The Oxide-Water Interface: How Valid Is the Site Dissociation-Surface Equilibria Model?

The great Dutch school of colloid science of Kruyt, Overbeek, and others developed theoretical and experimental models of the silver halide-water interface. Potentiometric titrations, electrokinetic measurements, and coagulation kinetics set high standards of experimentation. They, further, led to the development of theoretical models, mostly thermodynamic, of the silver halide-aqueous electrolyte interface, which allowed quantitative understanding of experimental results. The fundamental step was to recognize that silver and halide ions, as potential-determining ions, controlled the Nernst potential of the interface. At ca. 25 degrees C, as the concentration of silver ions in the bulk solution changed by a factor of 10, the potential of the silver halide-water interface changed by 59 mV. Colloid scientists across the globe in the post-1948 era, additionally wished to understand the properties of colloidal dispersions of simple inorganic oxides such as silica, hematite, and alumina, and more recently, the properties of "latex" particles. In short, it became difficult to apply the theories that allowed understanding of the silver halide-water interface to the understanding of the properties of latex, oxides, and similar colloidal dispersions. Finally, a very recent resurgence in the interest in the electrical double layer (e.d.l.) at the air-water and oil-water interface has fuelled the discussion on the ubiquitous role of protons as potential-determining ions (p.d.i.'s) on interfaces ranging from oxides, to lattices, close packed monolayers, and oil-water and air-water interfaces. We explore the new thinking on all of these aqueous interfaces.