Anisotropic Carbon Nanotube Films Fabricated from a Lyotropic Liquid-Crystalline Polymer

Highly conductive single-walled carbon nanotube thin film preparation by direct alignment on substrates from water dispersions

A safe, scalable method for producing highly conductive aligned films of single-walled carbon nanotubes (SWNTs) from water suspensions is presented. While microfluidic assembly of SWNTs has received significant attention, achieving desirable SWNT dispersion and morphology in fluids without an insulating surfactant or toxic superacid is challenging. We present a method that uniquely produces a noncorrosive ink that can be directly applied to a device in situ, which is different from previous fabrication techniques. Functionalized SWNTs (f-SWNTs) are dispersed in an aqueous urea solution to leverage binding between the amine group of urea and the carboxylic acid group of f-SWNTs and obtain urea-SWNT. Compared with SWNTs dispersed using conventional methods (e.g., superacid and surfactants), the dispersed urea-SWNT aggregates have a higher aspect ratio with a rodlike morphology as measured by light scattering. The Mayer rod technique is used to prepare urea-SWNT, highly aligned films (two-dimensional nematic order parameter of 0.6, 5 μm spot size, via polarized Raman) with resistance values as low as 15-1700 Ω/sq in a transmittance range of 2-80% at 550 nm. These values compete with the best literature values for conductivity of SWNT-enabled thin films. The findings offer promising opportunities for industrial applications relying on highly conductive thin SWNT films.

Aligned SWNT films from low-yield stress gels and their transparent electrode performance

Carbon nanotube films are promising for transparent electrodes for solar cells and displays. Large-area alignment of the nanotubes in these films is needed to minimize the sheet resistance. We present a novel coating method to coat high-density, aligned nanotubes over large areas. Carbon nanotube gel dispersions used in this study have aligned domains and a low yield stress. A simple shearing force allows these domains to uniformly align. We use this to correlate the transparent electrode performance of single-walled carbon nanotube films with the level of partial alignment. We have found that the transparent electrode performance improves with increasing levels of alignment and in a manner slightly better than what has been previously predicted.

Oriented, polymer-stabilized carbon nanotube films: influence of dispersion rheology

Thin carbon nanotube films have great potential for transparent electrodes for solar cells and displays. One advantage for using carbon nanotubes is the potential for solution processing. However, research has not been done to connect solution rheological properties with the corresponding film characteristics. Here we study the rheological properties of single-walled carbon nanotube/polythiophene composite dispersions to better understand the alignment that can be achieved during deposition. Several parameters are varied to explore the cause of the alignment and the requirements of achieving a uniform, aligned carbon nanotube/polythiophene film. By understanding the dispersions thoroughly, the film quality can be predicted.