In a serendipitous discovery, researchers have created a new class of materials called “glassy gels,” which are semiliquid but difficult to break.
The surprising properties of these gels are stretchy, strangely adhesive and can ‘self-heal’ when cut. They make them potentially useful for a wider range of applications than commonly used plastics, which are hard and brittle, or soft and easy to tear.
“We have created a class of materials we have called glassy gels, which are as hard as glassy polymers, but – if you apply enough force – can stretch up to five times their original length, rather than breaking,” says Michael. Dickey, a materials scientist at North Carolina State University (NCSU).
But like so many accidental scientific discoveries, the intention was never to create an entirely new class of substances, Dickey tells ScienceAlert.
“We came across these interesting materials,” he says, when NCSU researcher Meixiang Wang was experimenting with ionogels, materials made from a polymer swollen with an ionic liquid that conducts electricity.
Wang sought to create stretchable, wearable devices that could be used in a pressure sensor, other medical devices or robotics. By changing the composition, Wang produced a gel that initially looked like an “everyday piece of transparent, flexible plastic”, before tests showed it was very hard, but not brittle like other common plastics.
“Once we realized they had remarkable properties, we dove in to understand them better,” says Dickey.
The glassy gels are made using an ionic liquid, which resembles water but consists entirely of charged particles, allowing it to conduct electricity. When mixed with a polymer precursor, the liquid pushes the polymer chains apart, making the material soft and stretchy. At the same time, the ions are also strongly attracted to the polymer chains, which means they can no longer separate.
“The end result is that the material is hard due to the attractive forces, but can still stretch due to the extra space between them,” Dickey explains.
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The glassy gels do not dry out even though they are 50 to 60 percent liquid, and tests have shown them to have “tremendous” breaking strength and toughness.
The material can also be ‘self-healing’, reforming when cut, and has a kind of memory whereby a stretched gel retains its shape but contracts back to its original shape when heated.
Although unusual, such regenerative properties are not particularly new, especially in stretchy, gel-like materials. Recently, scientists have succeeded in the much more difficult task of creating typically stiff materials, such as metals, glass, solar panels and concrete, that heal when they crack. If these types of materials, which can repair themselves if damaged, are brought to market, they could help reduce waste in the construction, electronics and fashion industries.
But the strange combination of the remarkable nature of the glassy gels is something researchers want to explore further.
“Perhaps the most intriguing feature of the glassy gels is how adhesive they are,” says Dickey. “We understand what makes them hard and stretchy, [but] We can only speculate about what makes them so sticky.”
Obviously, more testing and optimization of the ‘gel’ is needed before these gels can be used in a practical way, but thinking of potential applications, Dickey says that strong materials that conduct electricity (like the gel does) are useful in batteries.
Other potential applications 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 production, while the glassy gels can be injected into a mold and cured with UV light.
But before working on applications, Dickey says his team wants to better understand the basics of how these materials are formed, and why there appears to be a “magic relationship” between solvent and polymer that creates the gels’ unique properties .
“Given the number of unique properties they possess, we are optimistic that these materials will be useful,” says Wang.
The research was published in Nature.