Orthotropic electro-thermal behaviour of highly-aligned carbon nanotube web based composites

A ‘forest’ of vertically aligned carbon nanotubes (CNTs), synthesised by chemical vapour deposition with an iron catalyst on a silicon substrate, is drawn into a horizontally-aligned CNT web. Previous work has shown that the electro-thermal properties of this web may be tuned by altering the individual length of the CNTs and the number of layers. This paper demonstrates, for the first time, that the orientation and multi-directional layering of the web provides further scope for tuning the electrical conductivity and heat distribution of the composite system. An analytical model based on the thermal conduction theory of anisotropic solids is proposed to predict the electrical conductivity of general multi-layered and multi-directional CNT webs. Specimens with different aspect ratios and web orientations were manufactured and their electrical conductivity and resistive heat distribution measured. All of them were shown to exhibit electrical properties and heating distributions which could be predicted or bounded by the analytical model. Consequently, through tuning the CNT web orientation and layup, various heating patterns may be obtained and designed for specific requirements.