Self-assembly Structures of Block Copolymers in Selective

Solvents and of Polysaccharide-

Surfactant Mixtures

Björn Lindman, Physical Chemistry, Lund University, Sweden

Center of Excellence

Contributions from Lennart Piculell, Tommy Nylander, Per Linse,

Paschalis Alexandridis, Ulf Olsson and other colleagues

HydrophilicHydrophilic HydrophobicHydrophobic

Amphiphilic moleculesAmphiphilic moleculesionic and non-ionic surfactants and lipids

block- and graft-copolymers

(polysaccharides and proteins), DNA

SelfSelf--Organize Organize

at Interfaces and in Solutionat Interfaces and in Solution

modify interfacial properties

enhance compatibility

compartmentalization

Form the basis of lifeForm the basis of life Biological membranes

Find widespread Find widespread

use use inin industryindustry

Pharmaceuticals, plastics, foods, detergents,

cosmetics, minerals, paper, oil,

remediations, etc.

SDS SDS CHCH33(CH(CH22))1111SOSO44-- NaNa++

CTAB CTAB CHCH33(CH(CH22))1515NN++(CH(CH33))33 Br Br --

CC1212EE88 CHCH33(CH(CH22))1111(OCH(OCH22CHCH22))88OHOH

Spherical Spherical

MicelleMicelleReversed Reversed

MicelleMicelle

Lamellar Lamellar

phasephaseBicontinuousBicontinuous

StructureStructure

Cylindrical Cylindrical

MicelleMicelle

VesicleVesicle

Surfactant selfSurfactant self--assemblyassembly

Lipophilic Lipophilic and and HydrophilicHydrophilic

Combine the properties of polar solutes

like salts with those of hydrocarbons

Ambivalence leads Ambivalence leads to to (in(in aqueous aqueous systems)systems)

And / or

Amphiphilic

Adsorption at interfacesAdsorption at interfaces

(water/air, water/hydrocarbon,

water/solid, water/macromolecule)

SelfSelf--assemblyassembly

(alone or with low molecular

or macromolecular cosolutes)

Amphiphilic Amphiphilic copolymerscopolymers

Amphiphilic Block CopolymersAmphiphilic Block Copolymers

EOn-POm-EOn

EOn-BOm-EOn

POn-EOm-POn

EO : ethylene oxide -(CH2-CH2-O)-

POPO : propylene oxidepropylene oxide -(CH2-CH(CH3)-O)-

BOBO : butylene oxidebutylene oxide -(CH2-CH(CH2CH3)-O)-

Commercially available

(BASF, ICI, Dow, Hoechst)

Molecular weight range: 2000 – 16000

EO composition range: 20 – 80 % (per weight)

Composition, molecular weight and architecture can be tailored to meet specific needs

(control over amphiphilicity)

Surface tension of EO37PO56EO37

-7 -6 -5 -4 -3 -2 -1

30

40

50

60

70γ

/ (m

N m

-1)

25°C

35°C

log [Cpolymer/(kg dm-1)]

The arrows denote the location of the cmc:s obtained from dye solubilization.

Pluronic P105

CMCs of EO block copolymers decrease strongly with T

BlockBlock--ccopolymer opolymer sselfelf--assemblyassemblyCH3 |

HO(CH2CH2O)n(CHCH2O)m(CH2CH2O)nH

PEO PPO PEO

Block copolymers: thermal ”gel” is cubic phase

Phase behavior of

amphiphilic block copolymer in water

tem

pe

ratu

re

tem

pe

ratu

re ��

polymerpolymerwaterwater

L1

I1

H1

V1

Lαααα

cloud

point

LL11 II11 HH11 VV11 LLαααααααα

increasing amphiphile concentrationincreasing amphiphile concentration

lamellar

Tailoring the Tailoring the molecular molecular packingpacking

Molecular packing imposes the topology of the structural elementMolecular packing imposes the topology of the structural elementss

Packing depends on molecular characteristics of amphiphile

(block sequence and architecture, block molecular volume ratio),

but can be adjusted by

�� solvent quality solvent quality

(modify relative swelling of blocks)(modify relative swelling of blocks)

�� “cross“cross--linking” of selflinking” of self--assemblies assemblies

(adsorb preferentially to the different blocks)(adsorb preferentially to the different blocks)

