(346g) High Resolution Length Fractionation of Surfactant Dispersed Single-Wall Carbon Nanotubes

Length fractionation of colloidal carbon nanotube dispersions is required for many studies. Size-exclusion chromatography (SEC) has been reported as a reliable method for high resolution length fractionation of DNA-dispersed single-wall carbon nanotubes (SWCNTs). However, no high resolution length fractionation method is currently available for the commonly used bile salt dispersed SWCNTs. Here we describe extension of the SEC method to high resolution length fractionation of bile salt dispersed SWCNTs using porous silica-based beads as the stationary phase, and bile salt solution as the mobile phase. The optical absorption spectra of the resulting fractions vary with fraction length, with diminished excitonic transition peaks for short tubes. We measure the length dependence of the extinction coefficient to enable quantification of the concentration of length-sorted fractions. We present evidence that the spectral variation is due to a large concentration of defective SWCNTs in the short fractions. Finally, the new SEC method is used to length-fractionate bile salt dispersed SWCNTs pre-purified by density gradient centrifugation methods. Unlike length-fractionated samples obtained from the raw material, and all length-fractionated samples previously reported, these double-purified samples show little dependence of optical absorbance spectra on length. These results support the notion that the optical absorbance spectrum of the defect-free SWCNT is approximately length-independent.