Gelation of silicone fluids using cholesteryl esters as gelators

Abstract

A variety of silicone fluids were found to gel using low concentrations ( < 2wt.%) of cholesteryl anthraquinone-2-carboxylate (CAQ) and cholestanyl anthraquinone-2-carboxylate (CHAQ). These compounds are known to be effective gelators for a variety of organic fluids. The gelation process involved the use of a co-solvent to incorporate the CAQ and CHAQ into the silicone fluid, followed by its removal via a thermal treatment. Semi-clear to clear irreversible gels were formed in this way and optical and scanning electron microscopy revealed that their microscopic features are similar to those reported for the organic fluids. They form intertwined microscopic fibres which create a three-dimensional network that effectively immobilizes the silicone fluid. The silicone gels were found to be more stable at high temperatures than the organic gels. This is attributed to the much lower solubility of the gelator in silicone fluids at all temperatures. A number of other simple cholesteric compounds were also investigated as gelators of silicones. From those, cholesteryl phenylacetate was found to form a macrocrystalline network and to entrap the silicone fluid in a fashion analogous to CAQ. Owing to their large macrofibres, opaque paste-like gels were obtained.