High-Resolution X-ray Spectromicroscopy Reveals Process-Structure Correlations in sub-5-μm Diameter Carbon Nanotube-Polymer Composite Dry-Spun Yarns

A persistent lack of detailed and quantitative structuralanalysisof these hierarchical carbon nanotube (CNT) ensembles precludes establishingprocessing-structure-property relationships that are essential toenhance macroscale performance (e.g., in mechanical, electrical, thermalapplications). Here, we use scanning transmission X-ray microscopy(STXM) to analyze the hierarchical, twisted morphology of dry-spunCNT yarns and their composites, quantifying key structural characteristicssuch as density, porosity, alignment, and polymer loading. As theyarn twist density increases (15,000 to 150,000 turns per meter),the yarn diameter decreased (4.4-1.4 mu m) and densityincreased (0.55-1.26 g center dot cm(-3)), as intuitivelyexpected. Yarn density, rho, ubiquitously scaledwith diameter d according to rho similar to d (-2) for all parameters studied here. Spectromicroscopyprobes with 30 nm resolution and elemental specificity were employedto analyze the radial and longitudinal distribution of the oxygen-containingpolymer content (similar to 30% weight fraction), demonstrating nearlyperfect filling of the voids between CNTs with a vapor-phase polymercoating and cross-linking process. These quantitative correlationshighlight the intimate connections between processing conditions andyarn structure with important implications for translating the nanoscaleproperties of CNTs to the macroscale.

Automated summary

Detailed and quantitative structural analysis of hierarchical carbon nanotube (CNT) ensembles, including the twisted morphology of CNT yarns and their composites, has been conducted using scanning transmission X-ray microscopy (STXM). The study reveals that as the twist density of the yarn increases, the diameter decreases and the density increases as expected. The distribution of the oxygen-containing polymer content has also been analyzed, showing a nearly perfect filling of the voids between CNTs. These findings highlight the important connections between processing conditions, yarn structure, and the properties of CNTs at the macroscale.