Graphene oxide crawler on a ruler

Spider-like graphene ‘robots’ crawl with no external power source

Image credit: Jilin University

Researchers at Jilin University, China, have used a graphene-based smart material to create a “crawler” and a claw which move in response to changes in humidity.

The material was created from a sheet of graphene oxide and an off-the-shelf camera flash.

“The development of smart materials such as moisture-responsive graphene oxide is of great importance to automation and robotics,” said Professor Yong-Lai Zhang, of Jilin University, China, who led the research.

“Our very simple method for making typical graphene oxides smart is also extremely efficient. A sheet can be prepared within one second.”

Previously, it has been established that graphene oxide can be made moisture-responsive through reduction, a chemical reaction which removes oxygen from molecules. The same team of Jilin University researchers have shown before that sunlight and artificial ultraviolet light can induce reduction, although the reaction is difficult to control.

They found that treating graphene oxide sheets to a very brief exposure of light – using a camera flash – showed controlled reversible bending in response to changing humidity. This was due to reduction being induced on just one side of the sheet.

When moisture is present in the air, the reduced side of the sheet absorbs less water, causing the other side to expand and making the sheet bend. The sheet flattens when the air is dry.

In order to use this property to create a crawler, the researchers cut the treated graphene oxide sheet into the shape of a small four-legged bug, just one centimetre wide. When humidity is switched rapidly on and off, the crawler was made to move 0.35cm in 12 seconds. The researchers also created an eight-fingered claw, which could open and close in response to changing humidity.

These movements arose with no external power required.

“These robots are simple and can be flexibly manipulated by changing the environmental humidity,” said Zhang. “These designs are very important because moving and capturing/releasing are basic functions of automated systems.”

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