Reconfigurable Microcube Assemblies at the Liquid/Air Interface: The Impact of Surface Tension on Orientation and Capillary-Force-Interaction-Driven Assembly.

Abstract

The systematic investigation of the dependence of the orientation and capillary interaction of hydrophobized polystyrene microcubes at the liquid/air interface on the surface tension of the aqueous subphase is reported. By decreasing the subphase surface tension, the preferential orientation of the cubes was observed to change independent of the surfactant type from the vertex up to the edge up and finally to the face up. Concomitantly, the structure of the aggregates obtained by cube assembly was observed to change from a close-packed hexagonal to tilted linear and finally to flat plate. In particular, the preferential orientation of the cubes was virtually independent of the surfactant charge at a constant surface tension. In addition, reconfigurable microcube assemblies at the liquid/air interface, which respond to the surface tension of the subphase, were observed for the first time. The dynamic reconfigurability of preformed microcube aggregates induced by adding surfactant to the subphase may open new pathways to dynamic assemblies at liquid/air interfaces, which may be interesting, e.g., for sensing applications.