Dynamics of the contact line on rough substrates

We have studied the spreading of a liquid He-4 meniscus on two different ce sium substrates with a controlled random roughness. The mean distance betwe en the ''mesa" defects is of the order of 20 mu m. In the case of strong pi nning, we find that the roughness of the contact line scales as L-1/2. Clos e to the wetting temperature, the liquid invades channels between the defec ts; this leads to a change in the scaling behavior of the roughness of the: contact line. (C) 2000 Elsevier Science B.V. All rights reserved.