Eur. Phys. J. E (2013) 36: 87
https://doi.org/10.1140/epje/i2013-13087-x

Regular Article

Droplets on liquids and their journey into equilibrium

¹ Experimental Physics, Saarland University, D-66123, Saarbrücken, Germany
² Weierstrass Institute, Mohrenstr. 39, D-10117, Berlin, Germany
³ Max Planck Institute for Dynamics and Self-Organization, D-37073, Göttingen, Germany
⁴ Institute of Mathematics, Technische Universität Berlin, Straße des 17. Juni 136, D-10623, Berlin, Germany

^* e-mail: r.seemann@physik.uni-saarland.de

Received: 10 November 2012
Accepted: 28 June 2013
Published online: 14 August 2013

Abstract

The morphological path of droplets on a liquid substrate towards equilibrium is investigated experimentally and theoretically. The droplets emerge in the late stage of a dewetting process of short chained polystyrene (PS) dewetting from liquid polymethyl-methacrylate (PMMA). The three-dimensional droplet profiles are obtained experimentally by combining the in situ imaged PS/air interface during equilibration and the ex situ imaged PS/PMMA interface after removal of the PS by a selective solvent. Numerically the transient drop shapes are calculated by solving the thin-film equation in lubrication approximation using the experimentally determined input parameter like viscosity, film thickness and surface tensions. The numerically obtained droplet morphologies and time scales agree very well with the experimental drop shapes. An unexpected observation is that droplets with identical volumes synchronise their motion and become independent of the initial geometry long time before equilibrium is reached.