Photoluminescence intensity PL measurements were taken for a range of PmPV concentrations, in which HiPco single walled carbon nanotubes (SWNTs) at 100%, 10%, 1%, 0.1%, 0.01% and 0% mass fractions were added. The PL intensity of the composite was shown to decrease for all mass fractions, relative to the polymer up to 1.56x10-3g/l of PmPV, above which there is an initial increase in the composite emission yield with respect to the polymer. This increase is associated with an interaction within the composite, which results in a decrease in polymer aggregate formation, which has been shown to quench intensity yields. Within the concentration range studied 5.9x10-8g/l to 2g/l the photoluminescence intensity yield for each system is highly non linear. Previously the ratio of the maximum PL intensity of the composite, which includes both, bound and unbound polymer chains, and the maximum PL intensity of the polymer, which includes only unbound polymer chains was plotted as a function of polymer concentration. From this the authors calculated the amount of free polymer within each composite and derived a model, which showed that as the polymer concentration is lowered the bundles break up until isolated SWNTs are stable at low concentrations. In particular for their 100% mass fraction polymer/HiPco SWNT it was shown that individual nanotubes are stable in solutions ~3x10-5kg/m3. Here we utilize this approach and results indicate that as the mass fraction of nanotubes in reduced, individual nanotubes are stable at higher polymer concentrations. In particular for our 100% mass fraction results indicate that below ~1.5x10-4g/l individual nanotubes are stable. This result indicates that the choice of polymer and or solvent has a significant effect on the debundling and aggregation within these systems.
Samples of raw nanotubes are compared to those deposited from solutions to examine separation of nanotube bundles. Single wall nanotubes bundles produced by the arc-discharge and HiPco methods were solubilised in toluene, DMF and 1,2 dichloroethane. Resonant Raman spectroscopy was used to determine if debundling of the tubes sample occurred. The results showed some degree of debundling, best for the 1,2 dichloroethane solvent, which also shows long term solubility.
This paper shows the solublisation and de-bundling of SWNT with an aim to obtaining individual SWNT. By achieving this goal their theoretically proposed properties can be verified and their industrial potential realised. It is well documented that Single Wall Carbon Nanotubes (SWNTs) show varying degrees of solubility in a number of organic solvents. Solubility of SWNTs in toluene was found to be negligible. With toluene having such a poor affinity for SWNT it is clear that the solvent interaction with the SWNT is negligible. Therefore toluene is an ideal candidate for monitoring the improvements in the solubility of the SWNTs as a result of interaction with dye molecules such as terphenyl and anthracene. The suspensions formed are stable for periods greater than thirty-six months. Spectroscopic analysis clearly shows interaction and de-bundling of SWNT on addition of the dye molecules. The fluorescence of the dye molecules is quenched on interaction with SWNTs and in the case of terphenyl, the spectrum is red shifted which gives further support to the notion of interaction. With the quenching in fluorescence of the dye molecules signifying interaction, a large range of concentrations were studied in order to quantify the degree of interaction between the SWNT and dye molecules. It was found at high concentrations such as 1 x 10-3 M, that both the dye molecules and SWNT formed aggregates. At lower concentrations such as 1 x 10-9 M for terphenyl and 1 x 10-6 M for anthracene, it was found that free dye and individual SWNT were interacting. Raman spectroscopy of the composites formed on interaction show vibrational modes that are not present in either the SWNTs or dye powders. It was found that both the dye and SWNTs had Infra Red (IR) active vibrational modes at the positions at which these new or unique Raman modes occur in the composite spectra. It is therefore thought that the new Raman modes in the composite samples are related to the IR modes. The Raman Radial Breathing Modes (RBMs) give detail as to how diameter selective the dye samples are when compared to the pristine SWNT modes. Red shifting of the RBMs for both composite spectra was observed. It is believed that such a result is due to the de-bundling of the SWNT on interaction with the dye molecules.
An analysis of the Raman spectra of single-walled HiPco carbon nanotube powder using laser energies of 1.92 eV, 2.4 eV, 2.5 eV, and 2.7 eV, including a comparison of the Stokes and anti-Stokes contributions is presented. The diameter distribution was determined to be 0.8-1.2nm from the spectral positioning of the Radial Breathing Modes. The diameter distribution is consistent with that determined by NIR absorption spectroscopy. At all excitation energies the profile of the G-line indicates a predominance of semiconducting tubes although at 2.4 eV there is some indication of some contribution from metallic tubes. In all cases the anti Stokes line was weak and the Stokes/anti Stokes ratio was at least an order of magnitude indicating at most weak resonance enhancement in either.
Interactions between Arc Discharge single walled carbon nanotubes within polymer composites have been well documented. Here hybrid systems of the conjugated organic polymer poly (p-phenylene vinylene-co-2,5-dioctyloxy -m-phenylene vinylene) (PmPV) and carbon nanotubes produced by Gas-Phase Decomposition of CO (HiPco) process are explored using Raman spectroscopy. Laser excitation wavelengths of 514.5nm and 633nm are employed to determine the specific nature of interaction. Also presented at laser energies 1.96eV and 2.4eV, are hybrid systems of Arc Discharge SWNTs at similar mass fractions to enable a direct comparison of solubility of each nanotube type within the polymer composite to be made. Comparisons are also made between the two hybrid systems in relation to range of nanotube diameters selected at 514.5 and 633nm.
Single wall carbon nanotubes are insoluble in most organic solvents such as toluene. Improvements in the solubility of the single wall carbon nanotubes are however seen as a result of specific interactions with molecules such as terphenyl and anthracene. Suspensions formed in toluene with these molecules and the single wall carbon nanotubes are seen to be stable over prolonged periods. Spectroscopic analysis clearly shows an interaction between the carbon nanotubes and the molecules. It is proposed in this study that the use of these more simple molecular systems may help elucidate the nature and extent of the interaction in more complex composite based systems.