PROBLEMS OF ADHESION

Many discrepancies in the theory of adhesion are connected with the co nfusion of processes of bond-forming and bond-breaking which have very different character. The former consumes several decimal orders of ma gnitude more work than would correspond to a reversible process. The m ost important cause of this is the work needed to separate the parts o f the electric double layer formed at the contact of two bodies. The c orresponding electrostatic attraction plays the most important part in adhesion of solid bodies and especially of powder particles. It expla ins especially the photo controlled adhesion of powders. In contrast t o this the separation of particles imbedded in a liquid may be realize d nearly reversibly when the rate of process is not very high. The the ory of adhesion (coagulation) of lyophobic colloid particles (the Derj aguin-Landau-Verwey-Overbeek theory) takes into consideration the Van der Waals forces and ionic-electrostatic interactions. Recently this t heory has included in its scope the phenomena of repeptization.