Abstract
Modern society is ever in demand for higher performing materials, with increased efficiency. Recognising this need, the work discussed here details the steps taken to develop and engineer a cost-effective manufacturing process, which could be easily commercially scalable for the production of large-areas of aligned carbon nanotubes. These aligned carbon nanotubes can then be directly applied in areas such as advanced ‘multi-functional’ composites. Of the available routes, the electrospinning technique demonstrated to be one of extreme promise towards achieving this goal. This thesis guides and justifies the investigative steps taken in scientifically engineering a suitable electrospinning method to achieve high-aligned arrays of carbon nanotubes. This includes the design and development of a novel, large-area high-throughput needleless electrospinning system, which is capable of not only producing nano-fibres in excess of 160 g per hour (700 times faster than conventional single needle electrospinning), but also in an aligned orientation, using purely aqueous based polymeric solutions. This success has led to the successful production of the World’s first large area sheets of highly aligned arrays of single walled carbon nanotubes by electrospinning. The analysis of these sheets found substantial increases in both mechanical and electrical performance. For the aligned nanotube-loaded nano-fibres, the tensile strength increased up to 320%, ductility increased up to 315% and Young’s modulus increased up to 430% (compared to the original polymer performances). The realisation of the significant enhancements CNTs pose on a composite material, led to an investigation into the chemical interactions that lead to these results. This resulted in the discovery of a new small angle X-ray scattering peak, which we attributed to a crystalline interface between the polymer and carbon nanotubes, giving rise to the enhancements seen during mechanical testing. In addition to mechanical performance, there was also a significant increase in electrical conductivity of 108 S/m, an improvement of 8 orders of magnitude compared to the original polymer. These results, combined with the realisation of industrially viable throughput, provide promise for impressive application into advanced multi-functional composites. While the primary objectives of this research focused on large area electrospinning, the work outlined in this thesis also discusses investigations into other important aspects, and significant scientific discoveries. These scientific achievements include the introduction of a novel, micro-centrifugal dispersion assessment method, for the efficient surfactant functionalisation of nano-materials. This method allows for a fast and effective assessment of a material suspension, without the need for any equipment other than a simple centrifuge and a balance. This process leads to fast and efficient use of surfactants, producing greater loadings of nano-materials which can be suspended within a solvent for further processing. As a method to recover the nanotubes once they have been processed and aligned, this thesis also explores post processing of the aligned nanotube-loaded sheets using steam purification. This led to the complete recovery, and purification, of the high quality aligned CNTs, which were found to significantly increase the resulting nanotubes resistance to oxidation, increasing their oxidation temperature in excess of over 900° C, a previously unreported achievement. The mechanisms behind the underlying chemistry were further probed using Raman spectroscopic analysis, this revealed how selective oxidation of CNTs was limited to that of metallic CNTs, leaving the remaining material as only semi-conducting species. This selective oxidation process could lead to selective manufacture of specific CNT species, allowing for better suited application in electrical devices.