Low-dimensional carbon allotropes, from fullerenes, carbon nanotubes, to graphene, have been broadly explored due to their outstanding and special properties. However, there exist significant challenges in retaining such properties of basic building blocks when scaling them up to 3-D materials and structures for many technological applications. Mechanically, the huge gap originates from the dissimilar bonding characteristics between carbon atoms within graphene or CNTs and the architected 3-D engineering materials: The intra-structure bonding is covalent in nature, while van der Waals bonding dominates between different layers/tubes or with other materials.
Researchers from LNM, Institute of Mechanics, Chinese Academy of Sciences, University of Colorado, Boulder, and MIT show theoretically the atomistic structure of stable 3-D carbon honeycomb (C-honeycomb) structures with superb mechanical and thermal properties. A combination of sp2 bonding in the wall and sp3 bonding in the triple junction of C-honeycomb is the key to retain the stability of C-honeycomb. The specific strength could be the best in structural carbon materials, and this strength remains at a high level but tunable with different cell sizes. C-honeycomb is also found to have a very high thermal conductivity, e.g. >100 W/mK along the axis of the hexagonal cell with a density only ~0.4 g/cm3. Such high specific strength, high thermal conductivity, and anomalous Poisson’s effect in C-honeycomb render it appealing for the use in various engineering practices.
The research was partially funded by the National Natural Science Foundation of China (NSFC) (11425211) to Y. Wei.
Figure 1. Bottom-up design of 3-D stable C-honeycomb (a) by graphene wall and sp3 bonding in the junction (b) for superb specific strength and high thermal (c).