Cosmology in a petri dish? Simulation of collective of colloids at fluid interfaces

¹ Max Planck Institute for Intelligent Systems, Heisenbergstr. 3, 70569, Stuttgart
² Institute for Theoretical and Applied Physics, University of Stuttgart, Pfaffenwaldring 57, 70569, Stuttgart

^a e-mail: bleibel@is.mpg.de

Published online: 10 April 2014

Abstract

Interfacially trapped, micrometer-sized colloidal particles interact via ranged capillary attraction which is analogous to two-dimensional screened Newtonian gravity with the capillary length λ as the tuneable screening length. Using Brownian namics simulations and density functional theory, we study the dynamics of an initially prepared distribution of colloids, either a random homogeneous distribution, or a finitely- sized patch of colloids. Whereas the limit λ → ∞ corresponds to the global collapse self-gravitating fluid, for smaller λ the dynamics crosses over to spinodal decomposition showing a coarsening of regions of enhanced density which emerge from initial fluctuations. For the finite patch of colloids and intermediate λ we predict theoretically and serve in simulations a ringlike density peak at the outer rim of the disclike patch, moving as an inbound shock wave. Experimental realizations of this crossover scenario appear be well possible for colloids trapped at water interfaces and having a radius of around micrometer. Finally, the influence of hydrodynamic interactions on this capillary collapse will be discussed briefly.