The wimple: A rippled deformation of a wetting film during its drainage Available to Purchase

It has long been accepted that hydrodynamic pressure in a draining fluid film can cause inversion of curvature of a fluid-fluid interface, creating the so-called dimple. However, it was recently discovered that a different shape, dubbed a wimple, can be formed if a bubble/drop is initially in the field of repulsive surface forces, so that a wetting film is formed. The film profile then includes a central region in which the film remains thin, surrounded by a ring of greater film thickness and bounded at the outer edge by a barrier rim. This shape later evolves to a conventional dimple, which then drains in the usual way. Here we carry out numerical simulations of the draining film evolution that allow us to uncover the physical mechanism responsible for wimple formation. Simple analytical estimates are then obtained for characteristic times of different stages of drainage, and are shown to be in good agreement with experimental data. We demonstrate that wimpling is a general phenomenon that can be encountered in many different systems.