(420d) New "Chemistry" of Colloidal Particles Induced by the Electric Field - Surprisingly New Results from an Old Experiment

Spherical colloids with isotropic properties have been used as building blocks to assemble a variety of 2D and 3D structures in past, such as FCC, HCP, and BCT crystals. We recently, however, have observed surprisingly new types of 2D and 3D structures under the influence of electric field on the surface of a conducting substrate. At low particle concentrations, the spherical colloids can form a series of well-defined colloidal clusters, ranging from 3 to 10. Those clusters can change bond angles freely while maintaining the overall structures intact. The analysis of cluster distributions shows strong peaks for trimer, tetramer, hexamer, and nonamer. In addition, a few types of isomers were observed for the haxamers and their population distributions are non-trivial. At higher particle concentrations, those colloidal clusters with flexible bond angles can further assemble and connect themselves into a good variety of hierarchical structures and non-close-packed networks that have not been observed before. The dynamic process of the assembly resembles closely to chemical reactions between molecular species. We will describe the experimental conditions and formation mechanisms for those surprisingly new structures. The potential applications in photonic crystal, plasmonic clusters, or filtration will also be discussed.