which decrease with increasing

temperature). Increasing the temperature to 50oC, the apparent hydrodynamic radius

were decreases to 72.5nm for PMMA7-b-PEO113 and 78nm for PMMA20-b-PEO113 which

show the change in size of the micelle [129]. The apparent hydrodynamic radius of

micelles decreases with temperature for the diblock copolymers because of the

repulsive interaction among the outer portions of micelles in bulk. When the number of

micelles is increased in a system, the reduction [130] occurred in their size as a result of

their closeness. The values of hydrodynamic radius (RH,app) decreases with increase of

temperature but increase with PMMAblock length.

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Figure 3.11: A typical autocorrelation functions obtained for PMMA50-b-PEO113 copolymer in

water

Figure 3.12: Apparent hydrodynamic radius (RH) as a function of Temperature (K) for

PMMA-b-PEO of amphiphilic diblock copolymer.

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3.4 Gel permeation Chromatography/Size Exclusion Chromatography

(GPC/SEC) The GPC/SEC measurements were carried out to determine the number average

molecular mass and polydispersity index of the block copolymers synthesized during this

investigation. The GPC traces of the block copolymers (PS-b-PEO) were found

symmetrical. The traces are observed to move towards lower elution volume with the

increasing molecular weights (figure 3.13). A slight tailing of the peaks towards lower

molecular weights was probably due to thermal self-initiation of styrene during the

course of the polymerization [131].

While, the traces of GPC are symmetrical and found to increase with increasing

molecular weights in the case of PMMA-b-PEO. The GPC traces confirm the formation of

diblock copolymers with the sequential addition and the polydispersities were found in

the range of 1.081.7. At lower molecular weights the polydispersities were greater and

decrease with increasing molecular weights [132]. Figure 3.14 shows the GPC profile of

PMMA50-b-PEO113.

The molecular weight and degree of dispersity of the polymer samples synthesized

measured through size exclusion chromatography are given in Table 3.1.

Figure 3.13: GPC traces of samples of block copolymers PS-b-PEO

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Figure 3.14: GPC traces of samples of PMMA-b-PEO diblock copolymer

Table 3.1: Molecular weight, degree of dispersity of the samples of the copolymers. S. No Polymer sample Mn x 104 (g/mol) PDI

1 PS61-b-PEO113 1.13 1.29

2 PS72-b-PEO113 1.25 1.21

3 PS88-b-PEO113 1.42 1.18

4 PMMA50-b-PEO113 1.43 1.08

5 PMMA20-b-PEO113 1.38 1.10

6 PMMA7-b-PEO113 0.45 1.78

3.5 Dilute Solution Behaviour of Block Copolymers The relative viscosity for the three PS-b-PEO copolymers was measured at different

temperatures as a function of concentration, and the one obtained at 30°C is plotted in

figure. 3.15. It was observed that the relative viscosity increased with the concentration

for all the samples, irrespective of investigated temperatures, indicating very strong

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interactive forces between the polymer and the solvent. The slope of these curves was

plotted in figure. 3.16. The figure demonstrated that the slopes were positive and were

increased with the increase in PS contents. This trend indicated that the solubility of the

polymers was controlled through PS block and longer the PS block more the interactions

were observed.

Figure 3.15: Variation of relative viscosity with concentration of amphiphilic block

copolymers PS-b-PEO having different PS block length and measured at 30°C

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Figure 3.16: Slopes of plots of relative viscosity versus concentration as a function of

temperature for PS-bPEO block copolymers

The reduced viscosity of the material was calculated for different block lengths of PS in

PS-bPEO and at different temperatures. The results obtained were plotted versus

concentration, and typical plots of reduced viscosity versus concentration for PS-b-PEO

at 20oC are displayed in figure. 3.17. The trend shown in the figure was attributed to

lowering of hydrodynamic volume of micelles [133] as observed through light scattering

data. The intrinsic viscosity obtained from the data of dilute region of concentration is

plotted as a function of temperature in figure. 3.18. The figure indicates that it increases

with the increase in temperature and is attributed to expansion of micelles with the

temperature.

Figure 3.17: Reduced viscosities of block copolymers as a function of concentration measured

at 20 °C for PSb-PEO

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Figure 3.18: Intrinsic viscosities of copolymers as a function of temperature

Viscometric investigations of the diblock copolymer (PMMA-b-PEO) were carried out at

different temperatures ranging from 293-323K. First of all Relative viscosity was

measured and then converted to specific viscosity ( sp) which was in turn converted to

reduced viscosity ( red).

For conversion of different types of viscosity equations no. (1.4, 1.5 and 1.6) were used.

All these types of viscosities calculated with the help of above equations decrease with

increase in temperature. It was also noted that at given temperature, with increase in

concentration all of these types of viscosities increase [134]. The relative viscosity for

the PMMA-b-PEO diblock copolymers at 20oC was plotted as a function of concentration

shown in figure 3.19. It was observed that the relative viscosity increased with the

concentration for all the samples, irrespective of investigated temperatures, indicating

very strong interactive forces between the polymer and the solvent. The slopes of these

curves are positive and increased with the increase in concentration. This trend

indicated that the solubility of the polymers was controlled through PMMA block and

longer the PMMA segment more the interactions were observed [135]. The

measurements were also carried out at three higher temperatures (20, 30, 40 and 50oC)

but are shown here because of showing similar trend.

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The result obtained for reduced viscosity were also plotted as a function of

concentration and are shown in the typical plots of reduced viscosity versus

concentration for PMMA-b-PEO having different block lengths of PMMA at 20oC figure

3.20. The reduced viscosity of diblock copolymer was found to increase as the

concentration increases but gradually decrease as the temperature increases. This trend

was attributed to lowering of hydrodynamic volume of micelles [136] as observed

through light scattering data.

In order to determine intrinsic viscosity, Huggins’s relationship (equ.1.4) was used.

When the temperature increases Huggins’s constant (KH) also increases and is shown in

figure 3.21. The decrease in intrinsic viscosity at a high temperature figure 3.22 is due to

the variation in shape of micelles which changes from spherical to cylindrical. The

cylindrical particles are more resistive as compared to spherical particles [137]. The

relative viscosity for the three PMMA-b-PEO copolymers was plotted as a function of

concentration at 30oC in figure 3.19. The relative viscosity increases with the increase in

concentration for all the samples at the whole range of temperatures investigated. The

plots clearly indicate a very strong interactive forces between the polymer and the

solvent which are responsible for the linearity of the plot.

