Multiscale Interface Design of Carboxylated MWCNTs/CIPs–OH Hybrid Magnetorheological Fluids for Enhanced Field-Induced Rheological Properties

Achieving simultaneous enhancement of field-induced rheological performance and sedimentation stability remains a persistent challenge for magnetorheological fluids (MRFs). Here, we propose a multiscale interfacial engineering strategy that integrates hydroxylated carbonyl iron particles (CIPs-OH) with carboxylated multiwalled carbon nanotubes (MWCNTs) to address this long-standing trade-off. By introducing abundant hydroxyl groups onto the CIPs' surface and incorporating mechanically robust carboxylated MWCNTs, a hybrid MRF system was constructed via a combination of mechanical mixing and ultrasonic dispersion. Molecular dynamics simulations, together with experimental characterization, reveal that dynamic hydrogen-bond interactions between oxygen-containing functional groups enable the stable adsorption of MWCNTs onto CIPs-OH. This adsorption reinforces particle-chain stiffness, enhances yield stress, and reduces loss modulus under applied magnetic fields. Meanwhile, MWCNTs dispersed in the carrier liquid form a molecular-scale bridging network that effectively suppresses particle aggregation and improves sedimentation stability. As a result, the hybrid MRF exhibits a favorable balance between enhanced field-induced rheological response and long-term stability compared with conventional CIP-based MRFs. This work demonstrates that multiscale interfacial coupling mediated by dynamic hydrogen bonding provides an effective and scalable pathway for the design of high-performance magnetorheological materials.