Micellar Diffusion in the Liquid Crystalline and Concentrated Isotropic Phases of Decylammonium Chloride/NH₄Cl/H₂O Systems

Abstract

We have measured the diffusion coefficient of a non-water-soluable dye in aligned lamellar and nematic phases, perpendicular to the optic axis, as well as in micellar isotropic solutions of decylammonium chloride (DACl)/NH₄Cl/H₂O in the 25–90°C temperature range. The micellar diffusion in the nematic had a range of 4–15 × 10⁻⁷ cm²/s, in the isotropic 4–30 × 10⁻⁷ cm²/s and depends strongly on the sample composition. Diffusion is faster for samples containing greater amounts of DACl or NH₄Cl. Decreasing the concentration of NH₄Cl decreases the dependence of the diffusion on the water content of the sample. A simple order-disorder model is unable to account for changes in the diffusion coefficient at the nematic-isotropic transition.