Structural transformations and phase transitions in hexagonal La-containing lyomesophases

Abstract

Understanding and identification of phase equilibrium in self-assembling systems like lyotropic liquid crystals (LLCs) plays a key role in their further practical applications. In this study the phase transitions in LLCs based on С12ЕО10 nonionic surfactant, lanthanum nitrate hexahydrate, and water are reported. Polarized optical microscopy, X-ray powder diffraction, and fluorimetry were used to find correlations between system composition and structural changes. A new approach to identify a reverse hexagonal mesophase by the analysis of concentration dependencies of mesophase structural parameters was proposed. Data from these experiments were further compared with pyrene fluorescence studies to confirm the phase inversion. Based on complex analyses of experimental data an inversion of hexagonal mesophases via intermediate lamellar phase in the С12ЕО10(LaIII)/H2O system was found at the concentration ratio of 85/15 wt.%. The interpreted temperature-composition phase diagram was plotted. The regions of existence of direct hexagonal, intermediate mesophases and reverse hexagonal were found in the С12ЕО10(LaIII)/H2O system.