Regensburg 2022 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 20: General Session to the Symposium: Interplay of Substrate Adaptivity and Wetting Dynamics from Soft Matter to Biology (joint session CPP/DY)
CPP 20.3: Vortrag
Mittwoch, 7. September 2022, 10:00–10:15, H39
Fast contact lines on soft solids — •Hansol Jeon1,2 and Stefan Karpitschka1 — 1Max Planck Institute for Dynamics and Self-Organization, Göttingen, Germany — 2Georg-August-Universität Göttingen, Göttingen, Germany
When a droplet is resting on a soft surface, the capillary forces deform the surface into a sharp wetting ridge. The amplitude of the wetting ridge is determined by elasto-capillary length, but the angles by which the interfaces meet at the ridge tip only depend on the balance of surface tensions, the so-called Neumann balance. For moving contact lines, dissipation in the wetting ridge leads to viscoelastic braking. In recent literature, various effects that could alter Neumann balance and viscoelastic braking have been suggested, ranging from free, extractable oligomers to point forces emerg-ing from bulk viscoelasticity. We visualize moving wetting ridges at high spatio-temporal resolution and determine the tip geometry for various liquids and PDMS substrates. We observe an increase of the ridge opening angle at large speeds, even for very mild deformations caused by the low surface tension of a fluorinated oil. We also find no significant change in ridge rotation and opening angle for gels with different fractions of cross-linked and free chains, nor for different bulk rheological properties. These findings highlight the need for a non-trivial surface constitutional relation that is different from the bulk.