Polymer Conformations & Dynamics in Nano-Confinement as a Function of Chain Length and Confining Radius

Understanding the structure and dynamics of polymers under nanoconfinement is critical in a variety of applications and industries, including semiconductor manufacturing, natural gas extraction, and polymer nanocomposites. Despite its importance, the relationship between the effect of chain length and pore radius on polymer properties (entanglement density, chain conformation, diffusion coefficient, relaxation time) is not well understood, with several studies indicating conflicting results. Using molecular dynamics, we simulated several systems with polymer chain lengths of N = 25-500 confined to discrete cylindrical pores of radii r = 2.5-20σ and examined their properties in confinement. These results are combined with unconfined polymer physics theories to develop scaling laws that describe confined polymer chain conformation and dynamics. Most interestingly, our results indicate a non-monotonic change in diffusion coefficient, D, as the pore radius is decreased, with longer chains exhibiting larger changes in D. We believe this is caused by the competing effects of chain disentanglement (increases D) and wall friction (decreases D).