Evaluating the optimum nanofiber alignment in conductive composites with a stereology-based anisotropic degree

Rationally tuning the anisotropic degree of orientation distribution for conductive fibers in composites can maximize the macro electrical conductivity in a specific direction. However, quantitative evaluation of the optimum anisotropic degree of networks with fibers of different shapes and orientation distributions remains largely unexplored. In this work, the optimum fiber orientation distribution at the maximum electrical conductivity is quantified by a newly proposed stereology-based anisotropic degree. This index applies to both straight and curved fiber networks and has one-to-one corresponding relation with the macro electrical properties. Using Monte Carlo simulations, it is found that with the increase of anisotropic degree, the electrical conductivity increases to its maximum and then decreases gradually, which shows good agreement with experimental results. Further, a universal expression to determine the optimum anisotropic degrees of networks at different fiber concentrations is obtained, which is independent of the curliness and orientation distribution laws of fibers.