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

TL;DR

This study investigates the connectivity of different phases in a lyotropic mixture using tracer diffusion and X-ray scattering, revealing highly connected structures near phase transitions.

Contribution

It provides new insights into the connectivity and structure of isotropic and cubic phases in C$_{12}$EO$_6$/H$_2$O mixtures through combined diffusion and scattering analysis.

Findings

Increased transverse diffusion indicates bridgelike defects near the transition.

Isotropic phase exhibits diffusion coefficients similar to cubic bicontinuous phase.

X-ray data shows local structural similarity between isotropic and hexagonal phases.

Abstract

The connectivity of the hydrophobic medium in the nonionic binary system C$_{12}$EO$_6$/H$_2$O is studied by monitoring the diffusion constants of tracer molecules at the transition between the hexagonal mesophase and the fluid isotropic phase. The increase in the transverse diffusion coefficient on approaching the isotropic phase reveals the proliferation of bridgelike defects connecting the surfactant cylinders. This suggests that the isotropic phase has a highly connected structure. Indeed, we find similar diffusion coefficients in the isotropic and cubic bicontinuous phases. The temperature dependence of the lattice parameter in the hexagonal phase confirms the change in connectivity close to the hexagonal-isotropic transition. Finally, an X-ray investigation of the isotropic phase shows that its structure is locally similar to that of the hexagonal phase.