Orientational order of biaxial solutes in nematic phases Size and shape effects

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Abstract
Experimental order parameters for a series of solutes with C 2v and D 2h symmetry dissolved in the nematic liquid crystal comprised of 55 wt % 1132 (Merck ZLI 1132) and 45 wt% EBBA-d 2 (N-(4-ethoxybenzylidene)-2,6-dideutero-4-n-butylaniline) are obtained from N.M.R. measurements. In this mixture the average gradient in the electric field experienced by 2H2 is zero. The order parameters are calculated using a model based on short range repulsive interactions, which depend on the dimensions of the solute. The calculated values are in excellent agreement with the experimental results which suggests that these short range interactions are responsible for solute ordering in the 55wt% 1132/EBBA-d 2 system. It is also shown that in the two component liquid crystal solvents, 1132 and EBBA-d 2, the interaction between the molecular quadrupole moment of the solute and the mean electric field gradient due to the liquid crystal plays an important role in determining the solute ordering.