Calculated Interfacial Free Energies and Hetrogeneous Nucleation of Isotactic Polypropylene

The surface free energy of crystalline isotactic polypropylene (iPP) and the interfacial free energy of crystalline iPP with a featureless Hamaker constant matched surface are determined by an all-atom lattice dynamics method including contributions from phonons treated quantummechanically and analytical "tail corrections" for long-ranged dispersion forces. The relative magnitudes of quantum effects, tail corrections, and finite system size effects on the surface free energy are assessed. The surface tension of iPP melt and the interfacial tension of iPP melt with a featureless substrate are determined from all-atom molecular dynamics simulations. We apply these results to a heterogeneous "cylindrical cap" nucleus on a featureless substrate, for which a contact angle of 79 degrees +/- 3 degrees is found. This value is in reasonable agreement with analysis of quiescent crystallization of commercial iPP samples, and thus lends support to the cylindrical cap model for heterogeneous nucleation.