Positive Adsorption of Charged Particles near a Like Charged Glass Plate

摘要

It is believed that negatively charged entities are repelled by a like charged plate, their concentration being small near the plate and increasing with distance up to the bulk concentration. However, we had noticed in previous work that the concentration of charged colloidal particles near a like charged cover glass became higher when the dispersion was deionized under density-matching conditions, using an H_2O-D_2O mixture as the dispersion medium. (See, for example, Figure 14 of ref 3.) Another example of the concentration increase at an interface, which cannot be understood in terms of conventional theory, was observed in a study of void structures in latex dispersions. Though the existence of a microscopic vacant space (a region with practically no particles inside) in a macroscopically homogeneous dispersion has been taken as extraordinary, the voids could be easily observed between distances of 10-50 μm from the cover glass. At shorter distances, it was difficult to find voids; in other words, the particles were found to be distributed rather homogeneously. It was therefore inferred that the particle concentration within 10 μm of the cover glass was higher than that in the interior of the dispersion: positive adsorption took place. We have now studied these phenomena more systematically, and we report here our results on the distribution of charged particles near the interface with a like charged glass plate.