Gathering of Charged Colloid Particles Near Like Charged Entities

Abstract

Negatively charged polymer colloid particles were found to gather near a like charged glass plate in deionized dispersions. The particle distribution near the glass plate was observed using a confocal laser scanning microscope. The number of particles about 5-10μm from the glass plate was about two times larger than that in the bulk dispersion and decreased gradually with distance. The tail of the peak in the particle distribution profile reached about 50μm from the glass plate, a very long distance compared with the range of ordinary electrostatic interaction. The 'positive adsorption' of the particles could be observed even in density matched H₂O-D₂O mixtures. It could not be observed at an NaCl concentration of 10^-4M. These results show that the driving force for the positive adsorption is not sedimentation of the particles, but an electrostatic interaction. The positive adsorption increased with the number of charges on the particles and the glass surface. This indicates that the driving force of the positive adsorption is an electrostatic attraction between like charged particles and glass plate.