Researchers at Rice University have developed a low-cost multilayer coating that repels near-boiling water.
Researchers in the US have developed a multilayered insulated superhydrophobic coating that repels near-boiling water, hot milk, coffee, and split pea soup, thus helping never-wet surfaces stay effective even at high temperatures.
Scientists at Rice University came up with a quick fix for superhydrophobic surfaces by experimenting with the material’s heat flow rather than focusing solely on its chemistry and texture.Superhydrophobic surfaces are highly water‑repellent. They mimic the lotus leaf and cause water droplets to roll off with only a slight tilt. But hot water remains their major weakness. When temperatures reach 104 degrees Fahrenheit , many of these coatings abruptly lose their water-repelling abilities. Instead of skittering off, the hot droplets start sticking and seeping into the surface texture, and leave wet patches behind. Solving the heat issueTo tackle this problem, the team designed a coating that repels water even when droplets approach 194 degrees Fahrenheit . The MISH design consists of a two-layer system. This includes an insulating underlayer , along with a microtextured superhydrophobic topcoat .The underlayer slows heat transfer from the droplet into the surface. It prevents the rapid evaporation-condensation cycle that normally destroys the trapped air pockets responsible for water repellency. “The insulation layer reduces the cooling of the hot droplet at the interface, which in turn reduces evaporation and recondensation cycles that normally flood the surface texture with condensate,” Daniel J. Preston, PhD, an assistant professor of mechanical engineering at Rice University, and corresponding study author, said.“Less condensate in the surface texture means fewer liquid bridges, which keeps repellency intact,” Preston added. Without those condensate bridges, even near-boiling droplets continue to glide off. He elaborated that the task had previously been difficult and could cost up to 4,000 times more than their method. “We also showed that this works outside the lab in real-world situations across both large and curved surfaces, from pipes to bowls to industrial equipment,” Preston pointed out.Real-world testsThe scientists subjected coating samples to a week-long barrage of hot droplets, nearly two million impacts. Traditional coatings broke down almost immediately.Meanwhile, the MISH surfaces, especially those with thicker insulation, maintained repellency for more than 80 hours, or about one million impacts, before gradually degrading. According to the researchers, the weak point wasn’t the concept, but the off-the-shelf topcoat. The insulation strategy remained intact, indicating future versions could last even longer with more durable outer layers.The researchers also fired hot water jets at the coatings to mimic splashes and continuous exposure. Image credit: Rice UniversityTo prove the concept’s scalability outside of the lab, the team applied the coating to large metal plates, curved pipes, and common kitchen-adjacent liquids such as hot milk, coffee, and even split pea soup. These fluids left less than one percent residue on MISH-treated surfaces. By comparison, they left more than 31 percent on standard coatings.“We’re excited about the potential applications of this approach, but there is also room for further improvement,” Preston stated. The team is now exploring more durable and thermally stable top layers, as well as coating architectures that go beyond simple spray-on methods. “As soon as you can keep hot liquids from sticking, a lot of downstream problems start to disappear,” Preston concluded in a press release. “That’s what makes this method exciting; it opens the door to surfaces that behave the way we designed them to, even under harsh conditions.” The study has been published in the journal ACS Applied Materials & Interfaces.
Materials Science Physics Rice University Science Superhydrophobic Surfaces Technology Thermal Insulation USA Water
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