Tailoring the Tailoring the Molecular Molecular PackingPacking

� solvent qualitysolvent quality (modify swelling)

� cosolutescosolutes (adsorb preferentially)

+

worsen solvent worsen solvent

for for redred blockblock

Change curvatureChange curvature

Change curvatureChange curvature

worsen solvent worsen solvent

for for blueblue blockblock

polymer

water oil

- 80

- 60

- 40

- 20

20 40 60 80

80

60

40

20

wt%

water

wt%

polymer

wt% oil

30%30%

50%50%

20%20%

Phase diagramPhase diagram

4 4 cubiccubic, 2 hexagonal, & 1 , 2 hexagonal, & 1 lamellar liquid lamellar liquid

crystalline phase crystalline phase + 2 + 2 isotropic solution phases isotropic solution phases in in a a ternary ternary ((isothermalisothermal) ) copolymer copolymer –– water water –– oil systemoil system

Lαααα

H1111

I1111

L1111L2222

I2222

H2222

V2222V1111

LL4444

EOEO1010POPO2323EOEO1010

MMww = 2200= 2200

LL6464

EOEO1313POPO3030EOEO1313

MMww = 2900= 2900

PP8484

EOEO1919POPO4343EOEO1919

MMww = 4200= 4200

PP104104

EOEO2727POPO6161EOEO2727

MMww = 5900= 5900

Experimental PI-PSfrom Khandpur et al

Macromolecules 1995, 28, 8796

Theoretical A-Bfrom Matsen et al

Macromolecules 1996, 29, 1091

Experimental

PEO-PPO-PEO

Block symmetryBlock symmetry

�� Approximately symmetric Approximately symmetric -- (EO)(EO)1919(PO)(PO)4343(EO)(EO)1919

�� Unsymmetric 80 wt% PEO Unsymmetric 80 wt% PEO -- (EO)(EO)4343(PO)(PO)1616(EO)(EO)4343

�� Unsymmetric 10 wt% PEO Unsymmetric 10 wt% PEO -- (EO)(EO)55(PO)(PO)6868(EO)(EO)55

80% PEO 40% PEO

10% PEO

Effect of copolymer architecture on Effect of copolymer architecture on

selfself--assemblyassembly

PO19EO33PO19

(25R4)

EO13PO30EO13

(L64)

3 3 cubiccubic, 2 hexagonal, & 1 , 2 hexagonal, & 1 lamellar liquid lamellar liquid

crystalline phases crystalline phases + 2 + 2 isotropic solution phases isotropic solution phases in in a a ternary ternary ((isothermalisothermal) ) block copolymer block copolymer –– water water –– oil systemoil system

Lαααα

H1111

I1111

L1111 L2222

I2222

H2222

V2222

Amphiphilic Amphiphilic graft graft

copolymer selfcopolymer self--assemblyassembly

Polymer

backbone

Hydrophobic

group

Hydrophobically modified water soluble polymers: HM-P

Features:

• can form inter- and intrachain

hydrophobic aggregates

• exhibit unique rheological

properties

• have strong tendency to associate

with surfactants and other polymers

Applications:

• Rheology modifiers and

thickeners in paint formulations

cosmetics/skin care products,

detergents, oil recovery

• Drug delivery systems

• Dispersing/stabilizing agents

The associative (hydrophobically modified)

water-soluble polymers

Polymer chain

Hydrophobe

grafted

end-capped

Associated structures in aqueous solutions of hydrophobically

modified polymers (HMPs)

Hydrophobically Hydrophobically modified water soluble polymers (HMP)modified water soluble polymers (HMP)

Polymer Polymer –– modified surfactantmodified surfactant

A Slightly Hydrophobic Cellulose DerivativeA Slightly Hydrophobic Cellulose Derivative

The degree of ethyl and The degree of ethyl and hydroxyethyl hydroxyethyl substitution determines substitution determines

the the hydrophobicity hydrophobicity of polymers in the EHEC family.of polymers in the EHEC family.

