Shock waves in capillary collapse of colloids: a model system for two--dimensional screened Newtonian gravity

Using Brownian dynamics simulations, density functional theory, and analytical perturbation theory we study the collapse of a patch of interfacially trapped, micrometer-sized colloidal particles, driven by long-ranged capillary attraction. This attraction {is formally analogous} to two--dimensional (2D) screened Newtonian gravity with the capillary length \hat{\lambda} as the screening length. Whereas the limit \hat{\lambda} \to \infty corresponds to the global collapse of a self--gravitating fluid, for finite \hat{\lambda} we predict theoretically and observe in simulations a ringlike density peak at the outer rim of a disclike patch, moving as an inbound shock wave. Possible experimental realizations are discussed.