New mechanism moving droplets at record-high speed and long distance without extra power

phys.org | 5/20/2019 | Staff
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Transporting droplets on solid surfaces at high speed and long distances without additional force, even against gravity, is a formidable task. But a research team comprising scientists from City University of Hong Kong (CityU) and three other universities and research institutes has recently devised a novel mechanism to transport droplets at record-high velocity and distance without extra energy input, and droplets can be moved upward along a vertical surface, which has never been achieved before. The new strategy to control droplet motion can open up new potential in applications in microfluidic devices, bio-analytical devices and beyond.

The conventional methods for transporting droplets include leveraging the wetting gradient on the surface to induce a driving force and move the droplet from hydrophobic to hydrophilic surface. However, the fundamental trade-off underpinning droplet hydrodynamics imposes limitations: transporting droplets at high speed necessitates a large wetting gradient and in turn is limited to a short distance, while long transport distance demands a small wetting gradient to reduce the adhesive force between the liquid and solid surface, and the transport velocity is then constrained.

Challenges - Researchers - Strategy - Liquid - Droplet

To overcome these challenges, the researchers have devised a new strategy that achieves the unidirectional and self-propelled liquid droplet transportation on diverse substrates. Their work demonstrates unprecedented performance: The highest transport velocity (1.1m/s) is 10 times higher than ever before reported, and represents the longest unlimited transport distance.

The key to this breakthrough lies in the manipulation of surface charge via liquid contact, which was realized for the first time. The research team first dropped a chain of water droplets on the specially designed superamphiphobic (super water- and oil-repellent) surface...
(Excerpt) Read more at: phys.org
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