Hydrophobic modification of Hydrophobic modification of a a waterwater--soluble soluble

polymer increases viscositypolymer increases viscosity

Vis

co

sit

y /

Pa

.s

Cross-links in HM-EHEC

physical bonds of associating segments of the EHEC backbone

physical bonds of associating hydrophobic tails

entanglements of polymer chains

Surfactant like behavior

polar head

hydrophobic tail

surfactant micelle

polymer aggregate

Polymer chain

Hydrophobe

Crosslink

Reversible inter-chain association

transient

network viscosity

O

H

CH

C

O

OH

OH

CH

C

C

H

C

O

H

H

H

H

Hydrophobic cavity

Cyclodextrin

OO

OO

O

O

OH

O

O

O O

OOH

O

O

O

O

OH OH

O

O

O

OH

O

OO

OHOH

O

O

Hydrophilic exterior

Hydrophobic molecules can hide

inside the cavity of a CD

water molecule

CD breaks the hydrophobic

associations

cCD

η/η

η/η

η/η

η/η

00 00

Too large hydrophobe

Surfactant-polymer systems.

General aspects

Polymer-Surfactant Association: pearl-necklace model

•• CooperativityCooperativity

PolymerPolymer--Surfactant InteractionSurfactant Interaction

•• Surfactant micellization induced by polymerSurfactant micellization induced by polymer

PolymerPolymer--Surfactant ComplexesSurfactant Complexes

micelle mixed micelle

alginate

+ C12TAB

Nonic cellulose

derivative + SDS

hydrophobically modi-

fied cellulosics + SDS

Hydrophobic association is always essential to the interactionHydrophobic association is always essential to the interaction

When do surfactants bind to polymers?When do surfactants bind to polymers?

•••• Ionic Surfactants

self-assembly induced by polymer

mixed micellization

•••• All Surfactants Hydrophobically modified polymers

Oppositely charged polymers

Non-ionic polymers

The structure of Associative

Polymers

Hydrophobic group Water soluble backbone

Hydrophobic modification of a waterHydrophobic modification of a water--soluble soluble

polymer increases viscositypolymer increases viscosity

Vis

co

sit

y /

Pa

.s

The influence of surfactant

concentration on viscosity

Viscosity

log cSurfactant

Hydrophobically modified

polymer

Polymer

hydrophobically modified 1% w/w EHEC

Viscosity and hydrophobic microdomainsViscosity and hydrophobic microdomains

Addition of:

Increase micelles size•••• Na+ Cl-

•••• DoTA+ Cl- Increase viscosity

-Broaden the area of high viscosity

Decrease in viscosity depends on the stoichiometry between polymer

hydrophobic side-chains and mixed micelles.

One way to alter the stoichiometry is to: Decrease the number of

micelles by increasing their size.

Screening electrolyte (NaCl)

Oppositely charged surfactant

(DoTAC)

The Viscosity and the Mixed micelles Concentration in

Mixtures of 1 w/w% HMHEC and 30 mm surfactant

(SDS+DoTAC) versus the molar ratio of DoTAC

The viscosity can increase with

addition of a surfactant that

changes the shape of the micelles

DoTAC

Polymer-modified surfactant mixed micelles

Oil droplet

Polymer-surfactant systems.

Phase separation

Segregating Polymer/Surfactant mixturesSegregating Polymer/Surfactant mixtures

Mixtures of oppositely charged polyelectrolyte + surfactant:Mixtures of oppositely charged polyelectrolyte + surfactant:

Associative phase separationAssociative phase separation

In a mixed solution

Interactions between cosolutes are:

Repulsive (most common)

or

Attractive (electrostatic, hydrophobic)

Depending on interaction

Segregation

Association, or

Miscibility

POLYELECTROLYTE EFFECTS

• A polyelectrolyte in aqueous solution dissociates

into 1 polyion and n counterions; typically n >> 1

• a large no. of particles: large ∆Smix

• If the counterions mix into a phase, the polyion has

to follow (condition of electroneutrality)

POLYELECTROLYTE

EFFECTS

• Dissociating counterions on one of the polymers increases miscibility

tremendously

• Added salt facilitates demixing in both cases.

