Dispersion of Single-Walled Carbon Nanotubes in Organic Solvents

This thesis contains a systematic study of the dispersion of pristine HiPco Single Walled Carbon Nanotubes (SWNTs) in a series of organic solvents. A double beamed UV-Vis-NIR absorption spectrometer coupled with an integrating sphere was employed to demonstrate the dispersibility of SWNTs in different solvents. Raman Spectroscopy and Atomic Force Microscopy (AFM) were used to confirm the debundling and exfoliation of SWNTs aggregates. An investigation of the solubility of SWNTs in four chlorinated aromatic solvents demonstrated that the similarity in structure between solvent molecules and nanotube sidewall is not a dominant factor to obtain stable SWNT solutions. A comparative study of the solubility of SWNTs between the aromatic solvents and other reported solvents was then conducted, in terms of the solvent solubility parameters, including Hildebrand and Hansen solubility parameters. Although the established correlation between extinction/absorption coefficients as a function of Hildebrand/Hansen solubility parameters indicated there may be a selective debundling of metallic and semiconducting SWNTs in different solvents, this was not confirmed by a detailed Raman investigation. A further study of the dispersion limit of SWNTs in different solvents as a function of the solvent solubility parameters was carried out. Good agreement with literature is demonstrated here in terms of Hildebrand parameters, but not in terms of the Hansen solubility parameters. It has been demonstrated that the degree of dispersion is critically dependent on sample preparation conditions, in particular sonication. Finally, the effect of sonication parameters and solvent properties during the dispersion of SWNTs was investigated. The results indicated that the sonication process is closely dependent on many of the physical parameters of the solvent, including vapour pressure, viscosity, surface tension, density and molecular weight. Longer sonication time and higher sonication power help debundling SWNTs in organic solvents but significantly damage the nanotubes. The choice of solvent should be guided by minimisation of sonication requirements

Ultrasound-Assisted SWNTs Dispersion: Effects of Sonication Parameters and Solvent Properties

Ultrasonication is widely used for preparing Single-Walled Carbon Nanotube (SWNT) dispersions in different solvent media and it has been shown to play a critical role in dispersing and debundling SWNTs. The strong shear force that can exfoliate the SWNT bundles during sonication comes from cavitation, which entails a process of bubble formation, growth, and collapse. The efficiency of the cavitation process is closely correlated to many solvent parameters, including vapor pressure, viscosity, and surface tension, as well as the sonication frequency, intensity, and time. In this study, SWNTs were dispersed in a range of organic solvents assisted by tip sonication. The effects of sonication intensity and time were investigated in o-dichlorobenzene (o-DCB) and dimethylformamide (DMF). The aggregation fraction below the dispersion limit of SWNTs in the range of organic solvents was found to be influenced by the solvent parameters, particularly solvent vapor pressure and viscosity. It is demonstrated that the parameters associated with the sonication process rather than solvent solubility parameters govern the dispersion process. It is further confirmed that significant degradation of the SWNTs is affected during the dispersion process

A Raman Spectroscopy Study of the Solubilisation of SWCNTS by POlycyclic Aromatic Hydrocarbons

The effectiveness of polycyclic aromatic hydrocarbons (PAHs) for selective solubilisation of single walled carbon nanotubes (SWCNTs) has been studied by Raman spectroscopy. Polyphenyl and polyacene PAHs of different lengths are used. Selective interaction between the PAHs and SWCNT is investigated by analyzing the Raman radial breathing modes the frequency positioning of which yields information concerning the diameter distribution of the SWCNT sample. Samples were dispersed at concentrations below the debundling limit and deposited on quartz substrates. A combination of four laser excitation energies was utilized to establish the distribution of diameters present. The results show that the PAHs interact with a range of SWCNT diameters. In general a preference for smaller diameter SWCNTs is evident, although the longer PAHs have the capacity to solubilise larger diameter SWCNTs, due to their increased binding energy. Although a small degree of structural specificity is evident, all PAHs solubilise both chiral and nonchiral SWCNTs

Modification of Li2MnSiO4 cathode materials for lithium-ion batteries: a review

Diversified and extended application of lithium-ion batteries require the development of innovative electrode materials with excellent electrochemical performances, which, to a large extent, depends on the cathode materials. In recent years, LiMnSiO has attracted widespread attention due to its high thermal stability, abundance, low-cost and environmentally friendliness. Some of the most attractive characteristics of LiMnSiO are that it possesses the high theoretical capacity of 333 mA h g and is much easier to achieve the transformation of Mn/Mn and Mn/Mn within the voltage range of the electrolyte system currently used in Li-ion batteries compared with the other lithium transition metal orthosilicates. However, LiMnSiO suffers from the intrinsic drawbacks of low electronic/ionic conductivity and capacity fading upon cycling, limiting its application in next-generation lithium-ion batteries. In this review, the recent efforts to improve the electrochemical performances of LiMnSiO were introduced. In particular, we provided a critical overview of the effective modification methods related to the LiMnSiO cathode materials. The synthesis, structure, morphologies and physicochemical (especially electrochemical) performances of these promising cathode materials have been discussed in detail. We anticipate that this review will shed light on the sustainable development of high-performance and low cost Li-ion batteries

A Systematic Study of the Dispersion of SWNTs in Organic Solvents

Dispersions of as-produced HiPco single-walled carbon nanotubes (SWNTs) in a series of organic solvents were prepared by dilution with the aid of tip sonication. Mild centrifugation (~ 945 g) was carried out to remove large bundles. Atomic force microscopy (AFM) studies revealed that the bundle size decreased as the dispersion was diluted. By measuring the UV-vis-NIR absorption before and after centrifugation as a function of the concentration, the dispersion limit of SWNTs in each solvent can be determined. Correlations between the dispersion limit and solvent solubility parameters, including the Hildebrand solubility parameter and three dimensional Hansen solubility parameters, are explored, demonstrating that SWNTs are easily dispersed in solvents with Hildebrand solubility parameter range from ~22-24 MPa1/2 and Hansen polarity component (δP) ~12-14 MPa1/2. No clear correlation between dispersion limits and the dispersion force (δD) or hydrogen bonding force (δH) are evident. It is found, however, that the degree of dispersion depends critically on sample preparation conditions and in particular sonication time. Increased sonication times increase the amount of SWCNTs debundled and solubilised but do not appear to affect the dispersion limit. However, increased sonication also induces discernible changes to the SWNTs themselves and in itself influences their solubility, under which conditions no clear solubility parameters can be determined