Magnetic alignment of Ni/Co-coated carbon nanotubes in polystyrene composites

Abstract

Multiwall carbon nanotubes (MWCNT) are coated with ferromagnetic nickel and cobalt by a solution method. It results in a coating on the carbon nanotube surfaces in form of Ni/CoO nanoparticles. As a result of nano-scale Ni/CoO coating, MWCNT–polystyrene composites exhibit superparamagnetism at room temperature. As 3 wt.% of Ni/CoO coated MWCNT is dispersed in polystyrene matrix, a viscous liquid with solvent is developed for magnetic alignment. It is found that the Ni/CoO coated MWCNT respond to magnetic field susceptibly in the viscous liquid and arrange themselves in the direction of the applied field up to 5 T. Upon drying with magnetic field on, MWCNT are found to be well aligned in the direction of the field in the polystyrene matrices, as evidenced in the SEM and TEM experiments. As a result, strong anisotropy in tensile strength has been observed in the MWCNT–polystyrene composites. Magnetic alignment mechanism, surface coating microstructure of MWCNT, and related mechanical behaviors are discussed.