Mesomorphic solutions of cellulose triacetate in halogenated organic acids and mixtures of trifluoroacetic acid and dichloromethane

Abstract

Abstract Cellulose triacetate (CTA) forms liquid‐crystalline solutions in trifluoroacetic acid, dichloroacetic acid, and mixtures of trifluoroacetic acid and dichloromethane. Brilliant iridescent coloration, high optical rotations, and birefringent regions with swirl‐like fingerprint patterns suggested the formation of cholesteric liquid crystals. Trifluoroacetic acid–dichloromethane is a particularly excellent solvent mixture to form liquid‐crystal solutions of cellulose acetate. Crude bulk viscosity measurements confirm the formation of an anisotropic phase, and the temperature dependence of the critical concentration for formation of the anisotropic phase, obtained by bulk viscosity measurements at various temperatures, provides confirming evidence. Viscosity decreases with aging, suggesting that CTA is slowly degraded in the solvents studied. This is also confirmed by optical rotatory measurements and by polarizing microscope observations. The miscibility gap is observed as a function of molecular weight, and the differences between the experimental data and Flory's prediction are discussed.