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Publications since Joining Beihang University (2010–current)

New Publications

2021

86. Strong, conductive aramid fiber functionalized by graphene
    Can Cao, Jingsong Peng, Xiumin Liang, Eduardo Saiz, Stephan E. Wolf,Hanoch Daniel Wagner,Lei Jiang, Qunfeng Cheng* Composites Part A., 2021, 140,106161. DOI: 10.1016/j.compositesa.2020.106161
    Abstract
    The surface modification of aramid fibers is an essential and potent approach to manipulate and improve fiber properties. Biogenic fibers are in stark contrast, as exemplified by the case of natural silk fibers. This highperformance fiber features a surface functionalization as a thin sericin film enwraps it for improving the mechanical properties of silks. Inspired by this unique sheath structure of biogenic silk, we improved the performance of aramid fibers by exploiting a coating composed of reduced graphene oxide nanosheets that selfassemble on the fiber surface guided by hydrogen bonding and π-π stacking interactions. The graphene functionalized aramid fibers show a remarkable 1 GPa improvement in tensile strength. Moreover, the functionalized aramid fiber also shows high electrical conductivity which preserved 99% of its conductivity even after 100 cycles. Our approach provides a universal strategy for improving the performance of the fiber via surface functionalization by graphene nanosheets.
    | PDF | Supporting Information
87. High-strength scalable MXene films through bridging-induced densification
    Sijie Wan, Xiang Li, Ying Chen, Nana Liu, Yi Du, Shixue Dou, Lei Jiang, and Qunfeng Cheng*
    Science, 2021, 374(6563), 96-99. DOI:10.1126/science.abg2026
    Abstract
    MXenes are a growing family of two-dimensional transition metal carbides and/or nitrides that are densely stacked into macroscopically layered films and have been considered for applications such as flexible electromagnetic interference (EMI) shielding materials. However, the mechanical and electrical reliabilities of titanium carbide MXene films are affected by voids in their structure. We applied sequential bridging of hydrogen and covalent bonding agents to induce the densification of MXene films and removal of the voids, leading to highly compact MXene films. The obtained MXene films show high tensile strength, in combination with high toughness, electrical conductivity, and EMI shielding capability. Our high-performance MXene films are scalable, providing an avenue for assembling other two-dimensional platelets into high-performance films.
    | PDF | Supplementary Information
88. Stiff and tough PDMS-MMT layered nanocomposites visualized by AIE luminogens
    Jingsong Peng, Antoni P. Tomsia, Lei Jiang, Ben Zhong Tang* & Qunfeng Cheng*
    Nature Communications., 2021, 12, 4539. DOI: 10.1038/s41467-021-24835-w
    Abstract
    Polydimethylsiloxane (PDMS) is a widely used soft material that exhibits excellent stability and transparency. But the difficulty of fine-tuning its Young’s modulus and its low toughness significantly hinder its application in fields such as tissue engineering and flexible devices. Inspired by nacre, here we report on the development of PDMS-montmorillonite layered (PDMS-MMT-L) nanocomposites via the ice-templating technique, resulting in 23 and 12 times improvement in Young’s modulus and toughness as compared with pure PDMS. Confocal fluorescence microscopy assisted by aggregation-induced emission (AIE) luminogens reveals three-dimensional reconstruction and in situ crack tracing of the nacre-inspired PDMS-MMT-L nanocomposite. The PDMS-MMT-L nanocomposite is toughened with mechanisms such as crack deflection and bridging. The AIE-assisted visualization of the crack propagation for nacre-inspired layered nanocomposites provides an advanced and universal characterization technique for organic-inorganic nanocomposites.
    | PDF | Supporting Information
89. Strong Reduced Graphene Oxide Coated Bombyx mori Silk
    Can Cao, Zongkai Lin, Xiaochen Liu, Yanyan Jia, Eduardo Saiz, Stephan E. Wolf, Hanoch Daniel Wagner, Lei Jiang, Qunfeng Cheng*
    Adv. Funct. Mater., 2021, https://doi.org/10.1002/adfm.202102923. DOI:10.1002/adfm.202102923
    Abstract
    Bombyx mori silks possess great potential in textile industries due to the large-scale green production. However, the demand for silks with functional as well as mechanical properties are continuously rising due to the emergence of other functional textiles. It remains a great challenge to functionalize natural silk and simultaneously improve its mechanical properties. Inspired by the relationship between natural core–sheath structure and mechanical properties of cocoon silk, the application of a thin reduced graphene oxide (rGO) layer coated B. mori silk (GS) is shown via hydrogen interfacial interaction. The resultant rGO-coated silk exhibits a remarkable tensile strength of 1137.7 MPa and toughness of 304.5 MJ m−3, which are 1.9 and 2.6 times higher than that of pure B. mori silk, respectively. Moreover, the GS shows a high electrical conductivity of 0.37 S m−1 with great thermal and deformation sensitivity. The bioinspired approach provides a universal and facile strategy for functionalizing natural fibers by applying rGO nanosheets surface coating.
    | PDF | Supplementary Information
90. Bioinspired Color Switchable Photonic Crystal Silicone Elastomer Kirigami
    Xintao Lai, Jingsong Peng, Qunfeng Cheng, Antoni P. Tomsia, Guanlei Zhao, Lei Liu, Guisheng Zou, Yanlin Song, Lei Jiang, Mingzhu Li*
    Angew. Chem. Int. Ed., 2021, 60(20), 14307-14312. DOI: 10.1002/anie.202103045
    Abstract
    Bioinspired dynamic structural color has great potential for use in dynamic displays, sensors, cryptography, and camouflage. However, it is quite rare for artificial structural color devices to withstand thousands of cycles. Male hummingbird’s crowns and gorgets are brightly colored, demonstrating frequent color switching that is induced by regulating the orientation of the feathers through movement of skin or joints. Inspired by this unique structural color modulation, we demonstrate a flexible, mechanically triggered color switchable sheet based on a photonic crystal (PhC)-coated polydimethylsiloxane (PDMS) kirigami (PhC-PDMS kirigami) made by laser cutting. Finite element modeling (FEM) simulation reveals that the thickness of PDMS kirigami and the chamfer at the incision induced by laser cutting both dominate the out-of-plane deformation through in-plane stretching. The bioinspired PhC-PDMS kirigami shows precisely programmable structural color and keeps the color very well after recycling over 10 000 times. This bioinspired PhC-PDMS kirigami also shows excellent viewability even in bright sunlight, high readability, robust functionality, technical flexibility, and mechanical durability, which are readily exploitable for applications, such as chromic mechanical monitors for the sports industry or for medical applications, wearable camouflage, and security systems.
    | PDF | Supporting Information
91. Chemical Strategies for Making Strong Graphene Materials
    Tianzhu Zhou, Qunfeng Cheng*
    Angew. Chem. Int. Ed., 2021, https://doi.org/10.1002/anie.202102761. DOI:10.1002/anie.202102761
    Abstract
    Graphene materials have been widely applied in various fields because of their remarkable mechanical and electrical properties. However, two obstacles arise during the assembly of graphene platelets into macroscale graphene materials and composites that impair the performance of the resultant graphene materials: 1) the voids between the graphene platelets, and 2) the wrinkling of the graphene platelets. In the past decade, several strategies have been developed to eliminate these obstacles. These strategies result in strong macroscale graphene materials, such as graphene fibers with tensile strengths of over 3.4 GPa and sheets with tensile strengths of over 1.5 GPa, which have many practical applications. This Minireview summarizes the effective strategies for assembling graphene materials and compares their advantages and drawbacks. The preparation processes as well as the resulting fundamental mechanical properties and wide spectrum of electrical and magnetic properties are also discussed. Finally, our outlook for the future of this field is presented.
    | PDF | Supplementary Information
92. High-strength scalable graphene sheets by freezing stretch-induced alignmentSijie Wan, Ying Chen, Shaoli Fang, Shijun Wang, Zhiping Xu, Lei Jiang, Ray H. Baughman* and Qunfeng Cheng*Nature Materials, 2021, DOI: 10.1038/s41563-020-00892-2Abstract
    Efforts to obtain high-strength graphene sheets by near-room-temperature assembly have been frustrated by the misalignment of graphene layers, which degrades mechanical properties. While in-plane stretching can decrease this misalignment, it reappears when releasing the stretch. Here we use covalent and π–π inter-platelet bridging to permanently freeze stretch-induced alignment of graphene sheets, and thereby increase isotropic in-plane sheet strength to 1.55 GPa, in combination with a high Young’s modulus, electrical conductivity and weight-normalized shielding efficiency. Moreover, the stretch-bridged graphene

    sheets are scalable and can be easily bonded together using a commercial resin without appreciably decreasing the performance, which establishes the potential for practical applications.

    | PDF | Supporting Information

2020

79. Strong sequentially bridged MXene sheets
    Sijie Wan, Xiang Li, Yanlei Wang, Ying Chen, Xi Xie, Rui Yang, Antoni P. Tomsia, Lei Jiang,and Qunfeng Cheng*
    PNAS, 2020, 117(44), 27154-27161. DOI:10.1073/pnas.2009432117
    Abstract
    Titanium carbide (Ti3C2Tx) MXene has great potential for use in aerospace and flexible electronics due to its excellent electrical conductivity and mechanical properties. However, the assembly of MXene nanosheets into macroscopic high-performance nanocomposites is challenging, limiting MXene’s practical applications. Here we describe our work fabricating strong and highly conductive MXene sheets through sequential bridging of hydrogen and ionic bonding. The ionic bonding agent decreases interplanar spacing and increases MXene nanosheet alignment, while the hydrogen bonding agent increases interplanar spacing and decreases MXene nanosheet alignment. Successive application of hydrogen and ionic bonding agents optimizes toughness, tensile strength, oxidation resistance in a humid environment, and resistance to sonication disintegration and mechanical abuse. The tensile strength of these MXene sheets reaches up to 436 MPa. The electrical conductivity and weight-normalized shielding efficiency are also as high as 2,988 S/cm and 58,929 dB∙cm2/g, respectively. The toughening and strengthening mechanisms are revealed by molecular-dynamics simulations. Our sequential bridging strategy opens an avenue for the assembly of other high-performance MXene nanocomposites.
    | PDF | Supplementary Information
80. Design Principles of High-Performance Graphene Films: Interfaces and Alignment
    Sijie Wan, Lei Jiang, and Qunfeng Cheng*
    Matter, 2020, 3, 696-707. DOI:10.1016/j.matt.2020.06.023
    Abstract
    Graphene, the strongest, stiffest, and most conductive material known to date, would enable very strong, stiff, and highly conductive materials that would be better than what is available currently. These would be useful in a variety of fields, particularly flexible electronics and aerospace. Thus, to realize this potential, it is necessary to transfer these remarkable properties from graphene nanosheets into macroscopic graphene films. Nacre provides an inspiration for assembling graphene nanosheets into high-performance graphene films by constructing abundant interfacial interactions and a highly aligned structure. However, several issues in the assembly process,including intersheet bonding, dewrinkling, and alignment of graphene nanosheets, have been ignored in descriptions of previously reported macroscopic graphene films. This Review clarifies and compares the interface architecture of macroscopic graphene films described in previous reports. The representative orientation strategies are then summarized and the relationship between alignment and properties is discussed. Finally, perspectives and challenges are proposed to highlight the guidelines on how to construct high-performance graphene films in the future.
    | PDF | Supporting Information
81. Super-tough MXene-functionalized graphene sheets
    Tianzhu Zhou, Chao Wu, Yanlei Wang, Antoni P. Tomsia, Mingzhu Li, Eduardo Saiz, Shaoli Fang, Ray H. Baughman, Lei Jiang and Qunfeng Cheng*
    Nature Communications, 2020, 11, 2077. DOI: 10.1038/s41467-020-15991-6
    Abstract
    Flexible reduced graphene oxide (rGO) sheets are being considered for applications in portable electrical devices and flexible energy storage systems. However, the poor mechanical properties and electrical conductivities of rGO sheets are limiting factors for the development of such devices. Here we use MXene (M) nanosheets to functionalize graphene oxide platelets through Ti-O-C covalent bonding to obtain MrGO sheets. A MrGO sheet was crosslinked by a conjugated molecule (1-aminopyrene-disuccinimidyl suberate, AD). The incorporation of MXene nanosheets and AD molecules reduces the voids within the graphene sheet and improves the alignment of graphene platelets, resulting in much higher compactness and high toughness. In situ Raman spectroscopy and molecular dynamics simulations reveal the synergistic interfacial interaction mechanisms of Ti-O-C covalent bonding, sliding of MXene nanosheets, and π-π bridging. Furthermore, a supercapacitor based on our super-tough MXene-functionalized graphene sheets provides a combination of energy and power densities that are high for flexible supercapacitors.
    | PDF | Supplementary Information
82. Ultratough graphene-black phosphorus films
    Tianzhu Zhoua, Hong Ni, Yanlei Wang, Chao Wu, Hao Zhang, Jianqi Zhang, Antoni P. Tomsia, Lei Jiang and Qunfeng Cheng*
    PNAS, 2020, 117, 8727-8735. DOI: 10.1073/pnas.1916610117
    Abstract
    Graphene-based films with high toughness have many promising applications, especially for flexible energy storage and portable electrical devices. Achieving such high-toughness films, however, remains a challenge. The conventional mechanisms for improving toughness are crack arrest or plastic deformation. Herein we demonstrate black phosphorus (BP) functionalized graphene films with record toughness by combining crack arrest and plastic deformation. The formation of covalent bonding P-O-C between BP and graphene oxide (GO) nanosheets not only reduces the voids of GO film but also improves the alignment degree of GO nanosheets, resulting in high compactness of the GO film. After further chemical reduction and pi-pi stacking interactions by conjugated molecules, the alignment degree of rGO nanosheets was further improved, and the voids in lamellar graphene film were also further reduced. Then, the compactness of the resultant graphene films and the alignment degree of reduced graphene oxide nanosheets are further improved. The toughness of the graphene film reaches as high as approximately 51.8 MJ m(-3), the highest recorded to date. In situ Raman spectra and molecular dynamics simulations reveal that the record toughness is due to synergistic interactions of lubrication of BP nanosheets, P-O-C covalent bonding, and pi-pi stacking interactions in the resultant graphene films. Our tough black phosphorus functionalized graphene films with high tensile strength and excellent conductivity also exhibit high ambient stability and electromagnetic shielding performance. Furthermore, a supercapacitor based on the tough films demonstrated high performance and remarkable flexibility.
    | PDF | Supporting Information
83. Inverse nacre-like epoxy-graphene layered nanocomposites with integration of high toughness and self-monitoring
    Jingsong Peng, Chuanjin Huang, Can Cao, Eduardo Saiz, Yi Du, Shixue Dou, Antoni P. Tomsia, Hanoch Daniel Wagner, Lei Jiang, and Qunfeng Cheng*
    Matter, 2020, 2, 220-232. DOI: 10.1016/j.matt.2019.08.013
    Abstract
    Epoxy nanocomposites have many promising applications in the fields of aerospace and aeronautics, as well as many others. Achieving tough epoxy nanocomposites remains a great challenge, however. One inspiration for improving the mechanical properties of epoxy nanocompositesisnacre,which hasremarkable fracture toughness for its layered ‘brick-and-mortar’ architecture. Inspired by this, we fabricated a lamellar graphene scaffold by the freeze-casting technique. An alternating-layered epoxy-graphene nanocomposite was made by infiltrating epoxy into this graphene scaffold. As our epoxy-graphene nanocomposite consists of ~99 wt % organic epoxy, in contrast to nacre containing ~96 wt % inorganic aragonite, we call it an ‘inverse nacre-like’ epoxy-graphene layered nanocomposite. It exhibits exceptional fracture toughness, 3.61 times that of pure epoxy, and demonstrates anisotropic conductivity due to the anisotropic graphene scaffold, which can be used to detect cracks. Our bioinspired strategy provides a promising approach to combine excellent mechanical properties with functional properties to fabricate high-performance nanocomposites.
    | PDF | Supplementary Information 1 | Supplementary Information 4

