Phase Behavior of Novel Liquid-Crystalline Salts Containing a Cholesteryl Group

Abstract

Abstract The phase behavior of liquid-crystalline salts having a cholesteryl group was investigated by differential scanning calorimetry and polarized-light microscopy. Cholesteryl hydrogen succinate (CHS) and cholesteryl hydrogen phthalate (CHP) were used as a mesogenic core, and a series of normal aliphatic amines with 12 ∼ 18 carbons were used as a flexible tail. The salts were prepared as a stoichiometric 1:1 complex of a cholesterol derivative and an amine from mixed solutions in ethanol by solvent evaporation. CHS exhibited a monotropic cholesteric phase, while the salts of CHS with amines showed a mesophase in both cooling and heating cycles and it was frozen into a glassy state at temperatures below 0°C without changing the anisotropic organization. A similar state of glassy liquid crystal was noted for CHP per se and its salts with amines. The temperature range where a fluid liquid-crystalline phase appeared was mostly wider in the salt systems, when compared with the cases using the cholesterol derivatives alone. An odd-even oscillation phenomenon was perceived in the dependence of the mesophase-isotropic transition temperature and enthalpy of the salts on the carbon number of the amine component.