Abstract

Bubble migration through a soft granular material involves a strong coupling between the bubble dynamics and the deformation of the material. This is relevant to a variety of natural processes such as gas venting from sediments and gas exsolution from magma. Here, we study this process experimentally by injecting air into a quasi-2D packing of soft hydrogel beads and measuring the morphology of the bubbles as they rise due to buoyancy. We systematically modulate the overall elasticity of the packing by confining it to different degrees with a rigid but fluid-permeable upper boundary. We find that this new combination of buoyancy, capillarity, and elasticity under confinement leads to complex morphologies of air migration, as well as nontrivial dynamics in the amount of trapped air in the system. Surprisingly, more confined packings are able to capture larger volumes of air, with a sharp transition between the so-called “small” and “large” air-capture regimes. This result alludes to the possibility of utilizing soft particles to enable control of the gas migration in practical applications, such as carbon capture and storage.