Polyethylene {201} crystal surface: interface stresses and thermodynamics

We describe a method to determine the mechanical and thermodynamic properties of the interface between a polyethylene crystal and melt by united-atom Monte Carlo simulations. In particular, the {201} fold surface is studied in the temperature range 380-450 K. The interface properties are defined by using the concept of a sharp Gibbs dividing surface, which in turn is used to define the interface internal energy and the interface stresses. We find that the internal energy of the interface is of the order 0.3-0.35 J/m2. The interface stresses are anisotropic for the {201} crystal surface with values of approximately −0.27 and −0.4 J/m2 for the xx- and yy-components, respectively. By way of the Herring equation, the surface tension of the fold surface is independent of shear strains in the interface. The temperature and strain derivatives of the interface properties are also measured and discussed in detail. The influence of the interface internal energy and of phase change contributions on the macroscopic heat capacity of the semi-crystalline material is examined.