Can a dynamic contact angle be understood in terms of a friction coefficient?

The kinetics of capillary rise of pure water and ethanol as well as mixtures thereof that under static conditions wet glass capillaries has been studied by a high-speed imaging technique. To adequately describe the experimental data, a rate-dependent dynamic contact angle must be added to the Washburn-Lucas equation. This result is discussed in terms of a molecular friction coefficient at the front of the liquid flowing over the substrate. Dynamic inertia effects are significant at the initial stages of spreading and may have further importance for capillaries of larger radii. In addition, it was found that the preparation and cleaning of glass capillaries, which are essential for the liquid substrate interaction, have a significant effect on the initial rate of rise of the liquid. (C) 2000 Academic Press.