Fractional polarity, surface tension measurement

The harmonic mean equation is generally considered to be applicable to low surface tension materials such as organic polymers and liquids. If y and yP are known for two liquids, and the contact angles of those liquids on the solid of interest are measured, equation (36) produces two simultaneous equations that can be solved to find the surface tension and polarity of a solid polymer surface. Numerous assumptions have been made in developing the theory of fractional polarity. For example, it ignores the possibility of induced polarity at the interface between polar and nonpolar materials (80). These assumptions limit the application of equation (36) to systems where at least one and preferably both of the... 

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