Studies of Phase Transition and Molecular Motion in Homologous Series of Cholesteryl ω-Monohydrofluoroalkanoates by Dielectric Measurements

Abstract

The phase transition and molecular motion in a homologous series of cholesteryl ω-monohydrofluoroalkanoates [CHFA, C27H45OCO(CF2)n CF2H, n=1, 3, 5, 7] were studied by dielectric measurements. Two phase transitions were found near -53 and -18°C in the n=5 crystals, but both the n=3 and n=7 crystals show no phase transition in the crystal state. The crystals of the esters longer than n=1 did not show the successive phase transitions which exist in the n=1 crystals. One dielectric relaxation was observed in the lower temperature range for all the crystals, and this was not associated with the phase transitions. The phase transitions and the dielectric behavior of the relaxation are reflected faithfully in the crystal structure.