On May 7th, Proceedings of the National Academy ofSciences of the United States of America (PNAS) published the latest research by the team led by Prof. Cheng Qunfeng and Academician Jiang Lei under the title of “Sequentially bridged graphene sheets with high strength, toughness, and electrical conductivity”. Prof. Cheng Qunfeng and Prof. Ray H. Baughman (a member of the National Academy of Engineering) are the corresponding authors. Wan Sijie, a bachelor-straight-to-doctorate student enrolled in 2014, is the first author. Beihang University is the first corresponding organization.
Light and high-strength carbon fiber composites have a wide application in daily life, especially in the fields of aerospace, automobile and sports equipment. However, there are some shortcomings with regard to their making and use. Firstly, the mechanical properties of carbon fiber composites are anisotropic even when carbon fiber sheets are plied. Secondly, delamination of carbon fiber from the polymer matrix, especially in the seams with other materials, causes fractures that lead to failures. Thirdly, the electrical conductivity of carbon fiber composites is lower than desired for some applications. Graphene has great mechanical and electrical properties, so it is one of the ideal materials for the making of new nanocomposites with high performance. However, it is hard and expensive to synthesize high-performance macro nanocomposites with the graphene made through the vapor deposition method. Graphene oxide made from natural mineral graphite powder through the chemical method is just the opposite, but how to produce the desired nanocomposite with this graphene oxide remains a big technical challenge.
The team led by Prof. Cheng has been devoted to research on bionic multifunction graphene nanocomposites for a long time and made a series of achievements. For example, based on a variety of interfacial interactions (hydrogen bond, ion bond, pi bond, covalent bond, etc.), they made a kind of graphene nanocomposite with high strength and conductivity in a bionic way (Adv.Mater.2016, 28, 7862; Adv.Mater.2016, 28, 2834; Angew. Chem.Int. Ed. 2013, 52, 3750; ACSNano2015, 9, 9830; ACS Nano2014, 8, 9511.). Also, based on the synergistic toughening effect of the 1D nanofiber and 2D nanochip, they developed a kind of bionic multifunctional graphene nanocomposite that is fire- (J.Mater. Chem. A2015, 3, 21194.) and fatigue-resistant (ACS Nano2015, 9, 708; ACS Nano2017, 11, 7074; ACS Nano2015, 9, 11568; Adv. Funct. Mater.2017, 27, 1605636; Adv. Funct. Mater.2017, 27, 1703459.)
On the research basis of bionic interfacial assembly, the team further developed a method of bridging sequentially π–π conjugated bond and covalent bond at low temperature to make multifunctional graphene sheet. This kind of sheet provide a tensile strength (944.5 ± 46.6 MPa) and toughness (20.6 ± 1.0 MJ·m−3) that are as 4.5 times and 7.9 times respectively as those of the graphene sheet without sequential bridging. More importantly, this sheet rivals the more expensive commercial carbon fiber composite in tensile strength, and its toughness is better than the latter one (Fig. 2). This research also revealed the mechanism of bridging sequentially π–π conjugated bond and covalent bond through in-situ Raman frequency shifts in the molecule scale, which provides important theoretical direction in making high-performance graphene nanocomposite. Meanwhile, this thin sheet (3~4μm) has high conductivity (512S/cm), good electromagnetic shielding property (about 27 dB in the frequency range between 0.3 and 12 GHz), corrosion and fatigue resistance. This kind of material enjoys a prospect of wide application in the fields of aerospace, automobile and soft electronic devices.
Fig.1. The process of making SBG sheets (A-B), photograph of an SBG sheet (C) and scanning
electron microscope images (D-E)
Fig.2. Mechanical property (A), electromagnetic shielding property (B) and Raman spectroscopy (C-F)
This research was supported by many projects, including the Excellent Young Scientist Fund of the National Natural Science Foundation of China, New Century Talents Scheme of the Ministry of Education, Hok Ying Dong Education Foundation, 111 Project, the National Science Foundation of the United States and so on.
The paper: http://www.pnas.org/content/early/2018/05/03/1719111115
The research team of Prof. Cheng: http://chengresearch.net/zh/home-cn/
Reported by Zhu Jingchao
Edited by Shi Yue
Translated by Liu Xinrui