# Global alignment of solution-based single-wall carbon nanotube films via machine-vision controlled filtration

## TL;DR

This paper presents a machine-vision controlled filtration method to produce globally-aligned single-wall carbon nanotube films with improved nematic order, enabling advanced nanotube electronics and optical devices.

## Contribution

It introduces an automated, feedback-controlled filtration process for large-scale, globally-aligned SWCNT films adaptable to various nanotube types and membranes.

## Key findings

- Enhanced nematic ordering through feedback-controlled filtration
- Achieved two-dimensional radial alignment via meniscus combing
- Identified alignment mechanisms involving intertube interactions and membrane charging

## Abstract

Over the past decade, substantial progress has been made in the chemical processing (chiral enrichment, length sorting, handedness selectivity, and filling substance) of single-wall carbon nanotubes (SWCNTs). Recently, it was shown that large, horizontally-aligned films can be created out of post-processed SWCNT solutions. Here, we use machine-vision automation and parallelization to simultaneously produce globally-aligned SWCNT films using pressure-driven filtration. Feedback control enables filtration to occur with a constant flow rate that not only improves the nematic ordering of the SWCNT films, but also provides the ability to align a wide range of SWCNT types and on a variety of nanoporous membranes using the same filtration parameters. Using polarized optical spectroscopic techniques, we show that meniscus combing produces a two-dimensional radial SWCNT alignment on one side of the film. After we flatten the meniscus through silanation, spatially-resolved nematicity maps on both sides of the SWCNT film reveal global alignment across the entire structure. From experiments changing ionic strength and membrane tribocharging, we provide evidence that the SWCNT alignment mechanism stems from an interplay of intertube interactions and ordered membrane charging. This work opens up the possibility of creating globally-aligned SWCNT film structures for a new-generation of nanotube electronics and optical control elements.