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The alloy catalysts have been introduced in synthesizing highly oriented and monolayer graphene because of the combination of excellent features of different metals. However, precise manipulation o...

Synthetic high-performance fibers, such as polyaramid fibers, have attracted particular attention owing to their excellent mechanical properties and promising applications in safety protection fields. However, fabricating fibers with high strength and toughness is challenging due to their intrinsic conflicts. Herein, we report a simultaneous improvement in strength and toughness of heterocyclic aramid fibers by 26% and 66%, respectively, via in situ polymerizing small amount (0.05 wt%) of short aminated single-walled carbon nanotube (SWNT) into heterocyclic aramid fibers, yielding 6.44 ± 0.11 GPa in tensile strength and 184.0 ± 11.4 MJ m−3 in toughness. Combined experimental evidences and atomistic simulations, it was uncovered that short aminated SWNTs with favorable dispersity and alignment significantly improve the crystallinity and orientation degree of heterocyclic aramid chains by a scope of 8.6 nm, and the in situ polymerization between short aminated SWNTs and heterocyclic aramid monomers increases the length of polymer chains and the interfacial interaction therein to promote stress transfer and suppress the strain localization. These two effects account for the simultaneous improvement in strength and toughness of heterocyclic aramid fibers via small addition of short aminated SWNTs. This composite manner of “small addition, big gains” through global optimization should guide further work on improving the strength and toughness of composites.

Structural superlubricity (SSL) is a state of contact between two sliding surfaces with no wear and ultralow friction. SSL has been characterized at contacts with van der Waals (vdW) layered materials, while its robustness under high pressure has not been assessed. Here we report experimental results showing that incommensurate vdW interfaces between graphite can maintain the state of SSL under the pressure of no lower than 9.45 GPa, and the vdW contact between a tungsten tip and graphite substrate remains stable up to 3.74 GPa, even higher than the strength of most solids. Beyond this critical pressure, wear is activated, signaling the breakdown of vdW contacts and SSL. This unexpected strong pressure resistance and wear-free feature of SSL signals a wear mechanism beyond the Archard law. Atomistic simulations reveal the microscopic processes of SSL breakdown, which originates from lattice destruction at the vdW contact by pressure-assisted bonding, triggering wear through shear-induced tearing of layered vdW materials. The correlation between the breakdown pressure and material parameters for a number of vdW contacts was analyzed. The results show that the bulk modulus and the first ionization energy, are the most relevant factors, which indicate the combined structural and electronic effects. The critical pressures of several metal/graphite contacts could exceed the strength of metals, demonstrating the robustness of SSL. These findings offer fundamental understandings of wear at the vdW contacts, and could guide the design of SSL-derived applications.

The rapid development of two-dimensional (2D) materials has significantly broadened the scope of 2D science in both fundamental scientific interests and emerging technological applications, wherein the mechanical properties play an indispensably key role. Nevertheless, particularly challenging is the ultrathin nature of 2D materials that makes their manipulations and characterizations considerably difficult. Herein, thanks to the excellent flexibility of vanadium disulfide (VS2) sheets, their susceptibility to out-of-plane deformation is exploited to realize the controllable loading and enable the accurate measurements of mechanical properties. In particular, the Young's modulus is estimated to be 44.4 ± 3.5 GPa, approaching the lower limit for 2D transition metal dichalcogenides (TMDs). We further report the first measurement of thickness-dependent bending rigidity of VS2, which deviates from the prediction of the classical continuum mechanics theory. Additionally, a deeper understanding of the mechanics within two dimensions also facilitates the modulation of strain-coupled physics at the nanoscale. Our Raman measurements showed the Gruneisen parameters for VS2 were determined for the first time to be γE2g1 ≈ 0.83 and γA1g ≈ 0.32.

The rapid development of two-dimensional (2D) materials has significantly broadened the scope of 2D science in both fundamental scientific interests and emerging technological applications, wherein the mechanical properties play an indispensably key role. Nevertheless, particularly challenging is the ultrathin nature of 2D materials that makes their manipulations and characterizations considerably difficult. Herein, thanks to the excellent flexibility of vanadium disulfide (VS

Multilayer graphene exhibits strong mechanical anisotropy in the nonlinear elastic regime, and tuning this mechanical anisotropy without damaging the graphene is a tough challenge. In this work, we propose an efficient strategy to tune the mechanical anisotropy of multilayer graphene via interlayer twist. The orientation-dependent strain–stress curve of monolayer graphene is described in analytical form, which is further generalized for predicting the mechanical anisotropy of twisted multilayer graphene by introducing a twist-induced “phase shift.” These predictions are supported by atomistic simulations. It is found that the strong nonlinear mechanical anisotropy of multilayer graphene can be effectively tuned and even eliminated via the twist-induced phase shift. These findings are finally generalized for other layered crystals.

