Lattice model studies of the effect of chain flexibility on the nematichyphen;isotropic transition. IV. Semiflexible chain solutes in solvent molecules composed of rigid cores and semiflexible tails

摘要

A steric, mean field, simple cubic lattice model, with and without attractive forces, for mixtures of semiflexible chain solutes in solvent molecules composed of rigid cores and semiflexible tails is presented. The calculated values and absolute trends of the following properties at the nematicndash;isotropic transitions of the mixtures are compared with relevant experimental data: coexistence curve slopes, solvent and solute order parameters, and solute excess properties as a function of the length and flexibility of the solute and of the solvent. With results intermediate between those for the completely flexible chain solute model and the rigid rod solute model, this semiflexible chain solute model is adequate to describe the general qualitative features and trends observed experimentally in mixtures ofnhyphen;alkanes in liquid crystal solvents at the nematicndash;isotropic transition. This model predicts four general curvature types for the coexistence curves as a function of solute length and flexibility. It also predicts maxima in coexistence curve slopes as a function of solute length for sufficiently long and sufficiently stiff chains. While steric repulsions alone are sufficient in this model to generate the general features and trends, attractive forces permit some adjustments in trends and produce significant improvements in energetics.