Enthalpy relaxation behavior of liquid-crystalline glasses of an esterified cholesterol derivative and its complex salts with aliphatic amines

A cholesteryl hydrogen phthalate (CHP) and its complex salts with normal al iphatic amines (C-n-amines) are capable of forming a glassy liquid-crystall ine phase, where an anisotropic organization of their fluid mesophase is fr ozen in an uncrystallized solid state. Differential scanning calorimetry (D SC) measurements were conducted for these glassy materials to examine an en thalpy relxation phenomenon, occurring when they were annealed adequately a t temperatures lower than the glass transition temperature. The enthalpy re laxation behavior, monitored as evolution of a DSC endothermic peak, was an alyzed in terms of a Kohlrausch-Williams-Watts type of stretched exponentia l equation, and the overall relaxation time tau and a parameter beta chract erizing the distribution of the relaxation mode were evaluated. It turned o ut that the tau values obtained for CHP/C-n-amine salts were rather smaller than those for CHP per se, and beta became close to unity when CHP was com plexed with the C-n-amines through ionic interaction, the latter component employed having 12, 16, and 18 carbons. The activation energy for the relax ation process of the CHP/C-n-amine samples was considerably small, compared with that in the case of CHP alone, and tended to decrease with an increas e in the carbon number of the amine component. An attempt was also made to estimate the fragility of these samples as glass.