Electrically aligned carbon nanofiber/epoxy composites

The objective of this investigation is to explore processes for manufacturing aligned carbon nanofiber (CNF) reinforced epoxy composites using AC electric fields. CNFs were aligned and networked over a distance of 25 mm using moderate electric field strengths such as 58 Vrms/cm. This distance is roughly an order of magnitude greater than previously reported distances obtained with AC electric fields and was accomplished without highly sophisticated electrical equipment. Successful alignment over such large distances was achieved by studying the kinetics of network growth as a function of applied voltage and frequencies. The morphology and growth rate of the chains was found to be dependent on the applied AC frequency. A uniform network of chains was observed at frequencies of 1 kHz and greater. The rate of growth of chains was maximum at a frequency of 1 kHz for a liquid temperature of 121°C. The formation of percolating chains decreased the electrical resistivity of the composites with aligned CNFs several fold in comparison to randomly oriented CNF composites and also introduced anisotropy in resistivity for CNF weight contents of 0.5 and 1%. For the 2 wt% case, resistivity remained isotropic in the plane of measurement.