(276g) Physical and Electrical Characterization of Single and Multi-Walled Carbon Nanotube Bulk Networks

Carbon nanotubes (CNTs) are a promising material to enhance the next generation of energy storage and transmission systems. When assembled into bulk structures, CNTs can be engineered into many different form factors (e.g. CNT papers, ribbons, yarns, ropes, wires, and cables) to meet the design requirements of a particular application. Conductors composed of CNT materials can benefit from their unique nanoscale properties, and CNTs offer improvements in weight savings, flexibility, and corrosion resistance. Advancements are still needed, however, in material processing (e.g. purification, chemical doping, and nanoscale network modification) to realize the electrical properties predicted from theory and measured at the individual nanotube level in these bulk systems. The susceptibility to doping and densification depends heavily on the CNT diameter and CNT nearest neighbor interactions which may result from close-packed bundling, which is prevalent for single-wall carbon nanotubes (SWCNTs).  In comparison, double walled carbon nanotubes (DWCNTs) and multi walled carbon nanotubes (MWCNTs) have network packing that is more rigid and rod-like. These differences in the nanoscale morphology translate into variations in the way the bulk network can be ordered and the resulting physical properties. Several strategies to understand and control these differences, in the present work, have been employed to measure the bulk properties of CNT materials including the combined effects of CNT type purity, mechanical densification, chemical doping, and nanoscale alignment. A constructed sample set of SWCNTs and MWCNTs mixed at varying weight loadings (0 % - 100 % w/w SWCNTs in MWCNTs at 20 % intervals) was used to measure differences in the way the two materials behave at the bulk scale. Four-point probe measurements of the electrical conductivity (S/m) were taken on Van der Pauw electrode squares of the SWCNT-MWCNT materials. Differences in the mixed CNT network’s susceptibility to known chemical dopants (e. g. KAuBr₄ and I₂ gas) were measured and show a correlation between CNT diameter and relative extent of SWCNTs present on conductivity. Additionally, the material was characterized using Raman spectroscopy, scanning electron microscopy (SEM), and thermal gravimetric analysis. Differences in the D and G bands of the Raman spectra before and after exposure to the chemical dopants indicate differences in SWCNT and MWCNT responses to chemical treatment. SEM analysis of the surface morphology shows reduced void volume in the SWCNT samples in comparison to the higher MWCNTs weight loadings. The impact of these measurements will be discussed in the context of CNT technologies and applications, for both energy storage and transmission systems.