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 T c (ϕ) and half time of crystallization t 1/2 (ϕ) on slow heating up to 5 K/min points to diffusioncontrolled mechanism with the energy barrier 57 kJ/mol, and (2) small effect of faster heating on T c (ϕ) and t 1/2 (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. ■ INTRODUCTIONThe well-known crystallization phenomenon is still not clearly described as it depends on many factors like a type of nucleation of crystal grains, a nucleation rate, and a rate of growth of crystallites in the melt substance. 1,2 Calculations of absolute nucleation and growth rates are difficult, but each substance has its own temperature ranges where nucleation and growth are favorable. Usually, the rate I(T) of nucleation has its maximum at lower temperature than the maximum for the rate G(T) of crystal growth. 2 Moreover, both rates may be complicated functions of temperature and of details of the experiment used (e.g., cooling rate). The driving force of overall crystallization depends on viscosity to entropy relationships and their temperature changes. 3 Lower temperature parts of I(T) and G(T) curves reflect growing viscosity (transport parts), while the higher temperature parts are the results of larger diffusivity/molecular mobility (thermodynamic parts) in the substance under study. 2 If these curves have no temperature range in common, no crystallization is detected on cooling. Instead, vitrification is observed, no matter how slowly the temperature is decreased. Then, crystallization is expected on heating. In isothermal studies of crystallization kinetics, degree D(t) of crystallinity (or crystallization ratio) is described in terms of Avrami model 4,5Linear dependence of log{−ln[1 − D(t)]} vs log t is expected: slope n A describes the dimensionality of the process and the nucleation mode (instantaneous, prolonged in time, 1-, 2-or 3-dimensional etc.), and the k parameter d...

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In this study, we apply differential scanning calorimetry (DSC) and polarizing microscopy (POM) to elucidate the interplay of crystallization mechanisms controlling the tendency for melt and cold crystallization from the partially ordered smectic B phase in 4-pentylphenyl 4-(trans-4-pentylcyclohexyl)­benzoate (5CPB5) mesogen. For this purpose, we pay attention to the kinetics of nonisothermal crystallization revealed by several complementary approaches, including Ozawa, Mo, and the isoconversional method. Additionally, we adopt the Hoffman–Lauritzen theory for analyzing the temperature dependence of crystallization activation energy, allowing us to describe the multistep crystallization of the smectic B mesophase. Our investigation shows the possibility of designing the mechanism controlling the different crystallization paths. Moreover, we demonstrate the ability to switch the dimensionality of crystal growth by modifying the dominance of molecular mobility through the experimental rate.