Elastic or granular: How a continuum model explains the dual nature of granular rafts*

Large and heavy non-Brownian particles can self-assemble at a fluid-fluid interface to minimize the total deformation of the interface. When the resultant monolayer structures or granular rafts are compressed, they fail in two distinct modes: a collective folding of the interface like an elastic film and expulsion of individual particles from the interface reminiscent of their granular characters. Experimentally it is possible to modify the raft failure modes by changing the particle stability at the interface. A traditional continuum model of rafts which is agnostic to the individual particle position at the interface is insufficient to capture these nuances. To address this current shortcoming, we include the effects of the particle location at the interface in our new continuum model and compute the shape of the compressed raft based on the Lagranigian formulation. In this talk, we discuss the new model results and the physical insight they bring to our experimental findings.