Practical adhesion, concept

As the scale of roughness becomes finer, the effective increase in A can become enormous. Consequently Fg may be raised to very high value. Indeed, as many engineering surfaces are fractal in nature [36], we can only retain the concept of area at all, if we accept that it can be considered as indefinitely large. The practical adhesion does not become infinite, because the joint with a strong interfacial region will fail (cohesively) in some other region where Fg is smaller [89],... 

Manson (72,) expanded the concept to the solid state by observing that the strength of composite materials also depended upon the acid-base interaction between continuous and dispersed phases. More directly, Vanderhoff et al. (21) addressed the issue of adhesion of polymeric materials to corroded steel. They synthesized eight corrosion products of iron, and used the interaction scheme developed by Fowkes and Manson first to characterize the iron corrosion products as Lewis acids or bases and then to select polymer vehicles for practical coating systems. Such results were employed to enhance the adhesion of epoxy systems to substrates which were predominantly iron oxide in nature. A good overview of these Issues was presented by Fowkes in 1983 (74). ... 

Most practical polymer-based electrophotographic photoreceptor systems now in use are in fact solid solutions of an active species in a binder host polymer 11). This system concept embodies the notion of full chemical control of the transport process. Thus, the concentration of dopant molecules directly controls the drift mobility, which is in turn controlled by the overlap of wave functions between active sites. The host polymer binder is then specialized for its mechanical and adhesive properties. Understanding the key features of small-molecule transport provides guidelines for the optimization of injected-carrier range. The key point is to understand how chemically induced traps arise in such systems and how molecularly doped materials containing various contaminants in substantial quantities can still efficiently transport charge. (Even part-per-million concentrations of con-... 

In the railroad industry, structures usually are designed by applying static load assumptions. In reality, however, cyclic loading, creep, temperature, and environmental influences occur which should be considered in adhesive joint design. Generic physical models taking into account all the possible effects are not applicable for a practical design concept. 

Polymer solvent interactions determine several properties, sueh as, solubility, solvent retention, plastieizer aetion, wettability, adsorption and adhesion. The solubility parameter is an important eriterion for the choice of solvents. However, acid-basic characters of bofli solvent and polymer are also determinant parameters, which can affect the solution and final film properties. This part, devoted to the influence of acid-base interactions on the aggregation of poly(methyl methacrylate) will first present some recent concepts in acid-base interactions, followed by two practical examples based on experimental results obtained for PMMA/solvent systems. 

The successful performance of many every-day products, and many common materials and construction techniques, is dependent upon adequate adhesion between two or more constituents. Most engineers, however, have only the haziest of ideas about the whole concept of adhesion. For to know how to prepare substrate surfaces for bonding does not necessarily require a knowledge of why adhesive materials should stick to them. It is the intention of this chapter to connect theory with practice, to enable the reader to appreciate why before discussing aspects of surface pretreatment pertinent to applications of adhesives in construction. 

Adhesion is an extremely important concept in both practical and theoretical terms. Unfortunately, there is no completely satisfactory definition of the term that fulfills the needs of both the theoretical surface chemist and the practicing technologist. So far in this book, the term adhesion has been encountered as applied in the ideal or theoretical sense—referring to the reversible thermodynamic process of separating unit area of two phases that originally had a common interface. That aspect of the term was defined in Chapter 2 and will not be repeated here, except where necessary for clarity. Some comments about the reality of that concept will be in order, however. 

A more practical definition of adhesion is a state in which two bodies (usually, but not necessarily dissimilar) are held together by intimate interfadal contact in such a way that mechanical force or work can be apphed across the interface without causing the two bodies to separate (Fig. 19.1). (This is, a force superior to that of the frictional forces discussed in the previous chapter.) It is the latter definition that will be of most concern in the discussion which follows, although the two concepts are, in fact, inseparable. Before entering into that discussion, it will be useful to clarify a few terms commonly encountered in the field of adhesion, but often misinterpreted. 

We have already encountered the concept of thermodynamic adhesion and its related terms such as the work of adhesion. The term is applied to a defined model system and does not take into consideration conditions before or after the formation of the interface, the presence of random flaws or defects in the system, or the bulk physical properties of the components, all of which are of primary importance in the practical application of the concept of adhesion. It is related to molecular interactions such as van der Waals, dipolar, and electrostatic forces but does not consider mechanical or chemical interactions as defined above. It is therefore not a very useful concept in terms of practical adhesion problems, but it serves as a good theoretical tool and to indicate a maximum force or work that a given interface may be expected to transmit before failure (i.e., separation) occurs. 

The practical aspect of the high Tg polymeric additive concept for adhesion becomes apparent when one considers certain temperature effects associated with a multi-lamp UV-radiation curable coating processing unit. If a... 

Adhesion is a subject with many important practical applications. The practical properties of an adhesive bond are a consequence of the bonding between the atoms and molecules involved (Adhesion fundamental and practical). Much of the theory of adhesion that can give an insight of practical importance makes use of concepts used in chemistry when discussing bonding between atoms and molecules. The distinction is widely made between strong primary bonds between atoms and weak secondary bonds between molecules. This article gives a brief explanation of terms commonly used for both. 

The surfaces of metals used in practical adhesion situations are very far removed from the concept of a clean metal surface the substrate to which adhesives and coatings manufacturers exhort us to apply their product. The surfaces of metals, unless very noble (gold or platinum), will invariably have a layer that reflects the interaction of the metal with the atmosphere. This may take the form of a simple oxide but is more likely to be of an oxyhydroxide form, and its composition may be mixed cations or the major or minor... 

Environmental sustainability is a concept fundamentally rooted in ethics and philosophy but has strong technological ramifications. In this article, the implications of sustainability and attitudes towards it are considered. In a further article. Environment and the impact of adhesive technology, practical consequences relating to the use of adhesives are discussed. 

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