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Graphene-based nanomaterials possess broad applications because of their excellent multi-functional properties. In this work, a facile self-assembling method was presented for preparing one kind of graphene oxide-based paper/hollow microspheres hybrid. It was found that most of the hollow microspheres can strongly anchored on the surface of graphene oxide paper (GOP) by an in-situ scanning electron microscope peeling testing combining with molecular dynamics (MD) simulation. In addition, the uniform distribution of hollow microspheres on the surface of GOP cannot only provide a better surface wettability, but also can effectively improve the interfacial stress-transfer capability between such hybrid and polymer matrix. Our work provides a guidance for the structural designs of graphene-based nanomaterials and broaden their applications.

Carbon nanotubes (CNTs) are regarded as the next generation of one-dimensional super-strong nanomaterials due to their extraordinary mechanical properties. Recently, much attention has been dedicated into super-strong CNT-based fibers resulting from twisting operation. However, the roles of a promising compression operation on the mechanical enhancement mechanisms of CNT fibers (CNFs) are not clear. Especially, the combined twisting-compression effect has not been known. In this work, with using coarse-grained molecular dynamic simulation method, the tensile mechanical properties and mechanical enhancements of randomly-distributed CNT fibers (RDCNFs) were studied. It was found that the mechanical performances of such RDCNFs could be significantly improved by increasing CNT length or decreasing initial bending degree of CNTs. Furthermore, both specific strength and specific modulus can be effectively tuned by twisting and compressing operations, where self-locking and unhitching mechanisms of CNT knots play critical roles. On the other hand, following theoretical guidance, a super-strong CNF with the maximum specific strength up to 296 mN/tex (∼6.8 GPa) was designed and fabricated. This work provides a theoretically and experimentally support to design super-strong CNT-based fibers and lays a foundation for their future applications.

Carbon nanotube fibers have attracted much interest because of their outstanding multifunctional properties. In this work, double-helix carbon nanotube fibers (DHCNFs) assembled by combined self-twisting and whole-twisting processes are presented, and their mechanical properties were studied based on atomic simulation. We found that the self-twisting of carbon nanotubes (CNTs) can lead to interesting intertube entanglements, with the formation of a helical structure. In addition, the twisting process can cause a remarkable decline of the mechanical properties of CNTs owing to their hollow structure collapse, thus deteriorating the tensile mechanical performances of DHCNFs. Meanwhile, by tuning related twisting parameters, different fracture failure modes, including simultaneous and stepwise breakages, can be found. More importantly, it was revealed that, as nanoenhancements, the helical morphology of DHCNFs can effectively enhance the interlocking effect between CNTs and the matrix, thereby improving the interfacial strength and toughness of DHCNF-reinforced nanocomposites. This work systemically studied the effect of the twisting operation on the mechanical properties of DHCNFs and provided an innovative way of simultaneously enhancing the strength and toughness of CNT-based nanocomposites.

Graphite carbon nitride (GCN), which can be regarded as a nitrogen heteroatom-substituted graphite framework, has attracted great attention as a new 2D layered structure material with semiconductor electronic characteristics. Using molecular dynamics simulations, the in-plane thermal conductivity and cross-plane thermal resistance of two GCN structures (i.e., triazine-based and heptazine-based) are investigated. Our results show that the in-plane thermal conductivities of the triazine-based and heptazine-based GCN monolayers along the armchair direction are 55.39 and 17.81 W m-1 K-1, respectively. The cross-plane thermal resistance decreases with increasing layer number and reaches asymptotic values of 3.6 × 10-10 and 9.3 × 10-10 m2 K W-1 at 40 layers for triazine-based and heptazine-based GCN, respectively. The in-plane thermal conductivity can be effectively manipulated by changing the temperature and applying strain, while it is insensitive to the number of layers, which is in sharp contrast to that of graphene. Moreover, the cross-plane thermal resistance decreases monotonically with temperature and coupling strength, and can be modulated by external strain. Surprisingly, the cross-plane tensile strain can reduce the thermal resistance of the heptazine-based GCN. Our study serves as a guide to groups interested in the physical properties of GCN.

