Thermal Transition Behavior of Liquid-Crystalline Cholesterol Derivative/Aliphatic Amine Complexes and Enthalpy Relaxation Characteristics in Their Glassy State

Through DSC and polarized optical microscopy measurements, thermotropic phase behavior was examined for ionic complexes of cholesterol hydrogen phthalate (CHP) or succinate (CHS) with normal aliphatic amines (C-amines; carbon number n = 4-18), and for two types of complexes; one was composed of one cholesterol derivative and two different alkyl amines [i.e., CHP/(C-m,C-n)-amine and CHSAC,C)-amine, m not equal n] and the other consisted of two cholesteryls and one C-n-amine [(CHP,CHSVC-amine]. Except for the cholesteryl complexes with shorter C-amine (n <= 6), all the complex salts easily formed a liquid-crystalline glass (smectic or cholesteric type) without crystallization and phase-separation after passing through the mesomorphic fluid state, when they were cooled from the respective isotropic melts. Enthalpy relaxation of these glassy materials, occurring during physical aging below their T-g, was followed as a function of the aging time and temperature, and the obtained data was analyzed in terms of a Kohlrausch-Williams-Watts function. Uniformity of the relaxation mode was quite high for the aged samples of CHP/C-amine (n = 10-18) forming a smectic liquid-crystalline glass, and a slow relaxation with diverse modes was observed for the mixed complexes, particularly for CHP/(C-m,C-n)-amine and CHS/(C-m,C-n)-amine.