The investigation of surfactant aggregation in micellar water solutions by SANS method Kamila Mikołajczuk Magdalena Mieścicka University of Natural Sciences and Humanities in Siedlce Direction 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

Micellization, CMC point and Krafft point Surfactants 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 point The 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. SANS is a technique where radiation is scattered on a sample and received data we are using to find informations about size, shape and orientation.

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 While - natomiast

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 As you know the reactor hasn’t worked yet, so we get data from our supervisior to work out. Our surfactant was NONIONIC HEPTA ..... Our solution concentration is 0 point 17, half and one percent. There are investigate at temperature 10, 15, 20, 25 and 35 Celsius degree

Here we got our experimental plots First is for 0 point 17 percent of concentration. Second one is for half percent and the third one is for 1 % solution. On the vertical axis we have number of neutrons which have been scattered in unit time on area unit On the horizontal axis there is scattering vector depending on scattering angle and neutrons wavelenght Bigger concentration and higher temperature is characteristic for higher intensity of neutron scattering. You can compare it. Fig.1. Intensity of neutron scattering vs scattering vector for concentration c1=0.17% at temperatures: 10o, 15o, 20o, 25o, 30o and 35oC.

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

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

This spectrum we obtain using PCG versus2 part IFT (Indirect Fourier Transformation) programme Prof..otto glater and his coworkers from Graz in Austria 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 Pi versus ar

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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