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

TL;DR

This paper presents a microscopy method to identify collapsed carbon nanotubes in high-strength fibers, revealing that up to 70% of CNTs can collapse depending on synthesis conditions, which impacts fiber performance.

Contribution

It introduces a novel microscopy technique for unambiguous identification of collapsed CNTs and analyzes how synthesis parameters influence collapse prevalence and CNT properties.

Findings

Close proximity in bundles promotes collapse.

CNT stoutness controls collapse onset.

Synthesis conditions can yield up to 70% collapsed CNTs.

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 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 $0.25 layer/nm$.