Structure and dynamics of a 1,4-polybutadiene melt in an alumina nanopore: A molecular dynamics simulation

We present results of molecular dynamics simulations of a chemically realistic model of 1,4-polybutadiene confined in a cylindrical alumina nanopore of diameter 10 nm. The simulations are done at three different temperatures above the glass transition temperature T_g. We investigate the density layering across the nanopore as well as the orientational ordering in the polymer melt, brought about by the confinement, on both the segmental and chain scales. For the chain scale ordering, the magnitude and orientation of the axes of the gyration tensor ellipsoid of single chains are studied and are found to prefer to align parallel to the pore axis. Even though double bonds near the wall are preferentially oriented along the pore walls, studying the nematic order parameter indicates that there is no nematic ordering at the melt-wall interface. As for the dynamics in the melt, we focus here on the mean-square-displacement of the monomers for several layers across the nanopore as well as the movement of the chain center of mass both of which display a slowing down of the dynamics in the layer at the wall. We also show the strong adsorption of the monomers to the pore wall at lower temperatures.