2019

74. A Butterfly-Inspired Hierarchical Light-Trapping Structure towards a High-Performance Polarization-Sensitive Perovskite Photodetector
    Yan Zhan, Yang Wang, Qunfeng Cheng, Chang Li, Kaixuan Li, Huizeng Li, Jingsong Peng, Bo Lu, Yu Wang, Yanlin Song, Lei Jiang and Mingzhu Li*
    Angew. Chem. Int. Ed., 2019, 58, 16456-16462. DOI: 10.1002/anie.201908743
    Abstract
    Extensive applications for photodetectors have led to demand for high-responsivity polarization-sensitive light detection. Inspired by the elaborate architecture of butterfly Papilio paris, a 1D nanograting bonded porous 2D photonic crystal perovskite photodetector (G-PC-PD) using a commercial DVD master and 2D crystalline colloidal arrays template was fabricated. The coupling effect from grating diffraction and reflection of the PC stopband renders the enhanced light harvesting of G-PC-PD. The porous scaffold and nanoimprinting process afford a highly crystalline perovskite film. White light responsivity and detectivity of G-PC-PD are up to 12.67 A W(-1) and 3.22×10(13) Jones (6 approximately 7 times that of a pristine perovskite photodetector). The highly ordered nanograting arrays of G-PC-PD enable polarization-sensitive light detection with a rate of -0.72 nA deg(-1) . This hierarchical perovskite integrated nanograting and 2D PC architecture opens a new avenue to high-performance optoelectronic devices.
    | PDF | Supplementary Information
75. Moiré-Potential-Induced Band Structure Engineering in Graphene and Silicene
    Mengting Zhao, Jincheng Zhuang,* Qunfeng Cheng, Weichang Hao and Yi Du*
    Small, 2019, 1903769. DOI: 10.1002/smll.201903769
    Abstract
    A moiré pattern results from the projection of one periodic pattern to another with relative lattice constant or misalignment and provides great periodic potential to modify the electronic properties of pristine materials. In this Review, recent research on the effect of the moiré superlattice on the electronic structures of graphene and silicene, both of which possess a honeycomb lattice, is focused on. The moiré periodic potential is introduced by the interlayer interaction to realize abundant phenomena, including new generation of Dirac cones, emergence of Van Hove singularities (vHs) at the cross point of two sets of Dirac cones, Mott-like insulating behavior at half-filling state, unconventional superconductivity, and electronic Kagome lattice and flat band with nontrivial edge state. The role of interlayer coupling strength, which is determined by twist angle and buckling degree, in these exotic properties is discussed in terms of both the theoretical prediction and experimental measurement, and finally, the challenges and outlook for this field are discussed.
76. Near-Infrared-Driven Photocatalysts: Design, Construction, and Applications
    Li Wang, Xun Xu,* Qunfeng Cheng,* Shi Xue Dou, Yi Du*
    Small, 2019, 1904107. DOI: 10.1002/smll.201904107
    Abstract
    Photocatalysts, which utilize solar energy to catalyze the oxidation or reduction half reactions, have attracted tremendous interest due to their great potential in addressing increasingly severe global energy and environmental issues. Solar energy utilization plays an important role in determining photocatalytic efficiencies. In the past few decades, many studies have been done to promote photocatalytic efficiencies via extending the absorption of solar energy into near-infrared (NIR) light. This Review comprehensively summarizes the recent progress in NIR-driven photocatalysts, including the strategies to harvest NIR photons and corresponding photocatalytic applications such as the degradation of organic pollutants, water disinfection, water splitting for H2 and O2 evolution, CO2 reduction, etc. The application of NIR-active photocatalysts employed as electrocatalysts is also presented. The subject matter of this Review is designed to present the relationship between material structure and material optical properties as well as the advantage of material modification in photocatalytic reactions. It paves the way for future material design in solar energy–related fields and other energy conversion and storage fields.
    | PDF
77. Ultrastrong graphene films via long-chain π-bridging
    Sijie Wan, Ying Chen, Yanlei Wang, Guangwen Li, Guorui Wang, Luqi Liu, Jianqi Zhang, Yuzhou Liu, Zhiping Xu, Antoni, P. Tomsia, Lei Jiang, and Qunfeng Cheng*
    Matter, 2019, 1, 389-401. DOI: 10.1016/j.matt.2019.04.006
    Abstract
    Converting natural graphite to high-performance graphene films is very attractive due to graphite’s abundance. However, this conversion is challenging to do inexpensively and under ambient conditions. One of themajor challenges is how to design the interface between adjacent graphene nanosheets to integrate high strength, high toughness, and high conductivity into graphene films. Here, we demonstrate that a long-chain p-p bonding agent can bridge reduced graphene oxide nanosheets into ultrastrong, supertough, and highly conductive graphene films. The strain dependence of Raman frequency shift and molecular dynamics simulations together reveal the strengthening and toughening mechanisms. Additionally, the long-chain p-bridging induces substantial improvement in the graphene nanosheet alignment. The tensile strength and toughness are 1,054 MPa and 36 MJ/m3, surpassing those of reported graphene films. Meanwhile, the electrical conductivity reaches 1,192 S/cm, comparable with high-temperature annealed graphene films. The bioinspired strategy opens an avenue for the assembly of nanoscale building blocks into high-performance films.
    | PDF and Supplemental Information
78. Ultra‐tough inverse artificial nacre based on epoxy‐graphene by freeze‐casting
    Chuanjin Huang, Jingsong Peng, Sijie Wan, Yi Du, Shixue Dou, Hanoch Daniel Wagner, Antoni P. Tomsia, Lei Jiang, and Qunfeng Cheng*
    Angew. Chem. Int. Ed., 2019, 58, 7636-7640. DOI: 10.1002/anie.201902410
    Abstract
    Inspiration is drawn from natural nacre to fabricate ultra‐tough inverse artificial nacre based on epoxy‐graphene. As shown by Q. F. Cheng et al. in their Communication (DOI: 10.1002/anie.201902410), many graphene oxide nanosheets can be manipulated into lamellar scaffolds, similar to nacre‐like structure through freeze‐casting technique. The inverse nacre‐inspired concept provides a platform for the fabrication of high‐performance bulk nanocomposites.
    | PDF | Supplementary Information
79. Enhancing the strength, toughness, and electrical conductivity of twist-spun carbon nanotube yarns by π bridging
    Xiumin Liang, Yuan Gao, Jianli Duan, Zunfeng Liu, Shaoli Fang, Ray H. Baughman, Lei Jiang, Qunfeng Cheng*
    Carbon, 2019, 150, 268-274. DOI:10.1016/j.carbon.2019.05.023
    Abstract
    The weak interfacial interactions between carbon nanotube (CNT) always results in low stress load transfer efficiency in CNT yarns, herein we fabricated strong, highly conducting CNT yarns at room temperature using molecules having aromatic end groups, π bridging neighboring CNTs. The resulting CNT yarns have high tensile strength with 1697 ± 24 MPa, toughness with 18.6 ± 1.6 MJ/m3, and electrical conductivity with 656.2 S/cm, which are 3.9, 2.5, and 3.5 times, respectively, as high as that of the neat CNT yarn. The specific tensile strength of the resulting CNT yarn is higher than that for previously reported CNT yarns fabricated at room temperature, even that for some CNT yarns fabricated using corossive environments or extreme temperature. This π bridging strategy provides a promising avenue for fabricating high performance CNT yarns under ambient conditions.
    | PDF | Supplementary Information
80. Ultratough nacre-inspired epoxy–graphene composites with shape memory properties
    Chuanjin Huang, Jingsong Peng, Yiren Cheng, Qian Zhao, Yi Du, Shixue Dou, Antoni P. Tomsia, Hanoch Daniel Wagner, Lei Jiang, Qunfeng Cheng*
    Journal of Materials Chemistry A, 2019, 7, 2787-2794. DOI: 10.1039/c8ta10725d
    Abstract
    Shape memory polymers are widely used in industrial applications. Despite extensive and continuous research studies, it is still a great challenge to improve the mechanical properties without affecting their shape memory properties. One approach to improving them is to seek inspiration from natural materials that exhibit superior performance and provide an infinite source of design guidelines. Inspired by the hierarchical architecture of nacre, we have prepared nacre-like shape memory epoxy–graphene composites via freeze-casting, a technique to create lamellar materials with complex hierarchical microstructures. Perpendicular to the lamellar direction, the fracture toughness of our composites is
    2.5 times that of the epoxy matrix, due to the synergy of extrinsic toughening mechanisms combining crack deflection, crack branching, crack bridging, and friction between the layered platelets. We achieved high damage-tolerance in our composites by having some degree of plasticity to relax stresses in an epoxy layer. The shape memory properties can be activated using external heating. Due to the electrical conductivity of graphene, we have also achieved electro-active shape memory composites. Our approach suggests an avenue for producing bioinspired shape memory composites with good mechanical and multi-functional properties by utilizing the design principles and strengthening/ toughening mechanisms active in nacre and other biological materials.
    | PDF | Supplementary Information
81. Strong bioinspired HPA-rGO nanocomposite films via interfacial interactions for flexible supercapacitors
    Chao Wu, Tianzhu Zhou, Yi Du, Shixue Dou, Hao Zhang*, Lei Jiang, Qunfeng Cheng*
    Nano Energy, 2019, 58, 517-527. DOI:10.1016/j.nanoen.2019.01.055
    Abstract
    Flexible supercapacitors with excellent performance are needed to meet the increasing demand for wearable and flexible electronics. The challenge remains to design exceptionally flexible supercapacitors with remarkable electrochemical properties. Natural nacre shows outstanding fracture toughness due to its alternating inorganic and organic layered structure and abundant interfacial interactions, providing an inspiration for designing flexible supercapacitors. Herein, we demonstrated nacre-inspired flexible supercapacitors via synergistic interfacial interactions of π-π conjugated bonds, hydrogen bonding, and electrostatic interaction between halloysite (HA)-polyaniline (PANI) nanocomposites and graphene oxide (GO) nanosheets. The resultant nacre-inspired HPA-rGO nanocomposite films demonstrate strong tensile strength (351.9 MPa), high electrical conductivity (397.0 S cm−1), and long cycle life with ~85% of capacitance retention after 10,000 cycles. Furthermore, the assembled all-solid-state supercapacitors (ASSSs) based on bioinspired HPA-rGO electrodes can not only display extraordinary flexibility with no decay of capacitance behavior after 5000 bending cycles, but also deliver remarkable mass energy density up to 16.3 Wh kg−1, outperforming other flexible graphene-based supercapacitors. This nacre-inspired strategy for designing flexible electrodes provides an avenue for the next-generation power source in the fields of aerospace and smart wearable electronics.
    | PDF | Supplementary Information

