A Model for Capillary Flow Between Rough Surfaces
Many micro and nano scale devices are influenced by the presence of liquid at the interface between contacting surfaces. Such liquid may induce large and undesired adhesive or “stiction” forces. In some cases, liquid may find its way into the interface of two rough surfaces that are already in contact. It is of interest to model the manner in which the interface proceeds to a new equilibrium configuration upon introduction of the liquid. Such a process involves interactions among viscosity, elasticity and capillarity. To simulate such effects, a multi-scale contact model is employed to account for surface deformation, a mixed-lubrication model is applied to analyze liquid flow and the Young-Laplace equation is implemented at the boundary of the wetted region to provide the capillary pressure. Calculations are performed to reveal the roles of liquid viscosity, liquid surface tension, surface roughness and elastic modulus on the generation of adhesive forces.