The Origin of the C-Potential on Carbon Black Particles Dispersed in Aqueous Solutions

Abstract

The ζ-potential of carbon black particles was measured in dispersion media, such as various aqueous solutions of acids, alkalis, alkali-metal chlorides, sodium halides, surface active agents and alkylamines. The ζ-potential of the carbon black particles was found to depend on the kinds of aqueous solutions and increase or decrease with an increase in the solute concentration of the aqueous solutions. A maximum or minimum point of ζ-potential against the solute concentration was occasionally observed on the graph. In the case of Emulgen (nonionic surface active agent), the c-potential was found to be constant. It was also found that the origin of the ζ-potential was related to both the magnitude of the surface charge density (σ) on the Stern layer and the position of the slipping plane in electrophoresis, because, with each dispersion medium, the correlation between σ and the concentration of the solute was positive. The magnitude of a was related to the density of the adsorbed ions on the surface of the samples and to the concentration of dissociated acidic functional groups on the particles. The position of the slipping plane generally lies in the diffusion double layer, but, in the case of a dispersion medium containing surface active agents or of alkylamines, its position is supposed to arise on the surface of the Stern layer. In this experiment, the effects of electroviscosity, surface conductance and dielectric polarization on the ζ-potential were neglected.