Extrapolation of Rheological Properties for Lubricant Components with Stokes-Einstein Relationships

In this paper we examine the scaling of transport properties obtained from molecular dynamics simulations on a number of model C16 isoparaffin systems and interpreted in a Stokes-Einstein framework. The properties span a wide range of temperatures and pressures. The scaling behavior can be nonlinear and shows variation among different isomers. Nonetheless, for a given molecule, the scaling behavior of transport property data appears to be well-behaved, and we propose two approximate methods by which viscosity can be estimated from the self-diffusion coefficient and geometric characterization of the molecule in terms of an inertially equivalent prolate ellipsoid. Both methods rely on high-temperature simulations, which provide important scaling information about transport properties with reasonable computational effort. We compare the accuracy of the predictions of these approaches with several examples of lube-ranged model compounds.