Torsional Properties of Bundles with Randomly Packed Carbon Nanotubes

Abstract

Carbon nanotube (CNT) bundles/fibers possess promising applications in broad fields, such as artificial muscles and flexible electronics, due to their excellent mechanical properties. The as-prepared CNT bundles contain complex structural features (e.g., different alignments and components), which makes it challenging to predict their mechanical performance. Through in silico studies, this work assessed the torsional performance of CNT bundles with randomly packed CNTs. It is found that CNT bundles with varying constituent CNTs in terms of chirality and diameter exhibit remarkably different torsional properties. Specifically, CNT bundles consisting of CNTs with a relatively large diameter ratio possess lower gravimetric energy density and elastic limit than their counterpart with a small diameter ratio. More importantly, CNT bundles with the same constituent CNTs but different packing morphologies can yield strong variation in their torsional properties, e.g., up to 30%, 16% and 19% difference in terms of gravimetric energy density, elastic limit and elastic constants, respectively. In addition, the separate fracture of the inner and outer walls of double-walled CNTs is found to suppress the gravimetric energy density and elastic limit of their corresponding bundles. These findings partially explain why the experimentally measured mechanical properties of CNT bundles vary from each other, which could benefit the design and fabrication of high-performance CNT bundles.

Torsional fracture of carbon nanotube bundles: a reactive molecular dynamics study

“…23 Molecular dynamics simulations were used to understand the torsional buckling of pristine and irradiated CNTs. 29,31,33,[35][36][37] As a general trend, these studies observed that in pristine CNTs, van der Waals (vdW) interactions are considered a crucial parameter in defining the mechanical and structural properties of the CNTBs upon torsional loading. During the twisting process, the increase in the interaction area by twisting the CNTB enhances the inter-tube interactions up to a critical angle.…”

“…This process is responsible for the CNTB unpacking, which dramatically diminishes its torsional stiffness. 35 On the other hand, irradiation-induced inter-tube defects can significantly increase the critical buckling torque and critical buckling angle while slightly increasing the torsional stiffness. 37 Albeit some relevant studies have investigated the mechanical properties of single CNTs and CNTBs upon torsional loading, their fracture patterns, and possible products yielded in this process remain not described.…”

“…19 However, when assembled into bundles, their strength reduces dramatically. 20 Recently, several experimental [21][22][23][24][25][26] and theoretical 18,[27][28][29][30][31][32][33][34][35][36][37][38] studies have investigated the mechanical properties of carbon nanotube bundles (CNTBs) in the form of long yarns, 23,34 nanofibers, 28 nanoropes, 27,32 and crystals. 18,36 Usually, torsional and tensile loadings are applied to analyze the behavior of these materials upon stress.…”

Estimation of the Band Gap of Carbon Nanotube Bundles

“…The conductivity of SWCNTs at equilibrium is determined by one pair of parameters (n,m) of the structural configuration, namely, the chiral index. Recently, CNTBs have attracted researchers' interests, and some efforts have been made regarding the mechanical resilience [12,13] and fracture patterns [14] under torsional strain. Singh [15] used CNTBs to build hybrid CMOS (complementary metal-oxide semiconductor)-compatible devices, among which the conductivity of CNTBs is one of the key issues to study.…”

Nanomechanics and Plasticity

“…Extensive works have employed low-dimensional nanomaterials to enhance the mechanical and thermal properties of composite materials [ 27 , 28 ]. For instance, the CNT has excellent mechanical properties, which is promising for artificial muscles and flexible electronics, while the mechanical performance of CNT fibers/bundles depend on various factors, such as the alignments and compositions of constituent CNTs as shown by Wei et al [ 29 ]. The excellent mechanical properties of nanomaterials also make them promising for extreme applications, such as the protective shields that alleviate the damage from the hyper-velocity impact.…”