Thermotropic and lyotropic properties of n-alkyl-β-D-glucopyranoside surfactants

Abstract

We have studied the thermotropic and lyotropic phase behaviour of different monoalkyl glycosides using polarizing microscopy, differential scanning calorimetry and rheology. The dependence of the liquid crystal transition temperature and mesophase formation on the chain length of the hydrophobic tail has been studied. The melting transition for each of the dry alkyl-glycosides corresponds to one or two solid–solid transitions, a solid–liquid crystalline transition and a liquid crystalline–liquid isotropic transition. The lyotropic behaviour follows the classical pattern established for the surfactants. In the system C_XG₁ (X=8, 10)–water, the mesophases observed with increasing the concentration are a hexagonal phase, a cubic phase and a lamellar phase. Caused by the strong kinetic hindrance, the cubic and hexagonal phases for the system C₁₀G₁(n-decyl-β-D-glucopyranoside)–water are only visible by polarization microscopy experiments. Rheological oscillation experiments permit detection of phase transition. In the low-frequency range the rheological data are consistent with the simple Maxwell model.