Surface free energy can be considered as the surface tension of a solid. Surface free energy is calculated through the contact angle measurements. By knowing the surface free energy of the solid, one can predict the behavior of any liquid on the surface.
OWRK is one of the most used surface free energy theories. It divides the interfacial interactions into two parts; polar and dispersive.
Surface free energy can be calculated through contact angle measurements. Automated instruments are available.
You might find it confusing when seeing all the different methods for surface free energy calculations. As surface free energy can give you more information on your surface compared to the contact angle measurements alone, it is time well spent to study the different theories more in detailed.
Calculate critical surface tension or surface free energy for a solid by testing against a series of liquids and measuring the contact angles.