THE THERMODYNAMICS OF SOLUTION OF NON-MESOMORPHIC SOLUTES IN THE LIQUID CRYSTAL 6CB REVISITED

Results from gas liquid chromatography were analyzed to express the infinite dilution solute activity coefficient gamma ^infinity 2 as a function of the Flory-Huggins size effect correction (gamma ^infinity FH ) and an interaction parameter (kappa ); the sum of the thermal (gamma^infinity T) and athermal (gamma^infinity 1-s ) contributions to gamma ^infinity 2. From regular solution theory, solute (delta 2 ) and solvent ( (delta1 ) solubility parameters were obtained at different temperatures for all the solutes in the nematic and isotropic solution phases.Plots of delta H versus delta S, the solute partial molar enthalpies and entropies of solution respectively, were reasonably linear. Such delta H - delta S compensation reflects similar solubility for the solutes in the nematic and isotropic phases. Also, an average of 1.11 ± 0.02 for gamma^infinity 2,N/ /gamma^infinity 2,I, where N and I refer, respectively, to the nematic and isotropic phases, indicates slightly lesser solute compatibilities with the nematic phase.For all the solutes studied plots of delta1 versus temperature (t) showed a drastic and sharp change in delta 1 at the nematic-to-isotropic transition (29.0 °C) which is reminiscent of enthalpy and density changes in first order transitions. The extent of the discontinuity in deltq 1 may be a measure of the strength of the transition while delta 1 which varies continuously across the phase transition or shows a kink at the phase transition would be associated with a second order transition. This finding can help in identifying second order transitions in liquid crystals or polymers.