Phase behavior of novel liquid-crystalline salts containing a cholesteryl group

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 similar to 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 degrees C without changing the anisotropic organization. A similar state of glassy liquid crystal was noted for CHP pc, 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.