Nucleation and crystallization of deeply supercooled benzocaine, a rapidly crystallizing organic compound: A Fast scanning calorimetry investigation

Abstract

Investigation of nucleation and crystal growth in rapidly crystallizing systems represents a serious experimental challenge. Fast Scanning Calorimetry (FSC) was successfully used to study isothermal nucleation and crystallization in deeply supercooled melts of polymers and metallic glasses, but only limited attention was devoted to small organic molecules. In the present work, we present data on the nucleation and crystallization of the rapidly crystallizing organic compound benzocaine. We demonstrate that benzocaine can nucleate and crystallize far below the glass transition temperature. In deeply supercooled conditions, the nucleation and crystallization of benzocaine can be described using the equations derived from the Classic Nucleation Theory (CNT). However, at moderate supercooling, nucleation is not observed. Since the crystal growth rate is high at such temperatures, crystallization occurs only in prenucleated samples. The transition between the different behaviors is sharp, and the temperature of the transition is sample dependent. The presented results show a venue for the development of theories and models of nucleation, and demonstrate an important precedent of nuclei development far in the glassy state that must be considered for the application of amorphous drugs.