Translational Diffusion of CH₄ and CH₂Cl₂ Dissolved in Cholesteric Liquid Crystals

Abstract

Translational diffusion coefficients of CH₄ and CH₂Cl₂ dissolved in five cholesteric mixtures of alkylcyanobicyclohexane-cholesterylchloride were measured in the temperature range 25°C to 75°C, using the NMR pulse gradient spin echo method. The pitch of the solvents studied depends on the cholesterylchloride concentration and ranged between ∞ and 2.2μ. The results indicate a slight difference in the diffusion constant parallel (D‖) and perpendicular (⊥) to the cholesteric pitch axis, with D _⊥/D‖ ≃ 1.1. The Arrhenius activation energies for the diffusion constants are about 6 to 7 kcal/mole for both probes. No dependence of the diffusion coefficients on the cholesterylchloride concentration and thus on the pitch was observed.