Effects of electrokinetic slip flow on lubrication theory

A lubrication theory that includes the coupled effects of electric double layer (EDL) and boundary slip is developed. The consideration of EDL (electro-viscous effect) and boundary slip near the solid surface increases and decreases apparent viscosity, respectively. Both effects are important for flow within microscales and lubrication problems. Under the usual assumptions of lubrication and Debye-Hückel approximation for low surface potential, the Navier-Stokes equation with body force due to the electrical potential, as well as the Navier slip boundary conditions, is utilized to derive the velocity distributions, apparent viscosity, and modified Reynolds equation. The apparent viscosity is expressed explicitly as functions of the Debye length, the electro-viscosity, and the slip length. The coupled effects of EDL and boundary slip on the apparent viscosity and one-dimensional slider-bearing performance are analysed and discussed. Results show that the load capacity increases as a decrease in inverse Debye length (K), a decrease in slip lengths (B), or an increase in electro-viscosity.