Tag Archives: Tobin Filleter

Nanoscale fletching for a safer alternative non-stick coating

Leave a reply

Before the ‘fletching’ explanation (in the news release), there’s the announcement in a July 27, 2025 news item on ScienceDaily,

A new material developed by researchers from University of Toronto Engineering could offer a safer alternative to the non-stick chemicals commonly used in cookware and other applications.

The new substance repels both water and grease about as well as standard non-stick coatings — but it contains much lower amounts of per- and polyfluoroalkyl substances (PFAS), a family of chemicals that have raised environmental and health concerns.

…

A July 23, 2025 University of Toronto (U of T) news release (also on EurekAlert but published July 25, 2025) by Tyler Irving, which originated the news item goes on to describe nanoscale fletching, Note: Links have been removed,

“The research community has been trying to develop safer alternatives to PFAS for a long time,” says Professor Kevin Golovin, who heads the Durable Repellent Engineered Advanced Materials (DREAM) Laboratory at U of T Engineering. 

“The challenge is that while it’s easy to create a substance that will repel water, it’s hard to make one that will also repel oil and grease to the same degree. Scientists had hit an upper limit to the performance of these alternative materials.” 

Since its invention in the late 1930s, Teflon — also known as polytetrafluoroethylene or PTFE — has become famous for its ability to repel water, oil and grease alike. Teflon is part of a larger family of substances known as per- and polyfluoroalkyl substances (PFAS). 

PFAS molecules are made of chains of carbon atoms, each of which is bonded to several fluorine atoms. The inertness of carbon-fluorine bonds is responsible for the non-stick properties of PFAS. 

However, this chemical inertness also causes PFAS to resist the normal processes that would break down other organic molecules over time. For this reason, they are sometimes called ‘forever chemicals.’ 

In addition to their persistence, PFAS are known to accumulate in biological tissues, and their concentrations can become amplified as they travel up the food chain. 

Various studies have linked exposure to high levels of PFAS to certain types of cancer, birth defects and other health problems, with the longer chain PFAS generally considered more harmful than the shorter ones. 

Despite the risks, the lack of alternatives means that PFAS remain ubiquitous in consumer products: they are widely used not only in cookware, but also in rain-resistant fabrics, food packaging and even in makeup. 

“The material we’ve been working with as an alternative to PFAS is called polydimethylsiloxane or PDMS,” says Golovin. 

“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.” 

To overcome this problem, PhD student Samuel Au developed a new chemistry technique that the team is calling nanoscale fletching [emphasis mine]. The technique is described in a paper published in Nature Communications. 

“Unlike typical silicone, we bond short chains of PDMS to a base material — you can think of them like bristles on a brush,” says 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. 

“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. That’s called fletching, so this is nanoscale fletching.” 

Au and the team coated their new material on a piece of fabric, then placed drops of various oils on it to see how well it could repel them. On a scale developed by the American Association of Textile Chemists and Colorists, the new coating achieved a grade of 6, placing it on par with many standard PFAS-based coatings. 

“While we did use a PFAS molecule in this process, it is the shortest possible one and therefore does not bioaccumulate,” says 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.” 

Golovin says that the team is open to collaborating with manufacturers of non-stick coatings who might wish to scale up and commercialize the process. In the meantime, they will continue working on even more alternatives. 

“The holy grail of this field would be a substance that outperforms Teflon, but with no PFAS at all,” says Golovin. 

“We’re not quite there yet, but this is an important step in the right direction.”

Here’s a link to and a citation for the paper,

Nanoscale fletching of liquid-like polydimethylsiloxane with single perfluorocarbons enables sustainable oil-repellency by Samuel Au, Jeremy R. Gauthier, Boran Kumral, Tobin Filleter, Scott Mabury & Kevin Golovin. Nature Communications volume 16, Article number: 6789 (2025) DOI: https://doi.org/10.1038/s41467-025-62119-9 Published: 23 July 2025

This paper is open access.

Graphene fatigue

Leave a reply

Graphene fatigue operates under the same principle as metal fatigue. Subject graphene to stress over and over and at some point it (just like metal) will fail. Scientists at the University of Toronto (Ontatrio, Canada) and Rice University (Texas, US) have determined just how much stress graphene can withstand before breaking according to a January 28, 2020 University of Toronto news release by Tyler Irving (also on EurekAlert but published on January 29, 2020),

Graphene is a paradox. It is the thinnest material known to science, yet also one of the strongest. Now, research from University of Toronto Engineering shows that graphene is also highly resistant to fatigue — able to withstand more than a billion cycles of high stress before it breaks.

