A group of scientists in the United States and Korea report on the synthesis of crumpled graphene balls [Luo et al., ACS Nano., DOI: 10.1021/nn203115u]
The crumpled particles are amazingly resistant to aggregation in both solution and solid state, and remain largely intact and re-dispersible after chemical treatment, wet processing, annealing and even pelletizing at high pressure. These new findings should greatly benefit applications using bulk quantities of graphene, such as in energy storage or conversion devices.
Imagine crumpling up a paper ball in your hand, these particles look exactly the same (but at sub-micron length scale), and actually share similar properties with the paper ball! One of the wonderful properties of crumpled paper balls is their strain-hardening effect think about how you crush the ball in your hand; the harder you compress them, the stiffer they become, due to the formation of folded ridges that increase the strength. The researchers found similar effects in the crumpled graphene balls.
One of the authors told Materials Today, “This finding translates to amazing aggregation and compression-resistant properties of the crumpled graphene particles. A major problem in the large scale application of graphene is the ease of aggregation of the sheet-like particles, which readily kills their properties like high surface area, and makes them unprocessable. With our crumpled particles, the graphene powders do not aggregate no matter how you process them”. He goes on to say, “This also makes them recyclable! And all this is achieved without degrading the electrical properties of the bulk material. Further, in terms of applications, the crumpled particles should help to standardize the graphene materials by delivering stable surface areas”.
From a basic science point of view, the researchers used mechanical deformation to induce 2D to 3D dimensional transitions, thus obtaining a structure that always has unfavorable/frustrated Van der Waals attraction either in solution or in dried (or even compressed) state, this is why the balls do not aggregate.
These particles represent a new type of material with very unique structures, not just at the surface but also inside. No material like this has previously been reported. Further work is continuing to elucidate structural and physical properties even further.