The glassy gel is as rigid as plastic and can extend up to seven times its original length.

When you think of gel, you might imagine something sludgy, but the new gel-like material has been engineered to be strong and transparent like glass, yet flexible enough to stretch to almost seven times its original length.

Michael Dickey The North Carolina State University researchers say they discovered the “glassy gel” when student Meishan Wang was experimenting with ionic liquids and kept finding unexpected mechanical properties. The material they came up with is more than 50 percent liquid, yet it's as strong as the plastic in water bottles, and it's also highly stretchable and sticky. “It has a lot of great properties,” Wang says.

Each glassy gel is made up of long molecules called polymers mixed with ionic liquid (essentially liquid salt). The gels are transparent solids that can withstand up to 400 times atmospheric pressure, yet easily stretch up to 670 percent. Dickey says this could make them suitable for building soft robotic grippers or for 3D printing deformable materials.

He and his colleagues created glassy gels from mixtures of several polymers and liquid salts, and found that their strength and stretchability depended on the exact ratios used.

“By simply changing the ratio of the two materials, we can make something as stretchy as a rubber band or as hard as glass,” Dickey says.

This is because the material's stretchability comes from the ionic liquid depositing in the spaces between the stiff polymer molecules, pushing them apart, while its strength comes from electrostatic attraction between the charged particles in the liquid and the polymer, which prevents the particles from moving apart completely.

The glassy gel is also capable of self-repair; cuts or breaks can be repaired by applying heat, causing the molecules at the broken edges to rejoin. Richard Hoogenboom Researchers at Ghent University in Belgium say the technique could be useful in some cases where traditional plastics are used, but that the formulations may need to be tweaked to only soften at high enough temperatures to avoid accidental softening.