Liquid crystal solutions at infinite dilution: Solute phase transfer free energy and solubility parameter variations at phase conversion temperatures

Abstract

Thermodynamic properties of three organic solute families in 4,4-bis(heptyloxyl)azoxybenzene (BHOAB) at infinite dilution were determined from gas–liquid chromatographic retention data. The reduced free energies of transfer of solutes between liquid crystal phases at transition temperatures were determined and related to the “disorder parameter” of Flory's liquid crystal theory. Reduced free energies of transfer between phases were functions of solute solubility parameters. From these, the “effective solubility parameters” of the liquid crystal phases could be evaluated. The effective solubility parameter of the smectic phase was lower than the other phases, despite being determined at lower temperatures and higher phase density. Changes in liquid crystal organization in the mesophases, which affect functional group contacts between the liquid crystal and solute molecules, are proposed to explain this behavior.