Soret effect in surfactant systems and microemulsions
Coordinator
Privatdozent Dr. Thomas Sottmann ; Privatdozentin Dr. Simone Wiegand
Grant period
2007 - 2015
Funding body
Deutsche Forschungsgemeinschaft
DFG
Identifier
G:(GEPRIS)47816710
Note: In the first funding period of this project, we mainly studied the thermal diffusion behavior of aqueous solutions of nonionic surfactants. By performing systematic phase behavior and SANS experiments we found that the dye Basantol® Yellow is incorporated in the micelles causing the second mode observed in the classical TDFRS experiments. Building up an infrared thermal diffusion forced Rayleigh scattering (IR-TDFRS) experiment we could avoid the addition of the dye for aqueous mixtures eliminating the second mode. Preliminary thermal diffusion experiments for water-in-oil microemulsions (originally scheduled for the third year of the project) show that the Soret coefficient strongly increases with temperature which indicates that the thermal diffusion behavior is strongly connected with the interfacial tension between the solute and the solvent. Accordingly, in the proposed second funding period we plan to investigate the thermal diffusion behavior of nonionic and ionic microemulsions, for which the interfacial tension between oil and water can be measured. In both cases the influence of the interfacial tension and the microstructure on the Soret coefficient will be investigated. Thereby it is of particular interest that the temperature dependence of the interfacial tension is different depending on whether one considers oil-in-water (o/w) microemulsions or water-in-oil (w/o) microemulsions. From this fact we expect that the sign of the Soret coefficient changes from negative to positive nearby the phase inversion. Finally, we plan to investigate how amphiphilic polymeric additives will influence the thermal diffusion of micelles and microemulsion droplets.
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