Effective work of adhesion

Some adhesion measuring equipment, notably the Surface Force Apparatus, comprises thin films of polymer mounted on an elastic substrate. The equivalent interface fracture problem to that considered above (Figure 6) is shown in Figure 10, where each elastic solid is covered by a viscoelastic layer of thickness h. The case of the opening crack has been examined by Huntley (75). He shows that the effective work of adhesion, given for viscoelastic solids by equation (18), is modified by the thickness of the layer approximately to ... 

Many of these features are interrelated. Finely divided soHds such as talc [14807-96-6] are excellent barriers to mechanical interlocking and interdiffusion. They also reduce the area of contact over which short-range intermolecular forces can interact. Because compatibiUty of different polymers is the exception rather than the rule, preformed sheets of a different polymer usually prevent interdiffusion and are an effective way of controlling adhesion, provided no new strong interfacial interactions are thereby introduced. Surface tension and thermodynamic work of adhesion are interrelated, as shown in equations 1, 2, and 3, and are a direct consequence of the intermolecular forces that also control adsorption and chemical reactivity. 

The augmentation of the work of adhesion by acid-base effects has, as a consequence, an effect on wettability properties. Identifying /sl in Eq. 26 as W and substituting it into Eq. 3 and Eq. 14, respectively leads to ... 

The energy release rate (G) represents adherence and is attributed to a multiplicative combination of interfacial and bulk effects. The interface contributions to the overall adherence are captured by the adhesion energy (Go), which is assumed to be rate-independent and equal to the thermodynamic work of adhesion (IVa)-Additional dissipation occurring within the elastomer is contained in the bulk viscoelastic loss function 0, which is dependent on the crack growth velocity (v) and on temperature (T). The function 0 is therefore substrate surface independent, but test geometry dependent. 

The process of viscoelastic braking just described has certain parallels with the dynamic adhesion of elastomers. When, for example, a rubber strip is peeled from a rigid substrate, the effective, or apparent, work of adhesion, W, is usually much greater than the intrinsic, or reversible, energy of adhesion, Wq, given by the Dupre equation [15] ... 

C) Illustration of the effect of work of cohesion of water and work of adhesion to mineral on the mineral wettability. 

Although Eq. 11 tries to take into account the effect of polar interactions, the role of acid/base interactions in adhesion became clear and theories describing them have been more and more accepted [35]. The boimdary case of such interactions is the formation of covalent bonds between the surfaces. Such interactions cannot be described by Eq. 11. As a consequence Fowkes [36] suggested that the reversible work of adhesion should be defined as ... 

The contact angle has a significant effect on repellency. The work of adhesion, Wa, required to remove the droplets, ignoring viscoelastic effects is ... 

Surfactants that effectively adsorb at the solid-water and dirt-water interfaces make the best detergents. Consider a dirt (oil, mineral, carbon, etc.) particle adhering to a solid surface immersed in a liquid. The work of adhesion (AG) between the dirt and solid is,... 

Thermodynamic Work of Adhesion. One other important aspect of surface energetics (71, 72) is the use of surface free energy to calculate the maximum reversible work of adhesion, Wad, which has been correlated to the adhesive strength (41, 44) and should not be equated to the strength of an adhesive joint (6). Since neither wetting nor adhesion is controlled purely by thermodynamic factors, we should use the maximum reversible work of adhesion, Wad on the basis of an idealistic approach. When all other variables are equal, we can use Wad to compare the effectiveness of adhesives for a specific substrate. 

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