Mobility of the surface and interior of thin films composed of amorphous polyethylene

We performed coarse-grained simulations of thin polyethylene films of different thicknesses at 509 K. The films, which present two surfaces to vacuum, are formed from monodisperse melts of C100H202 The mobility increases toward the free surfaces at the scale of individual beads and chains due to the decrease in density. The diffusion of the chains parallel to the surfaces increases as the film thickness decreases. In contrast, the diffusion in the direction normal to the surfaces slows down as the film thickness decreases. This slowing down seems to be primarily a result of the confinement of the chains between the surfaces.