Existence of the Navier slip condition for liquids

The Navier slip condition is regularly used to characterize the interaction of a fluid with a solid boundary. Its use at the gas-solid boundary is justified rigorously from Boltzmann's kinetic theory of gases, however no such parallel exists at the liquid-solid boundary. The strongest evidence for existence of the Navier slip condition at the liquid-solid interface comes from molecular dynamics simulations. As dictated by kinetic theory, the Navier slip length is a constitutive property that holds when the flow is continuum away from the solid interface. Here, we present an experimental protocol that is used to measure the Navier slip length on individual and isolated particles with exquisite precision. Experiments consisting of thousands of measurements on individual gold nanoparticles give a constant slip length of 2.7$\pm$0.6 nm---independent of particle size---providing experimental validation of the Navier slip condition for liquids.