Figure 3.19:Variation in relative viscosity with concentration of block copolymers at 30 oC

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Figure 3.20: Variation in reduced viscosity with concentration of block copolymers at 20 oC

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Figure 3.22: Plots of Intrinsic viscosity values of three block copolymer PMMA-b-PEO

versus temperatures

3.6 Morphological/Self Assembling Behaviour of

Block copolymers TEM micrographs of PS61-b-PEO113 diblock copolymer cast from 1-wt.% toluene solution

onto carbon coated copper grids and stained with osmium tetraoxide (a) at low

magnification (b) at high magnification are given in figure. 3.23. Morphology of two-

dimensional arrays of hexagonal-like holes was distinctly observed in the samples cast

Figure 3.21: Plots of Huggins’s constant values of three block copolymer PMMA - b - PEO versus temperature

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onto the carbon coated copper grid. Other groups have also reported hexagonal

patterns [138] and the self-assembling behaviour of PS61-b-PEO113 diblock copolymers in

selective solvents. They suggested that the formation mechanism was self-assembling of

coil segments into hollow spherical micelles with diameter of a few micrometers, and

subsequently self-organized into two-dimensional hexagonal super lattice prior to film

casting and evaporation of the solvent. From their findings, the selection of the right

solvent was a critical parameter to obtain the ordered superstructure [139]. However, it

has also been demonstrated that triblock coil–rod–coil copolymers in a volatile

nonselective solvent form two-dimensional ordered hexagonal structure [140]. In this

work, the structure of hexagonal holes was observed in a coil–coil diblock copolymer in

a non selective solvent, but not a rod-coil block copolymer. Other scientists also found

such morphologies in linear PS or linear carboxylate-terminated PS in volatile solvent

and suggested that formation of such morphologies are due to the film forming process

and are less influenced by molecular architecture [141]. Rapid evaporation of the

solvent resulted in cooling of the surface of polymer solution due to which small water

droplets were absorbed on the surface.

Figure 3.23:TEM micrographs of PEO61-b-PS113 di-block copolymer casted from 1-wt.%

toluene solution onto carbon coated copper grids and stained with osmium tetraoxide (a) at

low magnification (b) at high magnification

During the phenomenon, the polymer could verify the pattern created by the

condensation of the water droplets due to evaporation of the organic solvent.

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Srinivasarao and Collings [142] have summarized the relevant literature and ascribed the

formation of hexagonal patterns. Thus, we suggest that the morphology of two-

dimensional arrays of hexagonal-like holes was formed due to the rapid evaporation of

solvent and the condensation of small water drops on the solution surface which was

mainly dependent over the film forming process [143]. Therefore, humidity level can

play key role in getting the final patterns. The hexagonal pattern was not observed in

TEM images of the mixed homo polymers PS and PEO cast from the same solvent

system stained with osmium tetraoxide figure. 3.24 and with phosphotungstic acid

figure. 3.25 which was contrary to block copolymer.

Figure 3.24:TEM micrographs of mixture of PS and PEO (50:50) stained with osmium

tetraoxide

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Figure 3.25: TEM micrographs of mixture of PS and PEO (50:50) stained with

phosphotungstic acid

3.7 Differential Scanning Calorimetry (DSC)

Measurements Differential Scanning Calorimetry (DSC) measures the temperatures and heat flows

associated with transitions in material as a function of time and temperature in a

controlled atmosphere. These measurements provide quantitative and qualitative

information about physical and chemical changes that involve endothermic or

exothermic processes, or changes in heat capacity and glass transition temperature

[144].

Figures (3.26-3.31) represents the data obtained from the DSC measurements for PS-b-

PEO and PMMA-b-PEO having different block length of PS and PMMA respectively.

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Figure 3.26: DSC heat scans of diblock copolymer PS61-b-PEO113

Figure 3.27: DSC heat scans of diblock

copolymer PS72-b-PEO113

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Figure 3.28: DSC heat scans of diblock copolymer PS88-b-PEO113

Figure 3.29: DSC heat scans of diblock copolymer PMMA7-b-

PEO113

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Figure 3.30: DSC heat scans of diblock copolymer PMMA20-b-PEO113

Figure 3.31: DSC heat scans of diblock copolymer PMMA50-b-

PEO113

The mid points of highest variations were considered as the Tg and are given in the

table. The Tgs of diblock copolymers of the type PMMA-b-PEO prepared by ATRP is

nearly equal to 125°C, reported by Moineau et., al and Quin et al, respectively [145].

Only a single glass transition temperature, appearing above 110°C reported by

researches [146] is observed for all block copolymers. This is an indication that these

block copolymers represent only one phase. The Tg of the block copolymers increases as

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the PS and PMMA segment increases in accordance with earlier reports [147]. The effect

of increased chain length gave also two Tg transitions, still confirming the existence of

phase separation. As the molecular weight increases a slight broadening of the

transition occurs. In general, the Tgs in block copolymers can be influenced by the sizes

of the phases generated and the compatibility of the different components (blocks).

According to Buzin et. al [148] in the case where the two blocks in a diblock copolymer

are incompatible, the lengths of the two segments are the determining factor for the

sizes of the phases generated due to micro phase separation; the morphology of the

later will depend on their ratio. The Tgs of all components are affected by the continuing

molecules that cross the interface.

Table 3.2: Tg and ∆H values of all polymer samples of PS-b-PEO and PMMA-b-PEO

determine from DSC measurements. S.N0 Samples Tg oC ∆H J/g

1 PS61-b-PEO113 88.42 43.39

2 PS72-b-PEO113 128.91 7.640

3 PS88-b-PEO113 167.34 2.980

4 PMMA7-b-PEO113 76.00 12.580

5 PMMA20-b-PEO113 117.80 89.040

6 PMMA50-b-PEO113 133.95 0.5130

3.8 Thermal Analysis (TGA/DTA) Measurements Thermogravmetric analysis of the all diblock copolymers PS-b-PEO and PMMA-b-PEO

having different block lengths were carried out to study thermal stability. The two main

thermal analysis techniques are Thermogravimetric analysis (TGA) which automatically

records the change in weight of a sample as a function of either temperature or time,

and the differential thermal analysis (DTA), which measures the difference in

temperature; DTA therefore detects change in heat content.

