Liquid drops attract or repel by the inverted Cheerios effect.
Solid particles floating at a liquid interface exhibit a long-ranged attraction mediated by surface tension. In the absence of bulk elasticity, this is the dominant lateral interaction of mechanical origin. Here, we show that an analogous long-range interaction occurs between adjacent droplets on solid substrates, which crucially relies on a combination of capillarity and bulk elasticity. We experimentally observe the interaction between droplets on soft gels and provide a theoretical framework that quantitatively predicts the interaction force between the droplets. Remarkably, we find that, although on thick substrates the interaction is purely attractive and leads to drop-drop coalescence, for relatively thin substrates a short-range repulsion occurs, which prevents the two drops from coming into direct contact. This versatile interaction is the liquid-on-solid analog of the "Cheerios effect." The effect will strongly influence the condensation and coarsening of drops on soft polymer films, and has potential implications for colloidal assembly and mechanobiology.
Physics of Fluids Group, Faculty of Science and Technology, University of Twente, 7500 AE Enschede, The Netherlands; s.a.karpitschka@utwente.nl.
Stefan
S
Karpitschka
Physics of Fluids Group, Faculty of Science and Technology, University of Twente, 7500 AE Enschede, The Netherlands;
Anupam
A
Pandey
Huygens-Kamerlingh Onnes Laboratory, Universiteit Leiden, Postbus 9504, 2300 RA Leiden, The Netherlands;
Luuk A
LA
Lubbers
Université Lyon, Ens de Lyon, Université Claude Bernard, CNRS, Laboratoire de Physique, F-69342 Lyon, France;
Joost H
JH
Weijs
School of Engineering and Materials Science, Queen Mary University of London, London E1 4NS, United Kingdom;
Lorenzo
L
Botto
Department of Mechanical Engineering, University of Maryland, College Park, MD 20742;
Siddhartha
S
Das
Laboratoire de Physique et Mécanique des Milieux Hetérogènes, UMR 7636 École Supérieure de Physique et de Chimie Industrielles-CNRS, Université Paris-Diderot, 75005 Paris, France;
Bruno
B
Andreotti
Physics of Fluids Group, Faculty of Science and Technology, University of Twente, 7500 AE Enschede, The Netherlands; Department of Applied Physics, Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands.
Jacco H
JH
Snoeijer
droplets; elastocapillarity; mechanosensing; soft matter; wetting