Magnetically aligned single wall carbon nanotube films: Preferred orientation and anisotropic transport properties

Abstract

Thick films of single wall carbon nanotubes (SWNT) exhibiting in-plane preferred orientation have been produced by filter deposition from suspension in strong magnetic fields. We characterize the field-induced alignment with x-ray fiber diagrams and polarized Raman scattering, using a model which includes a completely unaligned fraction. We correlate the texture parameters with resistivity and thermal conductivity measured parallel and perpendicular to the alignment direction. Results obtained with 7 and 26 Tesla fields are compared. We find no significant field dependence of the distribution width, while the aligned fraction is slightly greater at the higher field. Anisotropy in both transport properties is modest, with ratios in the range 5-9, consistent with the measured texture parameters assuming a simple model of rigid rod conductors. We suggest that further enhancements in anisotropic properties will require optimizing the filter deposition process rather than larger magnetic fields. We show that both x-ray and Raman data are required for a complete texture analysis of oriented SWNT materials. Comments Postprint version. Published in Journal of ABSTRACTThick films of single wall carbon nanotubes (SWNT) exhibiting in-plane preferred orientation have been produced by filter deposition from suspension in strong magnetic fields. We characterize the field-induced alignment with x-ray fiber diagrams and polarized Raman scattering, using a model which includes a completely unaligned fraction. We correlate the texture parameters with resistivity and thermal conductivity measured parallel and perpendicular to the alignment direction. Results obtained with 7 and 26 Tesla fields are compared. We find no significant field dependence of the distribution width, while the aligned fraction is slightly greater at the higher field.Anisotropy in both transport properties is modest, with ratios in the range 5 -9, consistent with the measured texture parameters assuming a simple model of rigid rod conductors. We suggest that further enhancements in anisotropic properties will require optimizing the filter deposition process rather than larger magnetic fields. We show that both x-ray and Raman data are required for a complete texture analysis of oriented SWNT materials.

Correlation of properties with preferred orientation in coagulated and stretch-aligned single-wall carbon nanotubes

“…Also the tubes/bundles in the fiber are not perfectly aligned. The largest κ measured to date, 19 W/mK, was obtained from a fiber with mosaic HWHM of 21 o [6], about half the value for the best magnetic field-aligned buckypaper: 48 W/m-K uncorrected for density, HWHM = 16 o [15].…”

An infiltration method for preparing single‐wall nanotube/epoxy composites with improved thermal conductivity

“…3 The electrical resistance associated with electron hopping between SWNT contributes to the~6 orders of magnitude difference in electrical conductivity between a 2wt% composite (~10 -3 S/cm) and a SWNT buckypaper (~10 3 S/cm). 20 (Nanotube buckypaper is produced by filtering a nanotube suspension to form a freestanding, all-nanotube film.) This electron hopping SWNT-SWNT electrical resistance is negligible compared to the SWNTpolymer electrical resistance, such that electrons reside primarily on SWNT and the hopping mechanism dominates electrical conduction through the composite.…”

Ultrastrong, Stiff and Multifunctional Carbon Nanotube Composites

“…Specifically, the shift of the intensity ratio (I G /I G⊥ ) of G band peaks was measured. Theoretically, Raman intensity change is proportional to cos 4 θ versus the CNT orientation angle (θ ) [32] at θ = 0 • or when the polarization of the excitation laser's oscillating electromagnetic field is parallel to the nanotube longitudinal axis, the Raman intensity is maximized because of enhanced absorption, molecular polarization, and optical conductivity [33]. In contrast, at θ = 90 • , the Raman scattering from the SWNTs displays a minimum value.…”