Application of the dynamic Wilhelmy plate to identification of slippage at a liquid-liquid-solid three phase line of contact

The dynamic Wilhelmy plate provides force-distance records that result from the plate passing through an interface at slow constant speed. The form of these force-distance records is determined by a combination of buoyancy and capillary forces. In the present work, wetting behavior of liquid-liquid-solid systems is investigated with changes in wetting properties of silica or glass substrates induced by crude oil. Two initial plate positions are analyzed. In the first, the plate is initially suspended in air above a vessel containing brine overlain by oil. The plate is then lowered through the air-oil and oil-brine interfaces. In the second, the plate is initially immersed in brine and then raised into the oil phase. In each case, the direction of plate motion is reversed during the course of measurement. Oil-brine-solid systems commonly exhibit contact angle hysteresis. Idealized force-distance records have been calculated for which receding and advancing contact angles are constant and the three-phase line of contact remains pinned during contact angle transitions that result from reversing the direction of motion of the plate. Comparison of experimental results with the idealized behavior shows that stabilized wetting conditions are not always achieved. It was often observed that slippage of the three-phase line of contact caused the distance of plate motion over which contact angle transitions occur to be much longer than that predicted by theory.