Synthesis and properties of a novel carbon nanotube-polymer thin film composite

Abstract

A novel method for carbon nanotube-polymer composite production is demonstrated in this thesis. The technique presented provides a way in which the position of nanotubes within a polymer matrix can be controlled. By controlling the position of nanotubes, we have a method of pre-determining the location of conduction channels through an insulating system. We can also avoid the need for nanotube dispersion and purification prior to composite formation. To achieve this, we grow carbon nanotubes onto a substrate by chemical vapour deposition. Nanotube growth is activated by a catalyst material. By selectively patterning a catalyst onto a substrate we can control the position of nanotube arrays. We use soft lithography to deposit catalyst patterns. Soft lithography is a convenient, inexpensive process which can be done under atmospheric conditions. This contributes towards the efficiency of nanotube production. Manipulation of the patterning and CVD conditions enables control over properties such as tube diameter, alignment and density. There is relatively little amorphous carbon deposition during the process. As-grown carbon nanotubes can be directly incorporated from substrates into a polymer matrix. A curable polymer is spin coated onto nanotube arrays. The viscous mixture intercalates between nanotubes. After curing, the composite can be peeled from the substrate. Nanotubes remain embedded in the polymer and detach easily from the substrate. To demonstrate the technique, we used a silicone elastomer (Sylgard 184) matrix. We were able to produce freestanding flexible thin film composites. The thickness of the film could be controlled by varying the spin speed. The properties of the composite were characterised and it was observed that adding nanotubes transformed the insulating matrix into a conducting polymer. Surface conductivity increased by six orders of magnitude (10/6) and bulk conductivity increased by an impressive eight orders of magnitude (10/8). Mechanical enhancement was not quite so dramatic. We measured a Young’s modulus increase by a factor of 2.1±0.9. However, we observed no increase in strength. We attribute this to poor interfacial bonding between the nanotubes and the polymer matrix. This was supported by differential scanning calorimetry. Further research could be used to refine this process into a simple, controllable and economical technique of composite fabrication.