Adhesion molecular diffusion, interpenetration

When the adhering materials are partially or fully miscible with one another, there will be formed between them an interphase consisting of interdiffiised molecules from each material. The thickness of this interlayer depends on the thermodynamic compatibility of the materials as well as molecular diffusion rates. Molecular interdiffusion is quite different from mechanical interlocking. The former involves interpenetration at the molecular level, whereas in the latter case, the bulk adhesive flows into and... 

It is sometimes easy to overlook the fact that molecular diffusion and interpenetration can occur during the formation of adhesive bonds. Adhesives, by themselves or in combination with carrier solvents, can have a solvating effect on the surface of plastic parts. This in turn allows interpenetration of polymer molecules and may lead to bonds of exceptional durability. 

Three primary mechanisms have been suggested for enhanced adhesion via silane coupling agents.5 The classical explanation is that the functional group on the silane molecule reacts with the adhesive resin. Another possibility is that the polysiloxane surface layer has an open porous structure. The liquid adhesive penetrates the porosity and then hardens to form an interpenetrating interphase region. The third mechanism applies only to polymeric adherends. It is possible that the solvent used to dilute and apply the silane adhesion promoter opens the molecular structure on the substrate surface, allowing the silane to penetrate and diffuse into the adherend. 

Several mechanisms of interaction between particles of solids are known [3]. Mechanical adhesion is achieved by flowing a metal into the support pores. The molecular mechanism of adhesion is based on the Van der Waals forces or hydrogen bonds, and the chemical mechanism on the chemical interaction of the metal particles with the support. The electric theory relates adhesion to the formation of an electric double layer (EDL) at the adhesive-substrate interface. Finally, the diffusion mechanism implies interpenetration of the molecules and atoms of the interacting phases, which results in the interface blurring. These insights into the nature of adhesion can be revealed in the papers about the interaction of transition metal... 

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