Thermodynamics of Solutions of Various Nonmesomorphic Solutes in the Nematic and Isotropic Phases of 7CB

Abstract

Thermodynamic results from gas-liquid chromatography, (GLC) are reported for thirty two nonmesomorphic solutes, at infinite dilution, in the nematic and isotropic phases of p-n-heptyl-p'-cyanobiphenyl (7CB). The solutes fall into five categories; normal alkanes, branched alkanes, alkenes, hexadienes and aromatics. The results are examined within the framework of statitical thermodynamic models. The observed trends are interpreted on the basis of solute structure (e.g. shape, size, flexibility, polarity and polarizability). The results conclusively show that the presence of one or more double bonds in the solute structure increases its compatibility with the nematic and isotropic phases of the liquid crystalline solvent. This effect is more drastic when the double bonds are conjugated. Other implications of this study include shape selective GLC separation of geometric isomers and an examination of the effect of solute structure on the stability of the nematic phase at finite solute concentrations.