THE KINETICS OF WETTING - THE MOTION OF A 3 PHASE CONTACTLINE IN A CAPILLARY

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 θd=cos θo-2(1+cos θo) 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. © 1991.