Self-propelled droplet transport on shaped-liquid surfaces

Abstract

The transport of small amounts of liquids on solid surfaces is fundamental for microfluidics applications. Technologies allowing control of droplets of liquid on flat surfaces generally involve the generation of a wettability contrast. This approach is however limited by the resistance to motion caused by the direct contact between the droplet and the solid. We show here that this resistance can be drastically reduced by preventing direct contact with the help of dual-length scale micro-structures and the concept of “liquid-surfaces”. These new surfaces allow the gentle transport of droplets along defined paths and with fine control of their speed. Moreover, their high adhesion permits the capture of impacting droplets, opening new possibilities in applications such as fog harvesting and heat transfer.

Autonomous transport and splitting of a droplet on an open surface

“…The physics of the droplet transport and splitting mechanisms is explained through scaling and with the help of the energy conservation arguments. To validate this work with experiment, one needs to create a Y-shaped wettability-gradient track of very low hysteresis [45] on a superhydrophobic background. The droplet shapes during the transport, droplet-splitting ratios for different branch width ratios, and the fluid motion inside the droplet can be matched with the corresponding experiment.…”

Droplet motion and oscillation on contrasting micro-striated surfaces

“…2018; Gordillo, Riboux & Quintero 2019; Launay et al. 2020). Although most works on droplet motion on micro-structured surfaces have reported the presence of an oscillatory behaviour (Yang et al.…”

“…2009; Launay et al. 2020) on the solid by adjusting the surface roughness on an intrinsically hydrophobic background, either imposed by the material itself or upon a subsequent coating. In the last century, the influence of roughness on static wetting has been investigated and has been shown to obey the theories of Wenzel (1936) or Cassie & Baxter (1944) depending on the intrinsic wettability, the structure of the solid surface and the nature of the liquid.…”

“…2018; Launay et al. 2020; Zhao et al. 2020) even when the droplet is deposited gently on the surface, the influence of such oscillatory behaviour on the droplet motion has not been further pursued or investigated.…”

Gradient Quasi‐Liquid Surface Enabled Self‐Propulsion of Highly Wetting Liquids

“…Surface‐mediated self‐propulsion of droplets provides a possible approach to passively remove highly wetting condensates during condensation. Specifically, droplets can move without any external energy with the help of asymmetric surface topographies, [ 10,15–23 ] gradient surface wettability, [ 24–29 ] liquid meniscus on SLIPS, [ 30,31 ] and gradient electrostatic charge on superomniphobic surfaces. [ 32 ] In condensation, the surface topographies are flooded by highly wetting liquids and the poor durability of liquid meniscus persists.…”