Liquid crystal solutions at infinitesimal dilution: Correlation of enthalpy of solution in different phases

• Based on Flory’s theory of liquid crystal solutions, the enthalpy of solution in a mesophase is a linear function of (<α>/α)δ of solutes.
• The plot of enthalpy of solution of solutes between two mesophases of the same liquid crystal is linear.
• The plot of enthalpy of solution of solutes between mesophases of different liquid crystals is linear.

Careful gas–liquid chromatographic (GLC) studies provide thermodynamic data for insights into solution processes in non-volatile solvents. In a previous study, thermodynamic properties of solutes at infinitesimal dilution of several liquid crystals measured by GLC were examined. It was noted that enthalpy of solutions in mesophases was positive and higher than those of isotropic stationary phases. The variation of enthalpy of solutions among different solutes was also shown to be higher than what can be explained by the solubility parameter model. The temperature dependency of the disorder parameter in Flory’s theory of liquid crystals was used to explain high values of the enthalpy and entropy of solution. In this study the interaction parameter expression derived with orientation dependent interaction was used to explain the solute dependency on the enthalpy of solutions. The theory showed that the enthalpy of solution depends on the polarizability anisotropy and the solubility parameter of solutes. The theory also predicted a linear plot of the enthalpy of solutions between the mesophases of the same liquid crystal, or between mesophases of different liquid crystals, for the same set of solutes.