Improved active stabilization of capillary bridges using acoustic radiation pressure and dynamics of a breaking bridge

Abstract

Liquid bridges between two solid surfaces have applications in low gravity, such as the solidification of floating zones. Long bridges naturally become unstable to a symmetric mode by bulging near one end while the opposite end thins. For a cylindrical bridge of radius R and length L, the slenderness S=L/2R has a natural (Rayleigh) limit of π beyond which the bridge breaks. Using acoustic radiation pressure in simulated low gravity as described previously [J. Acoust. Soc. Am. 99, 2540 (1996)], stable bridges significantly beyond the Rayleigh limit can be produced. Improvements in the acoustics, optics, and electronics have enabled stabilization of bridges with S as large as 4.3. To be useful in low gravity, this technique will have to be modified to work on liquid bridges in air. Currently, acoustic resonators in air that have the required property that the sound amplitude can be spatially redistributed rapidly are being investigated. The laboratory experiments with simulated low gravity have made it possible to observe the dynamics of a breaking super-long bridge. [Work supported by NASA.]