The collapse of a granular raft

Known as granular rafts, fluid-fluid interfaces laden with heavy, discrete particles are simple composite materials that exhibit both elastic and granular properties. In this talk, we demonstrate the emergence of their dual nature upon compression by combining experiments and mathematical modeling. Our compression experiments reveal that the granular rafts fail via two distinct modes: system-wide buckling and the expulsion of individual particles, the latter of which cannot be captured by the existing continuum model. To rationalize the experimental observations, we build a "composite" model that compares the energy required for buckling to that required to expel a single particle from the interface. The model successfully captures the transition in the failure modes for varying fluid densities, particle sizes, and particle wettability. Guided by this theoretical framework, we also demonstrate control over the raft's failure mode by tuning the physicochemical properties of individual particles.