Eur. Phys. J. Special Topics 219, 131-141 (2013)
https://doi.org/10.1140/epjst/e2013-01788-0

Regular Article

Droplet actuation induced by coalescence: Experimental evidences and phenomenological modeling

¹ Department of Mechanical Engineering, University of Canterbury, Christchurch, New Zealand
² Department of Electrical and Computer Engineering, University of Canterbury, Christchurch, New Zealand
³ École Normale Supérieure, Cachan, France
⁴ Laboratoire Interdisciplinaire de Physique, CNRS and Université Grenoble I, UMR 5588, Saint-Martin-d'Hères, France

^a e-mail: mathieu.sellier@canterbury.ac.nz

Received: 1 July 2012
Revised: 18 January 2013
Published online: 19 March 2013

Abstract

This paper considers the interaction between two droplets placed on a substrate in immediate vicinity. We show here that when the two droplets are of different fluids and especially when one of the droplet is highly volatile, a wealth of fascinating phenomena can be observed. In particular, the interaction may result in the actuation of the droplet system, i.e. its displacement over a finite length. In order to control this displacement, we consider droplets confined on a hydrophilic stripe created by plasma-treating a PDMS substrate. This controlled actuation opens up unexplored opportunities in the field of microfluidics. In order to explain the observed actuation phenomenon, we propose a simple phenomenological model based on Newton's second law and a simple balance between the driving force arising from surface energy gradients and the viscous resistive force. This simple model is able to reproduce qualitatively and quantitatively the observed droplet dynamics.