Growth of spherulites: foundation of the DSC analysis of solidification. Maria Raimo. Chemtexts, (2015) 1:13.

Solidification is a practically and theoretically important issue, since it allows to design experimental conditions for desired material properties and also to discuss basic relationships between thermodynamics, kinetics and morphology. In this article, an overview on the crystallization theory and on the main traditional techniques to determine the crystallization rates, under constant and variable external temperature, is provided. The differences and similarities of isothermal and non-isothermal crystallization mechanisms are highlighted in the framework of the nucleation and growth theory, also by comparisons of the differential scanning calorimetry (DSC) peaks. The origin, broadness and symmetry of DSC peaks are explained in detail by considering the need for heat removal from the solid front and the coalescence of grains that originated in several points of the liquid phase. Although impingement is responsible for the general slowdown of crystallization, it is shown that the growth rate of a spherulite in the initial stage of coalescence continues to increase up to a maximum even if with a rate of change (i.e., a growth ''acceleration'') lower than that before impingement.