ORIENTATIONAL ORDER OF PLANAR SOLUTES IN A ZERO AVERAGE ELECTRIC-FIELD GRADIENT NEMATIC ENVIRONMENT

The order matrices for 19 dihalobenzenes of C(s) and C2v symmetry have been measured using the NMR spectra of these molecules as solutes in the nematic mixture of 55 wt% Merck ZLI-1132 and 45 wt% N-(4-ethoxybenzylidene)-2,6-dideutero-4’-n-butylaniline. In this liquid crystal, the contribution to the orientational potential from the interaction between the molecular quadrupole moment and the mean electric field gradient of the liquid crystal can be neglected. The results are compared with predictions of a model which describes the anisotropic intermolecular potential in terms of (1) an elastic distortion of the liquid crystal and (2) an anisotropic surface interaction between solute and liquid crystal. Not only are the largest (in magnitude) order parameters very well fitted, but also the calculated anisotropies in the order matrices agree with the experimental ones. It is demonstrated that the results cannot be fitted with a bond-additive approach.