2018

66. Ultratough Bioinspired Graphene Fiber via Sequential Toughening of Hydrogen and Ionic Bonding
    Xiaohui Wang, Jingsong Peng, Yuanyuan Zhang, Mingzhu Li, Eduardo Saiz, Antoni P. Tomsia, Qunfeng Cheng*
    ACS Nano, 2018, 12, 12638-12645. DOI:10.1021/acsnano.8b07392
    Abstract
    Graphene-based fibers synthesized under ambient temperature have not achieved excellent mechanical properties of high toughness or tensile strength compared with those synthesized by hydrothermal strategy or graphitization and annealing treatment. Inspired by the relationship between organic/inorganic hierarchical structure, interfacial interactions, and moderate growth temperature of natural nacre, we fabricate an ultratough graphene fiber via sequential toughening of hydrogen and ionic bonding through a wet-spinning method under ambient temperature. A slight amount of chitosan is introduced to form hydrogen bonding with graphene oxide nanosheets, and the ionic bonding is formed between graphene oxide nanosheets and divalent calcium ions. The optimized sequential toughening of hydrogen and ionic bonding results in an ultratough graphene fiber with toughness of 26.3 MJ/m(3) and ultimate tensile strength of 743.6 MPa. Meanwhile, the electrical conductivity of the resultant graphene fiber is as high as 179.0 S/cm. This kind of multifunctional graphene fiber shows promising applications in photovoltaic wires, flexible supercapacitor electrodes, wearable electronic textiles, fiber motors, etc. Furthermore, the strategy of sequential toughening of hydrogen and ionic bonding interactions also offers an avenue for constructing high-performance graphene-based fibers in the near future.
    | PDF | Supplementary Information
67. Synergistic reinforcing effect from graphene and carbon nanotubes
    Xiumin Liang, Qunfeng Cheng*
    Composites Communications, 2018, 10, 122-128. DOI:10.1016/j.coco.2018.09.002
    Abstract
    Carbon nanomaterials show excellent physicochemical properties, especially for carbon nanotubes (CNTs) and graphene nanosheets. A large amount of bioinspired hybrid materials based on graphene/CNTs have been reported. The mechanical and electrical properties of resultant carbon nanomaterials based hybrid materials have been dramatically improved, indicating the synergistic effect between carbon nanotubes and graphene. In fact, the synergistic effect always plays a key role in the natural materials such as nacre and bone, and bioinspired materials based on carbon nanomaterials. Herein, this mini-review summarizes recent progress in synergistic effect from CNTs and graphene in the bioinspired hybrid materials and also make the perspective of the synergistic reinforcing effect from CNTs and graphene in enhancing the performance of carbon nanomaterialsbased nanocomposites.
    | PDF
68. Bioinspired Supertough Graphene Fiber through Sequential Interfacial Interactions
    Yuanyuan Zhang, Jingsong Peng, Mingzhu Li, Eduardo Saiz, Stephan E. Wolf, Qunfeng Cheng*
    ACS Nano, 2018, 12, 8901-8908. DOI:10.1021/acsnano.8b04322
    Abstract
    Natural nacre exhibits extraordinary functional and structural diversity, combining high strength and toughness. The mechanical properties of nacre are attributed to (i) a highly arranged hierarchical layered structure of inorganic minerals (95 vol %) containing a small amount only of organic materials (5 vol %), (ii) abundant synergistic interfacial interactions, and (iii) formation under ambient temperature. Herein, inspired by these three design principles originating from natural nacre, the supertough bioinspired graphene-based nanocomposite fibers (BGNFs) are prepared under room temperature via sequential interfacial interactions of ionic bonding and pi-pi interactions. The resultant synergistic effect leads to a super toughness of 18.7 MJ m-3 as well as a high tensile strength of 740.1 MPa. In addition, the electrical conductivity of these supertough BGNFs is as high as 384.3 S cm-1. They can retain almost 80% of this conductivity even after 1000 cycles of loading-unloading testing, which makes these BGNFs promising candidates for application in flexible and stable electrical devices, such as strain sensors and actuators.
    | PDF | Supplementary Information
69. Strong, Conductive, Foldable Graphene Sheets by Sequential Ionic and pi Bridging
    Sijie Wan, Shaoli Fang, Lei Jiang, Qunfeng Cheng*, Ray H. Baughman*
    Adv. Mater., 2018, e1802733-e1802733. DOI:10.1002/adma.201802733
    Abstract
    The goal of this work is to develop an inexpensive low-temperature process that provides polymer-free, high-strength, high-toughness, electrically conducting sheets of reduced graphene oxide (rGO). To develop this process, we have evaluated the mechanical and electrical properties resulting from the application of an ionic bonding agent (Cr3+ ), a pi-pi bonding agent comprising pyrene end groups, and their combinations for enhancing the performance of rGO sheets. When only one bonding agent was used, the pi-pi bonding agent is much more effective than the ionic bonding agent for improving both the mechanical and electrical properties of rGO sheets. However, the successive application of ionic bonding and pi-pi bonding agents maximizes tensile strength, toughness, long-term electrical stability in various corrosive solutions, and resistance to mechanical abuse and ultrasonic dissolution. Using a combination of ionic bonding and pi-pi bonding agents, high tensile strength (821 MPa), high toughness (20 MJ m-3 ), and electrical conductivity (416 S cm-1 ) were obtained, as well as remarkable retention of mechanical and electrical properties during ultrasonication and mechanical cycling by both sheet stretch and sheet folding, suggesting high potential for applications in aerospace and flexible electronics.
    | PDF | Supplementary Information
70. Role of Interface Interactions in the Construction of GO-Based Artificial Nacres
    Sijie Wan, and Qunfeng Cheng*
    Adv. Mater. Interfaces, 2018, 1800107. DOI:10.1002/admi.201800107
    Abstract
    The hierarchical interfacial architecture of nacre inspires the fabrication of
    novel high performance graphene-based nanocomposites. Graphene has
    great promise for applications in aerospace and especially for flexible electronic devices, etc., due to its remarkable mechanical and electrical properties.Thus, it is significant to summarize the role of interface interactions in the construction of nacre-inspired graphene-based nanocomposites, which is the distinctive characteristic and important scientific progress of the review. This review first makes a comparison for the interfacial architecture of above biological materials and finds inspiration from nacre to design the interface in graphene-based nanocomposites, which contains single interface interaction, synergistic interface interactions, and synergistic building blocks. Then, the focus is attached to the effect of different interfacial design strategies on the mechanical and electrical properties of state-of-the-art GO-based artificial nacres (GANs), including 1D fibers, 2D films, and 3D bulk materials. Additionally, the multifunctional GANs with such functions as fatigue resistance, fire retardant property, and smart nanogating, etc. are also discussed. Moreover, some potential applications and corresponding challenges and solutions of GANs are detailedly summarized. Finally, from the views of theoretical simulation and experimental research, a perspective on the roadmap of GANs in the future is also proposed.
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71. Multiple Synergistic Toughening Graphene Nanocomposites through Cadmium Ions and Cellulose Nanocrystals
    Yuan Gao, Hanjie Xu, and Qunfeng Cheng*
    Adv. Mater. Interfaces, 2018, 1800145. DOI:10.1002/admi.201800145
    Abstract
    Robust and functional graphene-based nanocomposites are attractive in flexible electric devices. Herein, a strong and conductive bioinspired graphenebased
    nanocomposite is demonstrated via multiple synergistic toughening effect from graphene oxide (GO), cellulose nanocrystals (CNC), and cadmium ion (Cd2+). The multiple synergistic toughening effect can be realized from building blocks of 2D GO nanosheets and 1D CNC, interface interactions of hydrogen bonding from CNC and ionic bonding from Cd2+, resulting in
    integrated graphene-based nanocomposites with high strength, and toughness as well as electrical conductivity. This ternary synthetic graphene-based nanocomposite possessing outstanding physical properties provides a clear vision in the application of flexible electric devices. Furthermore, this bioinspired strategy could also serve as a guideline for the development of highperformance graphene-based nanocomposites in the future.
    | PDF | Supplementary Information
72. Glycera-Inspired Synergistic Interfacial Interactions for Constructing Ultrastrong Graphene-Based Nanocomposites
    Yiren Cheng, Jingsong Peng, Hanjie Xu, and Qunfeng Cheng*
    Adv. Funct. Mater., 2018, 1800924. DOI:10.1002/adfm.201800924
    Abstract
    The interest in bioinspired graphene-based nanocomposites (BGBNs) is rising recently due to their exceptional mechanical properties as well as high electrical conductivities. Numerous works have suggested that the synergistic interfacial design of ionic bonding (IB) co-working with other interfacial interactions effectively improves the mechanical properties of BGBNs. However, as the ions are conventionally chelated with graphene oxide (GO) nanosheets, the relatively weak and short interlayered IB may hinder the load transfer between GO nanosheets leading to poor synergistic effects. Herein, inspired by the jaw of Glycera, the synergistic effect is further amplified via special IB, which stiffens the organic component. Compared with the traditional IB, the metal–ligand coordinate bonding by copper ions that is used in this work and originates from Glycera, selectively cross-links the chitosan chains. This Glycera-inspired synergistic effect strategy boosts record tensile strength to an extraordinary value of 868.6 MPa, five times higher than that of the pure reduced graphene oxide film. The additional high electrical conductivity enables applications in many fields such as flexible energy devices, supercapacitors, and other electronic devices.
    
    | PDF|Supplementary Information
73. Sequentially bridged graphene sheets with high strength, toughness, and electrical conductivity
    Sijie Wan, Yuchen Li, Jiuke Mu, Ali E. Aliev, Shaoli Fang, Nicholas A. Kotov, Lei Jiang, Qunfeng Cheng* and Ray H. Baughman*
    PNAS, 2018, 115, 5359-5364. DOI:10.1073/pnas.1719111115
    Abstract
    We here show that infiltrated bridging agents can convert inexpensively fabricated graphene platelet sheets into high-performance materials, thereby avoiding the need for a polymer matrix. Two types of bridging agents were investigated for interconnecting graphene sheets, which attach to sheets by either π–π bonding or covalent bonding. When applied alone, the π–π bonding agent is most effective. However, successive application of the optimized ratio of π–π bonding and covalent bonding agents provides graphene sheets with the highest strength, toughness, fatigue resistance, electrical conductivity, electromagnetic interference shielding efficiency, and resistance to ultrasonic dissolution. Raman spectroscopy measurements of stress transfer to graphene platelets allow us to decipher the mechanisms of property improvement. In addition, the degree of orientation of graphene platelets increases with increasing effectiveness of the bonding agents, and the interlayer spacing increases. Compared with other materials that are strong in all directions within a sheet, the realized tensile strength (945 MPa) of the resin-free graphene platelet sheets was higher than for carbon nanotube or graphene platelet composites, and comparable to that of commercially available carbon fiber composites. The toughness of these composites, containing the combination of π–π bonding and covalent bonding, was much higher than for these other materials having high strengths for all in-plane directions, thereby opening the path to materials design of layered nanocomposites using multiple types of quantitatively engineered chemical bonds between nanoscale building blocks.
    | PDF|Supplementary Information
74. A new strategy for air-stable black phosphorus reinforced PVA nanocomposites
    Hong Ni, Xiaochen Liu, Qunfeng Cheng*
    J. Mater. Chem. A, 2018, 6, 7142-7147. DOI:10.1039/c8ta00113h
    Abstract
    Black phosphorus (BP) has attracted extensive scientific interest due to its particularly unique electrical properties. In recent years, an increasing number of researchers have shown great interest in the electrical and optical performance of BP in practical applications. However, the exploration of its mechanical properties is rare because BP tends to be oxidized in the atmosphere. In this study, BP nanosheets as two-dimensional nanofillers were used to reinforce the poly(vinyl alcohol) (PVA) matrix. The resultant BP-PVA nanocomposites presented excellent air-stability due to the formation of saturated P-O bonds outside the PVA-coated BP nanosheets. In addition, friction between the BP nanosheets and the PVA matrix led to increased strength, toughness, and modulus, which was confirmed by Raman spectrum analysis. The maximum tensile strength is up to 316.9 +/- 12.1 MPa, which is 1.9-times higher than that of a pure PVA film. This strengthening effect of BP in the PVA matrix is superior to that of graphene reinforced PVA nanocomposites with similar content of graphene, indicating a favorite mechanical increase of BP in nanocomposites.
    | PDF|Supplementary Information
75. Smart Nacre-inspired Nanocomposite
    Jingsong Peng and Qunfeng Cheng*
    Chemphyschem, 2018, 19, 1-8. DOI:10.1002/cphc.201701390
    PDF
76. Bioinspired graphene-based nanocomposites via ionic interfacial interactions
    Shanshan Gong, and Qunfeng Cheng*
    Composites Communications, 2018, 7, 16-22. DOI: 10.1016/j.coco.2017.12.002
    Abstract
    In nature, small amount of metal ions play a critical role in improving mechanical properties, such as the jaws of marine polychaete Nereis and Glycera. Recently, the multivalent cations metals have been successfully introduced to enhance the interfacial strength of graphene based-nanocomposites through forming ionic crosslinking networks with graphene oxide (GO) nanosheets by coordination. Combination with other interfacial interactions, the synergistic effect was constructed in the resultant bioinspired nanocomposites, leading to outstanding integrated performance, including thermal, electrical, fatigue resistant and mechanical properties. These excellent properties make this bioinspired graphene-based nanocomposites to be great candidates for applications in many fields, for example, flexible electronics devices, artificial muscles, supercapacitors, and aerospace.
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2017

