Liquid crystals in emulsions, creams, and gels containing ethoxylated sterols as surfactant.

Abstract

Depending on the concentration and the hydrophilicity of the surfactant, different mesophases have been demonstrated by X-ray analysis, polarizing microscopy and transmission electron microscopy of freeze-fractured samples. These mesophases participate in the microstructure of ternary mixtures. Mixtures of sterol-PEG5- and stereol-PEGlO-ether form lamellar liquid crystals which are organized into multilamellar vesicles with a size of up to several microns. At low concentrations of the surfactant the ternary systems consist of fluid emulsions of liquid crystalline vesicles and droplets of liquid paraffine dispersed in the outer hydrous phase. With increasing concentrations of the surfactant the mixtures become creamy and semisolid but remain emulsions with an increased volume ratio of the inner phase. The phase diagram of mixtures with sterol-PEG16-ether shows three different regions of liquid crystals: lamellar liquid crystals of planar arrangement at high concentration of the surfactant, a hexagonal mesophase with dispersed liquid paraffine and a ringing gel of close-packed mixed micelles. The higher the volume fraction of the liquid paraffine the larger are the oily droplets which are dispersed in the outer liquid crystalline phase of the close-packed micelles. The phase diagram of the most hydrophilic sterol-PEG25-ether is similar to that of sterol-PEG16-ether except for the absence of lamellar liquid crystals.