Melt memory of a spherulite nucleus formed through a seeding process in the crystal growth of isotactic polystyrene

Abstract

The melt memory effect on the crystal growth of isotactic polystyrene is investigated using optical microscopy. After a spherulite is melted at a slightly higher temperature than the melting point and completely disappears, a polymer crystal nucleates and grows at the same position as the original spherulite when the temperature is decreased below the melting point. After the melting-recrystallization processes are repeated by raising and lowering the temperature, the melt memory effect becomes weak. This effect completely disappears at ∼40 °C above the equilibrium melting point when the melt temperature is gradually increased during the melting-recrystallization processes. The formation of spherulite nuclei is promoted by the seeding process, which consists of the following consecutive procedures: quenching a sample to a temperature below the glass transition temperature and annealing the sample slightly above the glass transition temperature. At the initial stage, the number density of spherulites rapidly decreases with the cumulative melting time. After the initial stage, the number density of spherulites exponentially decays with the cumulative melting time and approaches a finite value. This asymptotic value decreases with the melt temperature.