Bidisperse magneto-rheological fluids consisting of functional SPIONs added to commercial MRF

Abstract

Magnetorheological fluids (MRFs) are smart materials with a reversible and fast transition from a liquid to a semi-solid state when an external magnetic field is applied (magnetorheological effect). The sedimentation of micron-sized magnetic particles in commercial MRFs is a crucial problem limiting the long-term use in industrial applications. Here, we develop a new MRF based on commercial 140-CG LORD® with the addition of surface functional superparamagnetic iron oxide nanoparticles (SPIONs). These new bidisperse MRFs are comprised of either poly(acrylic acid) (PAA) coated SPIONs or lauric acid (LA) coated SPIONs and micron-sized fatty acid-coated magnetic particles of the commercial MRF. SPIONs have specific coatings to interact with the fatty acid coating of the micron-sized Fe-particles. Sedimentation behaviour and the magnetorheological properties of these bidisperse MRFs with 6–12wt% SPION were examined. Bidisperse MRFs improved the stability and redispersibility of MRFs. Bidisperse MRFs with 12wt% SPION-PAA showed similar or better magnetorheological behaviour than the commercial MRF despite lower content of the micron size Fe-particles. Hence, a combination of magnetizable nano and micron-sized particles and utilization of correct surface chemistry that allows their favourable interaction improves the stability of MRFs without sacrificing magnetic response but even by improving it.