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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 50: Focus Session: Wetting on Adaptive Substrates III (joint session CPP/DY/O)

CPP 50.2: Vortrag

Freitag, 22. März 2024, 10:00–10:15, H 0110

Modelling droplets on substrates with travelling-wave deformations — •Josua Grawitter and Holger Stark — Technische Universität Berlin, Institut für Theoretische Physik, Hardenbergstr. 36, 10623 Berlin, Germany

Motivated by strategies for targeted microfluidic transport of droplets, we investigate how sessile droplets can be steered toward a preferred direction using travelling-wave deformations of the substrate. To perform our numerical study, we develop a formalism to apply the boundary-element method to dynamic wetting. It solves the governing Stokes equations for the fluid flow field inside the droplet that is pushed forward by the deforming substrate.

We find two distinct modes of droplet motion. For small wave speed the droplet surfs with a constant velocity on the wave, while beyond a critical wave speed a periodic wobbling motion occurs, the period of which diverges at the transition. In the related case of a flat substrate with travelling waves in wettability, such an observation is well rationalized by the nonuniform oscillator model and the transition described by a SNIPER bifurcation. Here, however, the mean droplet velocity in the wobbling state is proportional to the wave speed at large speed values since the droplet always has to move up and down. To rationalize this behavior, the nonuniform oscillator model has to be extended. Since the critical wave speed of the bifurcation depends on the droplet radius, this dependence can be used to sort droplets by size.