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Abstract Structural superlubricity (SSL) is a state of contact with no wear and ultralow friction. SSL has been characterized at contact with van der Waals (vdW) layered materials, while its stability under extreme loading conditions has not been assessed. By designing both self-mated and non-self-mated vdW contacts with materials chosen for their high strengths, we report outstanding robustness of SSL under very high pressures in experiments. The incommensurate self-mated vdW contact between graphite interfaces can maintain the state of SSL under a pressure no lower than 9.45 GPa, and the non-self-mated vdW contact between a tungsten tip and graphite substrate remains stable up to 3.74 GPa. Beyond this critical pressure, wear is activated, signaling the breakdown of vdW contacts and SSL. This unexpectedly strong pressure-resistance and wear-free feature of SSL breaks down the picture of progressive wear. Atomistic simulations show that lattice destruction at the vdW contact by pressure-assisted bonding triggers wear through shear-induced tearing of the single-atomic layers. The correlation between the breakdown pressure and material properties shows that the bulk modulus and the first ionization energy are the most relevant factors, indicating the combined structural and electronic effects. Impressively, the breakdown pressures defined by the SSL interface could even exceed the strength of materials in contact, demonstrating the robustness of SSL. These findings offer a fundamental understanding of wear at the vdW contacts and guide the design of SSL-enabled applications.

Abstract Synthetic high-performance fibers present excellent mechanical properties and promising applications in the impact protection field. However, fabricating fibers with high strength and high toughness is challenging due to their intrinsic conflicts. Herein, we report a simultaneous improvement in strength, toughness, and modulus of heterocyclic aramid fibers by 26%, 66%, and 13%, respectively, via polymerizing a small amount (0.05 wt%) of short aminated single-walled carbon nanotubes (SWNTs), achieving a tensile strength of 6.44 ± 0.11 GPa, a toughness of 184.0 ± 11.4 MJ m−3, and a Young’s modulus of 141.7 ± 4.0 GPa. Mechanism analyses reveal that short aminated SWNTs improve the crystallinity and orientation degree by affecting the structures of heterocyclic aramid chains around SWNTs, and in situ polymerization increases the interfacial interaction therein to promote stress transfer and suppress strain localization. These two effects account for the simultaneous improvement in strength and toughness.

Abstract Two-dimensional (2D) materials are promising candidates for uses in next-generation electronic and optoelectronic devices. However, only a few high-quality 2D materials have been mechanically exfoliated to date. One of the critical issues is that the exfoliability of 2D materials from their bulk precursors is unknown. To assess the exfoliability of potential 2D materials from their bulk counterparts, we derived an elasticity-based-exfoliability measure based on an exfoliation mechanics model. The proposed measure has a clear physical meaning and is universally applicable to all material systems. We used this measure to calculate the exfoliability of 10,812 crystals having a first-principles calculated elastic tensor. By setting the threshold values for easy and potential exfoliation based on already-exfoliated materials, we predicted 58 easily exfoliable bulk crystals and 90 potentially exfoliable bulk crystals for 2D materials. As evidence, a topology-based algorithm indicates that there is no interlayer bonding topology for 93% predicted exfoliable bulk crystals, and the analysis on packing ratios shows that 99% predicted exfoliable bulk crystals exhibit a relatively low packing ratio value. Moreover, literature survey shows that 34 predicted exfoliable bulk crystals have been experimentally exfoliated into 2D materials. In addition, the characteristics of these predicted 2D materials were discussed for practical use of such materials.

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. [ABSTRACT FROM AUTHOR]

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 <5 nm can be prepared by tailoring the diameters of raw nanorods in nanomolding process or modulating the necking temperature. Molecular dynamics simulation reveals that the formation of the nanotip geometry is determined by the interplay between dislocation-based and diffusion-based deformation mechanisms, intrinsically arising from the nonlinear dependence of atom diffusion on temperature and sample size. The good controllability, mass production and low cost of the developed nanomolding-necking technology make it highly promising in developing nanodevices for a wide range of applications, such as probing, sensing, antireflection coating and nanoindentation. [ABSTRACT FROM AUTHOR]