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Siegel der Universität
Department für Chemie - Arbeitsgruppe Prof. Strey

Selbstorganisierende Netzwerke in Mikroemulsionen

Peter Uhrmeister, Februar 2002

In efficient microemulsions the curvature of the amphiphilic film is close to zero. For systems of the water n-alkane CiEj type this situation is realized close to the mean temperature Tmean, in literature often referred to as the PIT (phase inversion temperature). Approaching Tmean from positive curvatures of the amphiphilic film, the discrete o/w-droplet to network transition in the model system water n-octane C10E4 has been studied by means of various scattering methods, NMR-selfdiffusion and viscosity, indicating consistent network onset-temperatures and concentrations. Using mixtures of n-alkane and hexylmethacrylate network structures have been fixed through microemulsion polymerisation and investigated by various electronmicroscopy techniques. Approaching from negative curvature, the phase behavior and microstructure of the randomly connected surfactant-bilayer-structure of the L3 or sponge phase in the system water n-decane C12E5 have been studied. By the variation of the oil content in the membrane and the membrane volume fraction in the sample composition the bilayer thickness and the interbilayer distance can be controlled. These characteristic length scales have been determined by small angle neutron scattering experiments and enabled the calculation of the bending moduli k and kbar. Combing these information, Morse's model for the stability of the L<sub3>-phase could be verified. This gives rise to a theoretical approach to understand the striking dynamics of the sponge phase that was observed using various relaxation techniques. Here it was found that 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. In cooperation with Leitao the concept of the wandering exponent was proposed as theoretical approach towards the L3-dynamics.</sub3>