Equilibrium shapes and rupture dynamics of a soap-film bridge

A thin soap film that bridges the gap between two coaxial equal diameter endrings forms a catenoid. This shape can be calculated using the calculus of variations and minimizing the surface area generated by revolving an arbitrary curve around a symmetry axis. Theory predicts a stability limit of a critical aspect ratio (ring separation/ring radius) above which value a static catenoid bridge cannot exist. This critical value is confirmed experimentally to within one percent reproducing classical results.;As the aspect ratio is increased above the critical value, the waist of the bridge at the midplane along the axis of symmetry decreases monotonically in time. The connected bridge loses stability and ruptures to a planar film covering each endring. The rupturing bridge passes through a sequence of intermediate shapes before the planar configurations are attained. The time scale for this transition is about 10;The static soap-film bridge is governed by surface tension. This suggests that the dynamics which carry the system through rupture must, at least initially, be dominated by surface tension. A primary goal is to explore the extent to which the actual rupture dynamics can be accounted for by a constrained static system. The results of a mathematical model are compared to extensive experimental observations of the rupture process. Rich experimental behavior is documented in a series of photographs.;A secondary goal investigates the equilibrium shapes a soap-film bridge assumes when a pressure distribution is supplied along its interface. This is accomplished by connecting a pressure source or sink to one endring. The resulting pressure drop across the endrings drives a constant flow of air through the bridge.;The air flow changes the mean (spatial) static pressure which creates a finite amplitude disturbance responsible for displacing the bridge interface. The bridge ruptures if an initial displacement is large enough to overcome an energy barrier. The pressure experiments mark the boundary between steady (stable) and unsteady (rupturing) configurations. It is observed that at higher flowrates capillarity is no longer solely responsible for the energy barrier; the limit to capillary dominated rupture is mapped out experimentally.