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In a new study, researchers have propelled water nanodroplets across a graphene surface at speeds of up to 250 km (155 miles) per hour—which, for comparison, is about twice as fast as a sprinting cheetah. The water droplets' ultrafast velocities don't require any pump, but instead occur simply due to the geometric patterns on the graphene surface, which create different contact angles at the front and back of the moving droplets to propel them forward.
The researchers, Ermioni Papadopoulou and Petros Koumoutsakos at ETH Zürich, Constantine M. Megaridis at the University of Illinois at Chicago, and Jens H. Walther at ETH Zürich and the Technical University of Denmark, have published a paper on the fast-moving water droplets in a recent issue of ACS Nano.
Transport - Water - Droplets - Nanoscale - Energy
"We can get very high-speed directed transport of water droplets on the nanoscale, without expending any energy but simply through the patterning of graphene," Koumoutsakos told Phys.org. "This may have important applications in nano-fabrication and precise drug delivery. It also provides for the first time a simple quantitative explanation for the ultrafast transport of water at the nanoscale."
This nano-/microscale mode of transport is very different than anything observed on the macroscale. The graphene surface was structurally patterned to create wettability gradients, ranging from hydrophobic to hydrophilic. The water nanodroplets, each consisting of approximately 1500 water molecules, were then placed on the surface. The different surface patterns created large contact angles on...
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