Researchers create a new class of materials called “glassy gels”

Researchers have created a new class of materials called “glassy gels” that are very hard and difficult to break even though they contain more than 50% liquid. Coupled with the fact that vitreous gels are simple to produce, this material shows promise for a variety of applications.

An article describing this work, entitled “Glassy Gels Toughened by Solvent,” appears in the journal Nature.

Gels and glassy polymers are classes of materials historically considered distinct from each other. Glassy polymers are hard, rigid and often brittle. They are used to make things like water bottles and airplane windows. Gels, like contact lenses, contain liquid and are soft and stretchy.

“We created a class of materials we called vitreous gels, which are as hard as vitreous polymers, but which, if you apply enough force, can stretch up to five times their original length, rather than break,” Michael explains. Dickey, corresponding author of a paper on the work and the Camille and Henry Dreyfus Professor of Chemical and Biomolecular Engineering at North Carolina State University. “Plus, once the material is stretched, you can return it to its original shape by applying heat. Additionally, the surface of vitreous gels is highly adhesive, which is unusual for hard materials.”

“A key element that distinguishes vitreous gels is that they are more than 50% liquid, making them more efficient conductors of electricity than common plastics with comparable physical characteristics,” says Meixiang Wang, co -lead author of the article and postdoctoral researcher. researcher at NC State. “Given the number of unique properties they possess, we are optimistic that these materials will be useful.”

Vitreous gels, as the name suggests, are actually a material that combines some of the most attractive properties of vitreous polymers and gels. To make them, researchers start from liquid precursors of glassy polymers and mix them with an ionic liquid. This combined liquid is poured into a mold and exposed to ultraviolet light, which “hardens” the material. The mold is then removed, leaving the vitreous gel behind.

“Ionic liquid is a solvent, like water, but it’s made entirely of ions,” says Dickey. “Normally, when you add a solvent to a polymer, the solvent separates the chains of the polymer, making the polymer soft and stretchy. This is why a wet contact lens is soft, and a dry contact lens is not. In glassy gels, the solvent pulls the molecular chains of the polymer apart, allowing it to be stretchable like a gel.

“However, the ions in the solvent are strongly attracted to the polymer, which prevents the polymer’s chains from moving. The inability of the chains to move is what makes it glassy. The end result is that the material is hard in due to the forces of attraction, but it is still able to stretch due to the extra spacing.

Researchers found that vitreous gels could be made with a variety of different polymers and ionic liquids, although not all classes of polymers could be used to create vitreous gels.

“Charged or polar polymers are promising for glassy gels because they are attracted to the ionic liquid,” says Dickey.

In tests, researchers found that vitreous gels do not evaporate or dry out, even though they are 50 to 60 percent liquid.

“Perhaps the most intriguing feature of vitreous gels is their adhesive nature,” says Dickey. “Because even though we understand what makes them hard and stretchy, we can only speculate about what makes them so sticky.”

Researchers also believe that vitreous gels hold promise for practical applications because they are easy to make.

“Creating glassy gels is a simple process that can be done by curing it in any type of mold or 3D printing it,” says Dickey. “Most plastics with similar mechanical properties require manufacturers to create a polymer as a raw material and then transport it to another facility where the polymer is melted and made into the final product.

“We are excited to see how vitreous gels can be used and are willing to work with collaborators to identify applications for these materials.”

The paper’s co-lead author is Xun Xiao of the University of North Carolina at Chapel Hill. The article was co-authored by Salma Siddika, a Ph.D. student at NC State; Mohammad Shamsi, former doctoral student. student at NC State; North Carolina State alumnus Ethan Frey; Brendan O’Connor, professor of mechanical and aerospace engineering at NC State; Wubin Bai, professor of applied physical sciences at UNC; and Wen Qian, research associate professor of mechanical and materials engineering at the University of Nebraska-Lincoln.