How merging droplets jump off a superhydrophobic surface: Measurements and model

Abstract

We investigate how drops merging on a nonwettable surface jump off this surface, for both symmetric and asymmetric coalescences. For this purpose, we design and build a microelectromechanical system sensor able to quantify forces down to the micro-Newton scale at a high acquisition rate (200 kHz). Using this device, we perform direct force measurements of self-propelled droplets coupled to high-speed imaging. Experimental data show that the total momentum of the drop after coalescence mainly depends on the size of the smaller drop. Exploiting this finding, we quantitatively predict the takeoff speed of jumping drop pairs and show how to correct the usual argument based on energy conservation.Received 6 June 2017DOI:https://doi.org/10.1103/PhysRevFluids.2.112001©2017 American Physical SocietyPhysics Subject Headings (PhySH)Physical SystemsDrop & bubble phenomenaInterfacial flowsTechniquesRheology techniquesFluid Dynamics