Manipulating drying-induced carbon nanotube assemblies through substrate surface engineering

Abstract

The unique one-dimensional structure and outstanding optoelectronic properties of carbon nanotubes (CNTs) have motivated extensive research into their directed assembly. Although the droplet evaporation method offers a straightforward strategy for aligning CNTs, controlling the final deposited structure remains challenging due to the inherently high aspect ratio of CNTs. In this study, we prepared four substrates with distinct wettability and friction properties through surface modification. Time-resolved contact angle analysis was employed to monitor the evolution of the three-phase contact line and the evaporation kinetics of CNT droplets on these substrates. Combined with detailed microstructural characterization, we found that on hydrophobic, highly friction surfaces (NBE-modified silica), strong friction stabilizes the contact line during droplet drying. At the same time, rapid solvent evaporation induces droplet shrinkage, leading to a pronounced circumferential flow along the droplet periphery. This flow promotes the formation of long-range aligned CNT orientation bands with a width of ∼150 μm (orientation degree of 9.2°) after drying. These findings provide insights for the design and modification of substrates used in evaporation-driven oriented assembly of CNTs.

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2026 The Author(s). Droplet published by Jilin University and John Wiley & Sons Australia, Ltd.