Polymer, Vol.172, 365-371, 2019
Spatial distribution of entanglements and dynamics in polymer films confined by smooth walls
Using Monte Carlo simulations combined with a geometric analysis method (Z1), we investigate the spatial distribution of entanglements and dynamics in polymer films confined by smooth walls, where the chain length spans a range from the un-entangled to the entangled region. Our results demonstrate a supersaturated region of entanglements as the distance of chains from the wall approaching 2R(g,e,) where R-g,R-e represents the coil size of chain segment of the entanglement length. As the distance is further increased, the entanglements become well-distributed as in the bulk. Moreover, when the film thickness is smaller than the bulk chain dimension, the variations of the dynamics of polymers with the film thickness can be divided into three cases: for the un-entangled short chains, the diffusion coefficient is a slowly decreasing function with the decrease of the film thickness; for the chains with a few entanglement points, the diffusion coefficient is almost independent of the film thickness; for the chains with considerable entanglement points, the diffusion coefficient becomes a rapidly increasing function with the decrease of the film thickness, which can be attributed to the competition between the spatial confinement and the disentanglement. Our work can provide an understanding of the microscopic distribution of entanglements and dynamics of polymer films deviating from what we know from the bulk.