The group investigates the behavior of complex fluids at their interfaces with solids and gases. For instance, ball pens work well on paper, but would typically fail on glass. The reason for this is the different interaction of the ink, a complex fluid, with the different kinds of surfaces. Similarly, the quality of an ink-jet print depends critically on the drying behavior of the ink which is deposited as tiny droplets onto almost any kind of surface. From ambient humidity to surface porosity, various parameters will impact this process. The impact of our projects spans from everyday occurrence (e.g. paper) over biology to computer technology (silicon microchips).
What happens if a droplet moves over solid that is so soft that it gets deformed by the capillary action of the droplet? And what if the solid would also responds to the contacting liquid by changing its surface properties? How would that change the dynamics of wetting or dewetting i.e., the rate at which the drop moves? And wouldn’t it be useful if, by some trick, we could change the surface “on demand” to be water-repellent or not? Nature plays these tricks every day, as in the water-repellent plumage of a kingfisher, or the slippery surface of carnivore plants on which not even insects can grab a hold. Such and similar questions are addressed in the newly established SPP 2171, to which Stefan Karpitschka is serving as a member of the coordination board, and his group is participating in this joint research effort.
The Max Planck-University of Twente Center for Complex Fluid Dynamics is an interdisciplinary platform shared between the MPI for Dynamics and Self-Organization in Göttingen, the MPI for Polymer Research in Mainz, and the University of Twente in Enschede, The Netherlands. Together, we aim to understand the complexities inherent to multi-component fluids on all length scales, from nanoscopic surface interactions to large-scale turbulent flows. The Groups of Stefan Karpitschka and Corinna Maass are participating in the Center, both in the context of Marangoni-driven flows. These flows are popularly known from the “Tears of Wine” effect, and early research dates back even to the 19th century where Carlo Marangoni and James Clerk Maxwell were working on it. Even today we do not understand many aspects of this effect, primarily due to the complex nature of the liquids that show it. Recent technological advances, e.g. in ink-jet printing, are demanding a better knowledge, and, at the same time, bring advancements into tangible reach.