Physical−Chemical Properties of Some Branched Alkyl Glucosides

Abstract

Four different alkylglucosides have been examined with respect to their physicochemical properties, viz. 2-ethylhexyl glucoside, isooctyl glucoside, 2-propylheptyl glucoside, and isodecyl glucoside. The substances have been examined by means of microscopy, crossed polarizers, 1H-NMR self-diffusion, 2H-NMR quadrupolar splittings, and small angle X-ray scattering. Properties such as critical micelle concentrations, solubilities, Krafft points, aggregation structures, and liquid crystallinity have been determined. For all substances, the only phases appearing in the binary (surfactant/water) system are the micellar and lamellar phases. For the two substances with eight carbons in the hydrophobic tail, there is a broad micellar region, a minor two-phase region, and a lamellar crystalline phase. The isodecyl glucoside, with 10 carbons in the hydrophobic tail, shows a liquid−liquid coexistence region from low surfactant concentrations up to ca. 18 wt % surfactant. In the case of the 2-propylheptyl glucoside, there is an extended two-phase region up to ca. 67 wt % surfactant consisting of a mixture of an isotropic solution and a lamellar phase. Above 67 wt % there is a lamellar phase. The isotropic solutions of 2-ethylhexyl glucoside, isooctyl glucoside, and isodecyl glucoside have been studied with self-diffusion 1H-NMR to obtain structural information about the micelles present. The concentration dependence of the surfactant self-diffusion follows the pattern that can be expected of spherical micelles. SAXS measurements show that the liquid crystalline phase formed by all the four surfactants has a lamellar structure. The SAXS results have been analyzed in terms of repetition distances and area/headgroup in the liquid crystalline region.