A key conceptual advance in the current study is that both Cassie- and Wenzel-state droplets can retain mobility on the slippery rough surface, foregoing the difficult process of preventing the wetting transition. In the last decade, tremendous efforts have been devoted to designing rough surfaces that prevent the Cassie-to-Wenzel wetting transition. Our idea is to solve these problems by enabling Wenzel state droplets to be mobile," said Xianming Dai, postdoctoral scholar in Wong's group and the lead author on the paper. The sticky Wenzel state results in many problems in condensation heat transfer, water harvesting and ice removal. "Droplets on conventional rough surfaces are mobile in the Cassie state and pinned in the Wenzel state. "Through careful, systematic analysis, we found that the Wenzel equation does not apply for highly wetting liquids," said Birgitt Boschitsch Stogin, graduate student in Wong's group and coauthor of "Slippery Wenzel State," published in the online edition of ACS Nano. While the Wenzel equation was published in 1936 in a highly cited paper, it has been extremely challenging to verify the equation experimentally. The two states are named for the physicists who first described them. #New sticky nano technology fullLiquid droplets on rough surfaces come in one of two states: Cassie, in which the liquid partially floats on a layer of air or gas, and Wenzel, in which the droplets are in full contact with the surface, trapping or pinning them. We have demonstrated for the first time experimentally that liquid droplets can be highly mobile when in the Wenzel state." Mobility of liquid droplets on rough surfaces is highly dependent on how the liquid wets the surface. "Our surfaces combine the unique surface architectures of lotus leaves and pitcher plants in such a way that these surfaces possess both high surface area and a slippery interface to enhance droplet collection and mobility. "This represents a fundamentally new concept in engineered surfaces," said Tak-Sing Wong, assistant professor of mechanical engineering and a faculty member in the Penn State Materials Research Institute. University Park, PA | Posted on August 31st, 2015Įnhancing the mobility of liquid droplets on rough surfaces could improve condensation heat transfer for power-plant heat exchangers, create more efficient water harvesting in arid regions, and prevent icing and frosting on aircraft wings. Now, Penn State researchers have developed nano/micro-textured, highly slippery surfaces able to outperform these naturally inspired coatings, particularly when the water is a vapor or tiny droplets.Īn engineered surface unsticks sticky water droplets As slippery as these surfaces are, however, tiny water droplets still stick to them. The leaves of the lotus flower, and other natural surfaces that repel water and dirt, have been the model for many types of engineered liquid-repelling surfaces. In contrast, the new slippery rough surface enables high mobility for Wenzel droplets.ĬREDIT: Xianming Dai and Tak-Sing Wong, Penn State In conventional superhydrophobic rough surfaces, tiny liquid droplets in the Wenzel state will remain pinned to the surface textures. Home > Press > An engineered surface unsticks sticky water droplets
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