Heterogeneous nucleation in the crystallization of polyolefins. III. Theory and mechansim

The nucleating activity of a large number of nucleating agents for the crystallization of polyolefins is not based on a high surface free energy of the substrate or on epitaxy, or on a minimum particle size just compatible with the thickness of the crystallizing polymer lamellae, or on any persistance of crystalline material in holes of the nucleating particles. The relevant mechanism is thought to be nucleation at steps of limited length in the surface of the nucleating particles. The nucleation is enhanced by a high degree of accommodation of polymer molecules at the surface of the substrate through the presence of ditches in the latter which cause prealignment of polymer chains and thus facilitate crystallization.