Super-slippery "SLIPS" Coating Is Now More Durable And Fully Transparent

Joanna Aizenberg, Ph.D. and her team at the Wyss Institute for Biologically Inspired Engineering at Harvard University have developed a new transparent, bioinspired coating which makes ordinary glass tough, self-cleaning and incredibly slippery.

The new coating could be used to create durable, scratch-resistant lenses for eyeglasses, self-cleaning windows, improved solar panels and new medical diagnostic devices, said principal investigator Joanna Aizenberg, who is the Amy Smith Berylson Professor of Materials Science at the Harvard School of Engineering and Applied Sciences (SEAS), a Core Faculty Member at the Wyss Institute for Biologically Inspired Engineering, and Professor of Chemistry and Chemical Biology.

Researchers create the ultraslippery coating by creating a glass honeycomb-like structure with craters (left), coating it with a Teflon-like chemical (purple) that binds to the honeycomb cells to form a stable liquid film, which droplets of both water and oily liquids (right)

The new coating builds on an award-winning technology that Aizenberg and her team pioneered called Slippery Liquid-Infused Porous Surfaces (SLIPS)—the slipperiest synthetic surface known. The new coating is equally slippery, but more durable and fully transparent.

The SLIPS technology was bio-inspired by the carnivorous pitcher plant, which lures insects onto the ultraslippery surface of its leaves, where they slide to their doom. Unlike earlier water-repelling materials, SLIPS repels oil and sticky liquids like honey, and it resists ice formation and bacterial biofilms as well.

The SLIPS technology was bio-inspired by the carnivorous pitcher plant

SLIPS’ thin layer of liquid lubricant allows liquids to flow easily over the surface, much as a thin layer of water in an ice rink helps an ice skater glide.

To create the new coating, the researchers placed particles of Styrofoam (polystyrene) on a flat glass surface, and poured liquid glass on them until the particles were half submerged. Once the liquid glass solidified, the particles were burned away, leaving what the team describes as a "network of craters that resembles a honeycomb." The researchers then covered the craters with the same lubricant coating used in SLIPS.

“The honeycomb structure is what confers the mechanical stability to the new coating,” said Aizenberg.

The tiny, tightly packed cells of the honeycomb structure make the SLIPS coating highly durable

The researchers found that by reducing the diameter of the individual honeycomb cells to less than the wavelength of visible light, the coating became transparent, while retaining its robustness and slipperiness.

These coated glass slides repelled a variety of liquids, just as SLIPS does, including water, octane, wine, olive oil, and ketchup. And, like SLIPS, the coating reduced the adhesion of ice to a glass slide by 99%. Keeping materials frost-free is important because adhered ice can take down power lines, decrease the energy efficiency of cooling systems, delay airplanes, and lead buildings to collapse.

Now that this method has been proven, the researchers are working to improve it to make it easier to apply to curved glass and clear plastics.

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Super-slippery "SLIPS" Coating Is Now More Durable And Fully Transparent