Transitions in a Lyomesophase: A Study by Thermal Analysis and Electron Microscopy

Abstract

The system Na decyl sulfate/water/decanol/Na sulfate, which forms a discotic nematic phase, N_L at room temperature, has been studied by differential scanning calorimetry (DSC) and by electron microscopy (EM). DSC reveals three first order phase transitions at 0[ddot]C, 12[ddot]C and 24[ddot]C. Latent heats show that the first transition must involve other processes in addition to the fusion of water, and that the last transition, between a coagel CG phase and the N_L phase, may be attributed to the order-disorder transition of the hydrocarbon chains (Krafft melting). Freeze-etch replicas have been obtained from samples initially in the N_L and CG phases. Micrographs obtained from the N_L phase show disc structures of about 2000 Å diameter. Micrographs obtained from the CG phase show large lamellar structures and regions of transition to the disc structures.