Variations of Rheological Properties and Wall Slip of Polyethylene in Nanoconfined Channels Studied by MD Simulation

In this work, the all-atom molecular dynamics (MD) simulation is employed to study the flow characteristics of polyethylene (PE) melts in a nanoconfined system. Except for the wall slip, the deviations of the non-Newtonian index of PE melts in the nanochannel from the bulk fluid were found. The simulation results demonstrated that the slip velocity (v_s) follows the power law v_s = aτ^b_w, and its correlation with the wall–fluid interaction was analyzed. More importantly, the anisotropic conformation of PE molecules and its discrepancy with the nonconfined system was manifested by the radius of gyration. The non-Newtonian index increased closer to 1 as the slit height decreased due to the elongation of polymer chains in the flow direction. The migration of polymer chains became smoother, and two fluid layers near the wall almost not exchanging with bulk region molecules were found. This work provides helpful insights for understanding nanoscale non-Newtonian fluid hydrodynamics behaviors.