ALKYL CHAINS IN A NEMATIC FIELD .2. TEMPERATURE AND CHAIN-LENGTH DEPENDENCE OF ORIENTATIONAL ORDERING

A model of flexible solutes which explicitly includes molecular shape anisotropy and flexibility (Photinos et al., preceding paper in this issue) exhibits quantitative agreement with observed temperature and chain-length dependence of deuterium NMR segmental order profiles of alkanes dissolved in a nematic solvent. A generalized order parameter for flexible chains is proposed and the average properties of the constrained chain are contrasted with the same properties calculated for chains in an isotropic medium. Conformer probabilities (corrected for inertial effects) are similar to those computed for isotropic (liquid) alkanes. The picture of these flexible solutes in the anisotropic mean field that emerges from our quantitative modeling of NMR data suggests that, although the alkanes may acquiesce and conform to the nematic constraints, they retain considerable conformational freedom and exhibit (average) properties that are only slightly perturbed from those found in the isotropic state. © 1990 American Chemical Society.