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.