Holes in granular rafts

A granular raft formed at an oil–water interface has several intriguing mechanical properties like the ability to self-repair defects, such as holes. We experimentally investigate the formation and stability of holes in granular rafts made of millimeter-sized particles at an oil–water interface. Holes are created through indention of the raft by a solid object or an array of objects which create menisci that prevent particle motion. Notably, when the indenter is a hollow cylinder, circular holes consistently form and shrink over time if their size is below a critical value but persist above it. We track holes with varying initial conditions, such as effective radius and circularity, and examine several particle types to identify a stability threshold. By tracking individual particle motion, we gain quantitative and qualitative insights into the dynamics of hole shrinkage. Our comprehensive study provides both a raft-scale structural perspective and a particle-scale dynamic analysis, contributing to a deeper understanding of granular hole behavior.