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Siegel der Universität
Department für Chemie - Arbeitsgruppe Prof. Strey

The Dynamics of L3 Phases

Anja Wehling, May 2001

As in ordinary fluids, the understanding of the dynamic processes is important to understand the equilibrium properties of complex fluids. As model system, the so-called L3 phase was studied by using different relaxation techniques. Temperature jump relaxation and a newly developed isothermal shear apparatus with different detection methods were applied. The influence of structure parameters, i.e. the bilayer thickness and the interbilayer distance, on the dynamics of the L<sub3> phase were examined in detail. For that purpose, ternary mixtures of water (A), n-alkane (B) and a nonionic surfactant CiEj (n-alkylpolyoxyethylenoxide, C) were chosen to be able to change the surfactant / (surfactant + oil) volume ratio as well as the bilayer volume fraction. Minor changes in the samples composition resulted in enormous changes of the relaxation time covering a range of many orders of magnitude from microseconds to minutes. A strong dependence of the relaxation time constants on the bilayer volume fraction was observed for a constant bilayer thickness. On the other hand, for a given bilayer volume fraction the relaxation time constant passes through a minimum in dependence of the surfactant / (surfactant + oil) volume ratio. A geometric model, which was tested and confirmed by SANS measurements, was defined to explain the influence of the structure parameters on the dynamics of the L<sub3> phase quantitatively. An interpretation of the experimental results was discussed towards a generalized description of the dynamics of the L3 phase.</sub3></sub3>