Self-Seeding Effect on Primary Nucleation of Isotactic Polystyrene

Primary nucleation behavior of isotactic poly(styrene) was studied in a wide range of crystallization temperatures (Tc), times, and melt temperatures (Tf). Samples were melted at several melt temperatures (Tf) from 225 to 250 °C (or vice versa) and then isothermally crystallized. Time dependence on the nucleation behavior showed a sigmoidal curve with an induction time (τ0). The spherulites sporadically appeared (the steady state of nucleation, I) until they reached a limiting number of nuclei (the saturated nucleation density, Ns). The number of nuclei reached saturation much earlier than the induction time (τover) in the overall crystallization. Ns was not associated with impingement of spherulites, since about 90% of the melt region remained. It was found that there was a critical spherulite size, in which induced nucleation sites began to appear within the outline of the original spherulite in the subsequent crystallization. When the crystallization was stopped before reaching the critical spherulite ...