Kinetics of Cold Crystallization of 4-Cyano-3-fluorophenyl 4-Butylbenzoate (4CFPB) Glass Forming Liquid Crystal. I. Nonisothermal Process As Studied by Microscopic, Calorimetric, and Dielectric Methods

Abstract

For 4-cyano-3-fluorophenyl 4-butylbenzoate (4CFPB), the process of the crystallization of the CrII phase was studied in microscopic (POM), calorimetric (DSC), and dielectric (BDS) nonisothermal experiments with various (0.5–50 K/min) heating of the metastable nematic phase obtained from its glass. Growth of areas of crystal CrII in the microscopic texture of nematic phase during heating allows estimation of degree of crystallinity D(T) vs temperature curves similar to these obtained basing on DSC heat flow curves and for slow heating with help of dielectric relaxation (BDS) method. Two types of CrII crystallization mechanisms seem to be identified: (1) strong ϕ dependence on temperature of full crystallization Tc(ϕ) and half time of crystallization t1/2(ϕ) on slow heating up to 5 K/min points to diffusion-controlled mechanism with the energy barrier 57 kJ/mol, and (2) small effect of faster heating on Tc(ϕ) and t1/2(ϕ) seems to illustrate thermodynamic mechanism with energy barrier 180 kJ/mol. The scenario of two mechanisms of CrII crystallization is in agreement with the results of new method proposed by Mo et al., using combination of Avrami and Ozawa equations for description of nonisothermal crystallization. In addition to crystallization of CrII of 4CFPB, at higher temperature range CrII–CrI transformation to a stable CrI crystal was digitalized based on microscopic and DCS results for heating at 1 K/min.