Rebar graphene under stress

‘Rebar graphene’ tough enough for flexible and wearable electronics

Image credit: Emily Hacopian/Rice University

Texas-based researchers have found that graphene can be made twice as tough by adding nanoscale reinforcement bars (rebars), making it ideal for use in flexible electronics.

Graphene is an atom-thick hexagonal lattice of carbon atoms with superlative properties. It is the strongest known material, and an excellent conductor of heat and electricity as well as being almost transparent.

Despite these useful properties – which could make graphene an ideal candidate for electronic device components – the extreme thinness of a layer of pure graphene means that it is torn very easily and has a strength far lower than its reported intrinsic strength. Researchers also found that molybdenum diselenide, another promising two-dimensional (2D) material, suffered from similar fragility.

However, researchers based at Rice University have found that graphene can be made considerably more fracture-resistant by reinforcing it with a “nanoscale analogue of rebar”; the embedded steel reinforcement bars used to improve the strength and durability of concrete for construction.

“Rebar graphene” was first developed in the laboratory of Rice chemist Professor James Tour in 2014, and uses carbon nanotubes rather than steel bars to reinforce the material. This form of graphene is made by coating nanotubes on a copper substrate, then growing graphene on top of them using chemical vapour deposition.

Rice materials scientists working with Tour have now demonstrated that rebar graphene is far more resistant to damage than pure, brittle graphene. During stress testing (which involved cutting microscopic pieces of rebar graphene and mounting it on a testbed using scanning electron and transmission electron microscope), they observed that the nanotubes diverted and bridged new cracks. This preserved the graphene’s conductivity, and prevented the cracks from propagating throughout the graphene and causing it to tear.

The nanotube reinforcement enabled the otherwise-delicate graphene to resist tearing under considerable stress. While pure graphene was found to have a native fracture toughness of 4MPa, rebar graphene measured 10.7MPa.

The lab’s physical testing of the rebar graphene’s toughness was backed up by simulations carried out by a team at Brown University.

According to Dr Jun Lou, these enhanced properties make rebar graphene useful not just for flexible electronics but also wearable devices which must be flexible, transparent, mechanically stable and stress tolerant in order to be worn comfortably and function seamless.

“We hope this opens a direction people can pursue to engineer 2D material features for applications,” said Lou.

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