Unexpected structural scaling and predictability in carbon nanotubes

Abstract

Carbon nanotubes (CNTs) hold immense promise for a wide array of applications due to their exceptional physical and chemical properties. Understanding and controlling their structural characteristics, particularly the diameter and number of walls, is crucial for harnessing their full potential. We investigated the relationship between these parameters for both commercially available and lab-scale CNTs, spanning a wide range of outer diameters (1–13 nm) and numbers of walls (1–13). Our findings revealed a commonality among the structural diversity, rather than a random distribution, as evidenced by a piecewise linear relationship between the outer diameter and number of walls, with an inflection point occurring at approximately 4 nm in diameter. This observation is unexpected, as the CNTs were synthesized using different approaches and growth conditions; yet, as a group, they exhibit a “structural scaling”. Additionally, we made an intriguing observation: despite increases in outer diameter and number of walls, the inner diameters remained relatively constant (4–5 nm) for thicker CNTs with more than three walls. These results suggest that structural properties can be estimated based on diameter, which not only advances our fundamental understanding of CNT synthesis but also provides practical insights for tailoring CNT properties for various applications.