Critical evaluation of the surface energy components of solids

Abstract

The most common procedures to extract both the dispersive (Lifshitz–van der Waals) and specific (polar/acid–base) interactions from wetting experiments are critically evaluated. For example, the very useful (vOCG) model of van Oss–Chaudhury–Good has been found to frequently produce artificial and enforced basic surface energy values which require a systematic intrinsic consistency test. Therefore, dramatically simplified models are developed assuming mono–bi- and mono–mono-dentate interactions. From an exceptionally extensive cross-correlation, it is shown that the mono–mono-dentate model complies with a symmetric model for enthalpic interactions introduced by Drago. Moreover, first hand experimental information is used in order to evaluate key parameters such as Girifalco–Good quotient and work of wetting. It is shown that a match of the surface tension of the probe liquids and the surface energy of the solids is required to obtain meaningful results. The aim is to distinguish Brϕnsted proton exchange equilibrium from Lewis electron polarisation type of adduct formation. In order to evaluate this separation, the influence of pH and ionic strength on the state of silica is tested. The contribution of impurities as well as the presence of a vapour film are considered as sources of errors.