| Wed December 8th 2010 16:00 HR Z109 | Seminar | 1. Air entrainment by advancing contact lines 2. Stability of contact lines Tak Chan, Koen Winkels |
Details:Air entrainment by advancing contact lines (Tak Shing Chan)The entrainment of air by a liquid jet plunging into a liquid reservoir has been studied in great detail. By contrast, the situation of a plunging solid, for which there is a moving contact line, is much less understood. We investigate this phenomenon by introducing a generalized form of lubrication theory that incorporates the flow in both the liquid and gas phases. We show that the critical speed for air entrainment strongly depends on the air viscosity, even though it is smaller than the liquid viscosity by orders of magnitude. We also carry out an experiment to study this plunging solid problem. The experimental results are compared with the predictions of our model. Stability of contact lines (Koen Winkels) How fast can a liquid drop slide over a solid surface? The maximum speed is strongly limited by the dynamics of the contact line that marks the boundary of ‘wet’ and ‘dry’ surface. We study both receding and advancing contact lines moving at high velocities (with possible influence of inertia). Above a critical speed the receding contact line forms a sharp corner with a tip that breaks up into smaller droplets. We analyze these cornered structures near the threshold of instability. A beautiful experiment to only study advancing contact line dynamics is droplet spreading on a partial wetting substrate. Although this experiment sounds very simple and basic, there are some interesting questions and is not completely understood. However it clearly shows the importance of inertia in contact line dynamics. | ||
