Using a new chemistry technique called nanoscale fletching, scientist have created a high-performance nonstick coating that repels water and oil and, importantly, provides a safer and more environmentally friendly surface – ideal for cookware and other everyday uses.
University of Toronto (U of T) engineers have designed a super-thin coating that begins with polydimethylsiloxane (PDMS), a flexible silicone polymer used widely in everything from contact lenses to medical devices. It's transparent, inert, nontoxic and has a high temperature resistance. On its own, however, it can't repel oils like coatings made from per- and polyfluoroalkyl substances (PFAS) – forever chemicals. One of the most famous PFAS for this kind of use is, of course, Teflon (the brand name for polytetrafluoroethylene, or PTEE).
“The material we’ve been working with as an alternative to PFAS is called polydimethylsiloxane or PDMS,” said Kevin Golovin, a professor at U of T Engineering. “PDMS is often sold under the name silicone, and depending on how it’s formulated, it can be very biocompatible – in fact it’s often used in devices that are meant to be implanted into the body. But until now, we couldn’t get PDMS to perform quite as well as PFAS.”
Looking much closer at PFAS, the group's molecules are made of chains of carbon atoms, each one bonded to several fluorine atoms. The inertness of these bonds is what gives PFAS its enviable nonstick properties.
To make PDMS behave like PFAS, the team developed an entirely new chemistry technique – nanoscale fletching – which essentially rearranges some important molecules. So, instead of using long PFAS chains (bad for the environment), the researchers added a few single fluorinated chemical (-CF3) groups. These are tiny – one carbon and three fluorine atoms – and are the least harmful kind of PFAS-related molecule we currently know of.
Because PDMS is flexible, the "slippery" -CF3 groups naturally move and settle on the outer surface of the treated PDMS – and this gives it an oil-repellent skin like PFAS.
“Unlike typical silicone, we bond short chains of PDMS to a base material – you can think of them like bristles on a brush,” explained researcher Samuel Au. “To improve their ability to repel oil, we have now added in the shortest possible PFAS molecule, consisting of a single carbon with three fluorines on it. We were able to bond about seven of those to the end of each PDMS bristle."
The engineers called this process nanoscale fletching, because it's like – well, in chemistry terms – fletching feathers to an arrow for performance.
“If you were able to shrink down to the nanometre scale, it would look a bit like the feathers that you see around the back end of an arrow, where it notches to the bow," he added. "That’s called fletching, so this is nanoscale fletching.”
The result is an ultra-thin layer that that repels water and grease on par with existing nonstick coatings – but with a much lower PFAS content. This large group of human-made chemicals, used in everything from cookware to electronics and fast food packaging, are known as forever chemicals as they don't degrade easily. As such, they spread through water, soil and our bloodstream and can stick around for decades.
And despite the hard work of researchers across the globe looking for safer, greener options, nothing has come close to the likes of Teflon, which has been in heavy use since the 1930s. These forever chemicals have so far been implicated in a wide range of medical studies, and scientists are only just beginning to unpack the health risks of long-chain PFAS exposure.
The researchers' new nonstick coating underwent tests and scored a six on a scale developed by the American Association of Textile Chemists and Colorists to rate performance. This was on par with existing PFAS-based coatings.
Sure, it's not entirely PFAS-free, but the researchers are hoping to cook that up in the lab as they work on reducing the coating's environmental and biological footprint further.
“While we did use a PFAS molecule in this process, it is the shortest possible one and therefore does not bioaccumulate,” said Golovin. “What we’ve seen in the literature, and even in the regulations, is that it’s the longest-chain PFAS that are getting banned first, with the shorter ones considered much less harmful. Our hybrid material provides the same performance as what had been achieved with long-chain PFAS, but with greatly reduced risk.”
The team is now hoping to work with industry and manufacturers looking to ditch standard nonstick coatings. And while there are some current scaling challenges, the new coating has already been applied to nylon, polyester, aluminum and stainless steel, hinting at wide applicability.
“The holy grail of this field would be a substance that outperforms Teflon, but with no PFAS at all,” said Golovin. “We’re not quite there yet, but this is an important step in the right direction.”
The study was published in the journal Nature Communications.
Source University of Toronto
