Collapse of a granular raft: Experiments from the particle perspective

Particles denser than the liquid can float by deforming the fluid-fluid interface and self-assemble into a closed-packed monolayer called particle rafts. We have found that when such rafts are compressed bi-axially, they collapse in two distinct modes – via expulsion of individual particles from the interface and via creasing in which the raft undergoes strong out-of-plane deformation while sinking. We have also found that creasing mode can be eliminated entirely, by gradually decreasing the interfacial tension or increasing the surface wettability of the particles. We hypothesize that understanding individual particle dynamics is needed to address the full range of phenomena in our raft experiments. In this talk, we discuss our new particle-scale experiments in which we directly visualize the equilibrium position and contact line dynamics of the individual particle for varying parameters. Our preliminary observations reveal a strong correlation between the individual particle position on the interface and the response of the particle raft to compression. Furthermore, we rationalize the new experimental results with energetic arguments.