The Average Orientation of Solute Molecules in Nematic Liquid Crystals by Proton Magnetic Resonance Measurements and Orientation Dependent Intermolecular Forces

Abstract

The average orientation of benzene and some chlorine substituted benzene derivatives in a nematic liquid crystalline solution has been determined. 1,2,3-trichlorobenzene was used to study the influence of a permanent electrical dipole moment. It was measured in different nematic solvents of positive and of negative dielectrical anisotropy. There is no or only little variation in the relative average orientation of the principal molecular axes. It shows that the forces between permanent electrical dipole moments are of minor importance for the average orientation. A simple relation with two adjustable parameters is assumed for the orientation dependent part of the intermolecular interaction potential between solute molecules and anisotropic solvent. The values of the energy parameters are calculated from the observed average orientation by a simplified statistical treatment. Regarding only the dispersion forces and with some other neglections these parameters for benzene and the different derivatives can be theoretically correlated to each other. The comparison with the experimental results gives an approximate agreement.