L-shaped stiffened composite panels provide an efficient structure for engineering applications. However, they often produce delamination in the preparation and service process due to a series of factors. To study the effect of different types of delamination on the compressive strength of stiffened composite panels, ABAQUS finite element software was used in combine with the progressive damage subroutine user-defined field variable (USDFLD), and the finite element model was established based on cohesive theory to realize the prediction of the progressive failure process and strength of the stiffened composite panels. The results showed that the delamination of a stringer had a greater impact on the strength of the stiffened composite panels than did the debonding between the skin panel and a stringer and the delamination of the skin panel. The debonding delamination and delamination of a stringer exhibited delamination growth near the damage position during static compression, but delamination of the skin panel exhibited no delamination growth. The experimental results were in good agreement with the finite element simulation results, which verified the validity of the finite element model.

The thermal conductivities of single-layer BC3 (SLBC) sheets and their responses to environmental temperature, vacancy defects and external strain have been studied and compared with those of single-layer C3N (SLCN) sheets by molecular dynamics (MD) simulations. We found that SLBC and SLCN are isotropic in the basal plane and that their predicted thermal conductivities for infinite length sheets are 488.54 W m−1 K−1 and 799.87 W m−1 K−1, respectively. Despite many similar features in the structures of these materials, SLBC exhibits a lower thermal conductivity than SLCN due to stronger flexural acoustic phonon-defect scattering rates and weaker interatomic bonding stiffnesses. The vibrational density of states (VDOS) are calculated in both structures to elucidate their thermal conductivity differences. SLBC exhibits a more substantial redshift phenomenon in the high- and low-frequency domains than SLCN. In addition, the thermal conductivities of these materials exhibit decreasing trends in response to increases in temperature and defect ratio, and the temperature effect in SLBC is more substantial than that in SLCN, while the defect effect in SLBC is less substantial than that in SLCN. The influences of uniaxial compressive and tensile strains on the thermal conductivities of these materials are analysed separately. These two deformation modes cause different effects on the thermal transport behaviours of SLBC and SLCN: the effect of uniaxial compressive strain is slightly negative, while the effect of uniaxial tensile strain is initially positive and then negative. Moreover, the biaxial strains result in a more severe reduction in thermal conductivity than the uniaxial strains. Remarkably, the impact of uniaxial and biaxial tensile strains on thermal transport was stronger in SLBC than in SLCN. We propose that SLBC nanomembranes are promising candidates for various thermal applications.

In-plane heterojunctions, obtained by seamlessly joining two or more nanoribbon edges of isolated two-dimensional atomic crystals such as graphene and hexagonal boron nitride, are emerging as nanomaterials for the development of future multifunctional devices. The thermal transport behavior at the interface of these heterojunctions plays a pivotal role in determining their functional performance. Using molecular dynamics simulations, the interfacial thermal conductance of graphene/hexagonal boron nitride (GE/BN) in-plane heterojunctions was investigated. The GE/BN heterostructure has a remarkably high interfacial thermal conductance, and thermal rectification occurs at the interface. The results also show that the interfacial thermal conductance is effectively modulated by strain and defect engineering. The atomic defect location can affect the phonon transmission at the interface. Interestingly, compared with the nitrogen doping effect, the boron doping defect can more effectively facilitate vibrational coupling at the interface in the graphene sheet. Stress distribution and vibrational spectral analyses are performed to elucidate the thermal transport mechanism. The results of this study may provide a foundation for future research attempting to manipulate the interfacial thermal conductance in other two-dimensional heterostructures.

Carbon nanotube (CNT) reinforced nanocomposites (CNTRNs) have been regarded as the most promising substitutes for traditional carbon fiber reinforced composites, due to their excellent multi-functional properties. However, the weak CNT-matrix interface which impairs the mechanical properties of CNTRNs is always an issue, limiting their practical applications. Here, inspired by strong pinning effect of screws, we partially unzipped the CNTs into graphene nanoribbons (GNRs) and a screw-like CNT/GNR hybrid (CGH) nanostructure was proposed to reinforce the nanocomposites. It was found that the fracture strength, Young’s modulus and fracture toughness of CGH reinfroced nanocomposites can be boosted by 155 %, 89 % and 117 %, respectively, comparing to those of CNTRNs. The molecular dynamic simulation on pullout of CGHs from matrix revealed that the CNT-GNR junction can lead to a mechanical interlocking, which can not only hinder the pullout of CGH, but also cause remarkable matrix shear deformation, contributing to energy dissipation to a large extent. In addition, the morphology of CGHs can be tuned by changing structural chirality of CNTs, by which the interfacial properties can be further improved. This work opens a new route to engineer high-performance nanocomposites, and provides an in-depth understanding on the mechanical enhancement of CNT-based nanocomposites.