Over the last year, research is increasingly showing that if you crumple graphene so that it has wrinkles, the material takes on attractive new properties. For instance, researchers at RIKEN in Japan discovered last year that by forming wrinkles in graphene you can restrict the movements of electrons to create a junction-like structure that changes from a zero-gap conductor to a semiconductor and back to zero-gap conductor.
This Japanese research and others like it that have looked at creating wrinkles in graphene have only examined the potential of wrinkling the material once.
Now research out of Brown University has looked to see what happens when you wrinkle graphene repeatedly.
“Our work is unique in that we show hierarchical graphene oxide architectures across multiple length scales due to repeated wrinkling and/or crumpling processes,” said Ian Wong, an assistant professor at Brown, in an e-mail interview with IEEE Spectrum. “Previous work only wrinkled the graphene once, resulting in a simpler architecture with a single length scale.”
In research described in the journal Advanced Materials, the Brown researchers deposited the graphene oxide onto polymer films that shrink when heated. When the polymer film shrinks from the heat, the graphene on top of it begins to compress to the point it begins to wrinkle.
The researchers tried different variations on this process by clamping opposite ends of the polymer film so that when heated it would shrink only along one axis. They found that when the polymer film was clamped at opposite ends, the graphene would wrinkle into parallel lines. When the film was unclamped, the wrinkles would form both along the film’s length and width, which would create random shapes in the graphene.
When the researchers started to take the same graphene sheet that they had wrinkled with the clamped method and then wrinkled it again with the unclamped method, they found that the graphene sheets would compress to 1/40th their original size.
As some of the previous research in crumpling graphene has indicated, a wrinkled version of graphene may be attractive for wearable electronic applications because of its flexibility. This latest work is no exception and has added the property of water-resistance to its quiver of capabilities.
“After crumpling and wrinkling, the graphene oxide is highly stretchable and flexible without breaking, is superhydrophobic and can retain good electrical conductivity,” said Wong. “Such functionality could be useful for wearable multifunctional devices that can sense and respond to external stimuli, such as chemical detection.”
Also, the researchers found that the repeated crumpling of graphene to the point where it was reduced to 1/40th its original size had promising properties for energy storage.
“Ideally, electrochemical electrodes should display high surface areas, but also permit efficient electrolyte transport to the liquid/solid interface,” said Wong. “Our repeated crumpling permits large areas of graphene oxide to be contained within a much smaller area after three-time compression, which enhances electrochemical current densities by 2000 percent.”
What may be most attractive about this graphene is that producing it is fairly scalable. But if the engineering challenges for making this material applicable to wearable electronics or batteries cannot be met, there may be other applications.
Wong added: “In principle, solution phase deposition of graphene oxide is scalable to roll-to-roll manufacturing. There are also technologies for wafer-scale transfer of nanomaterials. Nevertheless, scale up from bench to manufacturing is extremely challenging. There may be other niche applications based on 2D nanomaterials or complex geometries where these approaches could be useful.”