Slip and coupling phenomena at the liquid-solid interface

The no-slip boundary condition, as a precept of interfacial fluid dynamics, constitutes a central dogma amongst some physicists and engineers. However, over the past decade, it has become a topic of some controversy because of the proliferation of theoretical and experimental evidence for the existence of slip, especially at micro- and nanoscopic scales. In this review, we consider the models, techniques, and results, both experimental and by simulation, concerning interfacial slip and mechanical coupling at solid-liquid (outer slip), and adsorbate substrate (inner slip) interfaces. Outer slip is a viscous process, normally described by a planar discontinuity between the upper layer of surface particles and the adjacent liquid layer. A number of factors can lead to slip, including surface-liquid affinity, high shear rates, surface roughness, and the elasticity of any intermediary film layer. Inner slip can be a viscoelastic process, and is related to adhesion and friction. Although it has received little attention, it will be important when dealing with self-assembled monolayers and more complex biosensor applications. Finally, we consider stochastic coupling as an aspect of the concept of slip.