CRITICAL-DYNAMICS OF CONTACT-LINE MOTION

The velocity V of the contact line where a fluid interface intersects the wall of a tube depends on the applied capillary pressure P-cap. We have used sensitive ac differential-pressure measurements, to study t he scaling of P-cap with V for water-alkane interfaces in tubes that h ave disordered surfaces. Our results are consistent with a critical de pinning transition. The derivative dP(cap)/dV similar to V-x over two decades in velocity in the critical regime near V=0. We find similar c ritical exponents for water-hexadecane, x=-0.77(5), and water-decane s ystems, x=-0.81(5). The exponent does not depend on the direction of f low or on the degree of surface roughness on the tube walls.