Surface and interfacial tensions from the profile of a sessile drop

Abstract

Sessile drops and captive bubbles resting at a plane solid surface but separated from the surface by a thin film of the surrounding fluid, appear to possess angles of contact of 180°. The limiting height, Z ∞ 180 of a very large sessile drop formed under these conditions is related to the interfacial tension, γ , by the expression γ = ¼∆ pg ( Z ∞ 180 ) 2 , where ∆ p is the density difference of the two fluids and g , the gravitational acceleration. As very large drops are not usually obtained experimentally the maximum height of a drop of intermediate size was measured and used in the equation with an appropriate correction factor. The correction factor was obtained from tables of the profiles of sessile drops. The correction factor is invariant for all values of γ , ∆ p and g . The method is tested experimentally and shown to agree with the results obtained by other methods for a number of widely differing systems. The reproducibility and sources of error are discussed.