The work of adhesion between solids and liquids contact angles

Dupre s equation (2) of Chapter I holds good for the case of a solid and a liquid W8L = ySA+yLA-ySL-, (1) 

Liquids frequently rest on solids at a definite angle 0 (measured in the 

Combining (1) and (2), the unknown solid surface tensions are eliminated, 

This equation has been known for over a century it was given by Young2 (without proof ) and by Dupre 3 it can be deduced also from Laplace s theory of Capillarity, or indeed from any theory of the cohesive forces, since it can be obtained from consideration of energies only. Until recent years it has been little noticed, which is unfortunate, as the meaning of the contact angles is much clarified when the work of adhesion is introduced, and the surface tensions of the solid surfaces, which are not measurable, are eliminated. Most authors are now, however, expressing their results in terms of the work of adhesion or of closely related expressions. 

The quantity yLA cos was termed by Freundlich the adhesion tension , and is frequently used it is equal to the difference between the solid-air and solid-liquid surface tensions, that is, to WSL—yLA. 

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