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Superslippery Liquid-Repellent Surfaces

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Creating a new generation of extremely slippery surfaces

Superhydrophobic surfaces have the potential to keep things dry, clean and bacteria-free. New research aims to turn this potential into marketable dry and durable materials.

Industrial Technologies

Superhydrophobic surfaces are renowned for being extremely water-repellent. “Because droplets just slide off, these surfaces offer significant potential for staying dry and clean, preventing fogging and icing, and repelling bacteria and other germs,” explains Robin Ras, a professor of Soft Matter Physics at Aalto University. As such, superhydrophobic materials could be used by a range of applications, including in the aerospace, defence, automotive, biomedical, engineering and textile sectors. So, what’s the catch? “Superhydrophobic coatings are mechanically fragile, meaning they lack the durability and robustness that many of these applications demand,” says Ras. These are challenges Ras aims to overcome. With the support of the EU-funded SuperRepel project, he set out to create a new generation of extremely slippery surfaces.

Award-winning technology

Before he could create new slippery surfaces, Ras first had to develop new technologies for fabricating such materials. “We started by developing a number of force-based techniques for mapping and scanning wetting heterogeneities and measuring droplet friction and adhesion forces with nanonewton-level precision,” he explains. An example of this technology is a scanning droplet adhesion microscope, which received the Anton Paar Research Award for outstanding scientific and metrological implementation.

Introducing armoured superhydrophobic surfaces

According to Ras, the project’s most important outcomes have to do with the fabrication of surfaces and the development of new methods for probing wetting defects and properties. “Working in collaboration with the University of Electronic Science and Technology of China, we manufactured what are called armoured superhydrophobic surfaces, which are currently the most durable water-repellent surfaces in existence,” he says. The project also advanced researchers’ understanding of the molecular effects of wetting and droplet slipperiness, an understanding that Ras says opens the door to making highly slippery water-repellent surfaces. “I am very pleased to have made these major steps forward in wetting research during this project,” he adds. One of those effects was the unexpected discovery that viscous droplets move faster than water droplets in superhydrophobic capillaries. “This finding is scientifically very interesting and could have important implications for future applications in microfluidics,” notes Ras.

Some unexpected challenges along the way

Speaking of the unexpected, as with most research, not everything always goes as planned. Take for example Ras’ research on a new vapour deposition method for fabricating water-repellent coatings. “Despite the long time required to get things started, we managed to succeed, and I am excited with the results we obtained,” remarks Ras. “I am hopeful that in the future we can use this deposition process to further advance repellent coatings.”

Bringing dry and durable materials to the market

Thanks to the SuperRepel project, which received support from the European Research Council, Ras and his team of researchers have laid the foundation for a new generation of durable water-repellent coatings. “I am very optimistic about durable superhydrophobic surfaces and see them finding their way to the market in the very near future,” adds Ras. Ras himself is already working to commercialise some of the dry and durable microstructuring technology materials developed during the project.

Keywords

SuperRepel, superhydrophobic surfaces, slippery surfaces, scanning droplet adhesion microscope, water-repellent surfaces, microfluidics

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