Collapse of a hemicatenoid bounded by a solid wall: instability and dynamics driven by surface Plateau border friction.

ABSTRACT

The collapse of a catenoidal soap film when the rings supporting it are moved beyond a critical separation is a classic problem in interface motion in which there is a balance between surface tension and the inertia of the surrounding air, with film viscosity playing only a minor role. Recently [Goldstein et al., Phys. Rev. E, 2021, 104, 035105], we introduced a variant of this problem in which the catenoid is bisected by a glass plate located in a plane of symmetry perpendicular to the rings, producing two identical hemicatenoids, each with a surface Plateau border (SPB) on the glass plate. Beyond the critical ring separation, the hemicatenoids collapse in a manner qualitatively similar to the bulk problem, but their motion is governed by the frictional forces arising from viscous dissipation in the SPBs. We present numerical studies of a model that includes classical laws in which the frictional force fv for SPB motion on wet surfaces is of the form fv ∼ Can, where Ca is the capillary number. Our experimental data on the temporal evolution of this process confirms the expected value n = 2/3 for mobile surfactants and stress-free interfaces. This study can help explain the fragmentation of bubbles inside very confined geometries such as porous materials or microfluidic devices.