Determination of the Surface Free Energy of Solids: A Critical Review

Knowledge of the surface free energy of solids is important to understanding a number of processes involving wetting and adhesion to solid surfaces. The measurement of surface free energy has been a subject of active interest for at least 50 years. Despite the importance of the problem to a variety of industries a universally accepted method or set of methods for determination of solid surface free energies has not been agreed upon. In this review article various methods that have been used for the calculation of surface free energies are discussed. The limitations and concerns for employment of each of these methods are furthermore highlighted. Of principal concern is the use of contact angles that meet the requirements to be Young's contact angles and the mixing of quantities obtained by contact angle measurements with those obtained by IGC, as surface free energies obtained by IGC tend to be larger than those obtained from contact angle measurements. Calculated values from IGC data are presumably larger than those from contact angle data as IGC data are often collected at very low surface coverages.