Thermodynamics of solutions with liquid crystal solvents. 9. Gas-liquid chromatographic study of nonmesomorphic solutes in nematic and isotropic N-(p-methoxybenzylidene)-p′-n-butylaniline and p-n-pentyl-p′-cyanobiphenyl

Thermodynamic results from gas-liquid chromatography (GLC) are reported for 20 nonmesomorphic solutes in the nematic and isotropic liquid phases of the two solvents N-(p-methoxybenzylidene)-p′-n-butylaniline (MBBA) and p-n-pentyl-p′-cyanobiphenyl (5CB), both of which exhibit room-temperature nematic phases. The infinite-dilution solute activity coefficients, partial molar excess enthalpies and entropies, and partial molar enthalpies and entropies of solution are examined within the framework of statistical-thermodynamic models. Discernible trends and differences in behavior between the two solvents, between the two phases, among the different solute groups (n-alkanes, branched alkanes, and aromatics), and within a given solute group are discussed and, where justifiable, are interpreted, with special emphasis on the effects of solute size, shape, and flexibility. The analytical implications of this study, i.e., shape-selective GLC separation of geometric isomers, are investigated. Also, a novel method, combining GLC and calorimetry, for generating phase diagrams (nematic-isotropic equilibria) for mixtures of nonmesogenic solutes at low concentration in mesogenic solvents is further developed and successfully applied.