Rearrangement and elimination of ordered surface layers of crystalline bubble structures due to gas diffusion

Abstract

We describe a hitherto unknown self-organising effect in wet crystalline bubble structures exposed to air. Due to the escape of gas from the bubbles in the top surface layer, bubbles shrink and create space for the bubbles of the lower layers to interpose themselves at the top. This occurs irregularly, but finally a newly ordered bidisperse top layer is formed. This process can be followed for several episodes of elimination of surface layers. The crystalline orientation influences the speed of shrinkage and formation of the bidisperse top layer. Compared with diffusion of a single bubble or monodisperse monolayer on top of a liquid pool, the diffusion is much faster. This may be accounted for by the extra buoyancy force leading to a larger exposure of the bubbles at the surface.