Wed January 26th 2011
Seminar 1. Rush hour for particles suspended in evaporating drops 2. A closer look at capillarity
Hanneke Gelderblom, Joost Weijs


1. If a droplet with suspended particles evaporates while its contact line is pinned, liquid and particles are dragged towards the contact line creating the well-known coffee-stain ring (Deegan et al Nature 389 (1997)). We analyze this process in detail by measuring the velocity field inside an evaporating drop using ยต-PIV. It is found that most of the particle transport occurs in the last moments of the droplet lifetime. This rush explains the different characteristic packing of the particles in the layers of the ring, which is much more ordered in the thin outer part than in the thick inner one, since almost all particles arrive at the end. The rush-hour behavior of particles in evaporating drops can be attributed to the vanishing of the contact angle and follows from mass conservation.

2. The connection between the energy (virtual work) picture and the force picture in capillarity can, even for simple systems, sometimes be nontrivial. In this talk, I will try to show that even for such simple systems (for example a drop sitting on a surface), one can ask some difficult questions. As a bonus, I will then also try to answer them.
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The 10th Complex Motion in Fluids 2021
Max Planck Gesellschaft
Centre for Scientific Computing