Comparative study on the surface free energy of a solid calculated by different methods

This paper presents analysis of differences in the surface free energy (SFE) values of a solid, calculated using the methods of Owens-Wendt (OW), van Oss-Chaudhury-Good (vOCG), and Neumann with three measuring liquids: water, formamide, and diiodomethane. The concept of the analysis has been based on the differences in SFE, which occur objectively and regardless of both the precision and the performing conditions of the contact angle (CA) measurements. These differences result from utilizing different mathematical relations between CA and SFE for each of the methods. The results obtained with these three methods are compared with one another over the SFE range common for polymers (20-50 mJ/m2). It is concluded that the relative difference in SFE between the results from the Neumann and vOCG (or OW) methods can reach 21%, while that between the results from the vOCG and OW methods is considerably lower and does not exceed 3%.