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Title: Graphene/carbon nanotube-based conductive materials
Author: Alsawafi, Suaad
ISNI:       0000 0004 7971 0004
Awarding Body: Loughborough University
Current Institution: Loughborough University
Date of Award: 2017
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This project is basically an investigation of graphene and carbon nanotube (CNT) based material's electrical properties. In its first part, graphene (G) and graphene oxide (GO)/carbon nanotubes (CNTs) hybrid films were successfully fabricated as high-performance electrode materials for an energy storage application using a simple water solution casting method and with an assistance of strong ultra-sonication. This was done with different contents of G, GO, single-wall CNT (SWCNT), multi-wall CNT (MWCNT) and multi-wall CNT with a hydroxyl group (MWCNT-OH). The films with MWCNTs showed well interconnected layered structures at the nanoscale range where GO worked as support insulated plates for the CNTs. The electrical properties were investigated in an alternating circuit (AC) which revealed a linear relationship between the dielectric constant and the weight percent of the CNTs. By increasing the CNT contents, the dielectric constant of the G/MWCNT and GO/MWCNT films raised almost linearly and their resistivity reduced. On the other hand, the dielectric constant was found to be decreased as the frequency went up. The maximum special capacitance reached 142 F/g in G (40wt %) /MWCNTs (60wt %) in which the dielectric constant reached 9.98 x107/g in the same film. In comparison, GO/SWCNT and G/SWCNT were found to be not applicable to be used as a capacitor system using the water solution casting method which resulted in a bad dispersion. G/SWCNT and GO/SWCNT films did not form layered structures leading to a very low dielectric constant. On the other hand, the dimension and the thickness of the film influence the capacitor performance and the conductivity. Shorter and thicker film can make a huge difference. Nonlinear behaviour of the dielectric constant with voltage was observed in both ofG/CNT or GO/CNT hybrid films. At some voltages, the dielectric constant reached to peak or valley. Obviously, it is quite dependent on the voltage loaded. In the second part, a well-dispersed MWCNT/HDPE nanocomposite powder was successfully prepared by coating the MWCNTs on the surface of the matrix particles (HDPE). The volume resistivity of the nanocomposites was investigated relating to the temperature and stress influences. Besides, the reproducibility of the nanocomposites was studied in this project and several conclusions could be drawn: Firstly, the average electrical resistivity for the MWCNT/HDPE nanocomposite sheets with the MWCNT contents of 0.1 wt%, 0.5 wt%, and 1.0 wt% were 792.64, 111.67, and 9.953 respectively, which indicated that the 1.0 wt% MWCNT/HDPE nanocomposite showed the best electrical conductivity. Furthermore, the results of the temperature electrical conductivity measurements revealed that with rising of temperature, the electrical resistivity for the MWCNT/HDPE nanocomposites increases due to the widening of the distances between the conductive nanofillers. In addition, the heat treatment could effectively improve the reproducibility of the MWCNT/HDPE nanocomposites, especially the nanocomposite with the MWCNT content of 1.0 wt%, as it has been found that the voids in the nanocomposite sheets were excluded during the heat treatment. Finally, the results of the tensional electrical resistivity measurements showed that the initial electrical resistivity for the MWCNT/HDPE nanocomposites increased with the increase of the applied tensional stress which caused the widening of the distances between the conductive nanofillers and some conductive networks to be damaged. Additionally, the reproducibility of the 1.0 wt% MWCNT/HDPE nanocomposites was better than that of the 0.5 wt% MWCNT/HDPE nanocomposite. It was found that the MWCNT/HDPE nanocomposite sheets exhibited 'viscoelastic' behaviour of the electrical recovery in which the electrical resistivity could not totally recover after relaxation.
Supervisor: Not available Sponsor: Ministry of Higher Education ; Oman
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Materials Engineering not elsewhere classified ; Graphene ; Carbon nanotube ; Conductivity ; Capacitance