Aligned carbon nanotube array stiffness from stochastic three-dimensional morphology

Abstract

The landmark theoretical properties of low dimensional materials have driven more than a decade of research on carbon nanotubes (CNTs) and related nanostructures. While studies on isolated CNTs report behavior that aligns closely with theoretical predictions, studies on cm-scale aligned CNT arrays (>10(10) CNTs) oftentimes report properties that are orders of magnitude below those predicted by theory. Using simulated arrays comprised of up to 10(5) CNTs with realistic stochastic morphologies, we show that the CNT waviness, quantified via the waviness ratio (w), is responsible for more than three orders of magnitude reduction in the effective CNT stiffness. Also, by including information on the volume fraction scaling of the CNT waviness, the simulation shows that the observed non-linear enhancement of the array stiffness as a function of the CNT close packing originates from the shear and torsion deformation mechanisms that are governed by the low shear modulus (∼1 GPa) of the CNTs.

Aligned carbon nanotube–epoxy composites: the effect of nanotube organization on strength, stiffness, and toughness

“…Recent simulations of CNT vertical arrays show that the effective modulus can be reduced by several orders of magnitude due to CNT waviness [27,28]. As-grown less-packed CNT arrays experience a larger local curvature and large reductions in effective modulus, while mechanically densified arrays are less curved and their stiffness is dominated by the low shear modulus of CNTs [28].…”

“…Recent simulations of CNT vertical arrays show that the effective modulus can be reduced by several orders of magnitude due to CNT waviness [27,28]. As-grown less-packed CNT arrays experience a larger local curvature and large reductions in effective modulus, while mechanically densified arrays are less curved and their stiffness is dominated by the low shear modulus of CNTs [28]. In respect to composite reinforcement, there have been several papers published from the early 2000s focused mostly on composites with low volume fractions (less than 25 vol%) of short discrete nanotubes [29][30][31] or nanofibres [32].…”

Influence of Waviness on the Elastic Properties of Aligned Carbon Nanotube Polymer Matrix Nanocomposites

“…These oversimplifications of the CNT morphology lead to large over-predictions of the stiffness contribution of the CNTs to elastic modulus of the A-PNC, and a truly three-dimensional description of the CNT morphology that accounts the stochastic (random) nature of the CNT waviness (See Figure 1b for illustration) and the evolution of w with CNT packing proximity is necessary for more representative mechanical property prediction. 27 In this work, a previously reported simulation framework capable of simulating 10 5 CNTs with stochastic waviness, 27,31,60 and representative scaling of w with with V f , is used to evaluate the scaling of the intrinsic CNT elastic modulus (E cnt ) with w. 27,31 This is achieved by studying the contribution of (axial) stretching, (radial) shear, and bending on the deformation of CNTs in the A-PNC using an analysis similar to applied to study wavy CNTs, 31 which originates from early work on the mechanical behavior of carbon nanocoils. 61 In conjunction with recent experimental data on an exemplary A-PNC system, 26 these results are used to compare the predicted scaling of the A-PNC elastic modulusp (E pnc ) with V f for the current scheme with the results of a previous finite element analysis (FEA) to show that more complete descriptions of the CNT morphology can lead to more accurate material property prediction.…”

“…This report draws heavily from very recent studies on the mechanical behavior of wavy A-CNT (Ref. 31) and wavy CNT polymer composites (Ref. 27), to explore the mechanisms of CNT reinforcement in A-PNCs more in-depth.…”

“…[18][19][20][21][22][23][24][25][26][27][28] However, the properties reported by these previous works did not live up to the behavior predicted using current theoretical frameworks. 12 Some of the main reasons why existing models cannot accurately predict the behavior of A-CNTs architectures, such as A-CNT arrays, are the various CNT morphology and proximity effects, 13,14,18,29 which can strongly impact properties, 27,30,31 but are not well understood and cannot be adequately described in current-generation theoretical frameworks.…”