Strength and Fatigue versus Morphology of Nanotubes Assemblies—Computer-Simulated

Intrinsic strength σ_i of nanotubes undoubtedly remains unmatched by any other material, due to the lattice regularity of chemical bonds and absence of edges – unlike that in graphene. However, the CNT practical macro-assemblies in fibers or composites by far do not reach the intrinsic potential and remain outperformed by other, organic and especially bio counterparts, who achieve their overall superior strength per weight by means or optimal morphology and interfaces. This shifts the focus to still lacking quantitative understanding and multiscale coarse-grained models of collinear assemblies. Our recent simulations [1] confirm that the composite strength scales as fL/d &lt; σ_i (f is interface friction, L is average length of the constituents and d is their diameter), and show the experimental data far below what must be achievable. At the same time, tendency of the CNTs to aggregate into domains of diameter D &gt; d, towards the smectic order, can reduce the strength further down to fL/D, although this effect is mitigated by irregular lengths of the CNTs [2], unlike in molecular-rods assemblies. Further, we explore the origin of fatigue, and determine that no intrinsic lattice-defect mobility (although topologically ‘enticing’) contributes to fatigue at any practical conditions; rather, a peculiar friction-slip with elastic recoil determine the multi-cycle fatigue [2] of CNTs or other linear fibers or composites. In order to optimize and engineer the performance of such light yet strong materials, a lot remains to be learned from the biomimetics of natural examples like nacre or spider silk.<br/>[1] N. Gupta, J.M. Alred, E.S. Penev, B.I. Yakobson, <b>ACS Nano</b>, <b>15</b>, 1342 (2021).<br/>[2] N. Gupta, E.S. Penev, B.I. Yakobson, submitted (2021)