The TGA and DTA thermograms of two different diblock copolymers PS-b-PEO and

PMMA-bPEO having different block lengths of PS & PMMA respectively are shown in

figures 3.32 and

3.33.

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Figure 3.32: TGA and DTA thermograms of amphiphilic block copolymer PS-b-PEO

Figure 3.33: TGA and DTA thermograms of amphiphilic block copolymer PMMA-b-PEO.

The TGA/DTA curves show that the block copolymer has one main weight loss region

that are plotted in figures. 3.32 and 3.33. The plots shows that the PS-b-PEO and

PMMA-b-PEO block copolymer degraded continuously at single step process [149]. The

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block copolymer was stable up to 250Co and 350Co respectively. The presence of PS

block decreases slightly the degradation temperatures. Besides The TGA curves showed

the maximum decomposition of the materials nearly at 397Co and 542Co.

Figure 3.33 indicates that Tonset (temperature at 5wt % loss) and Tmax (maximum

degradation temperature) increase slightly with increasing PMMA length. This is

probably due to the easier degradation of PMMA part, as its tertiary carbon is more

prone to thermal degradation. The TGA thermograms show the weight loss with a

heating rate of 10°C/min in the temperature range from 0°C to 600°C for all diblock

copolymer. It is clear that in figure 3.33 the initial weight loss from the TG curve is 11%

from the temperature of 35°C to 299°C and 20% weight loss in the temperature range of

32°C to 289°C for shorter PMMA block length .This weight loss corresponds to the

decomposition of the main chain [150]. The difference in the thermal degradation could

be attributed to the difference in the microstructure and arrangement of copolymer

segments. It is expected that PMMA segments have a more pronounced effect on

thermal degradation. In the DTA curve, two exothermic peaks are observed at 200°C

(sharp) and 299°C (strong), respectively as shown in figure 3.33 demonstrating the

degradation of each polymers, no weight loss is observed above 500°C for both

polymers, which indicates the completion of the degradation process of polymer at this

temperature. The thermal degradation of PMMA is usually attributed to chain scission,

resulting in depolymerisation [151] and it is influenced by the type of polymerization

[152]. The TGA curve of both diblock copolymers displays one main reaction stage,

which is reflected in one peak in the DTA curve. The maximum temperature of

degradation for this polymer is observed at 299°C. It has been noted that the evolved

energy was increased with the increase in molecular mass of the polymer and the

pattern was similar to other thermal properties.

3.9 Rheological Measurements To see the effect of shear forces over the both PS-b-PEO and PMMA-b-PEO having

different block lengths of PS and PMMA respectively, the rheological measurements

were performed just after the preparation of solutions using various oscillating

frequencies.

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Figure 1-3 represents the loss modulus, storage modulus and viscosity as a function of

frequency for PS61-b-PEO113, PS72-b-PEO113, PS88-b-PEO113.

Figure 3.34: Master curves of G' and G" as a function of frequency for the diblock copolymer

(A) PS88-bPEO113 (B) PS72-b-PEO113 (C) PS61-b-PEO113

Figure 3.35: Master curves of G' and G" as a function of frequency for diblock copolymer (A)

PMMA50-bPEO113 (B) PMMA20-b-PEO113 (C) PMMA7-b-PEO113

Measurements at higher temperatures were not performed because of possible

degradation of PMMA and PS during the relatively long duration of shear oscillations.

Since diblock copolymers consist of two different block length which generally are

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associated with different Williams-Landel-Ferry shift factors. Furthermore,

morphological characteristics might change with temperature because of the

temperature dependence of the Flory- Huggins interaction parameter. In this work

curves were constructed in order to demonstrate the quality of the fit and to discuss the

frequency behavior of the polymer [153].

The data for the PS61-b-PEO113, PS72-b-PEO113 and PS88-b-PEO113 diblock copolymer is

given in figure 3.34 and for the PMMA7-b-PEO113, PMMA20-b-PEO113 and PMMA50-b-

PEO113 diblock copolymer is given in figure 3.35. In the frequency range from 10 rad/s to

1000 rad/s the entanglement plateau appear with G' larger than G". The width of this

rubbery plateau attains the largest value for the block copolymer with the largest block

length i.e PS88-b-PEO113 and PMMA50-b-PEO113 and the lowest value for the block

copolymer with a lower block length i.e PS61-b-PEO113 and PMMA7-b-PEO113.

Furthermore the cross over point of G' and G" at low frequencies cannot be detected in

the master curves since the all block copolymers are in the microphase separated state

up to our highest block length [154]. The curves of G' and G" in the low frequency range

for the data of PS72-b-PEO113 and PS61-b-PEO113 are roughly parallel which corresponds to

power-law behavior. Such a power-law with a power-law exponent in the order of

½ is typical for block copolymer with a lamellar morphology has been theoretically

explained by Kawasaki and Onuki [155].

On increasing the block length of copolymer, storage modulus (G') and loss modulus (G")

increased as the frequency increased up to 4Hz, but decreased sharply with increase in

frequency. This indicated that the gels, produced with PMMA50-b-PEO113 were not

strong or in other words they were not as flexible as to form appropriate gel. The rate of

increase for G' is greater than G", and when the G' crossover G" at a frequency point at

which G'=G". This crossover frequency is the characteristic frequency (ω*). This ω* is

also a transition point where the sample changes its behavior from liquid to solid like.

From the rheological studies we found that PS61-b-PEO113 gel had poor mechanical

property in a highly swollen state and the reason of this was thought to be rapid

precipitation and a smaller polymer weight unit volume [156]. When we look to diblock

copolymers profile, storage modulus and loss modulus increased when the frequency

increase figure 3.34 and 3.35. Sharp change for diblock copolymer started 2 to 6 Hz. It

was assumed that the frequency change in the gel formation was because of the

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content of the PMMA and PS segments in the larger diblock-co-polymer. PMMA and PS

is hydrophobic polymer that prolongs the precipitation of PEO as a results it prolongs

the formation of gel. When we compare the G' and G" of both polymer there is a huge

difference between G' and G", this means polymers form the gel with an increasing

frequency and maintain the form of the gel figure 3.34. Because copolymerization

increases polymer mass per unit volume [157].

