Nucleation Density from Isotropic and Self-Nucleated Melts of Isotactic Polystyrene: An Overview from the Molten to a Glassy State

Abstract: Nucleation density is a fundamental parameter influencing the microstructure, properties, and performance of polymeric materials. Controlling and manipulating nucleation density allows for tailoring polymeric materials with specific characteristics, enabling advancements in various fields of industrial applications. The present study investigates nucleation density from an isotropic and self-nucleated melt of isotactic polystyrene (iPS). A wide range of temperatures, from 225 to 260°C are considered, and the samples are subjected to partial or isotropic melt followed by isothermal crystallization. In the case of partial melting below 230°C, the nucleation density is attributed to the seed nuclei originating from self-nucleated melts due to incomplete crystal melting. Crystallization from isotropic melts involves a limited number of heterogeneous nucleation sites activated on the surfaces, impurities, or foreign particles within the melt. On the other hand, crystallization from the glassy state was found to rely on the molecular conformation and mobility in the amorphous phase, which plays a crucial role in achieving an optimal nucleation density. The experimental findings indicate that in molten and glassy states, the predetermined active nucleus sites significantly influence the nucleation process during crystallization. The nucleation density directly affects the crystallization kinetics and morphology of crystals. A higher nucleation density leads to a more significant number of smaller crystals, resulting in a finer microstructure. This can have significant implications for polymer properties such as mechanical strength, optical transparency, electrical conductivity, permeability, and thermal properties.