Identification of Collapsed Carbon Nanotubes in High-Strength Fibers Spun from Compositionally Polydisperse Aerogels

Abstract

Carbon Nanotubes (CNTs) of sufficiently large diameter and a few layers self-collapse into flat ribbons at atmospheric pressure, forming bundles of stacked CNTs that maximize packing and thus CNT interaction. Their improved stress transfer by shear makes collapsed CNTs ideal building blocks in macroscopic fibers of CNTs with high-performance longitudinal properties, particularly high tensile properties as reinforcing fibres. This work introduces cross-sectional transmission electron microscopy of FIB-milled samples as a way to univocally identify collapsed 2 CNTs and to determine the full population of different CNTs in macroscopic fibers produced by spinning from floating catalyst chemical vapour deposition. We show that close proximity in bundles is a major driver for collapse and that CNT "stoutness" (number of layers/diameter), which dominates the collapse onset, is controlled by the growth promotor. Despite differences in decomposition route, different C precursors lead to similar distributions of the ratio layers/diameter. The synthesis conditions in this study give a maximum fraction of collapsed CNTs of 70% when using selenium as promotor, corresponding to an average of 0.25 layer/nm.

Simultaneous improvements in conversion and properties of molecularly controlled CNT fibres

“…Since the comparison is now made across different types of CNTs and at equivalent degree of alignment (note, all fibres were collected at the same constant drawing rate of 28 m/min, and not stretched/post-processed to increase alignment), we attribute this improvement in properties to improved CNT packing and/or longer CNT length. Indeed, few-layer CNTs that collapse into ribbons [24] show more efficient packing [22,25] and thus form longer domains for stress transfer, which would translate into simultaneous increases in tensile strength and modulus, as observed here (Supplementary Material, Fig. S7.2).…”

Scalable High Tensile Modulus Composite Laminates Using Continuous Carbon Nanotube Yarns for Aerospace Applications

“… 35 , 45 , 46 Previous investigations in MIRALON CNT yarns as well as in other CNT yarns found collapsed CNTs formed dog-bone-like graphitic crystal molecular structures, which proved to be a critical contributor to their high strength. 20 , 22 , 47 , 48 Figure 1 b,c displays the unique CNT self-assembling phenomenon observed in the CNT yarns investigated in the study, similar to those investigations. Large diameter tubes with a smaller number of walls tend to collapse at diameters above 7.8 nm for double-walled CNTs (DWCNTs).…”

“…Figure b illustrates the alternating-layer microstructures of aligned CNTs coming from the cross-section (bright circular shapes) and misaligned CNTs (long, gray lines) as well as relatively uniform sizes of the residual catalyst particles (black dots appearing from Z contrast). The misaligned CNT layers could also include amorphous carbon and other organic impurities formed during the manufacturing process. ,, Previous investigations in MIRALON CNT yarns as well as in other CNT yarns found collapsed CNTs formed dog-bone-like graphitic crystal molecular structures, which proved to be a critical contributor to their high strength. ,,, Figure b,c displays the unique CNT self-assembling phenomenon observed in the CNT yarns investigated in the study, similar to those investigations. Large diameter tubes with a smaller number of walls tend to collapse at diameters above 7.8 nm for double-walled CNTs (DWCNTs).…”

Scalable High Tensile Modulus Composite Laminates Using Carbon Nanotube Yarns

“…The misaligned CNT layers could also include amorphous carbon and other organic impurities formed during the manufacturing process 19,26,27 . Previous investigations into MIRALON ® CNT yarns as well as in other CNT yarns found collapsed CNTs formed dog-bone-like graphitic crystal molecular structures which proved to be a critical contributor to their high strength 7,9,28,29 . Figures 2(e shows the integration of the WAXS scattering intensity from 20° < 2θ < 30° range including the (002) peaks.…”