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

We have studied the thermotropic and lyotropic phase behaviour of different monoalkyl glycosides using polarizing microscopy, differential scanning ca lorimetry and rheology. The dependence of the liquid crystal transition tem perature and mesophase formation on the chain length of the hydrophobic tai l has been studied. The melting transition for each of the dry alkyl-glycos ides corresponds to one or two solid-solid transitions, a solid-liquid crys talline transition and a liquid crystalline-liquid isotropic transition. Th e lyotropic behaviour follows the classical pattern established for the sur factants. In the system C(X)G(1) (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 he xagonal phases for the system C(10)G(1)(n-decyl-beta-D-glucopyranoside)-wat er are only visible by polarization microscopy experiments. Rheological osc illation experiments permit detection of phase transition. In the low-frequ ency range the rheological data are consistent with the simple Maxwell mode l.