LYOTROPIC LIQUID CRYSTALS AT PHASE TRANSITIONS

摘要

In this paper some theoretical and experimental contributions to the study of lyotropic liquid crystals at the phase transition are presented. A modality is proposed to include the concentration dependence in the Landau-de Gennes theory for the nematic-isotropic phase transition by introducing a critical concentration for the lyotropic solution. The temperature dependence of density at normal pressure, for two compositions of sodium lauryl sulphate/water/decanol solutions, exhibiting either calamitic or discotic lyonematic phase is presented. Within the experimental precision limits, the systems show no density jump at the nematic-isotropic phase transition. The temperature dependence of ultrasound velocity and ultrasonic absorption for the two systems studied at 12 MHz frequency is reported. Both velocity and absorption present monotonous temperature dependence with no jump at the transition temperatures.