A carefully patterned water-repellent surface can make an impacting drop detach sooner than it does on a smooth control surface. In a 2013 laboratory study, a ridge changed how liquid spread and recoiled, breaking the drop’s usual radial symmetry and shortening its contact with the solid. The result points to a possible way to limit icing, but it is a research demonstration—not evidence of a field-ready aircraft coating.
Why contact time matters when a drop bounces
After striking a superhydrophobic surface—a surface designed to strongly repel water—a drop spreads, recoils, and may rebound. The interval from impact until it leaves the surface is its contact time. During that interval, the drop can exchange mass, momentum, and energy with the solid.
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Earlier approaches to shortening contact time focused on reducing interactions with the surface and limiting contact-line pinning. The authors of the 2013 Nature paper describe a conventional expectation that symmetric spreading and recoil impose a lower limit. Their approach was different: alter the flow inside the drop by shaping the surface.
How a ridge changes the rebound
The team—James C. Bird, Rajeev Dhiman, Hyuk-Min Kwon, and Kripa K. Varanasi—used surface morphology to redistribute liquid as the drop spread. A ridge interrupts the otherwise radial pattern of the flow. In the explanation reported by Chemistry World, the film above the ridge becomes thinner than nearby parts of the drop, so it retracts more quickly. That faster retreat divides the spreading liquid into smaller regions that have less distance to travel before detaching.
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The recoil is therefore non-axisymmetric: instead of contracting evenly toward the impact point, different portions of the drop retract in response to the ridge. The authors wrote, “Here we demonstrate that it is possible to reduce the contact time below this theoretical limit by using superhydrophobic surfaces with a morphology that redistributes the liquid mass and thereby alters the drop hydrodynamics.” Read the Nature paper.
What the reported timings show
Nature’s 2013 supplementary material gives representative contact times for three tested surfaces. These are examples from the study’s experimental conditions, not universal performance specifications.
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| Surface tested | Representative contact time |
|---|---|
| Micropillar array | 18.0 ms (Nature supplementary material, 2013) |
| Control surface | 12.4 ms (Nature supplementary material, 2013) |
| Designed macrotextured surface | 7.8 ms (Nature supplementary material, 2013) |
Chemistry World reported an approximately 40% contact-time reduction for the simplest geometry, quoting Varanasi in 2013. He described larger reductions as a goal for future work, not as an achieved result in that statement. The percentages and timings should not be generalized beyond the tested setup.
A molten-tin demonstration—and its limits
The supplementary material also describes a molten-tin drop at 250 °C. Under the reported conditions, it bounced from a macrotextured ridge in 6.8 ms; a drop on the unridged substrate stuck after local solidification. This is a specific demonstration with tin, not proof that the technique works across materials or real operating environments.
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Could faster rebound help prevent icing?
Shorter contact offers a possible way to limit the exchange between a drop and a surface. The Nature abstract identifies resistance to icing as one motivation for water-repellent surfaces, and Chemistry World mentions freezing rain on aircraft engines as a potential application. But the reported work establishes a laboratory result, not a commercial engine coating or validated aircraft deployment.
The study also describes non-axisymmetric recoil on natural surfaces, including a Nasturtium leaf and a Morpho butterfly wing, whose ridges or veins affect the drop’s motion. That observation does not establish that those structures evolved for this function; Chemistry World characterizes such a functional interpretation as speculative.
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The paper behind the finding
Bird, Dhiman, Kwon, and Varanasi published “Reducing the contact time of a bouncing drop” in Nature 503, pages 385–388. Nature lists publication on 20 November 2013 and an issue date of 21 November 2013.
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- EXTREME WATER REPELLENCY: This spray wax creates a slick surface that repels water instantly, allowing it to bead and roll off, reducing drying time and preventing unsightly water spots
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