Flexible solutes in a uniaxial field: a deuterium NMR study of n-alkanes in a nematic solvent

Abstract

/sup 2/H NMR spectra for homologous series of perdeuteriated n-alkanes solubilized in nematic solvents are reported. These flexible solutes acquiesce to the uniaxial environment of the solvent and thereby reflect the nature of the nematic mean field. Quantitative simulations of the quadrupolar splittings exhibited by the alkanes are carried out using a parametrized potential of mean torque in conjunction with an ensemble average over alkane conformers. Two parameterizations were selected in order to gauge the relative importance of attractive (dispersion) forces and repulsive (excluded volume) forces. A detailed examination of the resulting angular dependence of the potential is shown for hexane along with a critical evaluation of the rotational isomeric state approximation itself. The findings suggest that while the latter approximation is adequate, a more elaborate specification of the orientational potential of mean torque for solutes is required - one that explicitly and rigorously couples attractive and repulsive intermolecular interactions.