What do van Oss-Good and Neumann say about each others theories

3 What do van Oss-Good and Neumann say about each other s theories  

Good and co-workers have frequently pointed out (e.g. van Oss et al., 1987) that the inability of Neumann theory to predict negative liquid-liquid interfacial tensions results in often poor agreement for liquid-liquid interfaces and for predicting misci-bUity (miscibUity is equivalent to zero or negative interfacial tensions). 

It is worth mentioning that Professor Good has not always been so critical. In his 1977 review (Good, 1977) he sees much promise in the - then - recently appeared Neumann theory, while he mentioned several reasons why the surface tension component theory could break down, among others the importance of entropic effects (incidentally discussed by others later, e.g. Douillard, 1997). Nevertheless, Professor Good and Professor Fowkes clearly converged to the notion that the surface tension component theories constitute the most successful approach, with special emphasis on the explicit treatment of the very important acid-base interactions. 

In addition, Kwok (Kwok and Neumann, 1996 Kwok et ai, 1998, 1999) showed that the van Oss-Good theory predicts problematic results for several liquid-liquid interfaces for which experimental data are available. While for many aqueous systems the interfacial tensions are predicted rather satisfactorily, the performance of van Oss-Good for several non-aqueous mixtures is not good. In some cases finite values for the interfacial tension are predicted for mixtures which are known to be miscible such as bromonaphthalene with alkanes and squalene-diiodo-methane. The results or at least the main conclusions appear to be independent of the source of reference liquids and parameters used for the van Oss-Good method (original ones or those from Lee, see Section 15.3.4). Kwok and Neumann (1996) state, on basis of these calculations, that it is surprising to see an approach published in well reputed journals when it can be shown to be false by anybody who possesses a simple calculator and a few drops of the liquids used in the approach . Statements like this can be found in several of the articles published by Neumann and coworkers. 

As mentioned, both theories have been extensively used by other researchers, with the van Oss-Good theory being more popular in independent studies. 

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