A conditional justification for the determination of surface energy of solids using contact angle methods

Abstract

We present a conditional justification for determining the surface energy (SE) of solids from contact angle (CA) methods using a proof with illustrations. To validate our observations, we compared the SEs of some materials from literature estimated using CA models (Owens-Wendt, Van Oss-Good-Chaudhury equation, Wu's equation, Lifshitz-van der Waals and Lewis acid-base, Girifalco) and other approaches such as thermodynamic methods, density functional theory, experimental or cleaving techniques. Results from literature have reported tens of mJm−2 and a few Jm−2 for the same materials determined using CA and other approaches respectively. Estimates of SE from other approaches exceed those obtained from CA models significantly (approximately a factor of 10). This comparison proves that the SE of solids determined from CA models depend solely on the test liquids. Hence, we conclude that other approaches provide more accurate total SE for solids. However, CA models are more suitable for determining the individual interactive force components of the solid surface such as the dispersion, polar, hydrogen bonding.