In case of dilute solutions the weak interdroplet interactions occurs, the diblock

copolymer behave like a liquid after being subjected to low stress for long time (low

frequency). But in concentrated solution there is no domination of the loss modulus G"

over the storage modulus G' its means that the applied stress is able to be stored in the

elastic component although at low shear rate [158].

3.10 Diffusion Order Spectroscopy (DOSY)

Measurements The critical micelle concentration (CMC) of the copolymer was determined by 2D DOSY.

The micelle copolymer solutions were prepared by direct dissolution of copolymer in

deuterated water at different concentrations [159]. The values for the diffusion

coefficients D were collected at these different concentrations. The CMC was

determined by plotting the diffusion coefficient against the inverse of the polymer

concentration. Two slopes are obtained and the CMC was taken as the intersection of

these two lines [160]. The diblock copolymers, namely PS61-bPEO113 and PMMA50-b-

PEO113 and homopolymer PS and PEO were characterized by DOSY NMR (figures. 3.36 to

3.40) in order to measure the CMC. The CMC was taken as the intersection of regression

lines calculated from the linear portions of the plot in figures (3.41 and

3.42). In fact, DOSY NMR can also provide evidence of block copolymer formation [161].

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Figure 3.36: 600 MHz 2D DOSY NMR spectra obtained at 298 K for the standard PEO solution in CDCl3

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Figure 3.37:600 MHz 2D DOSY NMR spectra obtained at 298 K for the standard PS

solution in CDCl3

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Figure 3.38: 600 MHz 2D DOSY NMR spectra obtained at 298 K for the copolymer PS61-b-

PEO113 solution in CDCl3.

Table 3.3: Diffusion analysis of PS61-b-PEO113 block copolymer

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Figure 3.39: 600 MHz 2D DOSY NMR spectra obtained at 298 K for standard PMMA

solution in CDCl3

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Figure 3.40: 600 MHz 2D DOSY NMR spectra obtained at 298 K for copolymer PMMA50-b-

PEO113 solution in CDCl3

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Table 3.4: Diffusion analysis of PMMA50-b-PEO113 block copolymer

Figure 3.41: Determination of the CMC for PS61-b-PEO113 from DOSY NMR measurements

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Figure 3.42: Determination of the CMC for PMMA50-b-PEO113 from DOSY NMR

measurements

Investigations concerning the formation of micelles in water were then carried out using

the DOSY NMR experiments. Figures 3.38 and 3.40 shows the DOSY NMR of the PS61-b-

PEO113 and PMMA50-b-PEO113 Copolymers in Chloroform solvent. Chloroform was

expected to preferentially solubilise the hydrophilic PEO part of copolymer. Indeed as

shown on the DOSY map figure 3.36 only the spot corresponding to PEO block was

visible whereas no spot corresponding to the hydrophobic PS or PMMA block was

observed due to the limited molecular motion of the moiety in aqueous solvent [162].

This phenomenon can be interpreted by the formation of micelles or aggregates where

the hydrophobic PS and PMMA part of the copolymer forms the core and the

hydrophilic PEO part forms the shell.

Critical micelle concentration (CMC) of this copolymer was determined by different

techniques including DOSY NMR, Fluorimetry, surface tension and Laser light scattering.

Similarly CMC values were obtained in all cases. Therefore one can conclude that DOSY

NMR is an efficient and accurate method to determine the CMC of amphiphilic block

copolymers although this technique is obviously complementary and is not an

alternative to other techniques of characterization such as 1H or 13C NMR spectroscopy,

SEC chromatography, or MALDI-TOF spectroscopy [163].

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3.11 Fluorescence Measurements:

Figures 3.43 and 3.44 represents the fluorescence spectra for the block copolymers PS61-

bPEO113 and PMMA50-b-PEO113 which was further used to determine the CMC by

plotting the I372/I393 ratio against the polymer concentration in figures 3.46 and 3.47

respectively. The CMC was taken as the intersection of regression lines calculated from

the linear portions of the plot.

Figure 3.43: Fluorescence emission spectra of diblock copolymer PS61-b-PEO113 at indicated

concentrations in aqueous solutions using pyrene (6*10-7 M) as hydrophobic fluorescent

probe

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Figure 3.44: Fluorescence emission spectra of diblock copolymer PMMA50-b-PEO113 at

indicated concentrations in aqueous solutions using pyrene (6*10-7 M) as hydrophobic

fluorescent probe

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Figure 3.45: Fluorescence emission spectra of pyrene (6*10-7 M) in aqueous solutions 1.1 g/L

(concentrated) and 0.3 g/L (Dilute) concentration of diblock copolymer

Figure 3.46: Determination of the CMC by fluorimetry measurements of the block copolymer

PS61-b-PEO113

Figure 3.47: Determination of the CMC by fluorimetry measurements of the block copolymer

PMMA50-bPEO113.

Diblock copolymer PS61-b-PEO113 and PMMA50-b-PEO113 were dissolvable in aqueous

solution to form micelles due to the existence of hydrophobic blocks of PMMA and PS

which aggregated in water to form the core in the micelle. The micelle formation was

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commonly monitored with fluorescence spectrum of pyrene probe. Figures 3.43 and

3.44 depict the emission and excitation spectra of pyrene probe in aqueous solution of

the copolymers PS61-b-PEO113 and PMMA50-bPEO113 at various concentrations. The

fluorescence intensity of both emission and excitation spectra increases with increasing

polymer concentration which is attributed to increase in fluorescence quantum yield

induced by the change in microenvironment surrounding the probe.[164]

Thus I372/I393 value from pyrene excitation spectrum can provide the information about

the location of pyrene probes in the solution which is more sensitive to micelle

formation than I372/I393 from emission spectrum and more popularly used to determine

the CMC for amphiphilic copolymers in aqueous solution [165].

3.12 Surface Tension Measurements

Surface tension measurements were carried out in solutions of the block copolymers in

order to obtain information on the surface activity. CMC and micelle formation by the

block copolymers indicates the decreasing surface tension with increasing

concentration. It is clear from the plot that the surface tension decreases linearly with

the increase in copolymer concentration according to the Gibbs adsorption isotherm,

i.e., a usual behavior of surface-active compounds. At some characteristic

concentration, there is a clear inflection point above which the surface tension remains

almost constant. However, two inflection points can be seen in figure 3.48 and

3.49 where the surface tension is still slightly constant. The CMC of each diblock

copolymer is 0.8 and 0.7 g/L respectively. The lower CMC values clearly indicate as the

length of PMMA and PS segment increased, a reduced CMC values were observed.

