Regensburg 2013 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 22: Focus: Wetting on smooth and rough surfaces: From spreading to superhydrophobicity I

CPP 22.8: Talk

Wednesday, March 13, 2013, 12:00–12:15, H34

Dynamics of water droplets on nanostructured hydrophobic surfaces with step gradients — •Tobias Neckernuß, Stefan Wiedemann, Alfred Plettl, and Paul Ziemann — Institute of Solid State Physics, University of Ulm

Droplets on a surface exhibiting different contact angles (CA) along their three-phase-contact-line experience a net force due to uncompensated Young forces. These forces play a major role in the dynamics of both, CA hysteresis and gradient-induced movement. A simple analytical model is developed based on these uncompensated Young components combined with geometrical constraints when a droplet laterally crosses a wettability step. Such steps are prepared with a micellar technique in combination with a hydrophobic Teflon-like coating leading to arrays of nanopillars (typical height: 100 nm, diameter: up to 40 nm). As a result, CAs of about 165° and 150° are observed for advancing and receding droplets, respectively. By varying parameters like pillar density and diameter, the forces acting on a moving droplet can be adjusted. The dynamics of moving droplets are investigated with a modified commercial CA measurement setup. To move a droplet towards the wettability step, the substrate can be tilted, allowing control of its shape and velocity in the vicinity of the step. Comparison of experimental data to the model prediction shows remarkable agreement.