Nematic-Like Alignment in SWNT Thin Films from Aqueous Colloidal Suspensions

Abstract

We present a modification of the vacuum filtration technique for fabricating transparent conductive SWNT thin films with local nematic-like orientational ordering. Dilute SWNT surfactant dispersions are filtered through a vacuum filtration setup in a slow and controlled fashion. The slow filtration creates a region of high SWNT concentration close to the filter membrane. While slowly moving through this region, SWNTs interact and align with each other, resulting in the formation of thin films with local nematic ordering. Scanning electron microscopy and image analysis revealed a local scalar order parameter (S 2D) of 0.7–0.8 for slow filtration, three times higher than those produced from “fast filtration” (S 2D ≈ 0.24). Orientational ordering is demonstrated with different stabilizing surfactants, as well as with dispersions enriched in metallic SWNTs, produced by density-gradient ultracentrifugation. Simple estimates of relative convective versus diffusive transport highlight the main differences between slow versus fast filtration and the resulting SWNT concentration profiles. Comparisons with previous studies on three stages of liquid-crystal phase transition provide insight into the spontaneous ordering process, indicating the lack of a “healing stage”, which results in a microstructure consisting of staggered domains in our SWNT films.

Wafer-scale monodomain films of spontaneously aligned single-walled carbon nanotubes

“…Transfer and characterization. For characterization and device fabrication, films were transferred onto solid substrates (e.g., SiO 2 /Si and quartz) using a wet transfer process 13 , in which the polycarbonate filter membrane was dissolved away with organic solvent (N-methyl-2-pyrrolidone or chloroform). The films were then thoroughly washed by acetone and nanopure water; subsequent X-ray photoelectron spectroscopy experiments did not detect any residual surfactants (see Supplementary Fig.…”

“…Stronger alignment, with a nematic order parameter, S, as high as ∼0.8, has been achieved by mechanically stretching a polymer film containing CNTs 10,11 ; however, the existence of the matrix material as well as low CNT densities in such films severely limit the range of applications. As far as spontaneous alignment of SWCNTs is concerned, large S values have been realized only locally [12][13][14] ; global ordering comes at the expense of S (< 0.4) 15,16 . Magnetic alignment of SWCNTs has been demonstrated 17,18 , but impractically large magnetic fields are required to obtain meaningful alignment.…”

Transforms and Operators for Directional Bioimage Analysis: A Survey

“…The area of applications based on the detection of orientation is continuously growing as the importance of directionality is becoming more and more relevant in image processing. The range of applications spans topics from astronomy (Bernasconi et al, 2005;Schuh et al, 2014;Yuan et al, 2011), aerial and satellite imagery (Jiuxiang et al, 2007;Tupin et al, 1998), material sciences (Dan et al, 2012), to biological and medical applications. Focusing on the last two categories, the palette is quite broad: detection of nodules in the lungs (Agam et al, 2005) and vessels in retinal fundus images (Lam et al, 2010;Patton et al, 2006), bioimaging (Honnorat et al, 2011), neuroimaging (Gonzalez et al, 2009;Meijering et al, 2004).…”

Science and applications of wafer-scale crystalline carbon nanotube films prepared through controlled vacuum filtration

“…( e ) Evaporation-driven self-assembly [55]. ( f ) The Langmuir–Blodgett method [56] and ( g ) Liquid crystal phase transition of CNTs [57]. …”