These results were in good agreement with those by other researches [166, 167]. This

indicate that the CMC decreases with increasing block length because the hydrophobic

block forms more aggregates and the polymer solvent interactions becomes less i.e.,

solvent quality deteriorated with increase in temperature [168]. In other words, the

CMC decreases with increase in PMMA and PS content in the block copolymer, high

PMMA and PS segments enhances the surface activity of the copolymer.

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Figure 3.48: Plots of Surface tension as a function of concentration for PS61-b-PEO113 at

different oC temperatures (♦) 20, (■) 30, (▲) 40, (x) 50

Figure 3.49: Plots of Surface tension as a function of concentration for PMMA50-b-PEO113 at

different temperatures (♦) 20, (■)30, (▲)40, (x)50oC

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Figure 3.50: Plots of lnCMC of both block copolymers (▲) PS61-b-PEO113 and (♦) PMMA50-b-

PEO113 as a function of inverse temperature according to Arrhenius equation for the

determination of thermodynamic and surface parameters.

The thermodynamic parameters of micellization like ΔGmic, ΔHmic and ΔSmic for these two diblock

copolymers were calculated using equations (1.9, 1.13, 1.15 and 1.16) respectively. The

values of thermodynamic parameters of micellization are listed in (tables 3.5 and 3.6).

Values of Gibbs’s free energy of micellization for all these diblock copolymers are negative

which indicate that process of formation of micelles of all these polymers in the given

solvent (toluene) is a spontaneous process and over all Gibbs free energy of the system

decreases during this process in all cases [169, 170]. Reason of decrease of Gibbs’s free

energy of the system at elevated temperature is poor solvent quality to dissolve polymer

at high temperature. This decrease in ΔGmic value with increase of temperature is

according to Equation 1. So, micelles can be obtained easily and more spontaneously at

high temperature [171]. Effect of PMMA block length on surface and micellar parameters

is shown in table 3.5 and 3.6. So process of formation of micelle becomes less

spontaneous with longer PMMA-block length. That is why ΔGmic becomes less negative

with increase of PMMA-block length. The enthalpy of micellization for PS61-b-PEO113 and

PMMA50-bPEO113calculated by plotting lnCMC as a function of inverse of temperature

using equation 2 is shown in figure 3.50. ΔHmic is positive for process of micellization of

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these two diblock copolymers at all temperatures which indicates that this process is

endothermic process [172].

Small values of ΔHmic show that no bond breakage and new bond formation takes place

during this process because micellization is a physical process and only physical

interaction takes place during this process. So enthalpy of micellization is independent of

temperature. We can simply shift the equilibrium between unimer and micelles in micelle

direction by increasing temperature but enthalpy difference between the processes

coordinates always remains constant [173]. Effect of temperature on CMC value becomes

less significant by the addition of solvent; hence the rate of change of lnCMC with respect

to inverse of temperature decreases with the increase in quantity of toluene. Therefore,

ΔHmic decreases with PMMA and PS-block length. Entropy of micellization is positive for

both the diblock copolymers over the range of temperature investigated, which shows

that entropy of the system increases during this process. This is according to second law

of thermodynamics Since Smic is greater than Hmic value at all temperature in

micellization of these diblock copolymers, so Smic has major contribution in ΔGmic value

that is why micellization of these block copolymers is known as entropy driven process. It

is also supposed that greater the length of block copolymer units more is the hydration

and thus Smic and Hmic are relatively increased. These results indicate that the surface

activity of both diblock copolymers mainly depend on influence of hydrophobic chain

(PMMA and PS block) [174,175]. Surface excess concentration (Г), interfacial areas per

molecule (A°) and Gibb’s free energy of adsorption at airwater interface (ΔGads) are known

as surface parameters and calculated by equation (1.7, 1.8 & 1.13) respectively. The

values of these parameters are given in the Tables 3.5 and 3.6. Surface excess

concentration of all these diblock copolymers was decrease with the increase of

temperature. It is due to the adsorption of polymeric surfactants at air-solvent interface.

The decrease in area per molecule with the increase of temperature due to thermal

expansion of hydrophilic coil at air-solvent interface [176,177]. It can also be attributed to

poor quality of solvent at elevated temperature because area per molecule is in fact, the

cross-sectional area of the hydrophilic group at the interface. Since interfacial area per

molecule becomes greater at high temperature, which results in inverse effect on the

surface excess concentration with the increase in temperature. Increase in the area per

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0

molecule at interface is a result of increased molecular motions at higher temperature

[178]. Surface excess concentration and surface area is also function of PS and PMMA-

block length as shown in tables. Gibb’s free energy of adsorption at air-solvent interface

ΔGads is negative for adsorption of these diblock copolymers at air-solvent interface which

indicates that process of adsorption is spontaneous process but ΔGads becomes less

negative for larger PS and PMMA-block copolymers. Ability of larger PS and PMMA-block

copolymer to go to bulk is greater than smaller PS and PMMA-block [179, 180].

Table 3.5: The critical micelle concentration (CMC) and thermodynamic parameters of

micellization, interfacial area per molecule, surface excess concentration and Gibbs free

energy of adsorption at various temperatures for PS61-b-PEO113in toluene.

S.No T (oC) CMC

(g/L)

ΔGmic

(KJ/mol)

ΔHmic

(KJ/mol)

TΔSmic

(KJ/mol)

A

(nm2)

Ґ x10-3

(mol/m)

ΔGads

(KJ/mol)

1. 20 0.8 -17.3 9.09 26.4 0.91 1.82 -4.3

2. 30 0.7 -18.2 9.09 27.3 1.07 1.54 -6.2

3. 40 0.6 -19.3 9.09 28.3 1.31 1.26 -9.3

4. 50 0.5 -20.4 9.09 29.4 1.50 1.10 -11.7

Table 3.6: The critical micelle concentration (CMC) and thermodynamic parameters of

micellization, interfacial area per molecule, surface excess concentration and Gibbs free

energy of adsorption at various temperatures for PMMA50-b-PEO113 in toluene.

