Surface Science of Adhesion

The thermodynamics of the surface free energy, y, of solids has been reviewed by Etzler [13-14]. The ideal work of adhesion, Vl, between materials A and B is defined by the following relation. 

Fowkes [15-16] suggested that surface free energy and thus the work of adhesion could be considered as a sum of components resulting from various types of intermolecular interactions. At present, it is conventional to express the work of adhesion as a sum consisting of a term for Lifshitz-van der Waals interactions and second term resulting from Lewis acid-base interactions [13]. Frequently, Lifshitz-van der Waals interactions are dominant. 

Intermolecular forces between molecules result from interactions between their corresponding electron orbitals. The principal non-bonding interactions result from induced dipole-induced dipole (London), dipole-induced dipole (Debye) and dipole-dipole (Keesom) interactions. The intermolecular potential energy function, U, for each of these three types of interactions is of the same form. Here, r is the separation distance between bodies. 

If only London dispersion forces are considered the constant in Equation (16.7) can be expressed as follows  

Here the subscripts 11, 22 and 12 refer to interactions between like molecules (11, 22) and dissimilar molecules (12). (3 is the coefficient in Equation (16.7). I is the ionization potential. If A = I2 then 

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