EXAMINATION OF NEUMANN EQUATION-OF-STATE FOR INTERFACIAL-TENSIONS

Advancing contact angles for water, glycerol, diiodomethane, and ethylene glycol on polytetrafluoroethylene, polyethylene, Asphalt Ridge bitumen, Circle Cliffs bitumen, Whiterocks bitumen resins, and Whiterocks bitumen asphaltenes were measured and the ''surface tension'' of these low energy solids was calculated using Neumann's equation-of-state. Also, the surface tension of several polymers and self-assembled monolayers was analyzed based on Neumann's approach and using advancing contact angle values reported in the literature. It is demonstrated that the equation-of-state for surface tension determination may only be used for systems with apolar liquids involving interactions of a physical nature. Reasonable surface tension values were obtained for polymers when advancing contact angles for diiodomethane were used in the calculations. Nevertheless, there appears to be an inconsistency in the surface tension values determined for self-assembled monolayers as calculated with the equation-of-state using contact angle data for different apolar liquids, diiodomethane and hexadecane. (C) 1994 Academic Press, Inc.