Oxide-adhesive chemical interaction

It appears from the evolution of the adhesion index that a distinction has to be made between the interactions carbon blacks are able to have with unsaturated or with saturated (or near-to-saturated) elastomers. Thus, the adhesion index of butyl rubber is enhanced upon oxidation of the black, while the reverse is observed with polybutadiene 38). The improvement of the reinforcing ability of carbon black upon oxidation, in the former case, has been interpreted by Gessler 401 as due to chemical interactions of butyl rubber with active functional groups on the solid surface. Gessler, relating the reinforcing characteristics of the oxidized carbon black for butyl rubber to the presence of carboxyl groups on the surface of the filler, postulated a cationic... 

If in the case of aluminized silicone we were able to evidence a drastic difference between sputtering and evaporation, it happens not to be the case for aluminized PET (13). Our preliminary results on this latter polymer indeed show no marked differences between the two deposition processes, both giving strong chemical interaction. By contrast we have also observed that with noble metals such as Au, no chemical interaction is taking place with silicone substrate with both deposition processes. This tells us that the nature of the polymer substrate and of the metal are most important for the interfacial and adhesive properties. The fundamental parameter seems to be the reactivity of both constituents of the interface. It has been confirmed by Pireaux et al. that the carboxylic function is one of the most reactive surface entity (14) and indeed for PET, the adsorption site for the Al atoms is found to be the carboxylic function (13). During this interaction, Al is oxidized and the diffusion of O into the Al film can occur. 

T o identify the nature of predominant interactions at interfaces between non-reactive metal M and ionocovalent oxide AO, different attempts have been made to correlate the energetic properties of interfaces (work of adhesion, work of immersion) to the energy of formation of M oxide or other quantities characteristic of the contacting phases, such as the surface energy of the metal or the gap energy of the ceramic. Any successful correlation between an energetic quantity of interfaces and the formation energy or enthalpy of MO oxide indicates the occurrence of a chemical interaction between M and AO at the interface, even... 

Thus, FO are acting as adhesion promoters and corrosion inhibitors, whose mechanism can be explained as follows. In the course of thermal molding of powder polymer coatings filled by FO the oxides enter into physical-chemical interactions with the polymer melt. As a result, the oxides are reduced in the surface layer of the particles to metals. This fact is confirmed by... 

From the above discussion, it follows that it should be possible to improve the durability of bonded joints by the introduction of suitable coupling agents at the interface. If the coupling agent is capable of chemically interacting with the metal or its oxide, displacement of the adhesive at the interface will be prevented. 

The role of silica-only systems on adhesion has been studied using model compounds with squalene [59]. It was shown that the mechanism for increased adhesion to brass-coated wire-to-rubber was not just a simple improvement of the physical properties of the rubber, but that silica moderated the thickness and composition of the interfacial layer by a chemical interaction. SEM-EDX (scanning electron microscopy with energy dispersive analysis of X-rays), XPS, AES and PIXE (proton induced X-ray emission spectroscopy) revealed that silica affected the relative concentrations of compounds present in the interfacial layer, promoting zinc oxide formation in particular. 

Chemical reaction theories propose that chemical reactions occur between the adhesive and the adherent forming primary chemical bonds. While it is unlikely that these theories are universally applicable to adhesives, chemical reactions may be present in some cases. Silanes, for example, are bifunctional molecules that are used as coupling agents [6]. One end of the molecule is intended to interact with a polymeric adhesive. The other end is intended to chemically react with atoms in the adherend s surface layer, such as oxygen in an oxide layer of a metal or the oxygen in a ceramic. 

These results demonstrate some interesting chemical principles of the use of acrylic adhesives. They stick to a broad range of substrates, with some notable exceptions. One of these is galvanized steel, a chemically active substrate which can interact with the adhesive and inhibit cure. Another is Noryl , a blend of polystyrene and polyphenylene oxide. It contains phenol groups that are known polymerization inhibitors. Highly non-polar substrates such as polyolefins and silicones are difficult to bond with any technology, but as we shall see, the initiator can play a big role in acrylic adhesion to polyolefins. 

Copper has been the most widely used material because of its high conductivity, solderability, low cost, and ability to be electrolytically or chemically plated. However, copper has a weak interaction with polyimides (102-104) and, consequently, poor adhesion. Furthermore, recent studies have shown that the polyimide precursor, polyamic acid, oxidizes copper... 

Mushroom tyrosinase has previously been used to convert tyrosine residues in chemically synthesized polyphenolic decapeptides to dopa residues (38), This enzyme also can convert dopa residues to quinones, but the enzymatic product can be maintained in the dopa form if reducing conditions are utilized. Using mushroom tyrosinase, we have converted at least 50% of the tyrosine residues to dopa and have evidence for quinone-lysine crosslinks in an oxidizing environment (T. Wei and R. Link, unpublished data). When these conditions are carefully controlled, we have observed adhesive properties for the recombinant polyphenolic protein. We are currently studying the parameters that can increase adhesivity and moisture resistance through better surface interactions and more extensive crosslinking. 

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