The electrochemistry of nonaqueous copper phthalocyanine dispersions in the presence of a metal soap surfactant: A simple equilibrium site binding model

The electrophoretic mobilities of copper phthalocyanine particles, disperse d in isoparaffin solutions containing zirconium octanoate, have been determ ined using phase-analysis light scattering. All the samples studied contain ed trace concentrations of water. The mobility values were converted to zet a potentials using the Huckel equation. All the systems studied exhibited a pronounced maximum in zeta potential as the zirconium octanoate concentrat ion increased. The maximum occurred at a bulk zirconium octanoate concentra tion equivalent to that required for complete coverage of the particles. Th e zeta potential data were converted to surface charge density values throu gh the use of the Poisson-Boltzmann equation. The latter were in the range 0.4 to 2.5 mu C m(-2). A simple two equation site binding theory, which con sidered the dissociation of zirconium octanoate and the subsequent adsorpti on of ions at a generic surface site, was successfully applied to the surfa ce charge data. It is proposed that the maximum in the zeta potential and s urface charge as a function of zirconium octanoate concentration was observ ed due to the preferential location of ZrO2+ ions at the particle surface, followed by charge neutralization with octanoate anions. It is suggested th at water facilitates the dissociation process of the zirconium octanoate, a lthough it does not directly contribute to the surface charge itself. Two p lausible qualitative mechanisms are described. The first involves the prese nce of water at the particle-solution interface, whilst the second consider s the formation of micelles in the bulk isoparaffin phase. (C) 1999 Academi c Press.