Analysis of traction properties of fluids using molecular dynamics simulations. (Part 1) Determination of appropriate simulation conditions

Traction properties of hydrocarbon fluids were studied using molecular dynamics simulations. The fluid layer was confined between two solid Fe walls under a constant normal force of 1.0 GPa. Traction simulations were performed by applying relative sliding motion on the Fe walls. The interfacial slip was suppressed by applying large Fe fluid interaction. In order to determine the condition that can simulate qualitatively equivalent with experiments, film thickness (1-10 nm) and shear rate (10 7 -10 9 s -1 ) dependence of traction coefficient were calculated for n-hexane. Although our calculated traction coefficients showed a higher value than experimental one over a whole simulation range, traction coefficients decreased with both decreasing shear rate and increasing film thickness, which made a qualitative agreement with experiment. In ultrathin film less then 2.5 nm, large stick-slip-like motion caused by a slip between fluid layers were observed. The results suggest that film thickness of at least 5.0 nm is needed to simulate experimentally observed viscoelastic traction behavior.