The breakthrough in the synthesis of graphyne, graphdiyne and graph-4-yne stimulates interest in studying new members of the graphyne family for promising applications. In this work, a new allotrope of graphyne with excellent stability and an ultrahigh specific surface area of 4255 m2 g−1, named C68-graphyne, is predicted by first principles calculations. Mechanical tests reveal that C68-graphyne exhibits much smaller in-plane tensile stiffness (∼50.5 N m−1) and out-of-plane bending stiffness (∼0.5 eV) than graphene (in-plane tensile stiffness 350 N m−1 and out-of-plane bending stiffness 1.4 eV), suggesting C68-graphyne as a superflexible material. Meanwhile, our results show that monolayer C68-graphyne is a semiconductor with a direct band gap of 1.0 eV, which can be tuned by strain-engineering, and the calculated carrier mobility is as high as 1.81 × 105 to 2.97 × 105 cm2 V−1 s−1 at 300 K. Finally, the potential application of C68-graphyne as an anode material for lithium-ion batteries is explored and predicted. The calculated results show highly efficient charge transfer from the adsorbed Li ions to C68-graphyne yet a low diffusion barrier for Li ions in C68-graphyne for fast charge/discharge rates. The storage capacities for Li in monolayer and bilayer C68-graphyne are calculated to be as high as 1954 and 1675 mA h g−1, respectively. These features make C68-graphyne a promising anode material for lithium-ion batteries with excellent energy storage capacities as well as fast charge/discharge rates.

Phosphorene, a two-dimensional material that can be exfoliated from black phosphorus, exhibits remarkable mechanical, thermal, electronic, and optical properties. In this work, we demonstrate that the unique structure of pristine phosphorene endows this material with exceptional quantum-mechanical performance by using first-principles calculations. Upon charge injection, the maximum actuation stress is 7.0 GPa, corresponding to the maximum actuation strain as high as 36.6% that is over seven times larger than that of graphene (4.7%) and comparable with natural muscle (20–40%). Meanwhile, the maximum volumetric work density of phosphorene (207.7 J/cm3) is about three orders of magnitude larger than natural muscle (0.008–0.04 J/cm3) and approximately six times larger than graphene (35.3 J/cm3). The underlying mechanism of this exceptional electromechanical performance in phosphorene is well revealed from the analysis of atomic structure and electronic structure. Finally, the influence of charge on the mechanical behaviors of phosphorene is examined by mechanical tests, indicating the sufficient structural integrity of phosphorene under the combined electromechanical loading. These findings shed light on phosphorene for promising applications in developing nanoelectromechanical actuators.

Graphene possesses extraordinary mechanical, electronic, and thermal properties, thus making it one of the most promising building blocks for constructing macroscopic high performance and multifunctional materials. However, the common material strength–ductility paradox also appears in the carbon-nanoarchitected materials and some of the key mechanical performance, for example, the tensile strength of graphene-based materials, are still far lower than that of graphene. Inspired by the exceptional mechanical performance of silk protein benefiting from the conformations of folded structures as well as their transitions, this work proposed a topological strategy to yield graphene-based materials with ultrahigh ductility while maintaining decent tensile strength by self-folding graphene sheets. This drastically improved mechanical performance of graphene-based materials is attributed to the exploitation of shearing, sliding, and unfolding deformation at the self-folded interface. Molecular dynamics simulations show that both modulating self-folded length and engineering interface interaction can effectively control the strength, ductility, and the ductile failure of van der Waals interfaces among the self-folded structures, where interfacial shearing, sliding, and unfolding open channels to dissipate mechanical energy. Based on the insights into the atomic-scale deformation by molecular dynamics simulations, the underlying mechanism of deformation and failure of these materials is finally discussed with a continuum mechanics-based model. Our findings bring perceptive insights into the microstructure design of strong-yet-ductile materials for load-bearing engineering applications.

The fabrication of nanotips has been driven by the increasing industrial demands in developing high-performance multifunctional nanodevices. In this work, we proposed a controlled, rapid as well as low cost nanomolding-necking technology to fabricate gold nanotips arrays. The geometries of gold nanotips having cone angle range of ∼28-77° and curvature radii of