Exploiting Stick and Slip in Nanofluidics

Recent experiments have measured large, shear-dependent liquid slip at partially wetting fluid-solid surfaces (Zhu and Granic, 2001). The origin of these dramatic violations of the no-slip boundary condition is still controversial and the consequences of these effects for microfluidic or nanofluidic devices have yet to be fully explored. One possible application is in fluid mixing. Mixing in flows with low Reynolds numbers is diffusion dominated and so is difficult to perform efficiently in microfluidics. Here we consider the possibility of patterning the slip at a surface (e.g by chemically patterning the surface or controlling its roughness), in order to induce mixing in the flow. We begin by solving the Navier-Stokes equations perturbatively for small variations in slip. We then compare these solutions to molecular dynamics simulations of flow in channels with varying wettability. Finally, we consider the possibility of using a surface with switchable wettability (Lahan to induce mixing and control a flow.