Dynamic evolution of liquid/liquid/solid contact line at micrometer length scale, corresponding to the Bond number Bo∼0, was investigated in a system with tuneable interfacial properties. Viscous oil was spontaneously displaced by water on a micron size spherical glass surface. By controlling wettability of the substrate and chemistry of surrounding aqueous solution, the displacement dynamics of three phase contact lines over a wide range of capillary numbers were studied. The rates of spontaneous oil displacement showed a strong dependence on fluid viscosity and interfacial properties of the system. The observed wetting dynamics were modeled using hydrodynamic and molecular-kinetic theory. Energy dissipation in the immediate neighborhood of the contact line was shown to determine the wetting dynamics of our micron scale experiments, even when capillary numbers were well above 10−4 in which hydrodynamic flow regime could be usually expected for conventional macroscopic systems.
