Growth dynamics of capillary bridges

We study the growth and equilibration of capillary bridges that form when a dry solid sphere is brought in contact with an initially flat oil film wetting a solid substrate. The surface profiles of the growing capillary bridge obtained by side-view imaging are matched to thickness profiles of the surrounding oil film as extracted from fluorescence measurements for various values of the initial film thickness, sphere radius, and sample size. Strong initial capillary suction is found to induce a transient local minimum of the film thickness next to the outer rim of the growing capillary bridge. Below a critical initial film thickness, which is governed by the equilibrium surface profile, this local minimum becomes very deep and leads to equilibration times, which exceed the classical lubrication timescale by orders of magnitude. We develop a numerical scheme that describes the dynamics of the entire process by patching a quasi-statically evolving macroscopic capillary bridge to the adjacent liquid film, which evolves according to the lubrication equation. The scheme reproduces the salient experimental features, namely the emergence of the deep local minimum, the critical film thickness, and the increase in equilibration time.