Dispersion forces surface energy component

An important point in the use of surface energy components is the realization that for non-polar liquids, such as alkanes, only dispersion forces act between molecules, so... 

Measurement of the contact angle at a solid-liquid interface is a widely used method for the determination of the surface energy of solid polymers. Fowkes [1] first proposed that the surface energy of a pure phase, y y could be represented by the sum of the contribution from different types of force components, especially the dispersion and the polar components, such that ... 

As shown by Fowkes (1968) the interfacial energy between two phases (whose surface tensions - with respect to vacuum - are y1 and y2) is subject to the resultant force field made up of components arising from attractive forces in the bulk of each phase and the forces, usually the London dispersion forces (cf. Eq. 4.2) operating accross the interface itself. Then the interfacial tension (energy) between two phases y12 s given by... 

Table A.4.1 Attractive Forces at Interfaces-surface Energy, y, and London-van der Waals Dispersion Force Component of Surface Energy, y(L) a>...

For low energy surfaces, the dispersion force component is larger than the nondispersion force component which, however, cannot be neglected or assumed to be nonexistent. An exception is paraffin wax. The results of Table III for paraflBn confirm that ya is zero, consistent with a surface composed completely of hydrocarbon entities with no polar components. By this treatment, Tefion turns out to have a small but definite polar component of y (10). 

One can show that E includes the leading component of the dispersion force between two atoms (Engel et al. 1998a). Thus, from a fundamental point of view, Eq2) is the first xc-functional which allows a seamless description of van der Waals bond molecules. As an example we show the energy surface of He2 in Figure 4.1 (Engel et al. 2000a). 

The essential assumption in all of these theories is the additivity of the different molecular interactions that determine the surface tension and surface energies of liquids or solids, i.e., dispersion forces, dipole and induced dipole interactions and hydrogen bonding. This assumption is based on linear additivity of the attraction constants for the various types of molecular interactions. Thus, the attraction constant for the interaction of materials i andj is separated into dispersion and polar components,... 

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