Direct observation of two-dimensional, dynamic clustering and ordering with colloids

Abstract

We describe a system where the dynamics of reversible clustering, ordering, and growth in two dimensions can be directly observed. The system consists of uniform colloidal particles trapped at an air/water interface. We attribute the attraction between particles mainly to pairwise potential with a longer-range van der Waals attraction and a shorter-range, electrostatic repulsion. Surface tension may also contribute as the cluster sizes increase. Reversible dynamics result from the combination of these forces with the disrupting influences of Brownian motion.