A granular analogue of the Plateau-Rayleigh instability in bubble rafts

Granular materials are useful as analogues to molecular systems due to their breadth of easily tuneable properties. In particular, a granular material may be described by continuum mechanics as the number of the particles transitions from few to many. For example, a raft of bubbles can exhibit dual properties of a granular system and a liquid system. Here, we examine the interplay between surface tension and buoyancy in the breakup of a raft of bubbles that is initially shaped into a thin strip. This breakup of a strip into nearly-circular domains is a 2D analogue of the Plateau-Rayleigh Instability breakup of a liquid jet into droplets that is observed in 3D. Bubbles are held at the surface of a water bath in a strip, which is suddenly released resulting in a breakup into regularly spaced, nearly-circular clusters of bubbles. Bubble radius and the width of the bubble raft strip are tuned to investigate different aspects of the 2D “granular Plateau-Rayleigh Instability”, including satellite clusters, and late stage coarsening.