Polymer Polymer –– Surfactant Surfactant

Phase DiagramsPhase Diagrams

SEGREGATING POLYMER/SURFACTANT MIXTURES

• In general (i.e,. in absence of electrostatic or hydrophobic attractions), effective

repulsion between a polymer and a surfactant micelle is expected

• Since a surfactant micelle is effectively a polymer, repulsion should lead to a

segregative phase separation, as for mixtures of dissimilar polymers

Nonionic polymer + nonionic surfactantNonionic polymer + nonionic surfactantSegregationSegregation

MIXTURES OF OPPOSITELY CHARGED

POLYELECTROLYTE + SURFACTANT:

ASSOCIATIVE PHASE SEPARATION

• For intrinsically hydrophilic polyions, the association is

driven only by electrostatic interactions

• Close analogy to polyelectrolyte complexes

Anionic polysaccharide + Cationic surfactantAnionic polysaccharide + Cationic surfactant

Association

Nature of conc phase: conc soln/gel, liq crystal, solid crystal

Effect of salt on polyelectrolyte + ionic surfactantEffect of salt on polyelectrolyte + ionic surfactant

Low saltLow salt Association

Intermediate saltIntermediate salt Miscibility

High saltHigh salt Segregation

Problem with conventional

approach

• Concentrated phase generally contains 4 ions in unknown proportions => complex system!

OPPOSITELY CHARGED MIXTURES: TWO

ALTERNATIVE REPRESENTATIONS

• Left hand diagram – conventional mixing plane

• Right hand diagram – alternative mixing plane

• Stoichiometric mixtures belong to both mixing planes

Segregation in a P-S- systems

40°C NaHy Mw = 90000

------ NaHy – SDS – H2O – 1M NaBr

NaHy – SDS – H2O

Network formation and gelation

• A gel contains at least two components, one solid-like and one liquid-like, where both are continuous throughout the gel.

What are polyelectrolyte gels?

• Polymer network with charged groups

Gel Swelling Experiment: How

& Why

=> Potential ”responsive gels” (drug delivery, water retention…)

=> Info on interactions between gel & additive

waterwater

+ additive

water

+ more

additive

• Make gel pieces of cross-linked polymer

• Immerse gel pieces in series of solutions with increasing conc of additive

General Swelling Isotherm

for ”Weakly Hydrophobic”

Nonionic Gel with Ionic

Surfactant

5

10

15

20

25

30

35

0.1 1 10 100

V/V

0

Cf,SDS

0 cac

HEC gels swollen in

alkyl sulfate solutions

Sjöström & Piculell

Langmuir 17(2001)3836

Gel Swelling Experiments Detect

Surfactant Binding

0

50

100

150

200

0.1 1 10 100

V /

m (m

l/g)

c (mM)

SHS STS SDS SDeS SOS

0

CMC:

=> HEC binds

alkyl sulfates with

> 8 carbon tails

Cat-HEC Gels + Different

Anionic Surfactants

10

100

1000

0.0001 0.001 0.01 0.1 1 10

V /

m (m

l/g)

c (mM)

0

STS SDSSD(EO)2SCMC:

Sjöström & Piculell

Colloids Surf A

183-185 (2001) 429

• Collapse & redissolution

• Two CAC:s!?

• Both correlate with CMC

=> both reflect surfactant

self-assembly

O

HOO

CH3

O

O

CH2

CH3

CH2

CH2

HO

HOOH

CH2

O

CH2

CH2

O

CH2

CH2O

CH2

CH3

O

HOO

CH2

O

O

CH2

CH3

CH2

O

CH2

CH2

CH2

OH

n

O

O

Adsorption of EHEC

Solvent Polymer

Surface

Aqueous systems:

Adsorption since water interacts unfavorably with polymer

(clouding polymer) or surface (hydrophobic surface)

Polar/nonpolar surfaces

T dependence: Solvency

The poorer the solvent

the better the adsorption

Poor solvent

Good solvent

The influence of the solvent

Concentration (M)

5

4

3

1

00 0.2 0.80.60.4

6

7

2

1.0

Na2SO4 NaCl

NaSCNNaI

Concentration (M)

45

40

35

30

250 0.2 0.80.60.4

NaI

NaSCN

NaClNa2SO4

Increase in

adsorption

Decrease

in CP

Increase in

CP

Decrease in

adsorption

Adsorption of EHEC on SiO2:

Solvency effects due to cosolutes

Interfacial behavior of polymer-

surfactant mixtures

PolymerPolymer--Surfactant at InterfacesSurfactant at Interfaces

General Swelling Isotherm

for ”Weakly Hydrophobic”

Nonionic Gel with Ionic

Surfactant

5

10

15

20

25

30

35

0.1 1 10 100

V/V 0

Cf,SDS

0 cac

EHEC/SDS on Hydrophobized Silica

• Substrate:Silanol groups reacted with dimethyloctylchlorosilane

• EHEC preadsorbed from 0.01 wt% solution. (Intermediate adsorption)

• SDS adsorbs on hydrophobized silica; Competitive adsorption!

