Otto LaPorte Lecture: Hydrodynamics of liquids at solid surfaces, from simple to complex fluids.

Hydrodynamics at the solid interface is a fundamental property of fluids, as important as their constitutive equation, in determining their flow. Historically, experimental evidence has been decisive in identifying the hydrodynamic boundary condition at the liquid-solid interface, and more particularly the so-called no-slip boundary condition that describes very successfully the flow of simple liquids on the macroscopic scale. But the growing interest in fluidic transport at small scales and in confined geometries, from friction and lubrication to ion transport in biological channels, membranes, or energy storage devices, has necessitated a more detailed understanding of the hydrodynamics of liquids on solids. Building on the pioneering experiments of Chan and Horn, I will show how the hydrodynamic force created by the drainage flow between two approaching surfaces, provides an unprecedented tool to probe the dynamics of liquids near surfaces. I will discuss the role of surface interactions and roughness, the role of liquid viscoelasticity and of solid compliance, for the formulation of an effective or intrinsic Navier boundary condition at the solid-liquid interface.