S.No T (K) CMC

(g/L)

ΔGmic

(KJ/mol)

ΔHmic

(KJ/mol)

TΔSmic

(KJ/mol)

A x 10-3

(nm2)

Ґ x 10-3

(mol/ m2)

ΔGads

(KJ/mol)

1. 293 0.7

-17.69 10.82 28.51 1.12 1.47 -5.2

2. 303 0.6 -18.68 10.82 29.5 1.45 1.14 -10.2

3. 313 0.5 -19.77 10.82 30.5 1.70 9.74 -12.01

4. 323 0.4

-21.01 10.82

31.8 2.08 7.97 -17.2

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3.13 Gold Nanoparticles, Sonication Time

Dependence The nanoparticles of gold were prepared (by loading different ratios) by using PS61-b-

PEO113,

PS72-b-PEO113, PS88-b-PEO113 and PMMA50-b-PEO113 as a micelle forming polymer by the

technique clearly mentioned in the experimental section.

Appendix-3: Mechanism for the preparation of gold and silver nanoparticles with block

copolymer. For the purpose of comparison of data, the gold nanoparticles were also

generated using PVP as well. The formation of elemental gold was confirmed by the

UV/Vis absorption spectra showing the typical Plasmon resonance around 520 nm [181].

Figure 3.51 shows a typical series of absorption spectra recorded during the borohydride

reduction reaction. The spectra for the gold nanoparticles (at different sonication times)

of the block copolymer samples and PVP each showed an absorption maximum in the

range of 519 nm to 525 nm depending upon the particle size (Figures 3.53 – 3.55). A

lower absorption maximum wavelength is associated with a smaller average size of the

Au particles [182,183].

It has been established that two major factors which control the size and arrangement

of the nanoparticles are the stability of the copolymer micelles in the media and the

strength of the interactions between the PEO block and the gold nanoparticles [184]. In

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0

this case, the interactions are relatively weak so that the micelles are not affected by the

process of particle formation and, in turn, do not influence particle growth to any great

extent, for example by adsorption of the polar block onto the growing nano-crystallites.

By comparison, the interactions between PVP and Au are rather strong [185] and it has

been reported that a high density of small Au crystals distributed in PVP did not

agglomerate because of the formation of polymer bridges between crystallites. The

bridging effect can potentially be eliminated by adding a third component [186,187].

Also of interest is the previously unreported time dependence of the UV spectra. Figure

3.53 shows that the absorbance increases as the reduction reaction proceeds due to the

formation of higher concentrations of nanoparticles. Significantly, the wavelength of

maximum absorption does not change, indicating only small variation, if any, in average

particle size [188]. However, of potentially greater interest is that further changes occur

after sonication is stopped. Figures 3.53 – 3.55) show the absorbance continues to grow

for around 10 min (except in the case of PS88-b-PEO113, the longest polystyrene block)

even when the reaction vessel is removed from the ultrasound bath but then falls

markedly. We ascribe this to agglomeration [189] of the small nanoparticles into larger

clusters. In the case of PS88-b-PEO113, the absorbance simply decreased with the

sonication time which may be due to its high molecular weight or disintegration of

bridged micelles and aggregated particles. In the same results for gold nanoparticles of

PMMAb-PEO shown in figure 3.56 with different sonication time [190]. The formation of

elemental gold was confirmed by the UV/Vis absorption spectra showing the typical

Plasmon resonance around 520 nm.

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0

Figure 3.51: Absorbance spectra for gold nanoparticles in PS61-b-PEO113 during sonochemical

borohydride reduction.

1

0

3

6

1= After one hour sonication before the addition of NaBH4 to the solution of LiAuC14and

block copolymer in toluene

2= 10min sonication after the addition of NaBH4 to the solution of LiAuC14and block

copolymer in toluene

3= 20min sonication after the addition of NaBH4to the solution of LiAuC14 and block

copolymer in toluene

4= 30min sonication after the addition of NaBH4 to the solution of LiAuC14 and block

copolymer in toluene

5= 40min sonication after the addition of NaBH4 to the solution of LiAuC14 and block

copolymer in toluene

6= 60min sonication after the addition of NaBH4 to the solution of LiAuC14 and block

copolymer in toluene

Figure 3.52: Colour of the samples at different sonication times before and after the

formation of gold nanoparticles

1 2

4 5

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0

Figure 3.53: Absorbance spectra for gold nanoparticles in PS61-b-PEO113 at different times

after sonication; the inset shows the absorbance just after the formation of nanoparticles at

two different loading ratios of gold: ethylene oxide.

Figure 3.54: Absorbance spectra for gold nanoparticles in PS72-b-PEO113 at different times

after sonication; the inset shows the absorbance just after the formation of nanoparticles at

two different loading ratios of gold: ethylene oxide.

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0

Figure 3.55: Absorbance spectra for gold nanoparticles in PS88-b-PEO113 at different times

after sonication; the inset shows the absorbance just after the formation of nanoparticles at

two different loading ratios of gold: ethylene oxide

Figure 3.56: Absorbance spectra for gold nanoparticles in PMMA-b-PEO at different times

after sonication

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0

Figure 3.57: Absorbance spectra for gold nanoparticles in PVP at different times after

sonication

3.14 Morphology and Phase Separation of gold

nanoparticles Transmission Electronic Microscopy images of the Au/PS-b-PEO and Au/PMMA50-b-

PEO113 composites and Au/PEO nanoparticles are illustrated in Figures 3.58, 3.59 and

3.60 respectively. The dark spots represent the micelle cores with clusters of gold

nanoparticles. This indicates that the gold was well dispersed in the micelles [191]. The

brighter areas between the dark spots represent the shell of the micelles which separate

the gold nanoparticles. The images indicate that the nanoparticles are larger than the

original cores and also than the remaining micelles. The size of the gold particles

corresponded to the Plasmon resonance [192]. The similarity of images for the block

copolymers with those using only PEO (Mn= 5000) confirms the nanoparticles were

formed inside the micellar cores.

