Contact angle, film, and line tension of foam films. I. Stationary and dynamic contact angle measurements

Abstract

It is established experimentally that slowly shrinking small air bubbles attached to a liquid-air interface form a nonequilibrium (dynamic) contact angle. Aqueous solutions of sodium dodecyl sulfate (SDS) are used at two different concentrations of added electrolyte. A black thin liquid film is formed at the top of the bubble. The experimental cell used allows measurements with shrinking and expanding bubbles as well as with bubbles of constant equatorial radius. Hysteresis of the contact angle was observed. The results show that the shrinking of the contact line (advancing meniscus) causes deviation of the contact angle from its equilibrium value. The reliability of some previous work interpreting the change in contact angle with the radius of shrinking bubbles as a line tension effect is discussed.