Polymer Conformation & Diffusion in Symmetric Thin Film Confinement

Polymer conformation and dynamics in thin film nanoconfinement controls a variety of properties important for advanced coating technologies and nanoplatelet composites. In this study, we examine the effect of chain length and film thickness on polymer conformation, entanglement density, and center of mass polymer diffusion using coarse grained molecular dynamics simulations. Polymer chain lengths of N = 25-400 and were confined between parallel plates to create polymer film thicknesses of h = 5-40σ. The plates are composed of discrete beads with athermal polymer-plate interactions. The simulations indicate that the diffusion coefficient, D, increases as the film thickness decreases, with longer chains exhibiting a larger increase in D. This increase in the diffusion coefficient correlates with chain disentanglement as confinement increases, similar to previous simulations of polymers confined to cylindrical pores. While we observe slowed diffusion in the most confined cylindrical geometries associated with chain segregation, polymer diffusion confined in thin films increases monotonically with increasing confinement.