Adhesion covalent bonds

Polymerization kinetics have been used to question whether or not phenolic adhesives covalently bond to wood. Chow (23)... 

Polymeric adhesives function by providing a bond between the two adherends. This bond is obtained by the adhesive wetting both surfaces. Wetting occurs when the adhesive has both a low-enough viscosity to flow over the surface and an attraction to the surface which causes it to be pulled into intimate contact with the surface topography. While in theory it is desirable to obtain chemical adhesion (covalent bonding), in practice this rarely occurs. Usually, mechanical bonding and attraction forces dominate between the adherend and the adhesive. 

The formation of covalent bonds between resin molecules in a coating and the surface of the substrate can enhance adhesion. Thus, adhesion to glass is promoted by reactive silanes having a trimethoxysilyl group on one end that reacts with a hydroxyl group on the glass surface. The silanes have... 

As is true for macroscopic adhesion and mechanical testing experiments, nanoscale measurements do not a priori sense the intrinsic properties of surfaces or adhesive junctions. Instead, the measurements reflect a combination of interfacial chemistry (surface energy, covalent bonding), mechanics (elastic modulus, Poisson s ratio), and contact geometry (probe shape, radius). Furthermore, the probe/sample interaction may not only consist of elastic deformations, but may also include energy dissipation at the surface and/or in the bulk of the sample (or even within the measurement apparatus). Study of rate-dependent adhesion and mechanical properties is possible with both nanoindentation and... 

The chemical bonding theory of adhesion applied to silicones involves the formation of covalent bonds across an interface. This mechanism strongly depends on both the reactivity of the selected silicone cure system and the presence of reactive groups on the surface of the substrate. Some of the reactive groups that can be present in a silicone system have been discussed in Section 3.1. The silicone adhesive can be formulated so that there is an excess of these reactive groups, which can react with the substrate to form covalent bonds. It is also possible to enhance chemical bonding through the use of adhesion promoters or chemical modification of the substrate surface. 

Chemical covalent bonding. The formation of covalent chemical bonds between elements at an interface may be an important factor. Such direct chemical bonding would greatly enhance interfacial adhesion, but specific chemical functional groups are required for the reactions to occur. 

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