The investigation of surfactant aggregation in micellar water solutions by SANS method

Kamila MikołajczukMagdalena Mieścicka

University of Natural Sciences and Humanities in SiedlceDirection of Chemistry

Frank Laboratory of Neutron Physics

Supervisor of the project:Aldona Rajewska, PhD

Frank Laboratory of Neutron Physics

FLNP is the place where:• ultracold neutrons were discovered; • enhancement of the space parity violation effect in neutron

resonances was found• use the neutron as an instrument to investigate the structure

and dynamics of condensed matter, including crystals and nanosystems, functional materials, complex liquids and polymers, rocks

What about surfactants?

Surfactants are compounds that lower the surface tension of a liquid, the interfacial

tension between two liquids, or that between a liquid and a solid.

A micelle - the lipophilic tails of the surfactant molecules remain on the inside of the micelle due to unfavourable interactions. The polar "heads" of the micelle, due to favourable interactions with water, form a hydrophilic outer layer that in effect protects the hydrophobic core of the micelle. The compounds that make up a micelle are typically amphiphilic in nature, meaning that not only are micelles soluble in protic solvents such as water but also in aprotic solvents as a reverse micelle.

Classification of surfactants for the sake of functional group

Classical/Gemini Surfactants

ionic Non-ionic

zwitterionic

cationic anionic

Micellization, CMC point and Krafft pointSurfactants molecules occur as monomers in very diluted solution. However after exceed permissible concentration participles are spontaneous associated. They form aggregations called micelles.Determined surfactant concentration cause micellization after exceed CMC point (critical micelle concentration).

Krafft pointThe temperature (more precisely, narrow temperature range) above which the solubility of a surfactant rises sharply. At this temperature it becomes equal to the critical micelle concentration. It is best determined by locating the abrupt change in slope of a graph of the logarithm of the solubility against t or 1/T.

Small-Angle Neutron Scattering (SANS)

In this technique radiation is elasically scattered by a sample and the resulting scattering pattern is analysed to provide information about the size, shape and orientation of some component of the sample.

SANS are used in situations where the important physical aspects ( size, range of interaction etc.) occur at distances extanding typically from 10 to 1000 Å.

IBR-2 Pulsed Reactor YuMO

1 – two reflectors;2 – zone of reactor with moderator;3 – chopper;4 – first collimator;5 – vacuum tube;6 – second collimator;

7 – thermostate;8 – samples table;9 – goniometer;10-11 – Vn-standard;12 – ring-wire detector;13 – position-sensitve detector "Volga";14 – direct beam detector.

What should we know about the experiment?

• Firstly the sample is prepared by chemists, who are responsible to determine a CMC and Krafft point, then physicists realized researchs in reactor

• The source of neutrons beam is plutionium (IV) oxide PuO2 which is located in reactor

• Collimated neutron beam fall on a sample • One part of radiation is scattered, second one is transmitted and

third is absorbed• Scattering beam is recorded by the detector • On the basis of obtain results by the detector, we can determine ex.

scattering angle, neutron intensity• We obtain experimental plots then analyse their by GIFT

programme (Generalized Indirect Fourier Transformation)• This analysis provide information about the shapes, aggregation

number, size of micelles for the sample

EXPERIMENTAL SECTION

Nonionic surfactant hepta (ethylene glycol) monodecyl ether (C10E7)* in dilute heavy water solutions.

• Surfactant hepta (ethylene glycol) monodecyl ether (C10E7) was study with SANS method.

• Solutions for concentrations: 0.17%, 0.5%, 1% was investigated at temperatures: 10oC, 15oC, 20oC, 25oC and 35oC for each sample (the temperature was kept constant with accuracy of ±0.5oC).

• The measurements were made for the momentum transfer Q range 0.02 -0.43 Å-1.

• The CMC value for surfactant C10E7 is equal 0.96 mmol/dm3,

*C10E7=>heptaethylene glycol monodecyl ether(C24H50O8)Surfactant type CiEj CH3(CH2)9O(CH2CH2O)7H

0.1 1

0.1

0.2

0.3

0.4

0.5

d(

Q)/

d, cm

-1

Q [A-1]

C10

E7+D

2O

c=0.17%

10oC

15oC

20oC

25oC

35oC

Fig.1. Intensity of neutron scattering vs scattering vector for concentration c1=0.17% at temperatures: 10o, 15o, 20o, 25o, 30o and 35oC.

0.1

0.1

1

C10

E7+D

2O

c=0.5%

10oC

15oC

20oC

25oC

30oC

35oC

d(Q

)/d

, cm

-1

Q [A-1]

Fig.2. Intensity of neutron scattering vs scattering vector for concentration c2=0.5% at temperatures: 10o, 15o, 20o, 25o, 30o and 35oC.

0.1

0.1

1

C10

E7+D

2O

c=1%

10oC

15oC

20oC

25oC

30oC

35oC

d(Q

)/d

, cm

-1

Q [A-1]

Fig.3. Intensity of neutron scattering vs scattering vector for concentration c3=1% at temperatures: 10o, 15o, 20o, 25o, 30o and 35oC.

0 2 4 6 80.000

0.002

0.004

0.006

0.008

p (r)

r [nm]

10 deg 15 deg 20 deg 35 deg 25 deg

• Fig. 4. Pair distance distributon function (PDDF) for the C10E7 (c=0,17%) system from SANS measurements for temperatures 10, 15, 20, 25 and 35 Celsius degree

Conclusions• If intensity of neurons scattering increases the number of

micelles grow up in micellar solution• For the bigger concentrations and temperatures the

maximum have a higher value• If the curve p(r) is symmethric – micelle have spherical

shape• Moreover, distance between zero point and point where

curve p(r) cross axis r is equal to diameter of micelle • When the curve is not symmetric it is example of micelle

with ellipsoidal shape• Received diagram is characteristc for ellipsoid micelles

References

• „Structure Analysis by Small-Angle X-Ray and Neutron Scattering” L.A. Feigin and D.I. Svergun, Plenum Press, New York and London

• Otto Glater and others Langmuire, 2000, 16, 8692-8701 „Nonionic Micelles near the Critical Point; Micellas Growth and Attractive Interaction”

• A.Guiner, G. Fournet „Small- Angle Scattering of X-rays”, John Wiley, 1955

• O.Glatter, O.Kratky „Small- Angle X-ray Scattering” Academic Press, 1982

• „Small Angle Neutron Scattering” Stephen M.King ISIS Facility, Rutheford Appleton Laboratory, December 1995

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