Berlin 2012 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 36: Wetting, Micro and nanofluidics I
CPP 36.3: Vortrag
Donnerstag, 29. März 2012, 15:45–16:00, C 264
Dynamics of Wet Granulates under Shear Deformation — •Somnath Karmakar1, Marc Schaber1, Marco Di Michiel2, Mario Scheel2, and Ralf Seemann1,3 — 1Saarland University, Saarbrücken, Germany — 2ESRF, Grenoble, France — 3Max Planck Institute for Dynamics and Self-Organization, Göttingen, Germany
Adding liquid to dry granular matter typically leads to stiffening of the granulate which arises due the formation of wet contacts between individual granules by the virtue of capillary forces. We study the mechanical properties of wet granulates which are composed of spherical glass or basalt beads. The glass is almost perfectly wetted by water whereas the basalt beads have a rather large contact angle with water. Our main focus is on the yield strength which is measured using a particularly designed shear cell which allows to vary shear speed, shear amplitude and absolute pressure. Due to the different wettability, the yield strength of glass granulates depend on the applied shear rate whereas for non-wetting basalt granules, the yield strength is independent of the applied shear rate. Surprisingly, for large absolute pressure, the stiffening of a wet granulate might be inversed and the liquid might rather act as a 'lubricant' lowering the yield strength with respect to dry granulates. With time resolved X-ray tomography, we could shed some light on the peculiar mechanical properties of wet granulates and could identify a liquid exchange process occurring between the individual liquid morphologies which depends on the wettability of wet granular systems.