When wall slip wins over shear flow: A temperature-dependent Eyring slip law and a thermal multiscale model for diamond-like carbon lubricated by a polyalphaolefin oil

Lubricant flow in nanoscale channels is complicated by various effects that are not considered in conventional thermo-elasto-hydrodynamic lubrication (TEHL) models, one of them being wall slip. The relationship between slip and thermal effects is intricate: some authors debate whether the friction reduction observed in experiments in the TEHL regime is due to slip or viscosity reduction in heated lubricants. To disentangle these mechanisms, a molecular dynamics study of the relationship between temperature and slip in the shear flow of 4 cSt polyalphaolefins (PAO4) in a nanoscale diamond-like carbon (DLC) channel is performed here. We derive a temperature- and pressure-dependent slip law and a pressure-dependent law for the interfacial thermal resistance between DLC and PAO4. These constitutive laws are employed in a continuum model that can answer questions about the competition of slip and thermal thinning of the lubricant. The model shows that slip is only relevant for thin lubricant films typical of boundary lubrication.