In Situ Microscopy of 2-Dimensional Carbon Nanotube Liquid Crystals at Liquid/Liquid Interfaces.

Abstract

Carbon nanotubes (CNTs) must be ordered into densely aligned arrays to fully exploit their electronic properties in next-generation integrated circuits. Recent advances have shown that CNTs can accumulate and self-order at liquid-liquid interfaces, from which the CNTs can be transferred onto a substrate to create dense CNT arrays with remarkable electronic characteristics. Here, by leveraging in situ polarized optical microscopy, we investigate the self-assembly of CNTs at organic solvent-water interfaces and answer key questions about CNT assembly structure and formation kinetics. We find that CNTs spontaneously form liquid crystalline (LC) phases at the liquid-liquid interface with a density strongly dependent on the concentration of CNTs in the organic solvent ink. This LC behavior is robust across a range of polymer wrappers, including polyfluorenes, triblock copolymers, and polycarbazole (PCz). Polarized microscopy reveals that the resulting LC domains are polycrystalline in nature with domain size governed by the kinetics of LC formation. Additives can alter interfacial dynamics─either by promoting Marangoni flow or by enhancing CNT transport─offering an avenue to tune domain characteristics. We find that the LC domain structure formed at the interface is largely preserved upon transfer to a solid substrate, indicating that optimizing interfacial ordering is key to achieving high-quality CNT arrays for electronic applications. In cases where distortions occur during transfer, they often arise from a mismatch between the substrate translation speed and the transport velocity of the LC to the solid surface.