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Register a new userBidirectional Motion of Droplets on Gradient Liquid Infused Surfaces
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We demonstrate spontaneous bidirectional motion of droplets on liquid infused surfaces in the presence of a topographical gradient, in which the droplets can move either toward the denser or the sparser solid fraction area. Our analytical theory explains the origin of this bidirectional motion. Furthermore, using both lattice Boltzmann simulations and experiments, we show that the key factor determining the direction of motion is the wettability difference of the droplet on the solid surface and on the lubricant film. The bidirectional motion is shown for various combinations of droplets and lubricants, as well as for different forms of topographical gradients.
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Liquid infused surfaces (LIS) exhibit unique properties that make them ideal candidates for a wide range of applications, from anti-fouling and anti-icing coatings to self-healing surfaces and controlled wetting. However, when exposed to realistic environmental conditions, LIS tend to age and progressively lose their desirable properties, potentially compromising their application. The associated ageing mechanisms are still poorly understood, and results reflecting real-life applications are scarce. Here we track the ageing of model LIS composed of glass surfaces functionalized with hydrophobic nanoparticles and infused with silicone oil. The LIS are fully submerged in aqueous solutions and exposed to acoustic pressure waves for set time intervals. The ageing is monitored by periodic measurements of the LIS wetting properties. We also track changes to the LIS nanoscale structure. We find that the LIS rapidly lose their slippery properties due to a combination of oil loss, smoothing of the nanoporous functional layer and substrate degradation when directly exposed to the solution. The oil loss is consistent with water microdroplets entering the oil layer and displacing oil away from the surface. These mechanisms are general and could play a role in the ageing of most LIS.
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