Strain‐Induced Alignment Mechanisms of Carbon Nanotube Networks

Abstract

Random networks comprised of millimeter-long multi-walled carbon nanotubes (CNTs) have shown unique microstructure change mechanisms under uniaxial strain. These networks can be modified into highly aligned microstructures from strain-induced plastic deformation. Applying a treatment consisting of an uncured resin as a load transfer enhancement medium leads to a dramatically increased degree of alignment and final mechanical properties of the CNT networks. The structural evolution of the CNT networks includes different modes: de-bundling, elongation to reduce waviness, sliding friction, and packing for self-assembly into large bundles. The high ductility of the treated networks, which allows the network to achieve high degrees of strain-induced alignment is mainly because the extra high aspect ratios of the individual CNTand their bundles as well as enhanced load transfer. High aspect ratio causes high degrees of entanglement and locking points between the nanotubes in the random network, which are critical to provide adequate nanotube to nanotube load transfer for ductile deformation and lead to substantially increased CNT alignment during mechanical stretching. The classical strain strengthening mechanisms used in metals and polymers such as strain hardening and crystallization of long molecular chains are discussed and compared to CNT network deformation mechanisms. The CNT network strain hardening parameter n value is as high as 0.65, over three times that of annealed low-carbon steel and more than four times of polycarbonate plastics. Strength coefficient K values for the CNT network also show high values up to roughly 450 MPa, comparable to that of annealed magnesium alloys. The results show how the high degree of alignment of CNT networks and strain strengthening can be achieved through simple uniaxial strain and load transfer medium.

Bioinspired Nanocomposite Hydrogels with Highly Ordered Structures

“…Currently, the mechanical-strain-induced strategy mainly focuses on the preparation of ordered structures of 1D nanotubes and 2D nanosheets within hydrogel matrixes, and these reported nanocomposite hydrogel materials exhibit anisotropic optical and mechanical performances. [81][82][83][84][85][86] Under tensile strain, polyacrylamide chains and 1D imogolite nanotubes in hydrogels were aligned, resulting in the formation of aligned internal structures (Figure 5a). [81,82] The obtained nanocomposite hydrogels, which had aligned structures, displayed strongly anisotropic mechanical/optical behaviors.…”

Mapping carbon nanotube orientation by fast fourier transform of scanning electron micrographs

“…In this study, it was not possible to apply strains greater than ~15% without breaking the veils. Higher strains have been reported using a variety of methods [4,18], but the maximum is likely dependent on the initial orientation of the veil, and other processing factors such as rate and lubrication. Here, different strains are applied simply to demonstrate the analysis method, although in the medium term, the approach should help to optimise the drawing process.…”

“…Aligning carbon nanotubes within such preformed arrays can improve mechanical [4,5,6,7], thermal [8,9,10,11] and electrical [12,13,14] properties. A number of studies have shown an linear increase in tensile modulus and strength with an increase in orientation ( Figure 1).…”

“…A number of studies have shown an linear increase in tensile modulus and strength with an increase in orientation ( Figure 1). [4,5,6,15,16] CNTs in these preformed arrays can be orientated by plastic deformation either when dry or following infusion with a resin for lubrication and cohesion. Improved alignment applies the intrinsically excellent axial properties of the CNTs in a desired direction, as well as promoting higher loading fractions and improved van der Waals intertube interactions [4].…”

3-D printing of multifunctional carbon nanotube yarn reinforced components

“…The material is now available in commercial quantities of sheets and yarns [11] with mechanical properties that support their use as structural reinforcement [12][13][14][15][16][17], and electrical conductivity sufficient for data cables [18]. Spun yarns with good mechanical properties have also been shown to carry useful levels of current [19].…”