Dresden 2020 – scientific programme
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O: Fachverband Oberflächenphysik
O 116: Wetting and Liquids at Interfaces and Surfaces II (joint session CPP/DY/O)
O 116.2: Talk
Friday, March 20, 2020, 10:00–10:15, ZEU 260
Spreading on viscoelastic solids: Are contact angles selected by Neumann's law? — Mathijs van Gorcum1, •Stefan Karpitschka2, Bruno Andreotti3, and Jacco H. Snoeijer1 — 1Physics of Fluid Group, University of Twente, Enschede, Netherlands — 2Max Planck Institute for Dynamics and Self-Organization, Göttingen, Germany — 3Laboratoire de Physique Statistique, Univ. Paris-Diderot, Paris, France
The spreading of liquid drops on soft substrates is extremely slow, owing to strong viscoelastic dissipation inside the solid. A detailed understanding of the spreading dynamics has remained elusive, partly owing to the difficulty in quantifying the strong viscoelastic deformations below the contact line that determine the shape of moving wetting ridges. Here we present direct experimental visualizations of the dynamic wetting ridge, complemented with measurements of the liquid contact angle. It is observed that the wetting ridge exhibits a rotation that follows exactly the liquid angle, as was previously hypothesized [Karpitschka et al., Nat. Commun. (2015)]. This experimentally proves that, despite the contact line motion, the wetting ridge is still governed by Neumann's law. Furthermore, our experiments suggest that moving contact lines lead to a variable surface tension of the substrate. We set up a new theory that incorporates the influence of surface strain, the so-called Shuttleworth effect, for soft wetting. It includes a detailed analysis of the boundary conditions at the contact line, complemented by a dissipation analysis, which shows, again, the validity of Neumann's balance.