Wetting and Adhesion Determination of Surface Polarity

It may be obvious to relate the equation of Young and Dupre (Equihion 8.3) to the Gibbs energy of adhesion between S and L It follows from Equation 5.11 

by measuring 0 and determining jt (from adsorption on the solid from the vapor phase), can be calculated for a liquid of known L that wets the surface with a finite contact angle. comprises an apolar (=dispersion) and a polar contribution. Assuming these contributions to be additive. 

In Section 5.6, it has been demonstrated that Fowkes approximation of the interfacial tension between a and p, or, for that matter, S and L, expressed in Equation 5.24 applies well for apolar components. Then, combining Equations 5.11 and 5.24 results in 

For many practical purposes, one is interested in the differences in wettability of different surfaces by a given liquid. For a series of surfaces, for which 0 15° and, hence, Jt is negligible, it follows from Equation 8.10 that the value of 0 can be taken 

FIGURE 8.6 Plot for the determination of the polarity of a solid surface. 

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