The Dynamics of L<3Phases (English shop)

Understanding dynamic processes in complex fluids is essential for explaining their equilibrium properties and structural behavior. Anja Wehling’s dissertation investigates the dynamics of the L₃ phase, an isotropic sponge phase characterized by a disordered, three-dimensionally interconnected bilayer structure. Ternary mixtures of water, n-alkanes, and nonionic alkylpolyoxyethylene surfactants are selected as model systems. The investigation focuses on how structural parameters, particularly bilayer thickness and interbilayer distance, influence relaxation behavior. Temperature-jump relaxation measurements and a newly developed isothermal shear apparatus are employed to investigate these dynamic processes experimentally. Systematic changes in sample composition allow controlled variation of the bilayer volume fraction and the surfactant-to-surfactant-plus-oil volume ratio. The experiments demonstrate that even minor changes in composition can produce substantial variations in relaxation times. The measured relaxation time constants extend over several orders of magnitude, ranging from microseconds to minutes. At constant bilayer thickness, relaxation times exhibit a strong dependence on the bilayer volume fraction. When the bilayer volume fraction is held constant, the relaxation time passes through a minimum as the surfactant fraction within the bilayer changes. Additional small-angle neutron scattering measurements provide detailed information about the microstructure and support the verification of a geometric model. This model quantitatively explains the relationship between structural parameters and the observed dynamics of the L₃ phase. Overall, the findings contribute to a deeper understanding of the relationships between structure, stability, and relaxation processes in sponge phases.