Investigation of molecular order in liquid‐crystalline solutions of cellulose triacetate using PMR spectroscopy

Liquid‐crystalline solutions of cellulose triacetate (CTA) in trifluoroacetic acid (TFA)–CH 2 Cl 2 , TFA–1.2‐dichloroethane (1,2‐DCE) solvent mixtures were examined by means of PMR spectroscopy. CTA forms both cholesteric and nematic phases in these solvents depending on the CTA concentration. In cholesteric solutions the CH 2 Cl 2 signal is initially a singlet and then splits into a doublet. The time dependence of the splitting and the effect of CTA concentration are reported. The results suggest that the cholesteric phase slowly changes into a nematic phase in the magnetic field. The splitting of the CH 2 Cl 2 proton signal into a doublet and the 1,2‐DCE signal into a quartet are due to direct magnetic dipole‐dipole interactions. Rotation of the sample in the magnetic field results in the disappearance of the doublet or quartet and suggests that the solvent molecules are originally oriented in the direction of the magnetic field. In the biphasic region, immediate splitting of the CH 2 Cl 2 proton signal suggests that the anisotropic phase is nematic.