Interfacial tension Owens-Wendt theory

The success of the Fowkes equation, but also the need for better theories, has been illustrated in Examples 3.3 and 3.4. Extensions of the Fowkes equation have been proposed, which account explicitly for polar and hydrogen bonding effects in the expression for the interfacial tension using geometric-mean rules for all terms. Two such well-known theories are the Owens-Wendt theory, which is often used for polymer surfaces, and the Hansen/Skaarup (van Krevelen and Hoftyzer, 1972 Hansen, 2000) model. Both models are presented below. The Hansen/Skaarup... 

Erbil (1997) writes that most researchers in the field today have abandoned the Owens-Wendt theory (which also predicts measurable interfacial tensions for certain mixtures which are known to be miscible). 

It can be seen that these theories resemble the Fowkes equation but one or two additional cross terms are added to account for the specific interactions (a combined specific terms is used for Owens-Wendt while both polar and hydrogen bonding terms are used in the Hansen equation). The relevant equations for the surface and interfacial tensions for these two theories are given in Equations 3.22-3.24 ... 

Many theories for estimating the interfacial tensions have been presented in Sections 3.5.1-3.5.3. The equations for the surface and interfacial tensions as well as for the work of adhesion are summarized in Table 3.6. Notice that the work of adhesion corresponds to the cross term of the interfacial tension expression (under the square roots), which reflects different contributions of intermolecular forces, according to the various theories (either the total surface tensions in Girifalco—Good and Neumann, only those contributions due to dispersion forces in Fowkes, due to both dispersion and specific forces in Owens-Wendt, separately dispersion, polar and hydrogen bonding ones in Hansen/Beerbower, or the van der Waals and as5mimetric acid/base effects in van Oss et ai). 

Analyse the results using both the Owens-Wendt and the van Oss-Good theories for interfacial tensions. Compare and discuss the results. Can we conclude that the new binders have simQar/higher surface tensions than the existing ones and could thus be considered useful alternatives to the existing products ... 

Testing the theories for interfacial tension, either for liquids or solids, is not an easy task. In the case of liquids, small impurities may affect the values of interfacial tensions, as Owens (1970) and others have stated. On the other hand, if accurate data are available for obtaining the surface components and if there is confidence on a specific theory we can get useful information about the solids, e.g. a semiquantitative measure of surface composition (Owens and Wendt,... 

The van Oss-Good equation can result in either positive or negative interfacial tensions, the latter simply meaning miscible liquids. Thus, it is possible for the van Oss-Good theory to predict repulsive van der Waals forces which can be present in certain systems (van Oss et al, 1988, 1989). Because van Oss-Good can also predict negative interfacial tensions, it has been shown to predict well the solubility in aqueous polymer solutions (van Oss and Good, 1992) where Owens-Wendt fails. It has also been applied with success to biopolymers (van Oss et al,... 

Which of the two classical theories, of Fowkes and Owens-Wendt, will perform best in describing or predicting the interfacial tensions for these three mixtures ... 

Compare the Fowkes, Owens-Wendt and van Oss-Good theories for these non-aqueous liquid-liquid interfacial tensions. Which model performs best ... 

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