Method according to Zisman
The method according to Zisman is a method for investigating the wettability of a solid by determining the critical surface tension with the help of the contact angle. The surface tension, which a liquid must have to just completely wet a solid, is calculated in this method.
In a Zisman investigation, the cosine of the contact angle θ is plotted against the surface tension of the appropriate liquid. The value of the surface tension extrapolated to cos θ = 1 (contact angle = 0°) is referred to as the critical surface tension σkrit.
This value is often interpreted as the surface free energy of the solid. Based on this equality, the surface free energy is often determined using test inks. The liquid which just completely wets the solid is sought from a series of liquids with set surface tension.
However, this equality can be called into question, as the nature of the interactions between the phases is not taken into account. According to the Fowkes and the Owens, Wendt, Rabel and Kaelble methods, which discriminate between a polar part and a disperse part of the surface tension, in practice σc is the same as the surface free energy only for non-polar systems.
W. A. Zisman, Relation of the Equilibrium Contact Angle to Liquid and Solid Constitution. In: Advances in Chemistry 43 (1964), P. 1-51.