Dynamics of Nanoconfined Polymer Melts via a Coarse-grained Modeling Approach*

Ultra-thin fluid film lubrication and nano-manufacturing commonly possess polymeric fluids confined in nanoscale channels where continuum theories fall short of explaining their motion. At this scale, the dynamics of the confined fluids are not just prone to their internal complexity and fluid-surface interactions but also to the ability to store elastic energy within its constituting polymer chains, the so-called viscoelasticity. In a polymer melt this behavior becomes more distinct as there is no solvent interaction, making it suitable to explore the molecular origins of the forces exerted on the surfaces. By conducting coarse-grained molecular dynamics simulations of minimal Couette flow configurations, we report that linear polymer melts, with chains short enough not to suffer from entanglement, enhance the viscoelastic response under confinement. Furthermore, we observe the presence of viscoelastic tension at low shear rates, which turns into compression as the shear increases. We further link the viscoelastic tension and compression to microscopic observation, such as the chain alignment, showing that the chains near the surfaces can carry the elastic force exerted on the walls.