55. Bioinspired graphene membrane with temperature tunable channels for water gating and molecular separation
    Jingchong Liu, Nü Wang*, Li-Juan Yu, Amir Karton, Wen Li, Weixia Zhang, Fengyun Guo, Lanlan Hou, Qunfeng Cheng, Lei Jiang, David A. Weitz and Yong Zhao*
    Nat. Commun., 2017, 8, 2011. DOI:10.1038/s41467-017-02198-5
    Abstract
    Smart regulation of substance permeability through porous membranes is highly desirable for membrane applications. Inspired by the stomatal closure feature of plant leaves at relatively high temperature, here we report a nano-gating membrane with a negative temperature-response coefficient that is capable of tunable water gating and precise small molecule separation. The membrane is composed of poly(N-isopropylacrylamide) covalently bound to graphene oxide via free-radical polymerization. By virtue of the temperature tunable lamellar spaces of the graphene oxide nanosheets, the water permeance of the membrane could be reversibly regulated with a high gating ratio. Moreover, the space tunability endows the membrane with the capability of gradually separating multiple molecules of different sizes. This nano-gating membrane expands the scope of temperature-responsive membranes and has great potential applications in smart gating systems and molecular separation.
    | PDF | Supplementary Information
56. High Performance Nanocomposites Inspired by Nature
    Jingsong Peng, and Qunfeng Cheng*
    Adv. Mater., 2017, 29, 1702959. DOI:10.1002/adma.201702959
    Abstract
    Natural materials, including nacre, bone, and the lobster cuticle, exhibit excellent mechanical properties, combining high strength and toughness. Such materials have the added benefit of being light in weight. These advantageous features are due to such natural materials’ orderly hierarchical architectures and abundant interface interactions. How to utilize these design principles created by nature to fabricate high-performance bioinspired nanocomposites remains a great research challenge. A logical roadmap for developing these nanocomposites can be described as “discovery, invention, and creation.” Here, the discovery of the relationship between natural materials’ design principles and such materials’ extraordinary mechanical properties is discussed. Then, the invention of bioinspired strategies for mimicking natural materials is considered and representative strategies addressed. Next, the creation of multifunctional nanocomposites is discussed and bioinspired nanocomposites, including fiber nanocomposites, 2D film nanocomposites, and 3D bulk nanocomposites reviewed. Finally, a perspective and outlook for future directions in making bioinspired nanocomposites is provided to offer inspiration to the community and a clear vision for future research.
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57. Fatigue Resistant Bioinspired Graphene-Based Nanocomposites
    Sijie Wan, and Qunfeng Cheng*
    Adv. Funct. Mater., 2017, 27, 1703459. DOI: 10.1002/adfm.201703459
    Abstract
    Graphene is an attractive building block for constructing functional materials of flexible electronic devices, due to its extraordinary mechanical and electrical properties. Up to now, large amounts of high-performance graphenebased nanocomposites are fabricated. However, the fatigue behavior of graphene-based nanocomposites, a key parameter for flexible electronic devices, is rarely investigated. According to the fatigue mechanisms of thermosetting polymer composites, the fatigue resistance of graphene-based nanocomposites can be significantly improved by effectively restricting the crack growth. Natural nacre demonstrates unique multisuppression of crack propagation, which is attributed to its sophisticated interfacial architecture over multiple length scales, resulting in remarkable fracture toughness. The crack suppression mechanisms corresponding to different interfacial design strategies within bioinspired graphene-based nanocomposites (BGBNs) are summarized in this feature article. The static mechanical properties, electrical conductivity, and fatigue resistance of these BGBNs are compared and discussed. The synergistic effect from various interfacial interactions and building blocks is highlighted to serve as the guidance for constructing novel fatigue-resistant BGBNs. The promising applications of fatigue-resistant BGBNs in flexible electronic devices are reviewed, and several challenges and corresponding solutions are proposed. The perspective of fatigue-resistant BGBNs for fundamental research and commercial application is depicted.
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58. Freeze Casting for Assembling Bioinspired Structural Materials
    Qunfeng Cheng, Chuanjin Huang, and Antoni P. Tomsia*
    Adv. Mater., 2017, 1703155. DOI:10.1002/adma.201703155
    Abstract
    Nature is very successful in designing strong and tough, lightweight materials. Examples include seashells, bone, teeth, fish scales, wood, bamboo, silk, and many others. A distinctive feature of all these materials is that their properties are far superior to those of their constituent phases. Many of these natural materials are lamellar or layered in nature. With its “brick and mortar” structure, nacre is an example of a layered material that exhibits extraordinary physical properties. Finding inspiration in living organisms to create bioinspired materials is the subject of intensive research. Several processing techniques have been proposed to design materials mimicking natural materials, such as layer-by-layer deposition, self-assembly, electrophoretic deposition, hydrogel casting, doctor blading, and many others. Freeze casting, also known as ice-templating, is a technique that has received considerable attention in recent years to produce bioinspired bulk materials. Here, recent advances in the freeze-casting technique are reviewed for fabricating lamellar scaffolds by assembling different dimensional building blocks, including nanoparticles, polymer chains, nanofibers, and nanosheets. These lamellar scaffolds are often infiltrated by a second phase, typically a soft polymer matrix, a hard ceramic matrix, or a metal matrix. The unique architecture of the resultant bioinspired structural materials displays excellent mechanical properties. The challenges of the current research in using the freeze-casting technique to create materials large enough to be useful are also discussed, and the technique’s promise for fabricating high-performance nacre-inspired structural materials in the future is reviewed.
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59. Fatigue Resistant Bioinspired Composite from Synergistic Two-Dimensional Nanocomponents
    Sijie Wan, Qi Zhang, Xiaohang Zhou, Dechang Li, Baohua Ji, Lei Jiang, and Qunfeng Cheng*
    ACS Nano, 2017, 11, 7074‐7083. DOI:10.1021/acsnano.7b02706
    Abstract
    Portable and wearable electronics require much more flexible graphene-based electrode with high fatigue life, which could repeatedly bend, fold, or stretch without sacrificing its mechanical properties and electrical conductivity. Herein, a kind of ultrahigh fatigue resistant graphene-based nanocomposite via tungsten disulfide (WS2) nanosheets is synthesized by introducing a synergistic effect with covalently cross-linking inspired by the orderly layered structure and abundant interfacial interactions of nacre. The fatigue life of resultant graphene-based nanocomposites is more than one million times at the stress level of 270 MPa, and the electrical conductivity can be kept as high as 197.1 S/cm after 1.0 × 105 tensile testing cycles. These outstanding properties are attributed to the synergistic effect from lubrication of WS2 nanosheets for deflecting crack propagation, and covalent bonding between adjacent GO nanosheets for bridging crack, which is verified by the molecular dynamics (MD) simulations. The WS2 induced synergistic effect with covalent bonding offers a guidance for constructing graphene-based nanocomposites with high fatigue life, which have great potential for applications in flexible and wearable electronic devices, etc.
    | PDF | Supplementary Information
60. Superior Fatigue Resistant Bioinspired Graphene-Based Nanocomposite via Synergistic Interfacial Interactions
    Sijie Wan, Feiyu Xu, Lei Jiang, and Qunfeng Cheng*
    Adv. Funct. Mater., 2017, 27, 1605636. DOI:10.1002/adfm.201605636
    Abstract
    Excellent fatigue resistance is a prerequisite for flexible energy devices to achieve high and stable performance under repeated deformation state. Inspired by the sophisticated interfacial architecture of nacre, herein a super fatigue-resistant graphene-based nanocomposite with integrated high tensile strength and toughness through poly(dopamine)-nickel ion (Ni2+) chelate architecture that mimics byssal threads is demonstrated. These kind of synergistic interfacial interactions of covalent and ionic bonding effectively suppress the crack propagation in the process of fatigue testing, resulting in superhigh fatigue life of this bioinspired graphene-based nanocomposite (BGBN). In addition, the electrical conductivity is well kept after fatigue testing. The proposed synergistic interfacial interactions could serve as a guideline for fabricating high-performance multifunctional BGBNs with promising applications in flexible energy devices, such as flexible electrodes for supercapacitors and lithium batteries, etc.
    | PDF | Supplementary Information
61. Thermochromic Artificial Nacre Based on Montmorillonite
    Jingsong Peng, Yiren Cheng, Antoni P. Tomsia, Lei Jiang, and Qunfeng Cheng*
    ACS Appl. Mater. Interfaces, 2017, 9, 24993‐24998. DOI:10.1021/acsami.7b07953
    Abstract
    Nacre-inspired nanocomposites have attracted a great deal of attention in recent years because of their special mechanical properties and universality of the underlying principles of materials engineering. The ability to respond to external stimuli will augment the high toughness and high strength of artificial nacre-like composites and open new technological horizons for these materials. Herein, we fabricated robust artificial nacre based on montmorillonite (MMT) that combines robustness with reversible thermochromism. Our artificial nacre shows great potential in various fields such as aerospace and sensors and opens an avenue to fabricate artificial nacre responsive to other external stimuli in the future.
    
    | PDF | Supplementary Information
62. Robust Bioinspired Graphene Film via π–π Cross-linking
    Hong Ni, Feiyu Xu, Antoni P. Tomsia, Eduardo Saiz, Lei Jiang, and Qunfeng Cheng*
    ACS Appl. Mater. Interfaces, 2017, 9, 24987‐24992. DOI:10.1021/acsami.7b07748
    Abstract
    Graphene composite films inspired by nacre are the subject of ongoing research efforts to optimize their properties for applications in flexible energy devices. Noncovalent interactions do not cause interruption of the delocalized conjugated π-electron system, thus preserving graphene’s excellent properties. Herein, we synthesized a conjugated molecule with pyrene groups on both ends of a long linear chain (AP-DSS) from 1-aminopyrene (AP) and disuccinimidyl suberate (DSS). The AP-DSS molecules are used to cross-link adjacent graphene nanosheets via π–π interfacial interactions to improve properties of graphene films. The tensile strength and toughness of resultant graphene films were 4.1 and 6.4 times higher, respectively, than that of pure rGO film. More remarkably, the electrical conductivity showed a simultaneous improvement, which is rare to be achieved in other kinds of covalent or noncovalent functionalization. Such integration demonstrates the advantage of this work to previously reported noncovalent functionalization of graphene.
    | PDF | Supplementary Information
63. Learning from nacre: Constructing polymer nanocomposites
    Chuanjin Huang, and Qunfeng Cheng*
    Compos. Sci. Technol., 2017, 150, 141‐166. DOI:http://dx.doi.org/10.1016/j.compscitech.2017.07.021
    Abstract
    Due to the small size and special physical properties of nanometer materials, polymer nanocomposites, combined nanoscale reinforcements with polymer matrix, possess outstanding mechanical properties and functional performances, which play a key role in many fields, especially for application in fields of industry and aerospace. However, poor dispersion and weak interfacial interactions are the critical factors that restrict the great improvement in performance of polymer nanocomposites. Although these issues have been solved in some extent via various methods, such as surfactant adsorption, polymer wrapping, surface modification, it still remains a great challenge for achieving high performance polymer
    nanocomposites as theoretically expected. Nacre, with 95% (volume fraction) inorganic calcium carbonate and 5% (volume fraction) biopolymers, is a typical binary cooperative complementary material system with hard inorganic component and soft organic matrix. Its typical “brick-and-mortar” hierarchical micro/nano-scale structure provides an excellent guideline for constructing polymer nanocomposites. It skillfully overcomes the bottleneck of traditional approaches for fabricating polymer nanocomposites, such as poor dispersion, low loading, and weak interfacial interactions. Recently, we have successfully demonstrated the bioinspired concept is a successful approach for constructing high performance polymer nanocomposites based on different reinforcement fillers, such as nanoclay, carbon nanotubes, and graphene. The resultant bioinspired polymer nanocomposites (BPNs) show layered hierarchical micro/nano-scale structure and outstanding mechanical properties. This feature article reviews our group’s work and other groups’ research results on BPNs in recent years, and discuss the advantages of BPNs through comparing with traditional methods, as shown in Fig. 1, including: i) Bioinspired assembly approaches for achieving the homogeneous dispersion and layered structure of reinforcement fillers in polymer matrix, such as layer-by-layer, infiltration, evaporation, freeze casting.; ii) various approaches for designing interfacial interactions; iii) the effect of synergy on the performance of BPNs; iv) representative applications of BPNs, such as energy storage devices, filter, sensors. Finally, this feature article also focuses on a perspective of BPNs, commenting on whether the bioinspired concept is viable and practical for polymer nanocomposites, and on what has been achieved to date. Most importantly, a roadmap of BPNs for near future will be depicted, including integrated mechanical properties and functions, intelligent properties, etc.
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64. Synergistically toughening nacre-like graphene nanocomposites via gel-film transformation
    Shanshan Gong, Qi Zhang, Ruliang Wang, Lei Jiang, and Qunfeng Cheng*
    J. Mater. Chem. A, 2017, 5, 16386-16392. DOI:10.1039/C7TA03535G
    Abstract
    The gold standard of natural nacre provides the inspiration for assembling bioinspired nanocomposites. Herein, the gel-film transformation method, a feasible and economical strategy, was applied to fabricate flexible, large-area, and hierarchical porous graphene oxide (GO)-based nanocomposites with excellent properties. In this study, the GO-polymer nanocomposite hydrogels could be transformed into nanocomposite films with hierarchically laminated structures via the evaporation self-assembly technique, followed by introduction of ionic cross-linking into the nanocomposite films. The obtained bioinspired nanocomposites, with synergistic effect originating from hydrogen bonds and ionic bonds, have an excellent tensile strength of 475.2 +/- 13.0 MPa and a toughness of 6.6 +/- 0.3 MJ m-3, as well as a high electrical conductivity of 297.1 S cm-1. Therefore, this type of strong integrated nacre-like graphene nanocomposites have great potential applications in aerospace and flexible supercapacitor electrodes.
    
