Kinetics of Crystal Nucleation in Polyethylene

Abstract

Observations of the freezing behavior of droplets of a linear polyethylene (Marlex‐50) suspended in an inert medium have been made. It is possible to cool such suspensions of molten droplets to 85°—87°C before the majority of the droplets freeze, provided precautions are taken to minimize nucleation by the vessel walls. This indicates unambiguously that spherulites formed near 120°C (the usual crystallization range) are nucleated by heterogeneities in the melt. Analysis of experiments performed at various cooling rates indicate an end surface interfacial energy of rod‐shaped nuclei of 168 ergs/cm². This is similar to the estimates made of the fold‐surface energy in crystals formed from dilute solution. The cooling‐rate experiments also indicated that the transport processes in the production of the polymeric nucleus are similar to those involved in the production of nuclei of n‐alkane crystals.