Molecular Dynamics Simulations of Polyethylene Bilayers

Abstract

By conducting molecular dynamics (MD) simulations of polyethylene (PE) melts consisting of two different films, each comprised of chains of different molar mass, in molecular contact with each other, we compare the structural and dynamical properties between these subsystems. Joining layers of the same chemical constitution but different molecular weights is explored as a route towards packaging materials that combine good mechanical and barrier properties with recyclability and therefore provide more sustainable solutions for contemporary industrial needs. Initially, we construct two independent PE thin films characterized by periodic boundary conditions in two directions, but of finite thickness in the third direction. An “amorphous builder” is used for this purpose, which constructs the chains bead by bead (united atom), using the TraPPE force field. A slab is made by joining the two films in the thickness direction and periodic boundaries are introduced in this direction. The slab is energy minimized and then subjected to NPT molecular dynamics (MD) simulation at 350 K and 1 bar, over times longer than the longest relaxation times of both films. Both structural and dynamical properties of the films are calculated, including the self-diffusion coefficient for the chain centers of mass.