    | PDF | Supplementary Information
65. Mimicking Nacre by Ice Templating
    Qunfeng Cheng, and Lei Jiang*
    Angew. Chem. Int. Ed., 2017, 56, 934-935. DOI:10.1002/anie.201610176
    PDF
66. Learning from nature: constructing high performance graphene-based nanocomposites
    Shanshan Gong, Hong Ni, Lei Jiang, and Qunfeng Cheng*
    ‎Mater. Today, 2017, 20, 210-219. DOI: 0.1016/j.mattod.2016.11.002
    Abstract
    After billions of years of evolution, natural materials, such as bamboo, bone, and nacre, show unique mechanical properties, due to their intrinsic hierarchical micro/nanoscale architecture and abundant interfacial interactions. This relationship between architecture, interfacial interactions, and mechanical properties of natural materials, supplies the inspiration for constructing high performance lightweight nanocomposites. Graphene’s high tensile strength, Young’s modulus, and electrical conductivity when compared with other nanomaterials make it an ideal building block for constructing high performance bioinspired nanocomposites. Such nanocomposites demonstrate promise for applications in many fields, including aerospace, aeronautics, submarine devices, car, and flexible electronic devices. In this review, we focus on the bioinspired strategy for preparing graphene-based nanocomposites (GBNs), and discuss the various interfacial interactions. Then the synergistic effects from building blocks and interfacial interactions are discussed in detail, along with the resultant GBNs used in the applications of sensors, actuators, supercapacitors, and nanogenerators, are also illustrated. These GBNs include, for example, one-dimensional (1D) fiber, two-dimensional (2D) film, and three-dimensional (3D) bulk nanocomposites. Finally, we provide our perspective on GBNs, and discuss how to efficiently mimic natural materials for creating new multifunctional bioinspired nanocomposites for practical applications in the near future.
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67. Super-tough artificial nacre based on graphene oxide via synergistic interface interactions of π-π stacking and hydrogen bonding
    Pingan Song*, Zhiguang Xu, Yuanpeng Wu, Qunfeng Cheng*, Qipeng Guo*, and Hao Wang
    Carbon, 2017, 111, 807-812. DOI: 10.1016/j.carbon.2016.10.067
    Abstract
    Inspired by interfacial interactions of protein matrix and the crystal platelets in nacre, herein, a super-tough artificial nacre was produced through constructing the synergistic interface interactions of π-π interaction and hydrogen bonding between graphene oxide (GO) nanosheets and sulfonated styrene-ethylene/butylene-styrene copolymer synthesized with multifunctional benzene. The resultant GO-based artificial nacre showed super-high toughness of 15.3 ± 2.5 MJ/m3, superior to natural nacre and other GO-based nanocomposites. The ultra-tough property of the novel nacre was attributed to synergistic effect of π-π stacking interactions and hydrogen bonding. This bioinspired synergistic toughening strategy opens a new avenue for constructing high performance GO-based nanocomposites in the near future.
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2016

42. Bioinspired robust nanocomposites of cooper ions and hydroxypropyl cellulose synergistic toughening graphene oxide
    Qi Zhang, Sijie Wan, Lei Jiang, and Qunfeng Cheng*
    Sci. China Tech. Sci., 2016, 60, 758-764. DOI: 10.1007/s11431-016-0529-3
    Abstract
    The hierarchical micro/nanoscale layered formation of organic and inorganic components of natural nacre, results in abundant interfacial interactions, providing an inspiration for fabricating bioinspired nanocomposites through constructing the interfacial interactions. Herein, we demonstrated the synergistic interfacial interactions of hydrogen bonding from hydroxypropyl cellulose and ionic bonding from copper ions upon the reduced graphene oxide based bioinspired nanocomposites, which show the integrated tensile strength, toughness and excellent fatigue-resistant property, as well as high electrical conductivity. These extraordinary properties allow this kind of bioinspired nanocomposites to potentially utilize in the fields of aerospace, flexible electronics devices, etc. This study also opens a door for fabricating excellent mechanical performance graphene-based bioinspired nanocomposites via synergistic interfacial interactions in the future.
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43. Robust bioinspired graphene-based nanocomposites via synergistic toughening of zinc ions and covalent bonding
    Shanshan Gong, Lei Jiang, and Qunfeng Cheng*
    J. Mater. Chem. A, 2016, 4, 17073-17079. DOI: 10.1039/C6TA06893F
    Abstract
    Robust graphene-based nanocomposites show promising applications in fields of flexible, wearable and intelligent devices. But, it is still a big challenge to construct high performance macroscopic graphene-based nanocomposites for practical application through cost-efficient graphene oxide (GO) nanosheets. Inspired by the hierarchical layered structure and interfacial interactions of nacre, we demonstrated robust graphene-based nanocomposites via synergistic interfacial interactions, which are constructed via divalent ions of zinc (Zn²⁺⁾, and linear molecules of 10,12-pentacosadiyn-1-ol (PCDO) with GO nanosheets. The synergistic interfacial interactions result in integrated high strength, toughness and fatigue life. Furthermore, the resultant bioinspired graphene-based nanocomposites (BGBNs) also possess high electrical conductivity. The extraordinary performance allows this kind of BGBN to be potentially utilized in aerospace, flexible electrodes of supercapacitors and other intelligent devices. The demonstration of synergistic interfacial interactions of ionic and covalent bonding also supplies an effective approach for building robust graphene-based nanocomposites in the future.
    | PDF | Supplementary Information
44. Science behind nacre: matrix-directed mineralization at ambient condition
    Qunfeng Cheng, and Lei Jiang*
    SCIENCE CHINA Materials, 2016, 59, 889-891. DOI: 10.1007/s40843-016-5116-3
    PDF
45. Low-Cost Coir Fiber Composite with Integrated Strength and Toughness
    Fengyun Guo, Nü Wang*, Qunfeng Cheng, Lanlan Hou, Jingchong Liu, Yanlei Yu, and Yong Zhao*
    ACS Sustainable Chem. Eng., 2016, 4, 5450-5455. DOI: 10.1021/acssuschemeng.6b00830
    Abstract
    With the growing environmental problems and depletion of petroleum resources, there is an urgent demand for the biorenewable, sustainable, and environmentally friendly composite materials. Here, we report a green coir fiber composite with specific mechanical properties superior to that of other reported natural fiber/polymer composites. After treatment, both strength and toughness of the composite fiber were substantially improved (91.13% and 175.7% higher than that of untreated counterpart), where exposed cellulose nanofibrils and stacking layer formed by NaOH infusion and the hydroxyl-containing hydrophilic poly(vinyl alcohol) coating play a crucial role in physicochemical interaction and thereby mechanical enhancement. By observing the process of the micro/nanostructure evolution, the strengthened mechanism from nanoscale to macroscale was demonstrated. We believe that this strategy could open new insights into the design of strong and sustainable composite fiber for further practical applications, such as textile, home furnishings, and industrial products.
    | PDF | Supplementary Information
46. Bioinspired Graphene-Based Nanocomposites and Their Application in Flexible Energy Devices
    Sijie Wan, Jingsong Peng, Lei Jiang, and Qunfeng Cheng*
    Adv. Mater., 2016, 8, 7862-7898. DOI: 10.1002/adma.201601934
    Abstract
    Graphene is the strongest and stiffest material ever identified and the best electrical conductor known to date, making it an ideal candidate for constructing nanocomposites used in flexible energy devices. However, it remains a great challenge to assemble graphene nanosheets into macro-sized high-performance nanocomposites in practical applications of flexible energy devices using traditional approaches. Nacre, the gold standard for biomimicry, provides an excellent example and guideline for assembling two-dimensional nanosheets into high-performance nanocomposites. This review summarizes recent research on the bioinspired graphene-based nanocomposites (BGBNs), and discusses different bioinspired assembly strategies for constructing integrated high-strength and -toughness graphene-based nanocomposites through various synergistic effects. Fundamental properties of graphene-based nanocomposites, such as strength, toughness, and electrical conductivities, are highlighted. Applications of the BGBNs in flexible energy devices, as well as potential challenges, are addressed. Inspired from the past work done by the community a roadmap for the future of the BGBNs in flexible energy device applications is depicted.
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47. Integrated Ternary Artificial Nacre via Syenrgistic Toughening of Reduced Graphene Oxide/Double-Walled Carbon Nanotubes/Poly(vinyl alcohol)
    Shanshan Gong, Mengxi Wu, Lei Jiang, and Qunfeng Cheng*
    Mater. Res. Express, 2016, 3, 075002. DOI: 10.1088/2053-1591/3/7/075002
    Abstract
    The synergistic toughening effect of building blocks and interface interaction exists in natural materials, such as nacre. Herein, inspired by one-dimensional (1D) nanofibrillar chitin and two-dimensional (2D) calcium carbonate platelets of natural nacre, we have fabricated integrated strong and tough ternary bio-inspired nanocomposites (artificial nacre) successfully via the synergistic effect of 2D reduced graphene oxide (rGO) nanosheets and 1D double-walled carbon nanotubes (DWNTs) and hydrogen bonding cross-linking with polyvinyl alcohol (PVA) matrix. Moreover, the crack mechanics model with crack deflection by 2D rGO nanosheets and crack bridging by 1D DWNTs and PVA chains induces resultant artificial nacre exhibiting excellent fatigue-resistance performance. These outstanding characteristics enable the ternary bioinspired nanocomposites have many promising potential applications, for instance, aerospace, flexible electronics devices and so forth. This synergistic toughening strategy also provides an effective way to assemble robust graphene-based nanocomposites.
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48. Bioinspired Ternary Artificial Nacre Nanocomposites Based on Reduced Graphene Oxide and Nanofibrillar Cellulose
    Jianli Duan, Shanshan Gong, Yuan Gao, Xiaolin Xie, and Lei Jiang, and Qunfeng Cheng*
    ACS Appl. Mater. Interfaces, 2016, 8, 10545-10550. DOI: 10.1021/acsami.6b02156
    Abstract
    Inspired by the nacre, we demonstrated the integrated ternary artificial nacre nanocomposites through synergistic toughening of graphene oxide (GO) and nanofibrillar cellulose (NFC). In addition, the covalent bonding was introduced between adjacent GO nanosheets. The synergistic toughening effects from building blocks of one-dimensional NFC and two-dimensional GO, interface interactions of hydrogen and covalent bonding together result in the integrated mechanical properties including high tensile strength, toughness, and fatigue life as well as high electrical conductivity. These extraordinary properties of the ternary synthetic nacre nanocomposites allow the support for advances in diverse strategic fields including stretchable electronics, transportation, and energy. Such bioinspired strategy also provides a new insight in designing novel multifunctional nanocomposites.
    | PDF | Supplementary Information
49. Graphene-based artificial nacre nanocomposites
    Yuanyuan Zhang, Shanshan Gong, Qi Zhang, Peng Ming, Sijie Wan, Jingsong Peng, Lei Jiang, and Qunfeng Cheng*
    Chem. Soc. Rev., 2016, 45, 2378-2395. DOI: 10.1039/C5CS00258C
    Abstract
    With its extraordinary properties as the strongest and stiffest material ever measured and the best-known electrical conductor, graphene could have promising applications in many fields, especially in the area of nanocomposites. However, processing graphene-based nanocomposites is very difficult. So far, graphene-based nanocomposites exhibit rather poor properties. Nacre, the gold standard for biomimicry, provides an excellent example and guidelines for assembling two-dimensional nanosheets into high performance nanocomposites. The inspiration from nacre overcomes the bottleneck of traditional approaches for constructing nanocomposites, such as poor dispersion, low loading, and weak interface interactions. This tutorial review summarizes recent research on graphene-based artificial nacre nanocomposites and focuses on the design of interface interactions and synergistic effects for constructing high performance nanocomposites. This tutorial review also focuses on a perspective of the dynamic area of graphene-based nanocomposites, commenting on whether the concept is viable and practical, on what has been achieved to date, and most importantly, what is likely to be achieved in the future.
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50. Nacre-inspired Integrated Strong and Tough Reduced Graphene Oxide-Poly(acrylic acid) Nanocomposites
    Qunfeng Cheng*, Sijie Wan, Han Hu, Jingsong Peng, Yuchen Li, Yuzun Fan, and Lei Jiang
    Nanoscale, 2016, Advance Article. DOI: 10.1039/C6NR00562D
    Abstract
    Inspired by the relationship of interface interactions with high performance mechanical properties of nacre, an integrated strong and tough nacre-inspired nanocomposite was demonstrated based on graphene oxide (GO) polyacrylic acid (PAA) via vacuum-assisted filtration self-assembly process. The abundant hydrogen bonding between GO and PAA results in the integrated high strength and toughness of the artificial nacre, which is 2 and 3.3 times higher than that of pure reduced GO film. Moreover, this nacre-inspired nanocomposite also displays high electrical conductivity of 108.9 S/cm. All these fantastic physical properties allow this kind of nacre-inspired nanocomposite to be used in many applications, such as flexible electrode, aerospace, and artificial muscles et al. This nacre-inspired strategy also opens an avenue for constructing the integrated high performance graphene-based nanocomposites in the near future.
    | PDF | Supplementary Information
51. Ultrastrong Bioinspired Graphene-Based Fibers via Synergistic Toughening
    Yuanyuan Zhang, Yuchen Li, Peng Ming, Qi Zhang, Tianxi Liu, Lei Jiang, and Qunfeng Cheng*
    Adv. Mater., 2016, 28, 2834-2839. DOI: 10.1002/adma.201506074
    Abstract
    Ultrastrong bioinspired graphene-based fibers are designed and prepared via synergistic toughening of ionic and covalent bonding. The tensile strength reaches up to 842.6 MPa and is superior to all other reported graphene-based fibers. In addition, its electrical conductivity is as high as 292.4 S cm⁻¹. This bioinspired synergistic toughening strategy supplies new insight toward the construction of integrated high-performance graphene-based fibers in the near future.
    | PDF | Supplementary Information

