Synergistic Effects of Nonmagnetic Carbon Nanotubes on the Performance and Stability of Magnetorheological Fluids Containing Carbon Nanotube-Co0.4Fe0.4Ni0.2 Nanocomposite Particles.

We investigated the magnetorheological (MR) properties of the carbon nanotube (CNT)-Co0.4Fe0.4Ni0.2 composite suspension to find a high-performance MR fluid with excellent stability. The composites were fabricated by chemical reduction of Co0.4Fe0.4Ni0.2 on the surface of amine-functionalized CNTs. A synergistic effect between the high aspect ratio of the CNTs and the strong magnetic polarization of the Co0.4Fe0.4Ni0.2 led to stronger MR performance of the nanocomposite particle suspension. The MR fluid exhibits an unexpected high yield stress value that is 13 times greater than that of a CNT-Fe3O4 suspension at a magnetic field strength of 343 kA/m. Nonmagnetic CNTs form a three-dimensional networklike structure, imparting surprisingly large additional yield stress to the CNT-Co0.4Fe0.4Ni0.2 nanocomposite MR suspension. The low density of the CNTs resulted in much better long-term stability for the CNT-Co0.4Fe0.4Ni0.2 nanocomposite suspension than the MR fluid containing only Co0.4Fe0.4Ni0.2.