In a surprising breakthrough, researchers have created a new class of materials called “glass gels” that are semi-liquid but hard to break.
Elastic, surprisingly sticky and capable of ‘self-healing’ if cut, the surprising properties of these gels potentially make them useful for a wider range of applications than commonly used plastics, which are either hard and brittle or soft and easily torn.
“We’ve created a class of materials we’ve called glass gels, which are as strong as glassy polymers, but – if you apply enough force – they can stretch up to five times their original length, instead of break,” says Michael. Dickey, materials scientist at North Carolina State University (NCSU).
But as with so many serendipitous scientific discoveries, the goal was never to create an entirely new class of substances, Dickey tells ScienceAlert.
“We stumbled upon these interesting materials,” he says, when NCSU researcher Meixiang Wang was experimenting with ionogels, materials made from a polymer swollen with an electrically conductive ionic liquid.
Wang was trying to make stretchable and wearable devices that could be used in a pressure sensor, other medical devices or robotics. By changing the composition, Wang produced a gel that at first looked like an “ordinary piece of transparent, flexible plastic” before testing showed it was very strong – but not brittle like other ordinary plastics.
“Once we realized they have extraordinary properties, we set out to better understand them,” says Dickey.
Glass gels are made using an ionic liquid, which is similar to water, but composed entirely of charged particles, allowing it to conduct electricity. When mixed with a polymer precursor, the liquid pulls the polymer chains apart, making the material soft and flexible. At the same time, the ions are also strongly attracted to the polymer chains, preventing them from separating.
“The end result is that the material is strong because of the tensile forces, but is still able to stretch because of the extra space,” explains Dickey.
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Glassy gels do not dry out, even though they are 50 to 60 percent liquid, and testing has shown them to have “extreme” strength and fracture toughness.
The material can also ‘self-heal’, reforming if cut, and has a type of memory that allows a stretched gel to retain its shape, only to shrink back to its original shape when heated.
Although unusual, such regenerative properties are not particularly new, especially in elastic gel-like materials. Recently, scientists have succeeded in the much more difficult task of making typically rigid materials such as metals, glass, solar panels and concrete that heal when cracked. If commercialized, materials like these, capable of being repaired when damaged, could help reduce waste in the construction, electronics and fashion industries.
But the strange combination of the glassy gel’s extraordinary nature is something researchers want to explore further.
“Perhaps the most intriguing characteristic of glass gels is how sticky they are,” says Dickey. “We understand what makes them hard and stretched, [but] we can only speculate what makes them so sticky.”
Obviously, more testing and optimization of the ‘gel’ is required before these gels can be used in any practical way, but thinking about possible applications, Dickey says that strong materials that conduct electricity (like gels do) are useful in batteries.
Other potential uses include 3D printing plastic-like materials using simpler techniques than melt processing – the method currently used to produce commercial plastics from starting resins. This process often involves shipping products to multiple facilities for each step of plastic manufacturing, while glass gels can be injected into a mold and cured with UV light.
But before working towards applications, Dickey says his team wants to better understand the basics of how these materials are formed and why there seems to be a ‘magic ratio’ of solvent to polymer that creates the gel’s unique properties.
“Considering the number of unique properties they possess, we are optimistic that these materials will be useful,” says Wang.
The study was published in Nature.