2015

32. Use of Synergistic Interactions to Fabricate Strong, Tough, and Conductive Artificial Nacre Based on Graphene Oxide and Chitosan
    Sijie Wan, Jingsong Peng, Yuchen Li, Han Hu, Lei Jiang, and Qunfeng Cheng*
    ACS Nano, 2015, 9, 9830-9836. DOI: 10.1021/acsnano.5b02902
    Abstract
    Graphene is the strongest and stiffest material, leading to the development of promising applications in many fields. However, the assembly of graphene nanosheets into macrosized nanocomposites for practical applications remains a challenge. Nacre in its natural form sets the “gold standard” for toughness and strength, which serves as a guide to the assembly of graphene nanosheets into high-performance nanocomposites. Here we show the strong, tough, conductive artificial nacre based on graphene oxide through synergistic interactions of hydrogen and covalent bonding. Tensile strength and toughness was 4 and 10 times higher, respectively, than that of natural nacre. The exceptional integrated strong and tough artificial nacre has promising applications in aerospace, artificial muscle, and tissue engineering, especially for flexible supercapacitor electrodes due to its high electrical conductivity. The use of synergistic interactions is a strategy for the development of high-performance nanocomposites.
    | PDF | Supplementary Information
33. Synergistic Toughening of Graphene Oxide–Molybdenum Disulfide–Thermoplastic Polyurethane Ternary Artificial Nacre
    Sijie Wan, Yuchen Li, JingsongPeng, Han Hu, Qunfeng Cheng*, and Lei Jiang
    ACS Nano, 2015, 9, 708-714. DOI: 10.1021/nn506148w
    Abstract
    Inspired by the ternary structure of natural nacre, robust ternary artificial nacre is constructed through synergistic toughening of graphene oxide (GO) and molybdenum disulfide (MoS₂) nanosheets via a vacuum-assisted filtration self-assembly process. The synergistic toughening effect from high mechanical properties of GO and lubrication of MoS₂ nanosheets is successfully demonstrated. Meanwhile, the artificial nacre shows high electrical conductivity. This approach for constructing robust artificial nacre by synergistic effect from GO and MoS₂ provides a creative opportunity for designing and fabricating integrated artificial nacre in the near future, and this kind of ternary artificial nacre has great potential applications in aerospace, flexible supercapacitor electrodes, artificial muscle, and tissue engineering.
    | PDF | Supplementary Information
34. Integrated Ternary Bioinspired Nanocomposites via Synergistic Toughening of Reduced Graphene Oxide and Double-Walled Carbon Nanotubes
    Shanshan Gong, Wei Cui, Qi Zhang, Anyuan Cao, Lei Jiang, and Qunfeng Cheng*
    ACS Nano, 2015, 9, 11568-11573. DOI: 10.1021/acsnano.5b05252
    Abstract
    With its synergistic toughening effect and hierarchical micro/nanoscale structure, natural nacre sets a “gold standard” for nacre-inspired materials with integrated high strength and toughness. We demonstrated strong and tough ternary bioinspired nanocomposites through synergistic toughening of reduced graphene oxide and double-walled carbon nanotube (DWNT) and covalent bonding. The tensile strength and toughness of this kind of ternary bioinspired nanocomposites reaches 374.1 ± 22.8 MPa and 9.2 ± 0.8 MJ/m³, which is 2.6 and 3.3 times that of pure reduced graphene oxide film, respectively. Furthermore, this ternary bioinspired nanocomposite has a high conductivity of 394.0 ± 6.8 S/cm and also shows excellent fatigue-resistant properties, which may enable this material to be used in aerospace, flexible energy devices, and artificial muscle. The synergistic building blocks with covalent bonding for constructing ternary bioinspired nanocomposites can serve as the basis of a strategy for the construction of integrated, high-performance, reduced graphene oxide (rGO)-based nanocomposites in the future.
    | PDF | Supplementary Information
35. Learning from Nature: Constructing Integrated Graphene-Based Artificial Nacre
    Qunfeng Cheng*, Jianli Duan, Qi Zhang, and Lei Jiang
    ACS Nano, 2015, 9, 2231-2234. DOI: 10.1021/acsnano.5b01126
    Abstract
    Natural nacre supplies a number of properties that can be used in designing high-performance bioinspired materials. Likewise, due to the extraordinary properties of graphene, a series of bioinspired graphene-based materials have recently been demonstrated. Compared to other approaches for constructing graphene-based materials, bioinspired concepts result in high-loading graphene, and the resultant high-performance graphene-based artificial nacres demonstrate isotropic mechanical and electrical properties. In this Perspective, we describe how to construct integrated graphene-based artificial nacre through the synergistic relationship between interface interactions and building blocks. These integrated graphene-based artificial nacres show promising applications in many fields, such as aerospace, flexible supercapacitor electrodes, artificial muscle, and tissue engineering.
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36. Nacre-inspired integrated nanocomposites with fire retardant properties by graphene oxide and montmorillonite
    Peng Ming, Zhaofei Song, Shanshan Gong, Yuanyuan Zhang, JianliDuan, Qi Zhang, Lei Jiang, and Qunfeng Cheng*
    J. Mater. Chem. A, 2015, 3, 21194-21200. DOI: 10.1039/C5TA05742F
    Abstract
    Natural nacre exhibits extraordinary strong and tough properties with its brick-and-mortar structure that was perfected after millions of years of evolution. Inspired by nacre’s hierarchical structure, we fabricated multifunctional bioinspired nanocomposites of graphene oxide (GO) and montmorillonite (MMT) nanosheets with poly(vinyl alcohol) (PVA) via a vacuum-assisted filtration self-assembly process. By combining graphene oxide and montmorillonite with PVA, we demonstrated an effective synergistic toughening effect and obtained integrated strong and tough bioinspired nanocomposites. Furthermore, these nanocomposites show high fatigue-resistant properties, high electrical conductivity and good fire retardant properties. As such, they have promising potential in many applications, including flexible electrodes, flame retardant insulation and as aerospace materials. The technique developed here provides new insights for designing nanocomposites with a complex hierarchical structure that mimic nacre.
    | PDF | Supplementary Information
37. Bioinspired highly electrically conductive graphene–epoxy layered composites
    Peng Ming,Yuanyuan Zhang, Jianwen Bao, Gang Liu, Zhou Li, Lei Jiang, and Qunfeng Cheng*
    RSC Adv., 2015, 5, 22283-22288. DOI: 10.1039/C5RA00233H
    Abstract
    Inspired by the nano/micro-scale hierarchical structure of nacre, we developed a new method for fabricating highly electrically conductive graphene–epoxy layered composites. In this new method, the graphene loading can be easily controlled, and the intrinsic three-dimensional network of graphene in the composites results in high electrical conductivity. Through effective surface modification, the interface strength between graphene and epoxy matrix was dramatically improved, leading to the 23-fold improvement in tensile strength, 136-fold in Young’s modulus, and 8-fold in electrical conductivity compared with the pure graphene foam. These high performance bioinspired graphene–epoxy layered composites have a great potential for applications in electromagnetic interference (EMI) shielding, aerospace, and other electrical devices.
    | PDF | Supplementary Information

2014

26. Bioinspired Green Composite Lotus Fibers
    Mengxi Wu, HuaShuai, Qunfeng Cheng*, and Lei Jiang
    Angew. Chem. Int. Ed., 2014, 53, 3358-3361. DOI: 10.1002/anie.201310656
    Abstract
    Owing to the growing global environmental problems, demands for environmentally friendly, fully biodegradable sustainable composites have substantially increased across various industries. Inspired by the composite structure of cocoon silk, we fabricated a fully green composite fiber (GCF) that is based on the lotus fiber (LF) and a biodegradable polymer, namely poly(vinyl alcohol) (PVA). After the formation of cross-linkages between the LF and PVA, the mechanical properties of this bioinspired GCF had substantially improved. In particular, the specific mechanical properties are superior to those of cocoon silk and other natural fibers. These findings suggest that LFs may be used as reinforcement materials for the fabrication of bulk green materials for various industries, such as the textile, medical, automobile, and aerospace industries.
    | PDF | Supplementary Information
27. Synergistic Toughening of BioinspiredPoly(vinyl alcohol)–Clay–Nanofibrillar Cellulose Artificial Nacre
    Jianfeng Wang, Qunfeng Cheng*, Ling Lin, and Lei Jiang
    ACS Nano, 2014, 8, 2739-2745. DOI: 10.1021/nn406428n
    Abstract
    Inspired by the layered aragonite platelet/nanofibrillar chitin/protein ternary structure and integration of extraordinary strength and toughness of natural nacre, artificial nacre based on clay platelet/nanofibrillar cellulose/poly(vinyl alcohol) is constructed through an evaporation-induced self-assembly technique. The synergistic toughening effect from clay platelets and nanofibrillar cellulose is successfully demonstrated. The artificial nacre achieves an excellent balance of strength and toughness and a fatigue-resistant property, superior to natural nacre and other conventional layered clay/polymer binary composites.
    | PDF | Supplementary Information
28. A Strong Integrated Strength and Toughness Artificial Nacre Based on Dopamine Cross-Linked Graphene Oxide
    Wei Cui, Mingzhu Li, Jiyang Liu, Ben Wang, Chuck Zhang, Lei Jiang, and Qunfeng Cheng*
    ACS Nano, 2014, 8, 9511-9517. DOI: 10.1021/nn503755c
    Abstract
    Demands of the strong integrated materials have substantially increased across various industries. Inspired by the relationship of excellent integration of mechanical properties and hierarchical nano/microscale structure of the natural nacre, we have developed a strategy for fabricating the strong integrated artificial nacre based on graphene oxide (GO) sheets by dopamine cross-linking via evaporation-induced assembly process. The tensile strength and toughness simultaneously show 1.5 and 2 times higher than that of natural nacre. Meanwhile, the artificial nacre shows high electrical conductivity. This type of strong integrated artificial nacre has great potential applications in aerospace, flexible supercapacitor electrodes, artificial muscle, and tissue engineering.
    | PDF | Supplementary Information
29. Bioinspired Layered Materials with Superior Mechanical Performance
    Qunfeng Cheng*, Lei Jiang, and Zhiyong Tang*
    Acc. Chem. Res., 2014, 47, 1256-1266. DOI: 10.1021/ar400279t
    Conspectus
    Nature has inspired researchers to construct structures with ordered layers as candidates for new materials with high mechanical performance. As a prominent example, nacre, also known as mother of pearl, consists of a combination of inorganic plates (aragonite calcium carbonate, 95% by volume) and organic macromolecules (elastic biopolymer, 5% by volume) and shows a unique combination of strength and toughness. Investigations of its structure reveal that the hexagonal platelets of calcium carbonate and the amorphous biopolymer are alternatively assembled into the orderly layered structure. The delicate interface between the calcium carbonate and the biopolymer is well defined. Both the building blocks that make up these assembled layers and the interfaces between the inorganic and organic components contribute to the excellent mechanical property of natural nacre.In this Account, we summarize recent research from our group and from others on the design of bioinspired materials composed by layering various primitive materials. We focus particular attention on nanoscale carbon materials. Using several examples, we describe how the use of different combinations of layered materials leads to particular properties. Flattened double-walled carbon nanotubes (FDWCNTs) covalently cross-linked in a thermoset three-dimensional (3D) network produced the materials with the highest strength. The stiffest layered materials were generated from borate orthoester covalent bonding between adjacent graphene oxide (GO) nanosheets, and the toughest layered materials were fabricated with Al2O3 platelets and chitosan via hydrogen bonding. These new building blocks, such as FDWCNTs and GO, and the replication of the elaborate micro-/nanoscale interface of natural nacre have provided many options for developing new high performance artificial materials.The interface designs for bioinspired layered materials are generally categorized into (1) hydrogen bonding, (2) ionic bonding, and (3) covalent bonding. Using these different strategies, we can tune the materials to have specific mechanical characteristics such as high strength, excellent strain resistance, or remarkable toughness. Among these design strategies, hydrogen bonding affords soft interfaces between the inorganic plates and the organic matrix. Covalent cross-linking forms chemical bonds between the inorganic plates and the organic matrix, leading to much stronger interfaces. The interfaces formed by ionic bonding are stronger than those formed by hydrogen bonding but weaker than those formed by covalent bonding.
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2013

