Abstract
The stability of hydrophobic sols is determined by the free energy of interaction between the particles; this energy of interaction can be divided into the electrical repulsion and the van der Waals attraction. As the latter is practically constant for a given system, the major interest lies in the repulsive energy due to the superposition of two electrical double layers. The Reerink and Overbeek theory deals with the influence of the double layer thickness at a constant Stern potential on sol stability, a situation which occurs when indifferent inorganic electrolytes are added to sols. While, the theory by Ottewill, Rastogi and the present author explains the coagulation due to changes in the Stern potential caused by adsorption. A.n extended theory was also given which covers the general case of changing ionic strength and potential. The theoretical treatment thus obtained was in good agreement with the optical measurements of the coagulation kinetics of silver iodide sols by various coagulating agents. It was shown by experiments that the coagulation theory held also for the coalescence of two mercury droplets polarized at various potentials in electrolyte solutions. This indicates that the interaction between finely dispersed particles in hydrophobic sols is essen-tially the same as that acting between macroscopic mercury droplets.
