Adhesive bond adsorption theory

The adsorption theory states that the bioadhesive bond formed between an adhesive substrate and tissue or mucosae is due to van der Waals interactions, hydrogen bonds, and related forces. Alternatively, when mucus or saliva are interacting with a solid dosage form, the molecules of the liquid are adsorbed on the solid surface. This is an exothermic process. The free energy of adsorption is given by Eq. (1). 

Adhesion is created by primary and secondary forces according to the theory of adsorption interaction. This theory is applied the most widely for the description of interaction in particulate filled or reinforced polymers [30]. The approach is based on the theory of contact wetting and focuses its attention mainly on the influence of secondary forces. Accordingly, the strength of the adhesive bond is assumed to be proportional to the reversible work of adhesion (W ), which is necessary to separate two phases with the creation of two new surfaces. 

Certain aspects of the adsorption theory of adhesion are developed more fully than has been done previously. The consequences of nonreciprocity of spreading are pointed out, and are used to develop a more general practical point of view with respect to the adhesive bonding of materials of low-surface free energy. The system epoxy adhesive-(nonsurface-treated) polyethylene, normally considered nonadherent, is investigated experimentally in some detail. It is shown how this system, without material modification, can be made adherent. An area of study for possible adhesives for materials of low-surface free energy is suggested. 

We develop certain aspects of the adsorption theory of adhesion more fully than has been done previously, based solely on (free) surface energetics, and show how they can be applied to real or practical systems. As a consequence, it is shown that the deBruyne adhesion rule [7] is incorrect in part. Our concern is mainly with what we believe to be the most important problem in the making of adhesive bonds—that is, the achievement of extensive and proper (no intermediate phase) interfacial contact. We discuss also the breaking strength of certain adhesive joints where this is necessary to the development of our thesis. However, the processes of making and breaking adhesive joints bear no... 

A number of adhesion theories have been proposed to identify the formation of adhesive forces. The contributed adhesion mechanisms are (1) chemical bonding such as chemisorption theory (2) physical interaction such as polarization, electrostatic, and diffusion theory (3) thermodynamical interpretation such as adsorption theory and (4) mechanical interlocking. No single theory exists to explain the entire property of adhesion oti various substrates and adhesives. However, those theories may provide a guideline to understand the principle of the adhesion as the following details (Fig. 2). 

The adsorption theory of adhesion attributes adhesive strength to the action of London dispersion forces, combined in many instances with contributions from other forces (dipolar, polar or primary bonding) Calculations indicate that, in spite of their relatively low strength compared with the other types of bonding, these force can account for far greater strengths than are ever achieved experimentally. It is because all these forces are... 

Thus, when investigating the nature and mechanism of adhesion between an adhesive, coating or polymer matrix and the substrate, it is important to consider the possibility of primary bond formation in addition to the interactions that may occur as a result of Dispersion forces and Poiar forces. In addition to the Adsorption theory of adhesion, adhesion interactions can sometimes be described by the Diffusion theory of adhesion, Electrostatic theory of adhesion, or Mechanical theory of adhesion. Recent work has addressed the formation of primary bonding at the interface as a feature that is desirable from a durability point of view and a phenomenon that one should aim to design into an interface. The concept of engineering the interface in such a way is relatively new, but as adhesives become more widely used in evermore demanding applications, and the performance XPS and ToF-SIMS systems continues to increase, it is anticipated that such investigations can only become more popular. 

Related articles are Adsorption theory of adhesion. Contact angles and interfacial tension. Dispersion forces. Pre-treatment of metals prior to bonding. Roughness of surfaces. Surface characterization by contact angles-polymers. Surface energy and Wetting and spreading. 

Adsorption theory of adhesion K W ALLEN Adsorption via primary or secondary bonds... 

Thermoplastic fibres often are more difficult to wet (see adsorption theory. Table 13.3). This is especially tme for the thermoplastics such as polyolefins and linear polyesters. Methods used to increase the wettability and improve adhesion include the surface treatments shown in Table 13.7. The effects of surface treatments generally decrease with time, so it is important to carry out adhesive bonding as soon as possible after surface preparation. 

Physical adsorption contributes to all adhesive bonds and so is the most widely applicable theory of adhesion. The basis for adsorption is that van der Waals forces, which occur between all atoms and molecules when they are close together, exist across interfaces. These are the weakest of all intermolecular forces, but their strengths are more than adequate to account for the strengths of adhesive joints, van der Waals forces are of three types, namely the forces of attraction between molecules with permanent dipoles, those between a permanent dipole and a nonpolar molecule, and those between nonpolar molecules. The nature of these forces is outlined below, and more detail is given by Atkins and de Paula [42]. 

Adsorption theory. The surface-active parts of the adhesive interact with the substrate, forming close secondary bonds and thus creating the adhesion. 

The adsorption theory requires intimate molecular contact between surfaces for a strong adhesive bond. Van der Waals forces when operative are considered as secondary bonds, whereas ionic, covalent, and metallic forces contribute to primary adhesive bonds. 

Unfortunately, problems of the adsorption or molecular theory of adhesion are in most instances solved exclusively at the qualitative level and are limited to consideration of a role of the polarity of components in adhesion (the so-called polarity rule high adhesion cannot be achieved between a polar substrate and apolar adhesive, and vice versa). It is very unfortunate that in many books on adhesion the description of adhesion is not given at the molecular level, which is now accessible for the description of intermolecular interactions in liquids and solids. At the same time, it is obvious that from a physical point of view the adsorption theory presents a rather correct concept of interfacial phenomena and agrees with thermodynamics. Within this context, adhesion can be regarded as a particular case of adsorption, inasmuch as the formation of molecular bonds at... 

The thermodynamic adsorption theory (dominant in many adhesion practices) is based on the secondary forces (van der Waals and acid-base ones/hydrogen bonding). The importance of these forces is discussed in this section. 

When two materials come into contact, there wOl be forces of attraction between them. What those forces will be will depend on the chemical nature of the surfaces of the materials concerned. If this is known, it may be possible to postulate, or even to prove experimentally, the formation of a specific type of bond. Thus, metallic bonds maybe involved in contact between a metallic solder and substrate metal (Some authors discuss secondary bonding in adhesion under the heading Adsorption Theory, and treat primary bonding under a different heading, e.g., Chemical Adhesion. ). 

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