Thermodynamics of Solutions with Liquid Crystals Solvents. VII. A Mixture of Cholesteryl Chloride and Cholesteryl Myristate

Gas-liquid chromatography (glc) was used in a theimodynamic investigation of solubility in a 1.743:1.000 (weight: weight) mixture of Cholesteryl chloride and Cholesteryl myristate. This mixture exhibits a β cholesteric phase (increasing pitch with increasing temperature) at low temperatures, a “nematic point” at 42°C, and an α cholesteric phase (decreasing pitch with increasing temperature) up to 62°C, where a transition to the isotropic liquid takes place. Infinite dilution activity coefficients and partial molar enthalpies of solution were obtained for 16 diverse nonmesomorphic solutes in the β and α phases. The results are interpreted in terms of a statistical thermodynamic model2 of solution in anisotropic solvents. Comparison of solubility behavior in the α and β phases suggests a pronounced difference in the molecular packing of the two phases. Evidence is presented that the β→α transition may involve a higher order thermodynamic phase transition at the “nematic point”.