Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, USA.
ACS Nano. 2011 Nov 22;5(11):8943-9. doi: 10.1021/nn203115u. Epub 2011 Oct 18.
Unlike flat sheets, crumpled paper balls have both high free volume and high compressive strength, and can tightly pack without significantly reducing the area of accessible surface. Such properties would be highly desirable for sheet-like materials such as graphene, since they tend to aggregate in solution and restack in the solid state, making their properties highly dependent on the material processing history. Here we report the synthesis of crumpled graphene balls by capillary compression in rapidly evaporating aerosol droplets. The crumpled particles are stabilized by locally folded, π-π stacked ridges as a result of plastic deformation, and do not unfold or collapse during common processing steps. In addition, they are remarkably aggregation-resistant in either solution or solid state, and remain largely intact and redispersible after chemical treatments, wet processing, annealing, and even pelletizing at high pressure. For example, upon compression at 55 MPa, the regular flat graphene sheets turn into nondispersible chunks with drastically reduced surface area by 84%, while the crumpled graphene particles can still maintain 45% of their original surface area and remain readily dispersible in common solvents. Therefore, crumpled particles could help to standardize graphene-based materials by delivering more stable properties such as high surface area and solution processability regardless of material processing history. This should greatly benefit applications using bulk quantities of graphene, such as in energy storage or conversion devices. As a proof of concept, we demonstrate that microbial fuel electrodes modified by the crumpled particles indeed outperform those modified with their flat counterparts.
与平坦的薄片不同，皱缩的纸球具有高的自由体积和高的抗压强度，并且可以紧密包装而不会显著减小可接触表面的面积。对于类似石墨烯的片状材料，这种特性是非常理想的，因为它们在溶液中容易聚集并且在固态中重新堆积，使得它们的性质高度依赖于材料处理历史。在这里，我们通过在快速蒸发的气溶胶液滴中进行毛细压缩来报告皱缩石墨烯球的合成。由于塑性变形，皱缩的颗粒被局部折叠的π-π堆积脊稳定，并且在常见的处理步骤中不会展开或坍塌。此外，它们在溶液或固态中都具有出色的抗聚集性，并且在化学处理、湿处理、退火甚至高压造粒后仍然基本完整并可再分散。例如，在 55MPa 的压力下压缩时，规则的平石墨烯片通过 84%的表面积急剧减少而变成不可分散的块状物，而皱缩的石墨烯颗粒仍可保持 45%的原始表面积，并且在常见溶剂中仍易于分散。因此，皱缩的颗粒可以通过提供更稳定的性质，例如高表面积和溶液可加工性，从而有助于标准化基于石墨烯的材料，而不管材料处理历史如何。这将极大地受益于使用大量石墨烯的应用，例如在储能或转换设备中。作为概念验证，我们证明了由皱缩颗粒修饰的微生物燃料电池确实优于由其平坦对应物修饰的微生物燃料电池。