22. Ultratough Artificial Nacre Based on Conjugated Cross-linked Graphene Oxide
    Qunfeng Cheng*, Mengxi Wu, Mingzhu Li*, Lei Jiang, and Zhiyong Tang*
    Angew. Chem., Int. Ed., 2013, 52, 3750-3755. DOI: 10.1002/anie.201210166
    Abstract
    Inspired by natural nacre, layered composites based on graphene oxide (GO) and 10,12-pentacosadiyn-1-ol (PCDO) have been successfully fabricated. PCDO molecules are grafted onto GO sheets and cross-linked with each other, resulting in a superior toughness that is two times higher than that of the natural nacre.
    | PDF | Supplementary Information
23. Understanding the relationship of performance with nanofiller content in the biomimetic layered nanocomposites
    Jianfeng Wang, Qunfeng Cheng*, Ling Lin, Linfeng Chen, and Lei Jiang
    Nanoscale, 2013, 5, 6356-6362. DOI: 10.1039/C3NR00801K
    Abstract
    Montmorillonite/poly(vinyl alcohol) (MMT/PVA) nanocomposites spanning the complete range of MMT content (0–100 wt%) are prepared by simple evaporation-induced assembly. Effects of MMT content on the structure and mechanical properties of nanocomposites are systematically investigated and exhibit two important transitions at MMT contents of 30 wt% and 70 wt%. In the range of 0–30 wt%, the nanocomposites show a random structure. With the content of PVA increasing, the mechanical properties of the resultant nanocomposites were dramatically enhanced and were higher than that by prediction according to the conventional composite model. In the range of 30–70 wt%, the nanocomposites show a nacre-like layered structure with alternating MMT platelets and PVA layers, and all PVA is completely restricted by MMT platelets. The mechanical properties of nanocomposites were further improved by increasing the content of MMT, and reached the maximum value at the MMT content of 70 wt%. The 70 wt% MMT/PVA nanocomposite has a tensile strength of 219 ± 19 MPa, which is 5.5 times higher than that of a pure PVA film and surpasses nacre and reported biomimetic layered clay/PVA composites. When the MMT content is higher than 70 wt%, the layered structure is transformed to tactoids, which deteriorate mechanical properties. These results offer comprehensive understanding for developing high-performance biomimetic layered nanocomposite materials with high nanofiller loading.
    | PDF | Supplementary Information

2012

20. Bioinspired Layered Composites Based on Flattened Double-Walled Carbon Nanotubes
    Qunfeng Cheng*, Mingzhu Li, Lei Jiang, and Zhiyong Tang*
    Adv. Mater., 2012, 24, 1838-1843. DOI: 10.1002/adma.201200179
    Abstract
    Inspired by the layered hierarchical nano- and microstructures of natural nacre, flattened double-walled carbon nanotube (FDWCNT) reinforced epoxy composites are fabricated. Impressively, the prepared composites exhibit layered structures analogous to nacre, and the FDWCNT loading can reach 70 wt%, which results in superior mechanical properties that evidently outperform other existing materials.
    | PDF | Supplementary Information
21. A Strong Bio-Inspired Layered PNIPAM–Clay Nanocomposite Hydrogel
    Jianfeng Wang,Ling Lin, Qunfeng Cheng*, and Lei Jiang
    Angew. Chem. Int. Ed., 2012, 51, 4676-4680. DOI: 10.1002/anie.201200267
    Abstract
    Inspired by nacre, a layered poly(N-isopropylacrylamide)–clay nanocomposite hydrogel was successfully fabricated by combination of vacuum-filtration self-assembly and photo-initiated in situ polymerization. This bio-inspired layered nanocomposite hydrogel shows excellent mechanical properties, which can rival some biological soft tissues (see picture).
    | PDF | Supplementary Information
22. Layered nanocomposites inspired by the structure and mechanical properties of nacre
    Jianfeng Wang, Qunfeng Cheng*, and Zhiyong Tang*
    Chem. Soc. Rev., 2012, 41, 1111-1129. DOI: 10.1039/C1CS15106A
    Abstract
    Nacre (mother-of-pearl), made of inorganic and organic constituents (95 vol% aragonite calcium carbonate (CaCO₃) platelets and 5 vol% elastic biopolymers), possesses a unique combination of remarkable strength and toughness, which is compatible for conventional high performance materials. The excellent mechanical properties are related to its hierarchical structure and precisely designed organic–inorganic interface. The rational design of aragonite platelet strength, aspect ratio of aragonite platelets, and interface strength ensures that the strength of nacre is maximized under platelet pull-out failure mode. At the same time, the synergy of strain hardening mechanisms acting over multiple scales results in platelets sliding on one another, and thus maximizes the energy dissipation of viscoplastic biopolymers. The excellent integrated mechanical properties with hierarchical structure have inspired chemists and materials scientists to develop biomimetic strategies for artificial nacre materials. This critical review presents a broad overview of the state-of-the-art work on the preparation of layered organic–inorganic nanocomposites inspired by nacre, in particular, the advantages and disadvantages of various biomimetic strategies. Discussion is focused on the effect of the layered structure, interface, and component loading on strength and toughness of nacre-mimic layered nanocomposites (148 references).
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23. An underwater pH-responsive superoleophobic surface with reversibly switchable oil-adhesion
    Qunfeng Cheng, Mingzhu Li, Fu Yang, Mingjie Liu,Lin Li, Shutao Wang*, and Lei Jiang
    Soft Matter, 2012, 8, 6740-6743. DOI: 10.1039/C2SM25421B
    Abstract
    An underwater pH-responsive superoleophobic surface successfully demonstrated a reversible switch of oil-adhesion on a nanostructured poly(acrylic acid) (PAA) surface by changing the environmental pH values. At low pH, intramolecular hydrogen bonding of PAA is formed, and results in high oil-adhesion. As for high pH, the oil droplets can easily roll off due to the intermolecular hydrogen bonding between PAA and surrounding water.
    | PDF | Supplementary Information

Publications before Joining Beihang University（2006 – 2010）

2012

16. Comparative Characterization of Multiscale Carbon Fiber Composite with Long and Short MWCNTs at Higher Weight Fractions
    Michael Zimmer*, Qunfeng Cheng, Shu Li, James Brooks, Richard Liang, Ben Wang, and Chuck Zhang
    J. Nanomater., 2012, 532080. DOl: 10.1155/2012/532080
    Abstract
    There are documented advantages to using carbon nanotubes (CNTs) in composites for various property enhancements. However, to date, only limited studies have been conducted on using of longer CNTs over 1 mm in length. This study used long multiwalled carbon nanotubes (LMWCNTs) and their longer extended networks to test multiple properties in thermal conductivity, electrical conductivity, mechanical strength, and modulus and then compared these properties to those of shorter multi-walled carbon nanotubes (SMWCNTs). For carbon fiber-reinforced composites, the longer graphite paths from LMWCNTs in the matrix were expected to improve all properties. The longer networks were expected to allow for more undisturbed phonon transportation to improve thermal conductivity. This in turn relates to improved electrical conductivity and better mechanical properties. However, results have shown that the LMWCNTs do not improve or decrease thermal conductivity, whereas the shorter MWCNTs provide mixed results. LMWCNTs did show improvements in electrical, mechanical, and physical properties, but compared to shorter MWCNTs, the results in other certain properties varied. This perplexing outcome resides in the functioning of the networks made by both the LMWCNTs and shorter MWCNTs.
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17. Preform-based toughening technology for RTMable high-temperature aerospace composites
    Xiao-Su Yi*, Qunfeng Cheng, and Zhizhen Liu
    Sci. China-Technol. Sci., 2012, 55, 2255-2263. DOI: 10.1007/s11431-012-4949-8
    Abstract
    This article describes the efforts that led to the development of surface-loaded preforms that may be used to significantly improve the compression-after-impact strength of high-temperature composites and correspondingly to dramatically reduce the area of damage because of impact. Moreover, by matching the toughening polymer surface-loaded and design of the surface pattern, in-plane mechanical properties are unaffected or even improved over laminates made from the identical materials. The proprietary preforms, so-called ES™-Fabrics, may be handled and infused with the high-temperature RTMable resins such as bismaleimide and polyimide in exactly the same manner as traditional fabrics without surface modification. The RTM conditions for the preform-based toughening is fully compatible with the traditional process procedure, making the technology cost-effective in production. This technology represents a key enabler for the use of low-cost RTM processes for high-temperature resins to supplant prepreg as the building-block material of choice for aeronautical composite structures.
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18. Thermal conductivity of MWCNT/epoxy composites: The effects of length, alignment and functionalization
    Jin Gyu Parka*, Qunfeng Cheng, Jun Lu, Jianwen Bao, Shu Lia, Ying Tian, Zhiyong Liang*, Chuck Zhang, and Ben Wang
    Carbon, 2012, 50, 2083-2090. DOI: 10.1016/j.carbon.2011.12.046
    Abstract
    Carbon nanotubes (CNTs) show great promise to improve composite electrical and thermal conductivity due to their exceptional high intrinsic conductance performance. In this research, long multi-walled carbon nanotubes (long-MWCNTs) and its thin sheet of entangled nanotubes were used to make composites to achieve higher electrical and thermal conductivity. Compared to short-MWCNT sheet/epoxy composites, at room temperature, long-MWCNT samples showed improved thermal conductivity up to 55 W/mK. The temperature dependence of thermal conductivity was in agreement with κ ∝ Tⁿ (n = 1.9-2.3) below 150 K and saturated around room temperature due to Umklapp scattering. Samples with the improved CNT degree of alignment by mechanically stretching can enhance the room temperature thermal conductivity to over 100 W/mK. However, functionalization of CNTs to improve the interfacial bonding resulted in damaging the CNT walls and decreasing the electrical and thermal conductivity of the composites.
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19. In situ characterization of structural changes and the fraction of aligned carbon nanotube networks produced by stretching
    Shu Lia, Jin Gyu Park, Zhiyong Liang*, Theo Siegrist, Tao Liu, Mei Zhang, Qunfeng Cheng, Ben Wang, and Chuck Zhang
    Carbon, 2012, 50, 3859-3867. DOI: 10.1016/j.carbon.2012.04.029
    Abstract
    The mechanism of carbon nanotube (CNT) alignment during stretching was examined by the in situ characterization of carbon nanotube networks (CNTNs) under tensile strains using X-ray and Raman scattering techniques. A method of quantifying the inhomogeneous alignment of macroscopic CNTNs is explored based on bulk property measurements of their electrical anisotropy and X-ray diffraction diagrams. The results show that the process of stretch-induced alignment of CNTNs included straightening the waviness of the long nanotube ropes, as well as the self-assembling and denser packing of the nanotubes. For samples at a strain of 40%, the fraction of aligned nanotubes was as high as 0.85. The aligned fraction of CNTs serves as an important parameter for the quality control of the alignment process and numerical simulations of structure–property relationships of CNTNs and their composites.
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2011

12. Janus interface materials: superhydrophobic air/solid interface and superoleophobic water/solid interface inspired by a lotus leaf
    Qunfeng Cheng, Mingzhu Li, Yongmei Zheng, Bin Su, Shutao Wang*, and Lei Jiang
    Soft Matter, 2011, 7, 5948-5951. DOI: 10.1039/C1SM05452J
    Abstract
    We discovered underwater superoleophobicity on the lower side of a lotus leaf, and fabricated Janus interface materials with in-air superhydrophobicity on one side and underwater superoleophobicity on the other side inspired by the Janus feature of the lotus leaf. The ingenious design on lotus leaf surfaces, superhydrophobicity on its upper side and underwater superoleophobicity on its lower side, not only helps us thoroughly understand the special surface wettability of the lotus leaf, but also gives a typical example of multi-functionality in biological systems. This study supplies us with an intelligent strategy to design and create bionic multi-functional interface materials.
    | PDF | Supplementary Information
13. Highly reflective superhydrophobic white coating inspired by poplar leaf hairs toward an effective “cool roof”
    Changqing Ye, Mingzhu Li*, Junping Hu, Qunfeng Cheng, Lei Jiang, and Yanlin Song*
    Energy Environ. Sci., 2011,4, 3364-3367. DOI: 10.1039/C0EE00686F
    Abstract
    The hair layer consisting of hollow fibers provides the poplar leaf with an energy efficient “cool roof” to protect it from being burned by strong light. Inspired by the hair structure, we use coaxial electro-spinning technology to achieve a highly reflective and superhydrophobic white coating towards making an eco-friendly and effective “cool roof”.
    | PDF | Supporting Information

