Instability of rotund capillary bridges to general disturbances: Experiment and theory

Abstract

Interfacial tension holds a fixed volume of incompressible fluid between coaxial circular endplates forming a capillary bridge. As the endplates are brought together very slowly the bridge fattens and eventually changes shape. In contrast to the much-studied configuration of slowly separating endplates (slender bridges), the rotund axisymmetric bridge is first unstable to nonaxisymmetric disturbances. We obtain the boundary of marginal stability (constant volume disturbances) as it depends on the aspect ratio and the volume of the bridge using an energy stability method. Furthermore, we map out the stability limit by experiment for a range of aspect ratios using neutrally buoyant fluids to simulate a zero-gravity environment. Theory and experiment are in excellent quantitative agreement and predict instability when the free interface meets each endplate tangent to its flat surface.