Electrical characteristics of carbon nanotube-doped composites

This paper reviews research into the electrical properties that are imparted to composite materials by introducing carbon nanotubes (CNTs) into their polymer matrices. Due to the large aspect ratio of CNTs, even a small amount of doping (at a level of 0.01 – 0.1%) is enough to increase the conductivity of the material by more than ten orders of magnitude, thus changing it from an insulator to a conductor. At low doping, charge transfer is of a percolation nature in the sense that nanotubes that are in contact with each other form conducting channels in the material. Importantly, the conductivity has a threshold nature, so that the conduction jump occurs upon an arbitrarily small increase in a doping level above the critical value. This paper summarizes experimental data on the position of the percolation threshold and the maximum magnitude of the conductivity for composites obtained using various polymer types and a variety of CNT geometries. Factors affecting the electrical characteristics of composites produced by distinct methods are analyzed. Methods for and basic results obtained from the simulation of the percolation conductivity of CNT-doped composites are discussed. Particular attention is given to contact phenomena that occur at adjacent nanotube boundaries and which determine the conductivity of CNT-doped composites.