Comparative investigations of the thermotropic and optical refractive properties in micellar isotropic phase and nematic-calamitic mesophase of hexadecyltrimethyl ammonium bromide/water and hexadecyltrimethyl ammonium bromide/water/1-decanol lyotropic liquid crystalline systems

Abstract

We report the thermotropic properties and measurements of the temperature and concentration dependences of the refractive index in isotropic micellar L 1 phase and nematic-calamitic N C mesophase of the hexadecyltrimethyl ammonium bromide/water (CTAB/H2O) and hexadecyltrimethyl ammonium bromide/water/1-decanol (CTAB/H2O/DeOH) lyotropic liquid crystalline systems. The effect of amphiphile and aliphatic alcohol concentrations on the refractive properties of L 1 phase and N C mesophase has been studied. Jump-like changes of the refractive properties in regions of the L 1 phase–N C mesophase lyotropic and thermotropic phase transitions have been found. The sufficient effect of CTAB addition on the refractive index value has been found for the CTAB/H2O and CTAB/H2O/DeOH lyotropic systems. In this work, the shape of micelles in L 1 phase and N C mesophase has been also estimated. Estimation showed that structural units of L 1 phase are the isometric spherical micelles, and structural units of N C mesophase are the anisometric rod-like micelles. Typical textures of N C mesophase in the CTAB/H2O and CTAB/H2O/DeOH lyotropic systems and the heterophase regions of the N C mesophase–isotropic liquid thermotropic phase transitions are presented.