Stabilization of a Capillary Bridge Far Beyond the Rayleigh–Plateau Limit Using Active Feedback and Acoustic Radiation Pressure

Abstract: A Equid bridge between two sofid surfaces is known as a capi~ary bridge. Long bridges naturwy become unstable to a symmetric mode by bti@ng near one end while the opposite end thins (the (2,0) mode) and suppressionof this mode is important for managing fluids in low gravity. For a cyhndrical bridge in low gravity of radius R and length L, the slenderness S = L/2R has a natural (Rayleigh-Plateau) hmit of m beyond which the bridge breaks. Using acoustic radiation pressure to control the bridge’s shape, and an optical sensor to detect the bridge’s shape, an active feedback system in simtiated low gravity was constructed. This system stabihzed bridges significantly beyond the Rayleigh–Plateau hmit, with S as large as 4.3. To be useful in low gravity, this technique will have to be modified to work on fiquid bridges in air. In preparation for an experiment to be performed on NASA’s low gravity KC-135 aircraft, acoustic resonators in air that have the required property that the sound amphtude can be spatia~y redistributed rapidly are being investigated and tested in normal gravity using soap-film bridges fled with stiur hexfiuoride (SFG).