The thermal and electrical conductivities in nanocomposites of single walled carbon nanotubes (SWNT) and polyethylene (PE) are investigated in terms of SWNT loading, the degree of PE crystallinity, and the PE alignment. Isotropic SWNT/PE nanocomposites show a significant increase in thermal conductivity with increasing SWNT loading, having 1.8 and 3.5 W/mK at a SWNT volume fraction of φ ∼ 0.2 in low-density PE (LDPE) and high-density PE (HDPE), respectively. This increase in SWNT/HDPE is more than additive and suggests a reduction of the interfacial thermal resistance. Fitting the thermal conductivity data of the SWNT/ HDPE nanocomposites with two models indicates that the thermal conductivity relies on a percolating SWNT network. Oriented SWNT/HDPE nanocomposites exhibit higher thermal conductivities, which are attributed primarily to the aligned PE matrix.
The use of single wall carbon nanotubes (SWCNTs) in current and future applications depends on the ability to process SWCNTs in a solvent to yield high-quality dispersions characterized by individual SWCNTs and possessing a minimum of SWCNT bundles. Many approaches for the dispersion of SWCNTs have been reported. However, there is no general assessment which compares the relative quality and dispersion efficiency of the respective methods. Herein we report a quantitative comparison of the relative ability of "wrapping polymers" including oligonucleotides, peptides, lignin, chitosan, and cellulose and surfactants such as cholates, ionic liquids, and organosulfates to disperse SWCNTs in water. Optical absorption and fluorescence spectroscopy provide quantitative characterization (amount of SWCNTs that can be suspended by a given surfactant and its ability to debundle SWCNTs) of these suspensions. Sodium deoxy cholate (SDOCO), oligonucleotides (GT)(15), (GT)(10), (AC)(15), (AC)(10), C(10-30), and carboxymethylcellulose (CBMC-250K) exhibited the highest quality suspensions of the various systems studied in this work. The information presented here provides a good framework for further study of SWCNT purification and applications.
The thermal and electrical conductivities in nanocomposites of single walled carbon nanotubes (SWNT) and polyethylene (PE) are investigated in terms of SWNT loading, the degree of PE crystallinity, and the PE alignment. Isotropic SWNT/PE nanocomposites show a significant increase in thermal conductivity with increasing SWNT loading, having 1.8 and 3.5 W/mK at a SWNT volume fraction of φ ∼ 0.2 in low-density PE (LDPE) and high-density PE (HDPE), respectively. This increase in SWNT/HDPE is more than additive and suggests a reduction of the interfacial thermal resistance. Fitting the thermal conductivity data of the SWNT/HDPE nanocomposites with two models indicates that the thermal conductivity relies on a percolating SWNT network. Oriented SWNT/HDPE nanocomposites exhibit higher thermal conductivities, which are attributed primarily to the aligned PE matrix.
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.
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