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Figure 3.58: TEM image for Au nanoparticles in block copolymers (a) PS61-b-PEO113, (b)

PS72-b-PEO113, (c) PS88-b-PEO113

Figure 3.59: TEM images for Au nanoparticles in block copolymers (a) PMMA7-b-PEO113 (b)

PMM20-b- PEO113 (c) PMMA50-b-PEO113

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Figure 3.60: TEM image for Au nanoparticles in PEO

Additional insight into the changes that occurred during the transformation process was

also obtained by TEM. It has been shown that amphiphilic diblock copolymer micelles in

a non-polar solvent can exhibit high kinetic stability and that films consisting of densely

packed micelles can be prepared by evaporation of the solvent [193]. The spherical

agglomerates of dark spots marked the micelles and represented the clusters of

elemental gold suggested by the UV spectra arising from a degree of agglomeration of

the individual nanoparticles. Taking into account the strong contrast between the core

and shell of the micelles as well as the evidence of the UV/visible spectra we conclude

that the Au is dispersed as small clusters of elementary gold within the cores of the

micelles [194]. It is known that Au nanoparticles exhibit a weak, broad absorbance band

below 500 nm. Thus, the reduction of the typical plasmon resonance of small Au

particles around 520 nm can be explained by the agglomeration at longer reaction times

[195].

The morphology and phase separation of cast films of the block copolymers PS-b-PEO,

PMMAb-PEO, determined by scanning electron microscopy, has been shown in Figure

3.61 and 3.62.

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1

Figure 3.61: SEM image for Au nanoparticles in a block copolymers (a) PS61-b-PEO113, (b)

PS72-b-PEO113, (c) PS88-b-PEO113

Figure 3.62: SEM image for Au nanoparticles in a block copolymers (a) PMMA7-b-PEO17

(b)PMM20-b-PEO45 (c)PMMA50-b-PEO113

We conclude that PS-b-PEO micelles provide an excellent means for the formation of

welldefined films containing nanoparticulate gold, the size of which can be controlled by

variation of the loading ratio and the micelle size as well as the reaction time [196].

However, care must be taken to select the optimum reaction and processing time to

achieve a balance between the individual nanoparticles and clusters. Kinetic control of

the block copolymer structure was found to be very effective in arranging the

nanoparticles coherently. Other nanoparticles, of for example platinum, palladium, TiO2,

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1

Ag or semiconductors, can be incorporated into micellar films using the described

approach [197].

3.15 Silver Nanoparticles, Sonication Time

Dependence Silver nitrate (AgNO3) added to block copolymer solution in toluene and sonicated for 1h

in an ultra sonic bath results whitish colour of the solution as shown in the following

figure. The spectra recorded on UV/Visible spectrophotometer show zero absorbance

figure 3.63 which is a clear cut indication of the fact that the formation of silver

nanoparticles does not occur until this position [198].

Figure 3.63: Absorbance spectra for silver nanoparticles in PS61-b-PEO113after 1h sonication

before the addition of sodium borohydride reduction the inset shows the colour just after the

1h sonication

After the addition of sodium borohydride (NaBH4) and sonication for 1h the colour of

the solution changes to yellowish brown, indicating the probable formation of silver

nanoparticles which was confirmed by the absorbance spectra shown in Figure 3.64. It is

well known fact that Ag nanoparticles show a yellowish brown colour in solution; this

color arises from excitation of surface plasmon vibrations in the metal nanoparticles

[199]. The formation of elemental silver was confirmed by showing the typical Plasmon

resonance around 410 nm. The spectra for the silver nanoparticles in the block

1

1

copolymer samples (PS-b-PEO) each showed an absorption maximum in the range of

410 nm to 415 nm depending upon the particle size Figure 3.64. A lower absorption

maximum wavelength is associated with a smaller average size of the Ag particles [200].

Figure 3.64: Absorbance spectra for silver nanoparticles in PS61-b-PEO113 for 1h sonication

after addition of sodium borohydride, the inset shows the colour of the solution just after the

1h sonication

It has been established that two major factors which control the size and arrangement

of the nanoparticles are the stability of the copolymer micelles in the media and the

strength of the interactions between the PEO block and the silver nanoparticles [201]. In

this case, the interactions are relatively weak so that the micelles are not affected by the

process of particle formation and, in turn, do not influence particle growth to any great

extent, for example by adsorption of the polar block onto the growing nano-crystallites

[202].

Also of interest is the previously unreported time dependence of the UV spectra. Figure

3.64 shows that the absorbance increases as the reduction reaction proceeds due to the

formation of higher concentrations of nanoparticles [203]. Significantly, the wavelength

of maximum absorption does not change, indicating only small variation, if any, in

average particle size. However, of potentially greater interest is that further changes

1

1

occur after sonication is stopped. Figures 3.65 and 3.66 shows the absorbance continues

to grow for around 10 min even when the reaction vessel is removed from the

ultrasound bath but then falls markedly. We ascribe this to agglomeration [204] of the

small nanoparticles into larger clusters.

2

3

6

1= After one hour sonication before the addition of NaBH4 to the solution of AgNO3 and

block copolymer in toluene

2= 10min sonication after the addition of NaBH4 to the solution of AgNO3 and block

copolymer in toluene

4= 30min sonication after the addition of NaBH4 to the solution of AgNO3 and block

copolymer in toluene

5= 40min sonication after the addition of NaBH4 to the solution of AgNO3 and block

copolymer in toluene

6= 60min sonication after the addition of NaBH4 to the solution of AgNO3 and block

copolymer in toluene

Figure 3.65: Colour of the samples at different sonication times before and after the

formation of silver nanoparticles

1

4 5

1

1

Figure 3.66: Absorbance spectra for silver nanoparticles at different sonication times of PS-b-

PEO diblock copolymer

Figure 3.67: Absorbance spectra for silver nanoparticles at different sonication times of

PMMA-b-PEO diblock copolymer

The formation of elemental silver was confirmed by showing the typical Plasmon

resonance around 410 nm. The spectra for the silver nanoparticles in the block

copolymer samples (PMMA-b-PEO) each showed an absorption maximum in the range

of 410 nm to 415 nm depending upon the particle size Figure 3.67.

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1

3.16 Morphology and Phase Separation of silver

nanoparticles Transmission Electronic Microscopy images of the Ag/PS-b-PEO and Ag/PMMA-b-PEO

composites nanoparticles are illustrated in figures 3.68 and 3.69 respectively. The dark

spots represent the micelle cores with clusters of silver nanoparticles. This indicates that

the silver was well dispersed in the micelles. The brighter areas between the dark spots

represent the shell of the micelles which separate the silver nanoparticles. The images

indicate that the nanoparticles are larger than the original cores and also than the

remaining micelles. The size of the silver particles corresponded to the Plasmon

resonance [205].

