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 20.5: Vortrag

Mittwoch, 7. September 2022, 10:30–10:45, H39

Steering droplets on substrates with periodic wettability patterns and deformations — •Josua Grawitter and Holger Stark — Technische Universität Berlin, Institut für Theoretische Physik, Straße des 17. Juni 135, 10623 Berlin

Droplets are set in motion on substrates with a spatio-temporal wettability pattern as generated, for example, on light-switchable surfaces. To study such cases, we implement the boundary-element method to solve the governing Stokes equations for the fluid flow field inside and on the surface of a droplet and supplement it by the Cox*Voinov law for the dynamics of the contact line. Our approach reproduces the relaxation of an axisymmetric droplet in experiments, which we initiate by instantaneously switching the uniform wettability of a substrate quantified by the equilibrium contact angle.

First, we investigate a droplet on substrates with planar-wave-like wettability profile by varying the speed an wave length of the pattern. When the profile moves slowly, it moves the droplet moves steadily forward. Above a critical pattern speed the droplet performs steady oscillations, the effective (time-averaged) velocity of which decreases with the square of the pattern speed.

Second, we investigate a droplet on substrates which deform periodically according to a planar-wave profile. We analyze the effective velocity again as a function of wave speed and length and investigate specifically the influence of curvature changes on droplet motion.