Berlin 2015 – scientific programme

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DY: Fachverband Dynamik und Statistische Physik

DY 38: Wetting, Micro and Nanofluidics (joint session CPP/ DY)

DY 38.12: Talk

Wednesday, March 18, 2015, 18:00–18:15, C 243

Wettability-independent bouncing on flat surfaces — Jolet de Ruiter, Rudy Lagraauw, Dirk van den Ende, and •Frieder Mugele — University of Twente; MESA+ Institute for Nanotechnology, Physics of Complex Fluids, Enschede, The Netherlands

The impingement of drops onto solid surfaces plays a crucial role in a variety of processes, including inkjet printing, fog harvesting, anti-icing, dropwise condensation and spray coating. Recent efforts in understanding and controlling drop impact behaviour focused on superhydrophobic surfaces with specific surface structures enabling drop bouncing with reduced contact time. Here, we report a different universal bouncing mechanism that occurs on both wetting and non-wetting flat surfaces for both high and low surface tension liquids. Using high-speed multiple-wavelength interferometry, we show that this bouncing mechanism is based on the continuous presence of an air film for moderate drop impact velocities. This submicrometre air cushion slows down the incoming drop and reverses its momentum. Viscous forces in the air film play a key role in this process: they provide transient stability of the air cushion against squeeze-out, mediate momentum transfer, and contribute a substantial part of the energy dissipation during bouncing.