Abstract

Concentrated suspensions of colloidal hard spheres near a hard wall were studied in real space by means of time-resolved confocal scanning laser microscopy. Both structure and dynamics of these systems are dramatically different from their bulk analogues (i.e., far away from a wall). In particular, systems that are a glass (a solid phase without long-range positional order) in the bulk show significant hexagonal order near a wall. The hexagonal order is observed to first increase with volume fraction of the colloids, reach a constant value and subsequently decrease. When hexagonal order decreases, the mobility of the particles starts increasing with volume fraction. These observations are consistent with a reentrant melting transition. However, the behavior of static correlation functions indicate that the in-plane structure near a wall is hexatic rather than crystalline, reflecting the two dimensional character of dense matter near walls.

© 2004 Optical Society of America