Chromatographic Separation of Single Wall Carbon Nanotubes
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0922-U09-01
Chromatographic Separation of Single Wall Carbon Nanotubes Barry J. Bauer, Vardhan Bajpai, Jeffrey A. Fagan, Matthew L. Becker, and Erik K. Hobbie Polymers, NIST, 100 Bureau Drive, stop 8541, Gaithersburg, MD, 20899-8541 ABSTRACT Size exclusion chromatography (SEC) is shown to be an effective method to characterize single wall carbon nanotube (SWNT) dispersions. SEC separates nanotube dispersions by size, and measures the intrinsic viscosity on-line as a function of hydrodynamic size as is determined by Universal Calibration. This scaling contains information about the shape of the dispersed particles. This characterization method was tested on three representative dispersions: octadecyl amine functionalization in tetrahydrofuran (THF), butyl group functionalization in THF, and DNA wrapping in aqueous solution. Significant differences between the dispersions were found. Small angle neutron scattering (SANS) and atomic force microscopy (AFM) produced results consistent with the SEC method. INRTRODUCTION* Single wall carbon nanotubes (SWNTs) have a variety of potential applications in materials, due to their outstanding mechanical, electrical, optical, and thermal properties1. However, current SWNT synthetic methods produce bundles of nanotubes comprised of tubes with a distribution of lengths, chiralities and diameters, and they are unsuitable for most applications and characterization methods without further processing. The dispersion of nanotubes in solution is necessary in order to achieve the goal of sorting and manipulating nanotubes by length and type and then to prepare high quality monodisperse samples. Monodisperse samples are required in order to properly characterize the optical, thermal and electrical properties of nanotube based materials. Several schemes have been developed to promote SWNT dispersion, which have demonstrated the ability to form stable suspensions that do not settle out over long time periods2. Methods are necessary to assess the quality of the dispersions; for example, it must be known if the original bundles/ropes of nanotubes have broken down into isolated nanotubes. The nature of the dispersion and our ability to characterize the dispersion on a size scale comparable to the SWNTs is thus of great importance. EXPERIMENTAL DETAILS SWNTs were obtained from Carbon Nanotechnologies Inc.3 The butyl grafting reaction (SWNT-butyl) was carried out according to the procedure of Billups et. al.4 and was reported previously5. The octadecyl amine grafted samples (SWNT-ODA) were prepared according to the standard Procedure6. The aqueous DNA dispersions (SWNT*
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DNA) were prepared according to the procedure of Zheng et al.7-9. Dispersion was induced by sonication, and insoluble material was removed through centrifugation resulting in a SWNT concentration between (0.1 and 0.4) mg/mL as determined by UV absorption before and after centrigugation. Size exclusion chr
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