Magnetorheological Fluid Based on Carbonyl Iron Particles Surface-Modified with Hydroxyapatite: Dual Optimization of Rheological Performance and Sedimentation Stability

Magnetorheological fluids (MRFs) have long faced the challenge of achieving high sedimentation stability and yield strength simultaneously. Regulating interfacial interaction between magnetic particles and carrier liquid is an effective strategy to address this issue. In this study, carbonyl iron particles (CIPs) were modified with hydroxyapatite (HAP) to strengthen and stabilize their interfacial interaction with poly(dimethylsiloxane) (PDMS), thereby improving both sedimentation stability and yield strength of MRFs. HAP/CIPs prepared by a wet chemical surface compositing method exhibited markedly improved thermal stability and acid corrosion resistance compared with pure CIPs. These composite particles were subsequently dispersed in PDMS to prepare HAP/CIP MRFs, for which sedimentation stability and rheological properties were systematically investigated. The results showed that HAP/CIP MRFs exhibited significantly enhanced sedimentation stability, yield strength, and storage modulus compared with CIP MRF. Molecular dynamics (MD) and first-principles simulations further revealed that stronger interfacial electronic interactions and more stable interfacial microstructures formed between HAP atomic layers and PDMS molecular chains, which are essential for the improved sedimentation stability and rheological performance of HAP/CIP MRFs. This work provides both experimental and theoretical insights into the interfacial mechanisms between HAP-modified CIP and PDMS, and proposes an effective strategy for developing high-performance MRFs.