In this research, the electrical conduction characteristics of CNT/Polymer composites filled by Carbon Nanotubes (CNTs) are evaluated by the numerical analysis and the experiment. As is well known, due to very high surface energy and adsorptive states for nano-materials, CNTs are easily aggregated and
it's very difficult to be uniformly dispersed in the composite. Therefore the relation between the agglomerations of CNTs and the electrical conductivity of the composite becomes very important for practical use.
The percolation theory is usually used to estimate the electrical conduction of the composite consisting of insulating matrix and conductive fillers. The electrical conductivity of the composite increases remarkably at the point, where a complete conductive path connected by fillers is formed between the two opposite cross sections of the composite. The volume fraction of filler at this point is called a percolation threshold.
The present numerical analysis is two-fold, i.e., the estimation of percolation threshold and the prediction of electrical conductivity of 3D composite. In both aspects of numerical analyses, the uniformly distributed straight and curved CNTs in polymer and an aggregation model of straight CNTs in polymer are considered to investigate the influences of shape and distribution of CNTs on macroscopic electrical properties of composites.
Furthermore, in the present experiments, CNT/Polymer composites consist of chemical vapor deposition grown multi-walled carbon nanotubes (MWNTs) as conductive filler and an epoxy system based on bisphenol-F resin and amine hardener. At first, the fabrication process is changed as CNTs content is kept to be 2wt%. The relationships between some important factors, e.g. agglomerations of CNTs etc. and the electrical conductivity of composites are investigated for different samples. After determining the comparatively good fabrication process, second, the CNTs content of composites is changed with the same fabrication process to manufacturing the different samples. Finally, the present experimental results plus other researchers' results are used to validate the effectiveness of the present numerical analyses.
Finally, based on the obtained numerical results for various aspect ratio and electrical conductivity of uniformly and randomly distributed straight CNTs in an insulating polymer, we get a simple percolation theory for evaluating the electrical properties of CNTs/polymer composites.
edited by Zen MASUDA