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Nanomaterials

Nanomaterials

Graphene oxide fibres fuse and fissure

20 May 2021 Isabelle Dumé
fusion-fission of GO fibres
Zhejiang University team members in the lab. Courtesy: Zhejiang University

Researchers in China have succeeded in assembling graphene oxide fibres using a process normally only seen in biological systems. The new process, which mimics cellular fusion and fission, could find use in applications such as the actuators or “artificial muscles” used in miniaturized medical devices, robotics and smart textiles.

Materials that respond to environmental changes in the same way that natural materials do are widely seen as ideal building blocks for emerging electronic devices. One natural mechanism that researchers are especially keen to mimic is biological self-assembly and, in particular, cellular fusion and fission. In fusion, two or more cells merge into one, while in fission they separate into two or more parts. Both processes are triggered by stimuli such as light, temperature or humidity.

Reversible solvent-triggered process

In the new work, Chao Gao of Zhejiang University and colleagues from Xi’an Jiaotong University began by assembling microfibres of graphene oxide (an oxidized version of carbon’s one-atom-thick form) using a technique called wet-spinning. The team chose this material because its super-flexible nature makes it relatively easy to wet-spin into fibres, while its oxygen functional groups make it chemically reactive. The resulting fibres have an outer “shell” that restricts the movement of the graphene oxide sheets.

When the researchers immersed the fibres in a suitable solvent, they found that the fibres self-assembled into a “hierarchical” yarn – that is, a yarn in which the same base structure repeats at different length scales – containing thousands of individual fibres. The team could also reverse this process by immersing the fibre assembly in water or polar organic solvents, thereby mimicking both parts of the biological fusion-fission cycle.

To understand what was happening at the scale of individual fibres, the researchers used optical and scanning electron microscopes to observe the fusion-fission processes. They found that when the fibres are placed in a water or polar organic solvents, they swell up, dramatically increasing in volume. The fibres’ elasticity is enhanced too, and the shape of the fibre shells reversibly switches between a wrinkled tube-like state and a flatter cylindrical state through swelling and deswelling. Gao and colleagues explain that this switching creates a transient fibre interface, leading to cyclic self-fusion and self-fission of an arbitrary number of graphene oxide fibres.

“A versatile strategy”

The researchers, who describe their work in Science, say that the fusion-fission behaviour they observed is a “versatile strategy” for designing functional responsive materials. Since graphene oxide fibres can easily be made to electrically conduct (via chemical reduction), the team argue that these fibres show promise for applications such as sensors, electronic components, smart textiles and actuators.

Rodolfo Cruz-Silva of Shinshu University in Japan and Laura Elias of Binghamton University in the US, who were not involved in the study, note that the new method is much less complex and involves fewer components than natural fusion-fission processes. Nevertheless, they argue in a related Perspectives article that the reversible assembly of graphene oxide fibres does indeed mimic nature, and thus “holds the refreshing potential to move the field forward”.

Gao and colleagues now plan to investigate the fusion-fission mechanism more carefully. “We also hope to explore applications in different areas,” Gao tells Physics World. The reversible fusion and fission property they discovered, he adds, “may help push forward the versatility of fibres like the ones we have studied”.

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