Inhomogeneous distribution of charged colloidal particles studied by confocal laser scanning microscopy

Various types of inhomogeneous particle distributions in macroscopically homogeneous, purified colloidal dispersions were observed with a confocal laser scanning microscopy with the facility for optical sectioning. Time evolution of nuclei size distributions on the initial stage of colloidal crystal growth was measured and the three-dimensional growing process was analyzed. The larger clusters grew further at the expense of the smaller ones, which indicated the existence of a net attraction between particles. The coexistence of ordered and disordered regions was observed and the disordered region was found not only in the interstitial areas between ordered regions but also inside the ordered region, called the Swiss cheese like structure. Stable voids, where the particle concentrations were almost nil on the time scale of the observation, coexisted with surrounding regions where the particles were distributed in a liquid-like structure. Charged particles in more dilute dispersions were observed being condensed near like-charged surfaces. A large number of particles gathered near the highly charged surfaces, but the gathering was not observed near uncharged surfaces, which pointed out the existence of electrostatic attraction between like-charged surfaces and particles. The inhomogeneous particle distributions can be explained by a net electrostatic attraction.