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Synthesis and Characterisation of Hybrid Carbon - Nanotube Silica Microparticles

Othman, Raja

[Thesis]. Manchester, UK: The University of Manchester; 2012.

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Abstract

Carbon nanotubes (CNTs) have been successfully grafted onto the surfaces of spherical silica gels via a floating-catalyst chemical vapour deposition method. Two types of silica gels were used as substrates; SG6 (6 – 8 nm pore size) and SG26 (26 – 34 nm pore size). The optimum growth conditions were found to be 760 °C growth temperature, 3 hours growth time, and 5 wt .% of ferrocene catalyst (dissolved in toluene) injected into the furnace at a rate of 0.04 ml/min. Under these conditions, CNTs coated the exterior surface of the gels with growth occurring from both the pores and from the surface. The geometry and porosity of the silica gel were also found to influence the alignment and density of the grafted CNTs, with SG6 producing the best quality hybrid particle under the above conditions (labelled SG6_3). Thermal Gravimetric Analysis showed the yield of CNTs grown under these optimum condition was 33.6 + 0.37 wt. %. As the CNTs remained strongly attached to the surface of the gel, the grafting process produced excellent dispersion of the CNTs within polymer matrices as CNT bundle formation was prevented. The inclusion of micron size silica introduced a large excluded volume within polymer matrices, with the dispersion of CNTs restricted to a region along the silica surface. This arrangement aided the formation of an electrically conductive network in a poly (vinyl) alcohol matrix, where the critical percolation threshold (pc) was calculated as 0.62 wt. % of SG6_3, equivalent to a CNT content of 0.2 wt. %.The inclusion of SG6_3 into an epoxy resin suspension did not alter the rheological behaviour of the resin up to the highest loading employed (5 wt. %, ≈1.65 wt. % of CNTs). Within the linear viscoelastic region the viscoelastic moduli of the neat resin remained within the same magnitude, whilst the addition of 1.65 wt. % of commercially available CNTs into the same resin increased the storage and loss moduli by up to seven and three orders of magnitude, respectively. The complex viscosity of the suspension remained unchanged regardless of the amount of SG6_3 added; whereas an increase in viscosity of up to five orders of magnitude resulted from the addition of 1.65 wt. % non – grafted CNTs.Grafting of CNTs onto the surface of micron size spherical silica gel has been shown to provide a means of incorporating CNTs into a polymer without increasing viscosity. In addition, the SG6_3 also formed an electrically-conductive percolated network in an epoxy resin composite at low levels of addition, with pc = 0.16 wt. % of CNTs (i.e. 0.5 wt. % SG6_3).