A THEORY OF THE HETEROCOAGULATION, INTERACTION AND ADHESION OF DISSIMILAR PARTICLES IN SOLUTIONS OF ELECTROLYTES

The theory of interaction of charged surfaces in electrolyte solutions based on computing the energy of overlapping of ionic atmospheres has up till now been applied only to the symmetrical case of two equally charged surfaces, or to wetting films with zero charge at their outer boundary when it is easy to reduce this system to the symmetric one. B ut there exist many phenomena, for instance coagulation of mixtures of sols, coacervation, dyeing, flotation, etc., which require considerat ion of the asymmetric case of unequally charged surfaces. Using the me thod of '' isodynamic curves '' it is possible to obtain the solution of the problem for any electrolyte and any constant value of the surfa ce potentials. The most important property of electric repulsion of su rfaces having charges of like signs is the existence of a maximum valu e of the repulsion at a definite gap-width between both surfaces which is independent of the maximum potentials of both surfaces. This rule holds strictly being independent of the form of either surface. Divers e criteria of stability are found theoretically. Two fundamentally dis tinct cases should be distinguished according to whether the net resul t of van der Waals' interactions leads to mutual attraction or mutual repulsion of both bodies-the latter case being impossible when both bo dies are similar in material. In the former case a modification of Eil ers and Korff's rule is given, which is adapted to the case when one s urface remains always strongly charged and the charge of the other one may acquire any value near to zero. In the other case the adhesion of surfaces or coagulation is only possible when the charges of both sur faces have unlike signs and the electrolyte concentration is not very high. When in addition both surfaces are strongly charged, an equation is obtained giving the critical concentration below which coagulation begins. This equation is very similar in form to that deduced by Land au and myself and includes the modified Hardy-Schulze's and Wolfe-Ostw ald's rules, but in contrast to it contains the valencies of anions an d cations symmetrically. Such a reversed Hardy-Schulze's rule is in ac cordance with the experiments of Frumkin, Gorodetskaja and Titijevskaj a on adhesion of mercury drops to glass in electrolyte solutions on di lution. Both these experiments and the theory developed can explain th e mechanism of the bipolar coacervation. The present theory of interac tion of unlike surfaces is in accordance with many facts in the fields of heterocoagulation and mutual coagulation of sol mixtures. For inst ance, this theory explains the existence of group coagulation in some cases and disorder coagulation-in other ones, the fixation of dye part icles prior to the onset of homogeneous coagulation, and many other ph enomena.