Adhesion energy, specific

It is known that the possible interaction between two materials 1 and 2 is determined by their surface energies, which consist of two components, dispersive, and specific or polar, y . When hydrogen bonding and acid-base interactions are also involved, the adhesion energy between the two materials, Wa will be" ... 

The interaction of the crystal with the substrate can be described in a more perceivable way by the specific adhesion energy, p. According to Kaischew [4.4, 4,5], the adhesion energy can be defined by the detachment energy, contact surface area... 

Design of Check Valves for Specific Adhesion Energy and/or Dimensions... 

In ideal world, one might modulate the adhesion energy of the valve seat to achieve the desired performance for a specific set of dimensions. This would likely be difficult as the chemistry of the fluidic environment, which obviously depends on the application, often affects interface toughness. However, one can measure the interface toughness for a given application and then choose the dimensions of the chambers to satisfy Equation 39.34 the result is a check valve that actuates to a specific clearance for a given interface condition. 

The interfacial layer that arises from the adhesive interaction is characterised by its own field force and the energy of whose value can overtake the cohesion energies, specific to every phases, or can take an intermediate average value. 

Here, o = WJS is defined as the specific free interfacial energy, and 0 = W, 2 S is defined as the specific free adhesion energy, the latter giving the work per unit surface area that has to be done to separate the crystal from the foreign substrate. Apparently, in the case of identical phases 1 and 2, Wi = W2 = i i,2, oj = 0, and + haseysoi = expected, the last relation... 

Finally, the Wulff s rule enables us to construct the equilibrium form of a crystal given the values of the specific free surface and adhesion energies. For that purpose perpendiculars with lengths proportional to the corresponding specific free energies are drawn from the Wulff s point to all possible crystallographic planes. The most inner from all obtained closed polyhedrons represents the equilibrium form (Figure 1.11). 

Without going into more details, we should stress that to construct a growth form is a difficult task which requires profound knowledge of the crystal stmcture, of the mechanism of growth, and last not least, of the values of the specific free surface and adhesion energies. Unfortunately, the latter are not always known with a sufficient accuracy. 

An important point in the nucleation theory and experiment concerns the mode of phase formation - two- or three-dimensional nucleation and growth - on a foreign substrate. The problem has been considered from a thermodynamic point of view [1.72, 1.73, 1.77-1.81], by comparing the works of two- and three-dimensional nucleation and analyzing their dependence on the supersaturation and on the specific free surface and adhesion energies. 

As reviewed so far, the contact-mechanics-based techniques (JKR and SFA methods) have been effective in the understanding molecular level mechanisms related to the adhesion of elastomers and in measuring the surface and interfacial energies of polymers and self-assembled monolayers. The current work in this area is aimed at understanding contact induced interfacial rearrangements and the role of specific interactions. The recent progress of these studies is discussed in this section. 

As indicated, an implicit assumption of the JKR theory is that there are no interactions outside the contact radius. More specifically, the energy arguments used in the development of the JKR theory do not allow specific locations of the adhesion forces to be determined except that they must be associated with the contact line where the two surfaces of the particle and substrate become joined. Adhesion-induced stresses act at the surface and not a result of action-at-a-distance interatomic forces. This results in a stress singularity at the circumference of the contact radius [41]. The validity of this assumption was first questioned by Derjaguin et al. [42], who proposed an alternative model of adhesion (commonly referred to as the DMT theory ). Needless to say, the predictions of the JKR and DMT models are vastly different, as discussed by Tabor [41]. 

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