Bidisperse magnetorheological fluids with strong magnetorheological response, long-term stability and excellent in-use performance

Abstract

There is a critical demand for magnetorheological fluids (MRFs) with high particle loading, long-term stability, and high magneto-viscous properties to be used in industrial MRF devices. Bidisperse MRFs composed of highly magnetizable micron-sized carbonyl iron particles and poly(acrylic acid) coated superparamagnetic iron oxide nanoparticles (SPIONs-PAA) that can chemically interact are proposed to achieve such MRFs, here. Coating bare, commercial CI with lauric acid (LA) enhanced its dispersibility in a hydrophobic carrier fluid, allowed high magnetic loading and significantly prevented the sedimentation of the particles when mixed with 9–12 wt% SPION. Different carrier fluids (mineral oil, paraffin, and hydraulic oil) were tested, and hydraulic oil was determined as the best for this particle combination. The most stable bidisperse MRF was achieved at 83%–84% magnetic content with 12 wt-%SPION-PAA, LA-coated-CI and 3 wt% polyvinyl alcohol. Such MRFs outperformed the commercial benchmark, 140-CG® from Lord Corp., in long-term stability (4 months) and stability under dynamic loading. Bidisperse MRFs were stable between 20 °C and 60 °C. Most importantly, the excellent performance of the bidisperse MRFs in dampers designed for washing machines suggests that these MRFs may provide comparable damping forces with much better stability, ensuring longer shelf-life and longer lifetime in use.