Molecular Rheology of Perfluoropolyether Lubricant via Nonequilibrium Molecular Dynamics Simulation

Rheological properties of perfluoropolyether (PFPE) systems can be particularly important in designing effective lubricants that control the friction and wear in their tribological applications. Using equilibrium/nonequilibrium molecular dynamics (MD) simulation, we examined the rheological properties of PFPE lubricant, such as viscosity and viscoelastic properties, by observing the time-dependent system in shear motion. Strong dependence of PFPE bulk viscosity on PFPE molecular structure (e.g., end group functionality) and external conditions (e.g., temperature) was observed. Via a nonlinear regression method, we further extracted the relaxation time spectrum based on our simulated dynamic moduli data, where the importance of end group couplings was emphasized. In addition, we adopted two solid surfaces to mimic the head and disk, which will provide a further understanding in lubricant nanorheology and nanotribology