Measurement of nanotube content in pyrolytically generated carbon soot

Abstract

Carbon nanotubes can be efficiently separated from impurity material in carbon soot using a conjugated polymer filtration system as monitored by EPR, allowing the calculation of purity of the crude carbon soot.Carbon nanotubes have generated interest in all areas of science owing to their novel structural, mechanical and electronic properties. In the physical sciences nanodevices have already been demonstrated including transistors 1 and rectifying heterojunctions. 2 In microbiology they have been used as probes to study the structure of biomolecules 3,4 and as templates for the self assembly of proteins. 5 However, at present, as-produced carbon soot remains low in nanotube content. 6 Furthermore, neither quantitative techniques to analyse soot content nor methods to measure nanotube content exist. This work presents the first measurement of nanotube content in impure carbon soot. Using a conjugated polymer as a nanotube 'filter', carbon nanotubes are separated from all other soot components. An absolute value for the nanotube content can then be calculated for the first time using electron paramagnetic resonance and thermogravimetric measurements. This is a vital step towards making nanotubes a practical material for novel scientific developments.The necessity for a technique to measure nanotube content in carbon soot is apparent when the present fabrication and purification methods are examined. During nanotube production unwanted carbon species such as turbostratic graphite (TSG) and carbon onions are invariably formed. Purification by oxidation 7 destroys many nanotubes and alters the electronic properties of the remaining tubes. Chromatographic techniques 8 have succeeded in purifying carbon soot but no quantitative measure of purity has been obtained. Furthermore, scale-up of these processes is problematic. The process outlined in this work approaches these issues in a novel manner via the production of a polymer nanotube composite. Thus a quantifiable purification method for carbon soot is presented which leads logically to a measurement of the purity of that soot.In order to produce the polymer nanotube composites used in this work 80 mg of poly(m-phenylene-co-2,5-dioctyloxy-pphenylenevinylene) (PmPV) were mixed with 25.5 mg of multiwall nanotube (MWNT) containing arc-generated carbon soot in 4 ml of toluene. The PmPV was synthesised using a standard polycondensation reaction, 9 while the carbon soot was generated in a Krätschmer generator. 10 The mixture was sonicated for 2 min using a high power sonic tip and then for 2 h in a low power sonic bath to ensure complete dispersion of the Krätschmer generated carbon soot. This was carried out for seven composite solutions with identical constituents. These solutions were then allowed to stand undisturbed for various amounts of time, from 30 min to 90 h. At the end of its settling time each solution was carefully decanted into a new sample bottle, leaving a black sediment at the bottom of the old bottle. These sediments were then dried and weighed.To determ...

Experimental observation of scaling laws for alternating current and direct current conductivity in polymer-carbon nanotube composite thin films

“…Thermogravimetric analysis was used to calculate the nanotube concentration in each composite solution. 3 This technique also established that the PmPV decanted solution held significantly more nanotube material ͑ϳ7.5 times͒ than PVA.…”

“…These were then sonicated with a high power sonic tip for 1 min and then subsequently in a low power sonic bath for 1 h. The solutions were then allowed to stand undisturbed for 24 h to let any non-nanotube impurities sediment out. Decantation then yielded composite solutions free from graphitic impurities as described by Coleman et al 3,4 Electron paramagnetic resonance was then used to show that only polymer and MWNTs remained in solution after settling and decantation. 3,4 Various lower mass fraction solutions were prepared by blending these composite solutions with pure polymer solutions in the required ratios.…”

“…Decantation then yielded composite solutions free from graphitic impurities as described by Coleman et al 3,4 Electron paramagnetic resonance was then used to show that only polymer and MWNTs remained in solution after settling and decantation. 3,4 Various lower mass fraction solutions were prepared by blending these composite solutions with pure polymer solutions in the required ratios. Thermogravimetric analysis was used to calculate the nanotube concentration in each composite solution.…”

“…While nanotube purity and processability have been a problem in the past, these issues have recently been addressed with some success. 3,4 Self-purifying polymer nanotube composite solutions can now be routinely made, allowing thin films to be fabricated using traditional techniques such as spin coating. 5 This has allowed the characterization of the electronic properties of the composite films themselves and the study of their potential as field injection and charge transport layers in traditional organic electronic devices such as light emitting diodes.…”

Enhanced brightness in organic light-emitting diodes using a carbon nanotube composite as an electron-transport layer

“…Advances in fabrication, 1 purification, [2][3][4][5] and processing techniques have allowed carbon nanotubes to show great potential in many areas of physics, chemistry, and engineering. Existing in two forms, multiwalled and single-walled, 6 this form of carbon has been shown, both experimentally and theoretically, to have excellent mechanical and electrical properties.…”