Solution processing of carbon nanotubes for electronic and environmental applications [electronic resource]
Keywords: Chemical Engineering

Single Walled Carbon Nanotubes (SWNTs) are nanomaterials with exceptional mechanical and electronic properties. There have been many proposed applications utilizing SWNTs; however integration of these nanomaterials into commercial applications has been limited because of synthetic and processing challenges. An important methodology to overcome these processing challenges is solution processing. Solution processing entails dispersion of SWNTs into appropriate solvents allowing the SWNTs to be processed and placed where desired. We explore the intermolecular interactions which influence the direct dispersion of SWNTs into neat organic solvents. A critical review of the current understanding of dispersion into organic solvents is presented. It has been found that aprotic solvents containing an amide moiety have the best SWNT dispersion qualities. To explore dispersions into neat organic solvents, we studied dispersions into two unreported organic solvents for SWNT dispersions. These solvents, 1,8-diazabicycloundec-7-ene (DBU) and 1,5-diazabicyclo(4.3.0)non-5-ene (DBN) are aprotic and contain an amidine moiety, which is analogous to the amide moiety. While these solvents have similar chemical structures and physical properties, DBU dispersed SWNTs, while DBN did not. Theoretical calculations explain this difference in dispersion due to the flexibility in the molecular structure of DBU allowing for stabilizing interactions with the SWNT. Next, Surface Sorting is introduced. In this new methodology developed in our group, SWNTs dispersions were spin-coated across silane-functionalized silicon/silicon oxide wafers. The functionality on the surface is tuned to exploit intermolecular interactions resulting in the preferential adsorption of either semiconducting (SC) or metallic (Met) SWNTs. The spin-assisted selective adsorption of SC-SWNTs on aminosilane-functionalized wafers was utilized to fabricate SWNT network field effect transistors (SWNT-FETs). These surface and deposition conditions were optimized to fabricate high-performance SWNT-FETs. The effect of dispersion conditions of SWNTs in NMP on the morphology, sorting of SC- and Met-SWNTs, and electrical performance of SWNT-FETs was investigated. It was found that extended solution processing resulted in shortening of the SWNTs, reduction in preferential adsorption of SC-SWNTs, and degradation of SWNT-FET performance. The degradation of SWNT-FET performance was explained as an effect of solution processing by the creation of defects on the SWNT wall and by processing induced solvent degradation. Finally, work furthering methods other than direct dispersion of SWNTs into organic solvents to utilize dispersions of SWNTs are discussed. The use of polymer dispersed and separated SWNTs are explored as an active material for intrinsically stretchable transistors. Density gradient ultracentrifugation (DGU) is a method to separate SWNTs dispersed in surfactants by isolating SWNTs species in a density gradient. Here, DGU was applied to arc-discharge SWNTs and a novel fractionation method was developed. Lastly, MWNTs were functionalized with amine moieties to investigated as a solid carbon dioxide capture material. In summary, this work investigated the dispersion of SWNTs in organic solvents and the sorting and transistor performance of SWNTs deposited from organic solvents. It is demonstrated that the final properties of a SWNT network transistor can be tuned by surface modification, deposition, and solution processing conditions. Also, it is shown that small differences in molecular structure of a solvent can affect SWNT dispersion.