Earlier systematic studies of the angle of contact θ exhibited by drops of liquid on plane, solid surfaces of low surface energy have revealed a regular linear variation in cos θ with the surface tension (yLV) of a large variety of liquids; this led to the concept of the critical surface tension of spreading (yc) and its use in characterizing the wettability of organic solids and of high-energy surfaces coated with adsorbed organic films.nThe wetting properties of low-energy organic surfaces are shown to depend upon the chemical structure and the physical packing of the atom groups in the outermost layer. For hydro- carbons, wettability decreases with increasing hydrogenation. Fluorine is the most effective hydrogen substitute in decreasing yc, whereas CI, Br, I, O, and N increase the wettability of organic surfaces.
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