It has been shown that amphiphilic diblock copolymer micelles in a non-polar solvent

can exhibit high kinetic stability and that films consisting of densely packed micelles can

be prepared by evaporation of the solvent [206-208]. The spherical agglomerates of

dark spots marked the micelles and represented the clusters of elemental silver

suggested by the UV spectra arising from a degree of agglomeration of the individual

nanoparticles. Taking into account the strong contrast between the core and shell of the

micelles as well as the evidence of the UV/visible spectra we conclude that the Ag is

dispersed as small clusters of elementary silver within the cores of the micelles [209-

211]. It is known that Ag nanoparticles exhibit a weak, broad absorbance band below

400 nm. Thus, the reduction of the typical plasmon resonance of small Ag particles

around 410 nm can be explained by the agglomeration at longer reaction times.

Figure 3.68: TEM image for Ag nanoparticles in a block copolymers (a) PS61-b-PEO113 (b)

PS72-b-PEO113 (c) PS88-b-PEO113

1

1

Figure 3.69: SEM image for Ag nanoparticles in a block copolymers (a) PMMA7-b-PEO17 (b)

PMM20-b-PEO45 (c) PMMA50-b-PEO113

The dark spots represent the micelle cores with clusters of silver nanoparticles and

white spots are represents silver nanoparticles. This indicates that the silver was well

dispersed in the micelles shows in figure 3.70 and 3.71.

Figure 3.70: SEM image for Ag nanoparticles in a block copolymers (a) PS61-b-PEO113, (b)

PS72-b-PEO113, (c) PS88-b-PEO113

1

1

Figure 3.71: SEM image for Ag nanoparticles in a block copolymers (a) PMMA7-b-PEO17 (b)

PMM20-b-PEO45 (c) PMMA50-b-PEO113.

The morphology of the silver nanoparticles was observed by SEM. The SEM images of

the silver nanoparticles of block copolymer PS-b-PEO and PMMA-b-PEO demonstrate

regular distribution and spherical shape that appear to be well separated and stable

over the preparation process shown in figure 3.70 and 3.71[212].

We concluded well- defined silver and gold nanoparticles of narrow size distributions

were obtained. The size and shape of particles could be modified controlling the

copolymer structure and the concentration of the reactants [212, 213]. The simplicity of

the silver and gold nanoparticles synthesis route suggests that could be used to control

the morphology and size of these in order to obtain characteristics useful in different

applications.

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CHAPTER-4 CONCLUSION

Synthesis of the amphiphilic diblock copolymer of PS-b-PEO and PMMA-b-PEO was

carried by ATRP. During the synthesis the length of PS and PMMA block were varied

whereas the PEO block length was kept constant. The synthesized material (copolymer)

composition was analyzed using H1 NMR spectroscopic technique. The results concluded

that the composition of two blocks was well controlled by monitoring the ratio of

reactants. The molecular mass and its distribution was estimated by using light

scattering and GPC/SEC.GPC analyses showed that these copolymers had comparatively

narrow molecular mass distribution and the degree of dispersity was in the range of

1.08-1.7. It was further observed that the samples having comparatively low molecular

weight have the greater had the greater degree of dispersity and was decreased by

increasing the molecular weights. It was observed that the intrinsic viscosity of the

polymer solution was decreased with the increase in temperature concluding that the

quality of the solvent was deteriorated with the increase in temperature of the system.

On the other hand the value of KH was increased with the increase in temperature

concluding that the interaction between micelles was increased and hence micellization

was favored. Characterization of these synthesized block copolymers were investigated

with reference to estimation of critical micelles concentration using surface tension,

DOSY NMR, and Fluorescence in the given solvent (toluene). It was observed that the

results obtained were consistent, irrespective of the techniques used. It was concluded

that the critical micelles concentration was decreased with the increase in PMMA and

PS block length for both diblock copolymers. This indicate that the CMC decreases with

increasing block length because the hydrophobic block forms more aggregates and the

polymer solvent interactions becomes less i.e., solvent quality deteriorated with

increase in temperature. Critical micelles concentration also decreases with the increase

in temperatures. The value of CMC determined through different techniques at different

temperatures for all the block copolymers synthesized with different block lengths is in

the range 0.5-1.09.

It was also observed that high PMMA segments enhanced the surface activity of the

copolymer. The results also concluded that the value of hydrodynamics radii was

1

2

decreased with the increase in temperature and were increased with block length.

Therefore, it was concluded that hydrophobicity was an important factor affecting the

value of RH. It was noted that the copolymers viscoelastic propertied were varied with

the variation of the block length. The magnitude of G' and G" were continuously

increased with the increase in oscillating frequency used for the measurement of these

parameters. Further the rate of increase of G' was greater than G". Due to the reason a

crossover was observed at which a transition of the sample from liquid like to solid like

took place.

The synthesized block copolymer micelles were successfully used for the extraction of

gold and silver nanoparticles and cast films having the homogeneous dispersion of these

nanoparticles. The distribution of nanoparticles in the micelles of the block copolymers

was investigated by carrying out their morphology analysis through transmission

electronic microscopy (TEM) and scanning electronic microscopy (SEM). That helped in

establishing the optimum conditions for having homogeneously dispersed particles of

uniform size in the required material. We have concluded that the Au and Ag is

dispersed as small clusters of elementary gold and silver within the cores of the micelles.

It is known that Au nanoparticles exhibit a weak, broad absorbance band below 500 nm

and Ag nanoparticles exhibit a weak, broad absorbance band below 400 nm. Thus, the

reduction of the typical plasmon resonance of small Au particles around 520 nm and Ag

particles around 410 nm can be explained by the agglomeration at longer reaction

times. We have also concluded that PS-b-PEO micelles provide an excellent means for

the formation of well-defined films containing nanoparticulate gold & silver the size of

which can be controlled by variation of the loading ratio and the micelle size as well as

the reaction time. The size of both nanoparticles gold and silver were determined from

the morphology data and was to be in the range of 20nm-100nm.

Nanometer-sized particles of metals and semiconductors have the influence upon the

dimensions which directly affect the electronic properties (structures such as quantum

wires, quantum wells and quantum dots).

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