New Finding about Graphene Oxide You May Want to Know

For ordinary materials, once two objects are fused, it is difficult to recover, and even if they are separated, they are no longer the original two objects. However, after 4 years of research, Professor Gao Chao’s group of Zhejiang University’s Department of Polymer Science and Engineering, China, found that graphene oxide sheets have the ability to adapt to deformation, and that graphene oxide fibers can achieve precise and reversible fusion on a macro scale. Splitting is like having a "back button". This result will have a positive impact on precise and reversible assembly in the future. On May 7, this result was published in Science.

Gao Chao said that compared with the existing research, the precise and reversible fusion-splitting process of graphene oxide fibers completed by the research group this time is controllable, and the material size is large, which has enlightening significance for the unique phenomenon of the interface of solids during reversible assembly, effective recovery and reuse of materials.

In real life, each solid unit has its own specific shape and size. It is not difficult for multiple solids to fuse together to form a whole, but the closer the combination, the more difficult it is to separate. Therefore, it cannot be separated and then assembled into another form of the whole.

Earlier, scientists got inspiration from the fusion and division of cells, and biomimetic designed functional assemblies, such as polymer vesicles that can achieve fusion and division under the stimulation of light or heat, and hope that they can be used in medicine. However, it has encountered obstacles in the "reversible" link of fusion and division.

However, the Gao Chao research team found that graphene oxide fibers challenge people's general cognition and can deform and assemble and disassemble and restore at a centimeter-level macroscopic scale. They turned a rigid column made of 13,500 graphene oxide fibers into a flexible net with fusion of nodes. After reversing the experimental process, the net changed back to a pillar.

"During this process, the graphene oxide fibers that make up the columns and nets have not changed. This research has achieved the precise and reversible assembly of graphene oxide macroscopic solid materials." Gao Chao said.

Why can graphene oxide be precise and reversible? This is related to the characteristics of the material itself. Gao Chao's group has been working on the macroscopic assembly of graphene. As early as 2016, the research team discovered that two-dimensional graphene oxide sheets have the characteristics of adaptive deformation and can be fused. They used the swelling of graphene oxide fibers to fuse them into a non-woven fabric before.

So, can graphene oxide fibers split again after fusion?

The research group found that graphene oxide itself has special properties, that is, two-dimensional topology, rich oxygen-containing functional groups, ultra-flexibility, self-bonding, large crude fiber density, less porosity, and moderate interfacial binding after fusion of multiple graphene oxide fibers, "which makes the affinity of the material just good and can easily fuse together, but the binding force is not as strong as steel, so it can be separated." Gao Chao said.

In the experiment, the research group first fused 13,500 graphene oxide fibers into an elongated black column with a diameter of 1.2 mm, which could withstand a force of 680 times its own weight, and then placed the black column in water solvent for dissociation and then splitting, when the thick column became 13,500 fibers. "In this process, the volume expansion rate of graphene oxide reaches nearly 40 times, providing sufficient space for surface deformation," said Changdan, lead author of the paper and director of the Department of Polymers at Zhejiang University, China.

When the fiber becomes soft in the solvent, it can be taken out and woven into a mesh of node fusion, and this mesh still maintains a certain strength, and there is no problem with putting a toy car on it. In other words, these fibers can still be used as functional materials after re-fusion.

In the restoration process, the research team put the net back into the water solvent, and the net was broken down into 13,500 fibers. After they were taken out, they would automatically fuse together, and finally changed back to the shape of the previous column.

So how do you prove that these 13,500 fibers are still the original 13,500 fibers? The research team proved that the internal structure of each fiber is indeed "I am me" and "he is him" by means of fluorescent dyes and color marking of silicon nanoparticles. The components in the fiber did not "communicate" with each other after multiple fusions and splits.

The magic is more than that. The special properties of graphene oxide fibers can also be applied to other materials.

In the study, the research group found that if a layer of graphene oxide is coated on the surface of organic polymers, natural polymers, metals, and inorganic non-metallic fibers such as nylon, silk, stainless steel wire, and glass fiber, these original common materials can also have the function of "assembly-accurate reduction".

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