Discovery and Elimination Strategies of Voids in Two-Dimensional Carbon Nanocomposites

ConspectusTwo-dimensional carbon nanocomposites (TDCN) are assembled by two-dimensional carbon nanosheets and show promising applications in many fields such as unmanned aerial vehicles, aerospace, and smart wearable devices due to their exceptional performance including light weight, high strength, high electrical and thermal conductivities, etc. Compared with traditional carbon-fiber-reinforced composites, two-dimensional carbon nanosheets represented by graphene and titanium carbide (MXene) have outstanding mechanical properties, making them ideal candidates for fabricating high-performance nanocomposites. Over the past two decades, many researchers have developed many strategies to solve intrinsic issues in the fabrication of TDCN, such as poor dispersion, low orientation, weak interfacial interactions, etc. Although many achievements in mechanical properties of TDCN have been obtained, the mechanical performance of TDCN is still far below theoretical expectations based on the intrinsic performance of two-dimensional carbon nanosheets. We first found that there is an important issue ignored so far, void, resulting in low load transfer efficiency in TDCN. Recently, the investigations about voids' characterization, analysis, and elimination have been demonstrated as a key scientific issue for further enhancing the performance of TDCN.In this Account, we will summarize significant advanced research in the discovery, characterization, influence, and elimination of voids in TDCN by our group and discuss the relevant reported works. We start by introducing the physical and chemical properties of two-dimensional carbon nanosheets, such as graphene and MXene, which are widely used for fabrication of TDCN. Then we systemically introduce fabrication strategies of TDCN such as filtration, layer-by-layer, superspreading, blade casting, and centrifugal casting. Employing these strategies, two-dimensional carbon nanosheets could be sufficiently dispersed and highly oriented, thus resulting in excellent mechanical properties. However, the mechanical properties of TDCN are still far lower than those of the intrinsic two-dimensional carbon nanosheet, which is mainly caused from existed voids. Then, we overview the research work about the discovery, characterization, and influence of voids on the mechanical properties of TDCN. Next, we systematically introduce a series of strategies to eliminate voids, such as synergistic interfacial interaction, filling, and force-induced alignment. Employing these strategies, TDCN results in excellent mechanical properties and remains high in electrical properties, which could be widely used in various fields such as electromagnetic interference shielding, thermal shielding, flexible supercapacitors, and flexible thermal management. Finally, we summarize the current technical challenges facing this field. We not only give a perspective of future void characterization and elimination strategies to further develop high-performance TDCN but also propose the concept for adjusting voids to achieve the functions in TDCN. More functional TDCN will be fabricated through control of voids size and distribution during the process of self-assembly of two-dimensional carbon nanosheets.