The surface energy and cohesion of solids

Measurement of the surface energy of a liquid is relatively easy to both perform and understand. All methods are based on measuring the work required to create a new surface by transferring molecules from bulk liquid. However, what about the surface energy of a solid Clearly, for solids it is impractical to move molecules from bulk to the surface. There are basically two ways by which we can attempt to obtain the surface energy of solids  

by studying the wetting behaviour of a range of liquids with different surface tensions on the solid surface. 

Only a few materials can be successfully studied in this way. One of them is the layered natural aluminosilicate crystal, muscovite mica, which is available in large crystals and can be cleaved in a controlled manner to produce two molecularly smooth new surfaces. 

In comparison, the adhesive energy per unit area Wa between two different solids is given by  

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