Interface bonding problem

Because the glass-to-EVA interface bonding problem seemed to be solved when all samples exhibited adherent and persistent bonds, the focus of the effort was shifted to back-sheet adhesion. An additional series of test (see Table II) confirmed the good results of Tedlar with the Du Pont adhesive 68040. Korad 63000 may be a useful material, but cure temperatures during lamination caused some degradation. Additional tests on this acrylic sheet may be run. A polyester film, Scotchpar 20CP, was interesting, because it would be less expensive than a polyvinyl fluoride film, such as Tedlar. This test series showed that a new primer or adhesive was needed for the Scotchpar film. 

Finally, it is noteworthy that if water (or indeed other highly polar liquids) is the environment of interest, then metallic and ceramic substrates are those which result in joints most likely to exhibit poor durability. This is a consequence, of course, of the relatively polar nature of their surfaces and their high surface free energies. Thus, ingressing water molecules are preferentially attracted to the surfaces of these substrates and will displace the physisorbed molecules of the adhesive. These comments are also reflected [5,6] in the values of Wa and Wai for joints based upon carbon-fibre-reinforced plastic (CFRP) substrates typically being of the order of 90 mJ/m and 30 mJ/m, respectively. The positive values of both of these terms indicate that the durability of adhesively bonded CFRP joints should not represent a major problem. This is indeed found to be the case, from the aspect of the stability of the interface. (Although problems may arise if (a) the... 

Let us consider some of the most common problems in an adhesively bonded joint. Bonding problems in a three-layer step-lap joint, for example, are illustrated in Fig. 1. Ultrasonic techniques to find voids, weak cohesive properties, and delaminations are available and are quite reliable. The weak interface or kissing bond detection situation, on the other hand, has a limited number of solutions useful only in special situations. No generalized technique is yet available to depict a weak interface or kissing bond reliably, although a number of promising techniques have emeiged. 

The mobile adhesive wets and then penetrates and absorbs into the wood fibers. Strong attractive forces are necessary for the adhesive to displace contaminants and adhere to wood fibers. The solvent, if present, will typically wet and absorb into the fibers at a greater rate than the adhesive polymer, leaving most of the adhesive resin concentrated at the wood interface and first few cellular layers. Bonding problems can occur if too little or too much adhesive flows into the wood. 

One would be in an ad-hoc fashion to assume that, because of the tendency toward interpenetration, near the crack tips the crack surfaces would come in smooth contact and form a cusp, and the resulting contact region would consist of a single uninterrupted zone rather than the sum of a series of discrete zones as implied by the oscillatory nature of the elastic solution (see Comninou [ll], Atkinson [l2]). Another way is to assume that near the crack tip the linear theory is not valid and to use a large deformation nonlinear theory. An asymptotic analysis using such a theory was provided by Knowles and Sternberg [l3] for the plane stress interface crack problem in two bonded dissimilar incompressible Neo-Hookean materials which shows no oscillatory behavior for stresses or... 

Ma.rine. In the presence of an electrolyte, eg, seawater, aluminum and steel form a galvanic cell and corrosion takes place at the interface. Because the aluminum superstmcture is bolted to the steel bulkhead in a lap joint, crevice corrosion is masked and may remain uimoticed until replacement is required. By using transition-joint strips cut from explosion-welded clads, the corrosion problem can be eliminated. Because the transition is metaHurgicaHy bonded, there is no crevice in which the electrolyte can act and galvanic action caimot take place. Steel corrosion is confined to external surfaces where it can be detected easily and corrected by simple wire bmshing and painting. 

Surface analysis has made enormous contributions to the field of adhesion science. It enabled investigators to probe fundamental aspects of adhesion such as the composition of anodic oxides on metals, the surface composition of polymers that have been pretreated by etching, the nature of reactions occurring at the interface between a primer and a substrate or between a primer and an adhesive, and the orientation of molecules adsorbed onto substrates. Surface analysis has also enabled adhesion scientists to determine the mechanisms responsible for failure of adhesive bonds, especially after exposure to aggressive environments. The objective of this chapter is to review the principals of surface analysis techniques including attenuated total reflection (ATR) and reflection-absorption (RAIR) infrared spectroscopy. X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and secondary ion mass spectrometry (SIMS) and to present examples of the application of each technique to important problems in adhesion science. 

A reaction interface is the zone immediately adjoining the surface of contact between reactant and product and within which bond redistributions occur. Prevailing conditions are different from those characteristic of the reactant bulk as demonstrated by the enhanced reactivity, usually attributed to local strain, catalysis by products, etc. Considerable difficulties attend investigation of the mechanisms of interface reactions because this thin zone is interposed between two relatively much larger particles. Accordingly, many proposed reaction models are necessarily based on indirect evidence. Without wishing to appear unnecessarily pessimistic, we consider it appropriate to mention here some of the problems inherent in the provision of detailed mechanisms for solid phase rate processes. These difficulties are not always apparent in interpretations and proposals appearing in the literature. 

These limitations, most urgently felt in solid state theory, have stimulated the search for alternative approaches to the many-body problem of an interacting electron system as found in solids, surfaces, interfaces, and molecular systems. Today, local density functional (LDF) theory (3-4) and its generalization to spin polarized systems (5-6) are known to provide accurate descriptions of the electronic and magnetic structures as well as other ground state properties such as bond distances and force constants in bulk solids and surfaces. 

One way to overcome the problem of chirality existing only at the metal-matrix interface is to encase the metal particle inside the chiral matrix. In that case, all of the metal surface atoms should be close to a chiral center however, this approach has some problems too. For example, access to the metal surface may be inhibited by the encasing matrix. In spite of this, several attempts have produced moderately successful catalysts by creating metal—polymer catalysts. Pd has been deposited on poly-(5)-leucine (Scheme 3.4) and Pd and Pt colloids have been encased in a polysaccharide to produce catalysts that enanti-oselectively hydrogenated prochiral C=C and C=N bonds (Scheme 3.5).7... 

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