AN EXPERIMENTAL-STUDY OF THE MENISCUS SHAPE ASSOCIATED WITH MOVING LIQUID FLUID CONTACT LINES

Using a new technique involving light reflection, the interfacial curv ature of a meniscus formed by a well wetting liquid steadily displacin g a gas in a glass capillary has been measured down to about 50 nm fro m the solid. Within the domain explored, the measured meniscus curvatu re increases strongly as the wall is approached, in agreement with cla ssical models which make use of the continuum approximation, no slip, etc. The inner length scale, at which such models fail, is inferred fr om the measurements to be of the order of a molecular dimension, sugge sting that non-continuum effects dominate. A comparison of measured dy namic contact angles of liquid-liquid pairs of large viscosity ratio w ith a model developed earlier by the authors, incorporating such an in ner length scale, suggests that the true contact angle in the advancin g fluid increases significantly with line speed in one of the cases.