2010

10. Carbon nanotube/epoxy composites fabricated by resin transfer molding
    Qunfeng Cheng, Jiaping Wang*, Jiajia Wen, Changhong Liu, Kaili Jiang, and Shoushan Fan
    Carbon, 2010, 48, 260-266. DOI: 10.1016/j.carbon.2009.09.014
    Abstract
    Carbon nanotube (CNT)/epoxy composites with controllable alignment of CNTs were fabricated by a resin transfer molding process. CNTs with loading up to 16.5 wt.% were homogenously dispersed and highly aligned in the epoxy matrix. Both mechanical and electrical properties of the CNT/epoxy composites were dramatically improved with the addition of the CNTs. The Young’s modulus and tensile strength of the composites reach 20.4 GPa and 231.5 MPa, corresponding to 716% and 160% improvement compared to pure epoxy. The electrical conductivity of the composites along the direction of the CNT alignment reaches over 1 × 104 S/m.
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11. Functionalized Carbon-Nanotube Sheet/Bismaleimide Nanocomposites: Mechanical and Electrical Performance Beyond Carbon-Fiber Composites
    Qunfeng Cheng, Ben Wang, Chuck Zhang, and Zhiyong Liang*
    Small, 2010, 6, 763-767. DOI: 10.1002/smll.200901957
    Abstract
    Since their discovery in 1991, carbon nanotubes (CNTs) have been considered as the next-generation reinforcement materials to potentially replace conventional carbon fibers for producing super-high-performance lightweight composites. Herein, it is reported that sheets of millimeter-long multi-walled CNTs with stretch alignment and epoxidation functionalization reinforce bismaleimide resin, which results in composites with an unprecedentedly high tensile strength of 3081 MPa and modulus of 350 GPa, well exceeding those of state-of-the-art unidirectional carbon-fiber-reinforced composites. The results also provide important experimental evidence of the impact of functionalization and the effect of alignment reported previously on the mechanical performance and electrical conductivity of the nanocomposites.
    | PDF | Supplementary Information

2009

8. The fabrication of single-walled carbon nanotube/polyelectrolyte multilayer composites by layer-by-layer assembly and magnetic field assisted alignment
   Ying Tian, Jin Gyu Park, Qunfeng Cheng, Zhiyong Liang*, Chuck Zhang, and Ben Wang
   Nanotechnology, 2009, 20, 335601. DOI: 10.1088/0957-4484/20/33/335601
   Abstract
   Single-walled carbon nanotube (SWNT)/polymer composites are widely studied because of their potential for high mechanical performance and multifunctional applications. In order to realize highly ordered multilayer nanostructures, we combined the layer-by-layer (LBL) assembly method with magnetic force-induced alignment to fabricate SWNT/poly(ethylamine) (PEI) multilayer composites. The SWNTs were functionalized with the anionic surfactant sodium dodecylbenzenesulfonate (NaDDBS) to realize negative charge at pH>7, while the PEI is positively charged at pH<7. The LBL method is based on the electrostatic absorption between the charged SWNTs and PEI resin to form multilayer composites on a solid substrate polydimethylsiloxane. Since the fabricated thickness of each SWNT-NaDDBS/PEI bilayer is uniform (~150 nm), the multilayer film thickness can be strictly controlled via the number of deposition cycles. A high magnetic field (8.5 Tesla) was used to align the SWNTs during the LBL process. The resultant LBL composite samples demonstrated high SWNT loading of approximately 50 wt% and uniform distribution of SWNTs in the multilayer structures, which was verified using a quartz crystal microbalance. Good alignment was also realized and observed through using high magnetic fields to align the nanotubes during the LBL deposition process. The results indicate that the LBL/magnetic alignment approach has potential for fabricating nanotube composites with highly ordered nanostructures for multifunctional materials and device applications.
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9. Electromagnetic interference shielding properties of carbon nanotube buckypaper composites
   Jin Gyu Park*, Jeffrey Louis, Qunfeng Cheng, JianwenBao, Jesse Smithyman, Richard Liang,Ben Wang, Chuck Zhang, James S Brooks, Leslie Kramer, Percy Fanchasis, and David Dorough
   Nanotechnology, 2009, 20, 415702. DOI: 10.1088/0957-4484/20/41/415702
   Abstract
   Preformed carbon nanotube thin films (10-20 µm), or buckypapers (BPs), consist of dense and entangled nanotube networks, which demonstrate high electrical conductivity and provide potential lightweight electromagnetic interference (EMI) solutions for composite structures. Nanocomposite laminates consisting of various proportions of single-walled and multi-walled carbon nanotubes, having different conductivity, and with different stacking structures, were studied. Single-layer BP composites showed shielding effectiveness (SE) of 20-60 dB, depending on the BP conductivity within a 2-18 GHz frequency range. The effects on EMI SE performance of composite laminate structures made with BPs of different conductivity values and epoxy or polyethylene insulating layer stacking sequences were studied. The results were also compared against the predictions from a modified EMI SE model. The predicted trends of SE value and frequency dependence were consistent with the experimental results, revealing that adjusting the number of BP layers and appropriate arrangement of the BP conducting layers and insulators can increase the EMI SE from 45 dB to close to 100 dB owing to the utilization of the double-shielding effect.
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10. Morphological and Spatial Effects on Toughness and Impact Damage Resistance of PAEK-toughened BMI and Graphite Fiber Composite Laminates
    Qunfeng Cheng, Zhengping Fang, Yahong Xu, and Xiao-Su Yi*
    Chin. J. Aeronaut., 2009, 22, 87-96. DOI: 10.1016/S1000-9361(08)60073-4
    Abstract
    The microstructure property relationships have been studied in terms of glass transition behavior, phase morphology, and fracture toughness on thermoplastic polyetherketone with a phenolphthalein side group (PAEK) toughened bismaleimdes (BMI) resins, and in terms of interlaminar morphology and compression after impact (CAI) on the graphite fiber (T700SC), the reinforced BMI matrix composites that are toughened with a so-called ex-situ concept, respectively. The characteristic morphology spectrum has been found to occur as the concentration of PAEK is varied. In particular, the relationship between the morphology and the fracture toughness has been explored on the PAEK-BMI blends. The fracture micromechanism has then been used to explain the delamination and impact damage behavior on the graphite laminated systems, where the morphology properties relationship held true. The complex nature of the diffusion-controlled phase behavior has also qualitatively been studied, which served as a model for understanding the ex-situ toughening concept.
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11. High Mechanical Performance Composite Conductor: Multi-Walled Carbon Nanotube Sheet/Bismaleimide Nanocomposites
    Qunfeng Cheng, Jianwen Bao, JinGyu Park, Zhiyong Liang*, Chuck Zhang, and Ben Wang
    Adv. Funct. Mater., 2009, 19, 3219-3225. DOI: 10.1002/adfm.200900663
    Abstract
    Multi-walled carbon nanotube (MWNT)-sheet-reinforced bismaleimide (BMI) resin nanocomposites with high concentrations (~60 wt%) of aligned MWNTs are successfully fabricated. Applying simple mechanical stretching and prepregging (pre-resin impregnation) processes on initially randomly dispersed, commercially available sheets of millimeter-long MWNTs leads to substantial alignment enhancement, good dispersion, and high packing density of nanotubes in the resultant nanocomposites. The tensile strength and Young’s modulus of the nanocomposites reaches 2088 MPa and 169 GPa, respectively, which are very high experimental results and comparable to the state-of-the-art unidirectional IM7 carbon-fiber-reinforced composites for high-performance structural applications. The nanocomposites demonstrate unprecedentedly high electrical conductivity of 5500 S cm⁻¹ along the alignment direction. Such unique integration of high mechanical properties and electrical conductance opens the door for developing polymeric composite conductors and eventually structural composites with multifunctionalities. New fracture morphology and failure modes due to self-assembly and spreading of MWNT bundles are also observed.
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2008

4. Fabrication and properties of aligned multiwalled carbon nanotube-reinforced epoxy composites
   Qunfeng Cheng, Jiaping Wang*, Kaili Jiang, Qunqing Li, and Shoushan Fan
   J. Mater. Res., 2008, 23, 2975-2983. DOI: 10.1557/JMR.2008.0356
   Abstract
   A method to fabricate continuous and aligned multiwalled carbon nanotube (CNT)/epoxy composites is presented in this paper. CNT/epoxy composites were made by infiltrating an epoxy resin into a stack of continuous and aligned multiwalled CNT sheets that were drawn from super-aligned CNT arrays. By controlling the amount and alignment of the continuous multiwalled CNT sheets, a CNT/epoxy composite with high content of well-dispersed CNTs can be obtained. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) results show that the thermal stability of these CNT/epoxy composites was not affected by the addition of CNTs. The mechanical properties and electrical properties of the CNT/epoxy composites were dramatically improved compared to pure epoxy, suggesting that the CNT/epoxy composites can serve as multifunctional materials with combined mechanical and physical properties.
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5. Ex-situ concept for toughening the RTMable BMI matrix composites. II. Improving the compression after impact
   Qunfeng Cheng, Zhengping Fang, Xiao-Su Yi*, Xuefeng An, Bangming Tang, and Yahong Xu
   J. Appl. Polym. Sci., 2008, 108, 2211-2217. DOI: 10.1002/app.27864
   Abstract
   The compression after impact (CAI) properties of bismaleimide (BMI) matrix composites manufactured by resin transfer molding (RTM) were significantly improved by ex-situ RTM technique. The thermoplastic polyetherketone with a functional group of phenolphthalein (PAEK) was used as toughener. The optical microscopy images of the cross-section of post-impact specimens revealed that the delamination resistance of specimens toughened through ex-situ RTM technique was dramatically improved. The energy absorption mechanism of composites toughened through ex-situ RTM technique was changed from the delamination to fiber fracture, which contributed to the improvement in CAI. The particle microstructure in interlaminar region of composites toughened through ex-situ RTM technique revealed that a reaction-induced phase decomposition and inversion happened in the interlaminar region. The BMI particles were surrounded with the PAEK phase, which can significantly improve the delamination resistance of composites. The in-plane static mechanical properties of G827/BMI composite toughened through ex-situ RTM technique were very well kept.
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6. “Ex situ” concept for toughening the RTMable BMI matrix composites, Part I: Improving the interlaminar fracture toughness
   Qunfeng Cheng, Zhengping Fang, Xiao-Su Yi*, Xuefeng An, Bangming Tang, and Yahong Xu
   J. Appl. Polym. Sci., 2008, 109, 1625-1634. DOI: 10.1002/app.27868
   Abstract
   Aerospace-grade bismaleimide matrix composites was toughened based on a novel ex situ resin transfer molding (RTM) technique using a special manufactured ES™ carbon fabrics. The toughening mechanism and toughening effect by the technique are studied using thermoplastic PAEK as toughener. Mode I fracture toughness (G_IC) of the composites toughened by ex situ RTM technique increased up to three times higher than that of the control system, and Mode II fracture toughness (G_IIC) increased two times higher as well. The composite without toughening was denoted as control system. The microstructure revealed that a reaction-induced phase decomposition and inversion happened in the interlaminar region, which resulted in a particles morphology that showed the thermosetting particles were surrounded with the PAEK phase. The plastic deformation and rupture of the continuous PAEK phase are responsible to the fracture toughness improvement. And the influence of PAEK concentration on toughness improvement was also investigated.
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2006

1. Improvement of the Impact Damage Resistance of BMI/Graphite Laminates by the Ex-situ Method
   Qunfeng Cheng, Zhengping Fang, Yahong Xu, and Xiao-Su Yi*
   High Perform. Polym., 2006, 18, 907-917. DOI: 10.1177/0954008306068296
   Abstract
   High-performance bismaleimide (BMI) matrix composites reinforced with graphite fibers were prepared and toughened with a thermoplastic component (PEK-C) by using different toughening methods. Four experimental options were conducted using the neat BMI matrix, toughened BMI matrix with PEKC, BMI laminates periodically interleaved with neat PEK-C films (Ex-situ concept 1) and BMI laminates periodically interleaved with BMI/PEK-C blend films (Ex-situ concept 2), respectively. The laminates were tested for compression strength after impact using an impact energy of 2 J mm^-1. The highest impact damage resistance was obtained for the laminates toughened using the Ex-situ concept 2, especially, when PEK-C/BMI two-component films, cast from a mixture of PEK-C: BMI = 60: 40 were interleaved between the BMI laminate plies. Interleaving the pure thermoplastic film also gave good results (Ex-situ concept 1). There were two peak temperatures evident in the dynamic mechanical thermal analyses of the ex-situ toughened laminates implying that phase separation had occurred. The glass transition temperature of the toughened BMI laminates was slightly reduced due to the lower glass transition temperature of PEK-C. Morphological investigations revealed that a granular structure was present in the interply region presumably due to spinodal decomposition and coarsening. The results of this study are presented herein.
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