The 1988 Method of van Oss, Chaudhury, and Good (vOCG)

van Oss and co-workers [22] introduced the notion of acidic and basic components to the surface energy (у+and у Г, respectively) to characterize the acid-base properties of materi­als and predict WAB:

WAB = 2(у+у2-)1/2 + 2(уГу2+)1/2 (16)

у+ and уГ for a solid can be determined by contact angle measurements using three reference liquids of known уL, у +, and уГ. The acidic and basic surface tension compo­nents for test liquids were established with model surfaces and liquids on the assumption that for water уГ = у+ = 25.5mJ/m2 and

уАВ = 2(у+уГ)1/2 (17)

Application of Eq. (17) to water (w) yields

уАВ= 2(25.5 x 25.5)1/2 = 51 mJ/m2

Table 6 reports the total surface tension and its components for some reference liquids. a-Bromonaphthalene, CH2I2, silicone oil, and tricresyl phosphate probe dispersive inter­actions only whilst the other liquids permit characterization of both dispersive and acid — base interactions of surfaces. Note that the surface tension of silicone oil is very low, so this liquid is expected to spread on surfaces.

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