Real Surface Energies
The only true way to measure a surface energy is via JKR. But people insist on using contact angles not because they are good but because they are easy to do. The table shown here indicates how useless contact angles are for many real polymer surfaces
This table, found in the wonderful book chapter by Mangipudi and Falsafi from 3M1 shows how erroneous it is to rely on contact angle derived surface energies. In the chapter they speculate that the contact angle liquids are "seeing" different surfaces compared to the real polymer-polymer interactions. Well, yes, so if you are interested in polymer-polymer adhesion, why do you look at polymer-liquid interactions? In any case, these very, very different polymers with very, very different adhesion capabilities differ only by a factor of 2 in the genuine surface energy, W, so who cares about W? As this site keeps saying, adhesion is a property of the system and for most relevant systems, the least interesting part of the measured adhesion is W, quoted here in mJ/m². Note, too, that although you can often find that one of the methods (especially one of the G-G methods) shows values close the the JKR ones, it is not always the same one - so you cannot tell a priori whether, for example, G-G DM or G-G GL will give the right value.
Key to measurement technique: JKR, Zisman and Wu are well-known. GM is Geometric Mean, HM is Harmonic Mean, G-G DM is Good-Girifalco Diiodomethane and GL is Glycerol
Key to polymers: PE Polyethylene, C-PE Corona-Treated PE, TPX Polymethylpentene, PVCH Polyvinylcylohexane, PS Polystyrene, PVP Polyvinylpyridine, PMMA Polymethylmethacrylate, PET Polyester.
1V.S. Mangipudi and A. Falsafi, Direct estimation of the adhesion of solid polymers, Ch 2 of AV Pocius, Ed, Adhesion Science and Engineering, Elsevier 2002