Additive effect of poly(N-methylaniline) coated Fe₃O₄ composite particles on carbonyl iron based magnetorheological fluid

Poly(N-methylaniline) (PNMA) coated magnetite (Fe₃O₄) (PNMA@Fe₃O₄) composite particles synthesized through both chemical oxidative polymerization and chemical co-precipitation processes were used as a magnetic additive for carbonyl iron (CI)-based magnetorheological (MR) fluid. The effect of the additive’s content on the rheological characteristics of the MR fluid in the presence of an externally applied magnetic field was studied along with its effect on the sedimentation ratio compared with that of CI-based MR fluid. Shear stress curves as a function of the shear rate of the CI-based MR fluids with the additive were found to be well-fitted by the Herschel-Bulkley equation and the slope of the dynamic yield stress was determined to be 2.0. The curves also showed yield stresses higher than those of the CI-based MR fluid for different magnetic field strengths. Specifically, the CI-based MR fluid with 1.0 wt% additive showed the highest yield stress and the best solid-like properties among the tested samples. Furthermore, the sedimentation issue for the CI-based MR fluid was found to improve significantly, especially for the lowest settling rate of the MR fluid with 1.0 wt% additive. The addition of 1.0 wt% PNMA@Fe₃O₄ additive resulted in the CI-based MR fluid exhibiting the best properties, owing to improved rheological features and a reduced sedimentation rate.