Molecular dynamics and crystallization behaviour of isopentyl cyanobiphenyl as studied by dielectric relaxation spectroscopy

Abstract

Isopentyl cyanobiphenyl may be cooled into the supercooled liquid state, forming a glass below 210 K. On heating the glass, the supercooled liquid crystallizes above 245 K. Dielectric relaxation spectroscopy (DRS) has been used in the frequency range 10−1 to 105 Hz to study (i) the reorientational motions of the molecules in the glassy and supercooled liquid states and (ii) the kinetics of crystallization. A primary (α) relaxation process is observed whose line-shape is discussed in terms of the Kohlrausch–Williams–Watts function and component relaxation processes. The temperature dependence of the dielectric relaxation time is found to conform with the Vogel–Fulcher–Tamman equation. The crystallization kinetics, as determined from DRS measurements on heating the supercooled liquid, are shown to follow the Avrami equation but the experimental values of the Avrami exponent are far smaller than the theoretical value for the sporadic growth of spherulites.