Dependence of solute orientational order on the structure and orientational order of the liquid crystal solvent. A deuterium N.M.R. study of p-xylene-d₁₀ dissolved in a series of 4-n-alkyloxy-4′-cyanobiphenyls

Abstract

The quadrupolar splittings from the ring and methyl deuterons have been used to determine the principal components S^zz and S^xx - S^yy of the second rank orientational ordering matrix for p-xylene dissolved in the first 12 members of the 4-n-alkyloxy-4′-cyanobiphenyls (NOCB). The two order parameters are used to obtain the coefficients a and b in a potential of mean torque

for the solute molecules at infinite dilution in the solvent. The ratio λ_exp = b/2a, which is a measure of the departure of U (β₂γ₂) from cylindrical symmetry, is found to vary with temperature for each solute-solvent pair, and to increase as N, the number of chain carbon atoms, increases. The dependences of aRT and bRT on the orientational order of the solvent is explored.