A non-empirical free volume viscosity model for alkane lubricants under severe pressures

Viscosities $η$ and diffusion coefficients $D_s$ of linear and branched alkanes at high pressures $P$$<$0.7 GPa and temperatures $T$=500-600 K are calculated by equilibrium molecular dynamics. Combining Stokes-Einstein, free volume and random walk concepts results in an accurate viscosity model $η(D_s(P,T))$ for the considered P and T. All model parameters (hydrodynamic radius, random walk step size and attempt frequency) are defined as microscopic ensemble averages and extracted from EMD simulations rendering $η(D_s(P,T))$ a parameter-free predictor for lubrication simulations.

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