Effect of carbon filler characteristics on the electrical properties of conductive polymer composites possessing segregated network microstructures

This thesis focused on making composites consisting of a polymethylmethacrylate matrix, with various carbon fillers. The fillers that were examined were 3 different carbon blacks: N-550, N-772 and pureblack, and short multi-wall carbon nano-tubes. The carbon fillers were coated onto the polymethylmethacrylate, and compression molded in order to form a segregated microstructure. The goal of this thesis is to compare the electrical and optical properties of the composites consisting of a segregated microstructure, containing various carbon fillers. Scanning electron microscopy was used to investigate the fracture surface of the composites. Impedance Spectroscopy measured the electrical response of the material, and was used to determine the conductivity and dielectric properties of the composites and estimate the percolation threshold. The multi-wall carbon nano-tubes were found to have the lowest percolation threshold, due to their rod like structure. All of the carbon black fillers displayed similar characteristics in their conductivity and dielectric properties. As the filler content increased, the conductivity and the dielectric constant of the composites increased. Optical absorption measurements determined the amount of light that travel through the specimen. These measurements, showed that the absorbance for the carbon black sample N-550 were lower than the multi-wall carbon nano-tubes at filler contents below a phr of 0.1 The absorption of the carbon black samples was then higher than multi-wall carbon nano-tubes at phrs higher than 0.1. This was found to be related to the nano-tubes starting to form a segregated microstructure at lower filler contents than the sphere-like carbon black nano-particles.M.S.Committee Chair: Rosario Gerhardt; Committee Member: Gleb Yushin; Committee Member: Hamid Garmestan