0

0.02

0.04

0.06

0.08

0.1

0.001 0.01 0.1 1 10 100

Ab

so

rba

nce

SDS concentration (mM)

1φ

2φ

1φ

SDS concentration (mM)

Ab

so

rba

nc

eTurbidity of bulk solution

100 ppm cat-HECCl (LR30M) + SDS

Increase in turbidity due to precipitation in the bulk solution.

polycation and anionic surfactant

-

-

--

----

- ---

HH22OO

P+S-

-

-

--

----

- ---

P+

S-

S-

+

PolymerPolymer--Surfactant applicationsSurfactant applications: : ShampooShampoo

HH22OO

-

-

--

----

- ---

P+S-

S-

H2O P+

OH

Cl

CH3

CH3

RN+

O

CH2OCH

2CH

2OH

OHOH

O

OH

OH O

CH2

O

(CH2CH

2O)

2CH

2CHCH

2

ττττ 1−τ1−τ1−τ1−τ

JR-400: R=CH3 τ =29mol% Mw =400000

LM-200: R=C12H25 τ =3mol% Mw =100000

CATIONIC CELLULOSE DERIVATIVESCATIONIC CELLULOSE DERIVATIVESCATIONIC CELLULOSE DERIVATIVESCATIONIC CELLULOSE DERIVATIVES

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

0.001 0.01 0.1 1 10

SDS [mM]

0

10

20

30

40

50

60

70

80

90

100

The effect of SDS addition to pre-adsorbed JR-400 layers

2Φ

0.1-0.6mM SDS

adsorption

- solubility of complex decreases

because of charge neutralization

- conformation of complex becomes

compact, since intramolecular

electrostatic repulsion is screened

desorption

>5mM SDS

cmc

- solubility of complex increases

because of cooperative SDS

binding

- complex expands due to the

increase of the net negative charge

of complex

--

-

-

---

-

---

--

---

---

--

--

---

-

P+-S -stoichiometric complex

Desorption process was too slow to be followed

cac

Ad

sorb

ed a

mo

unt

[mg

/m2]

Thick

ness [n

m]

Polar surface

Rinsing of adsorbed JR-400/SDS layers on silica

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

0 1000 2000 3000 4000 5000

time [sec]

adsorb

ed a

mount

[mg/m

2]

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

0.001 0.01 0.1 1 10

SD S [m M ]

adsorbed am

ount [m

g/m

2 ] 2φ

Reference

Adsorption of JR-400/SDS complexes

from pre-mixed solutionsRinsing was started (t=1000)

Rinsing was started after adsorption

of the complex from pre-mixed solution

reached steady state

- For the complexes which were formed in post-precipitation region,

the adsorbed amount jumped up by rinsing

Effect of rinsing (10mM NaCl) on adsorption

5mM SDS

10mM SDS

0.06mM SDS

0.006mM SDS

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

0 1000 2000 3000 4000 5000 6000

Time [sec.]

Effect of rinsing on adsorbed JR-400/SDS layerson hydrophobized silica

a

b

c

The complexes adsorbed from mixed polymer (100 ppm)/surfactant (5 mM) solutions and rinsing was

started at t = 1000 sec.

(a) adsorption was carried out in water followed by rinsing with water

(b) adsorption was carried out in 10 mM NaCl followed by rinsing with water

(c) adsorption was carried out in 10 mM NaCl followed by rinsing with 10 mM NaCl.

no SDS high SDSlow SDS

po

lyca

tio

n a

dso

rpti

on

adsorption phase

separation

desorption

added anionic surfactant rinsing

General trends of co-adsorption of cationic

cellulose

derivatives with SDS

++

++

++++++

++++++++++

++++

++

++