Mesomorphism in Cholesterol-fatty Alcohol Systems

Abstract

During a study of mixing and unmixing of binary mixtures of polymorphic fatty alkanols in the solid state, the special case of cholesterol and these alcohols was examined, and a liquid crystalline phase was observed with C12, 13, 14, 16 and 18 alkanols but not with the shorter decanol and octanol. Mlodziejowski has reported liquid crystalline phases in the hexadecanolcholesterol system but gives no figures for composition and temperatures. This has been done and fig. 1 shows the phase equilibria for this system. Extreme care needs to be taken in observing transitions owing to extreme supercooling of cholesterol in cooling runs and to its very slow rate of dissolution in heating runs; supercooling also occurs at the lc to solid transition but these temperatures were observed easily on the heating stage of a polarizing microscope. The points up to 25% of cholesterol were readily found by cooling curves; with 25% the arrest at the liquid to liquid crystal transition was only about one fifth of that at the freezing point. As usual, supercooling does not occur at the liquid to liquid crystal transition.