According to a recent report by the Physicists Organization Network, researchers at Carnegie Mellon University in Pittsburgh, Pennsylvania, covered a graphene coating on a fragile carbon nanotube aerogel, making it look like wearing a superman cape. The strength and pressure will change to the state of collapse and become tough and withstanding pressure, and when the load is removed, it can be fully restored. The results of the study are published in the journal Nature Nanotechnology.
The researchers said that they demonstrated that the carbon nanotube network transforms from brittleness to superelasticity, which is only achieved through the graphene coating. The superelasticity and fatigue resistance that it provides will make the carbon nanotubes aerogel. It is widely used in various fields including electrode materials, artificial muscles, and other mechanical structures.
Under normal circumstances, the coating increases the material corrosion resistance, lubrication, aesthetics, surface chemical changes, sealing and other characteristics, but is not conducive to changes in mechanical properties. The researchers said: "Normal gels are mostly made up of a network of liquid materials with their surfaces intertwined. The aerogel replaces the liquid material in the gel with a gas. The gel is dried at a critical temperature. The resulting aerogel is a lightweight material consisting of 99.9% air by volume, but it is also dry, rigid, and solid as a solid."
In the current study, the researchers used an air-entrained carbon nanotube aerogel consisting of dispersed carbon nanotubes about 1 micron long. Carbon nanotube aerogels retain their shape under pressure because of the intermolecular interactions at the nodes, and the carbon nanotubes cross each other at various points. However, when these aerogels are compressed up to 90% based on their original size, they will collapse or cause permanent deformation, thereby limiting their potential applications.
In non-coated aerogels, after strong compression, the struts supporting the aerogel network at the nodes can flex and rotate freely, thereby increasing the contact area between the carbon nanotubes and the new nodes formed. When removing the load, restoring these nodes to their original state requires more force than applying pressure. It is because the carbon nanotube aerogel does not recover the force to break through the new nodes formed in the compression process and thus does not return to its original shape.
To overcome this lack of flexibility, the researchers coated CNT aerogels with 1 to 5 layers of graphene coating. The researchers believe that the graphene coating can strengthen the node pillars, giving it its hyperelastic properties. In contrast, when the nodes are strongly compressed, the graphene-coated CNT aerogels have strong struts that are difficult to rotate, graphene at the nodes are compressed and creased, and such graphene flakes provide Resilience, like a spring, breaks the new node formed.
Studies have shown that graphene-coated carbon nanotube aerogels can withstand high compression and can rebound back to their original shape. It can withstand more than 1 million compression cycles and still recover its original shape after pressure release. This not only enables the aerogel to resist strong compression and become a superelastic material, but also maintains its properties such as porosity and electrical conductivity. Obviously, this feature opens the door for new aerogel applications in the future. (Hua Ling)
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