ABSTRACT
Abstract Four different approaches to determination of solid surface free energy (van Oss et al.’s (LWAB), Owens and Wendt’s (O-W), Chibowski’s contact angle hysteresis (CAH) and Neumann’s equation of state (EQS)) were examined on glass, silicon, mica and poly(methyl methacrylate) (PMMA) surfaces via measurements of advancing and receding contact angles. Sessile drop and tilted plate methods were employed to measure the contact angles of probe liquids water, formamide and diiodomethane. The results obtained show that on a given solid the advancing contact angle is slightly larger and the receding one smaller if measured by tilted plate method. Hence, the resulting hysteresis is larger than that from the contact angles measured by sessile drop. The calculated (apparent) surface free energy is the greatest if determined from O-W equation. Unexpectedly, EQS fails for weakly polar polymer PMMA surface, giving significantly lower value of the calculated energy. In rest of the tested systems LWAB, CAH and EQS approaches give comparable results for the apparent surface free energy of the tested solids. A hypothesis is put forward that using a probe liquid only apparent surface free energy of a solid can be determined because the strength of interactions originating from the solid surface depends on the strength of interactions coming from the probe liquid surface.
