Connectivity of the Hexagonal, Cubic, and Isotropic Phases of the C$_{12}$EO$_6$/H$_2$O Lyotropic Mixture Investigated by Tracer Diffusion and X-ray Scattering

摘要

The connectivity of the hydrophobic medium in the nonionic binary systemC$_{12}$EO$_6$/H$_2$O is studied by monitoring the diffusion constants oftracer molecules at the transition between the hexagonal mesophase and thefluid isotropic phase. The increase in the transverse diffusion coefficient onapproaching the isotropic phase reveals the proliferation of bridgelike defectsconnecting the surfactant cylinders. This suggests that the isotropic phase hasa highly connected structure. Indeed, we find similar diffusion coefficients inthe isotropic and cubic bicontinuous phases. The temperature dependence of thelattice parameter in the hexagonal phase confirms the change in connectivityclose to the hexagonal-isotropic transition. Finally, an X-ray investigation ofthe isotropic phase shows that its structure is locally similar to that of thehexagonal phase.