Berlin 2008 – scientific programme
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 26: Micro and Nano Fluidics I: Liquids at structured materials
CPP 26.6: Talk
Wednesday, February 27, 2008, 15:30–15:45, C 264
Dewetting dynamics in triangular grooves: A possible way to measure the slip length — •Krishnacharya Khare1, Martin Brinkmann1, Bruce M. Law2, Stephan Herminghaus1, and Ralf Seemann1,3 — 1Max-Planck Institute for Dynamics and Self-Organization, D-37073 Göttingen — 2Kansas State University, Manhattan, KS-66506 — 3Saarland University, D-66041 Saarbrücken
Static wetting morphologies of liquid in triangular grooves and their dynamics are studied experimentally and theoretically. For contact angles smaller than 90° minus half the opening angle of the groove, the liquid forms filaments with negative mean curvature extended along the entire length of the groove. For larger contact angles, liquid either forms elongated filaments of finite length and positive mean curvature or drop-like morphologies. Electrowetting is used to vary the contact angle and to switch between different wetting morphologies. In this way, liquid filaments can be pulled out of a large feeding drop forming elongated filaments in prefabricated surface grooves. When being quenched from the filling to the non-filling regime, the liquid filaments become unstable and break into isolated droplets with a preferred distance. This preferred droplet distance compares favorably with the linear stability model assuming the instability to be driven by the local variation of the Laplace pressure with filament width. Dynamics of the instability is studied via in situ scanning force microscopy at elevated temperature. From the measured time constant of the instability, we derived the slip length for the system which is in good agreement with the dewetting experiments on plane substrates.