Intermolecular potentials in liquid crystals: Comparison between simulations and NMR experiments

The anisotropic intermolecular forces responsible for the orientational ord ering in liquid crystals are probed by comparing Monte Carlo (MC) simulatio ns with experimental nuclear magnetic resonance (NMR) results for solutes i n nematic liquid crystals. In a special liquid crystal mixture where all lo ng-range interactions are assumed to be minimized, the models for short-ran ge interactions which best fit NMR experimental solute order parameters als o best fit solute order parameters from MC simulations of hard ellipsoids. This is taken as an indication that in this special mixture the intermolecu lar potential is dominated by short-range forces. However, for liquid cryst als where long-range interactions are important, simulations of hard ellips oids with point quadrupoles cannot reproduce even the gross effects observe d with experimental NMR data.