Upper Limits to the Contact Angles of Liquids on Solids

Graphical plots of the cosine of the equilibrium contact angle vs. the difference in the surface tension of a pure liquid and the critical surface tension of wetting of the solid group data for each liquid into a zone bounded by a straight line passing through the origin (cos Θ = 1; γLV - γc = 0). From the parameters defining this straight line the limiting contact angles for each liquid can be estimated. They indicate that the maximum contact angle possible for water is 156°; for hexadecane, 109°. A rectilinear relation between liquid surface tension and the minimum value of (γLV - γc) required for a surface to exhibit a 90° contact angle can be extended to provide a good fit to available data for a pure liquid metal like mercury.