The Research On Electrical Properties Of Carbon Nanotubes/Polymer Composites

Since the discovery of the carbon nanotubes(CNTs), The super high strength, ductility, large aspect ratio and excellent electrical conductivity of carbon nanotubes make it an ideal reinforcement additive for composites. The carbon nanotubes/polymer composites have become an area of significant interest in recent years.Conventional polymers usually have good processability, low density and good mechanical properties, but have not high conductive properties. Conjugated polymers have a relatively good electrical conductivity, but a poor processing performance. So its wide range of applications is restricted in a large part. However, carbon nanotubes have excellent electrical conductivity properties and large aspect ratio. So if a small amount of carbon nanotubes have been added in polymer matrix, composites not only have the original processing but also light, etc., and its electrical conductivity has been well improved. As a result, CNTs/polymer composites have the great potentials in many fields such as electromagnetic shielding, electrostatic spraying, static electricity eliminating.The applications of these composites in field emission, nanoscale electronic devices, and other fields have been restricted by the disorder of CNTs in polymer matrix. In order to conquer this handicap, the repeated stretching method during the process of solution casting, stretching the semidried Single-walled carbon nanotubes(SWNTs)/ bisphenol-A type epoxy resin(E-51) composites along one direction repeatedly, has been adopted to achieve the even disperse and good realignment of SWNTs. The SEM observation demonstrated that SWNTs in the SWNT/E51 composites tend to align in the stretching direction and well disperse. The results also revealed the obvious percolation effect and anisotropy of composites, as well as that the electrical conductivity and the mechanical properties of composite have been improved visibly. Composites showed higher conductivity and lower percolation threshold along the stretched direction than perpendicular to it.Based on the Effective-Medium Theory (EMT), the electrical conductivity and percolation thresholds of orientated SWNT/epoxy composites have been simulated, and the percolation effect which can not been explained by traditional theories has been predicted. Both low Percolation thresholds and strong anisotropic properties in aligned SWNT/epoxy composites are well predicted. It is spontaneously obtained that an extremely low SWNT content can lead to a dramatic enhancement in the electrical conductivity of SWNT/epoxy composites when the SWNT content is larger than the percolation threshold, as well as the electrical conductivity and the percolation thresholds are relative to the orientation factor, the aspect ratio and the structure of SWNTs in the composites matrix strongly. The simulated percolation threshold of the orientated SWNT/epoxy composites, concluded by computing the increased ratio of electrical conductivity, is 0.0035 vol% when the SWNT aspect ratio is 500. The simulated results are consistent with the experimental results basically, and the discrepancy between simulated results and experimental results has been interpreted reasonably.