Groove-Assisted Global Spontaneous Alignment of Carbon Nanotubes in Vacuum Filtration

TL;DR

This study reveals that the surface morphology of filter membranes, especially pre-existing or imprinted grooves, controls the direction of carbon nanotube alignment during vacuum filtration, enabling precise and reproducible macroscale CNT assemblies.

Contribution

It demonstrates that filter membrane surface grooves dictate CNT alignment direction, advancing understanding and control of macroscale CNT assembly during vacuum filtration.

Findings

Surface grooves on filter membranes control CNT alignment direction.

Imprinted grooves can precisely define CNT alignment.

Global CNT alignment can be reproducibly directed by membrane surface patterning.

Abstract

Ever since the discovery of carbon nanotubes (CNTs), it has long been a challenging goal to create macroscopically ordered assemblies, or crystals, of CNTs that preserve the one-dimensional quantum properties of individual CNTs on a macroscopic scale. Recently, a simple and well-controlled method was reported for producing wafer-scale crystalline films of highly aligned and densely packed CNTs through spontaneous global alignment that occurs during vacuum filtration [\textit{Nat.\ Nanotechnol}.\ \textbf{11}, 633 (2016)]. However, a full understanding of the mechanism of such global alignment has not been achieved. Here, we report results of a series of systematic experiments that demonstrate that the CNT alignment direction can be controlled by the surface morphology of the filter membrane used in the vacuum filtration process. More specifically, we found that the direction of parallel grooves pre-existing on the surface of the filter membrane dictates the direction of the resulting CNT alignment. Furthermore, we intentionally imprinted periodically spaced parallel grooves on a filter membranes using a diffraction grating, which successfully defined the direction of the global alignment of CNTs in a precise and reproducible manner.