A model for wall slip prediction of alkanes confined between smooth surfaces
Abstract
The aim of this work is to suggest a model for predicting wall slip based on the characterization of both the fluid and the surfaces. The different behaviours can in fact be explained as the result of the competition between the lubricant resistance to shearing and the capability of the surface to transfer a tangential momentum to the fluid molecules at the interface. In order to characterize the solid surfaces a corrugation parameter is proposed for both canonical and complex crystal lattices: it takes into account the surface-fluid interaction stemming from the Lennard-Jones interatomic potential [1], as well as the commensurability between lubricant molecules and the crystal lattice [2]. Lowly corrugated surfaces lead to high wall slip compared to highly corrugated ones, which on the other hand cause locking of the lubricant molecules at the surface. The corrugation parameter is then used in order to create master curves for alkanes, which quantitatively describe the tangential momentum transfer at the interface. Finally, a simple model for wall slip prediction including both the fluid effective viscosity and the surface corrugation parameter is proposed. This is can be regarded as a preliminary step for linking the molecular scale with larger ones.