The kinetics of wetting: The motion of a three phase contactline in a capillary

Abstract

The movement of the three phase contact line (liquid—air—solid) is studied under complete wetting conditions by means of silicon oils in glass capillaries. It is found that the Washburn, Rideal, and Lucas equation is followed for a receding meniscus but not for an advancing one. In the latter case the dynamic contact angle depends on the capillary number, a phenomenon we account for by the empirical equation cos θ d= cos θ o−2(1+ cos θ o) ηυ σ 1 2 . The radii of the capillaries and the viscosities of the silicon oils are varied and experiments are performed in different set-ups: capillary rise and withdrawing in vertical capillaries, spontaneous imhibition in horizontal capillaries, and the movement of a liquid column in a vertical capillary, for which the thickness of the film behind the receding meniscus can be predicted by the Carroll-Lucassen equation. At high velocities (wide capillaries) air entrainment is predicted.