Thermotropic liquid crystalline properties of amphiphilic branched chain glycolipids

Abstract

Glycolipids are amphotropic liquid crystals forming lyotropic liquid crystals in aqueous solutions and thermotropic liquid crystals in their dry form. We report studies on the thermotropic properties of seven different neat glycolipids: four maltoside, two glucoside and one pyranoside lipids. Optical birefringence, electrical conductivity, differential scanning calorimetry, and dielectric spectroscopy measurements were employed to characterize the phase structures of the materials. In general, they exhibit a wide (>100°C) mesophase (smectic, columnar) range with low (0.01–0.04) birefringence. They have large (60–120) dielectric susceptibility basically proportional to the number of polar sugar heads. Depending on the temperature the relaxation frequency of the susceptibility varies between <100 Hz and >1 MHz, mainly determined by the hydrogen bonding between the polar sugar heads.