Graphene resembles a sheet of interlocking hexagonal rings, similar to the pattern you might see in bathroom flooring tiles. At each corner is a single carbon atom bonded to its three nearest neighbours. While the sheet could extend laterally over any area, it is only one atom thick.

The intrinsic strength of graphene has been measured at more than 100 gigapascals, among the highest values recorded for any material. But materials don’t always fail because the load exceeds their maximum strength. Stresses that are small but repetitive can weaken materials by causing microscopic dislocations and fractures that slowly accumulate over time, a process known as fatigue.

“To understand fatigue, imagine bending a metal spoon,” says Professor Tobin Filleter, one of the senior authors of the study, which was recently published in Nature Materials. “The first time you bend it, it just deforms. But if you keep working it back and forth, eventually it’s going to break in two.”

The research team — consisting of Filleter, fellow University of Toronto Engineering professors Chandra Veer Singh and Yu Sun, their students, and collaborators at Rice University — wanted to know how graphene would stand up to repeated stresses. Their approach included both physical experiments and computer simulations.

“In our atomistic simulations, we found that cyclic loading can lead to irreversible bond reconfigurations in the graphene lattice, causing catastrophic failure on subsequent loading,” says Singh, who along with postdoctoral fellow Sankha Mukherjee led the modelling portion of the study. “This is unusual behaviour in that while the bonds change, there are no obvious cracks or dislocations, which would usually form in metals, until the moment of failure.”

PhD candidate Teng Cui, who is co-supervised by Filleter and Sun, used the Toronto Nanofabrication Centre to build a physical device for the experiments. The design consisted of a silicon chip etched with half a million tiny holes only a few micrometres in diameter. The graphene sheet was stretched over these holes, like the head of a tiny drum.

Using an atomic force microscope, Cui then lowered a diamond-tipped probe into the hole to push on the graphene sheet, applying anywhere from 20 to 85 per cent of the force that he knew would break the material.

“We ran the cycles at a rate of 100,000 times per second,” says Cui. “Even at 70 per cent of the maximum stress, the graphene didn’t break for more than three hours, which works out to over a billion cycles. At lower stress levels, some of our trials ran for more than 17 hours.”

As with the simulations, the graphene didn’t accumulate cracks or other tell-tale signs of stress — it either broke or it didn’t.

“Unlike metals, there is no progressive damage during fatigue loading of graphene,” says Sun. “Its failure is global and catastrophic, confirming simulation results.”

The team also tested a related material, graphene oxide, which has small groups of atoms such as oxygen and hydrogen bonded to both the top and bottom of the sheet. Its fatigue behaviour was more like traditional materials, in that the failure was more progressive and localized. This suggests that the simple, regular structure of graphene is a major contributor to its unique properties.

“There are no other materials that have been studied under fatigue conditions that behave the way graphene does,” says Filleter. “We’re still working on some new theories to try and understand this.”

In terms of commercial applications, Filleter says that graphene-containing composites — mixtures of conventional plastic and graphene — are already being produced and used in sports equipment such as tennis rackets and skis.

In the future, such materials may begin to be used in cars or in aircraft, where the emphasis on light and strong materials is driven by the need to reduce weight, improve fuel efficiency and enhance environmental performance.

“There have been some studies to suggest that graphene-containing composites offer improved resistance to fatigue, but until now, nobody had measured the fatigue behaviour of the underlying material,” he says. “Our goal in doing this was to get at that fundamental understanding so that in the future, we’ll be able to design composites that work even better.”

Here’s a link to and a citation for the paper,

Fatigue of graphene by Teng Cui, Sankha Mukherjee, Parambath M. Sudeep, Guillaume Colas, Farzin Najafi, Jason Tam, Pulickel M. Ajayan, Chandra Veer Singh, Yu Sun & Tobin Filleter. Nature Materials (2020) DOI: DOIhttps://doi.org/10.1038/s41563-019-0586-y Published: 20 January 2020

This paper is behind a paywall.