Environmentally friendly magnetorheological fluids based on hydrogen bonds surface stabilized nickel microparticles

• We present a new class of low-viscosity H ydrophobic D eep E utectic S olvents • The study present HDES with enhanced responsiveness to external magnetic fields • The method improves the strategy for designing a superior and green smart fluids • Results show strong influence of the hydrogen bonding network of the solvent matrix • Our findings show the advance of HDES-MRF with applicability in engineering systems This study presents the development of magnetorheological fluids (MRFs) using a hydrophobic deep eutectic solvent (HDES) with low viscosity, synthesized from eco-friendly, cost-effective DL-menthol and decanoic acid. The HDES serves as a biodegradable carrier fluid, enabling safer disposal and reducing environmental and operational hazards. Due to its hydrogen - bond interactions and low viscosity, HDES efficiently forms MRFs with nickel microparticles of different morphologies - spherical, filamentary, and rough - exhibiting superior magnetorheological performance compared to conventional engine oil - based MRFs. Key improvements include higher viscosity, enhanced dynamic and static yield stress, greater shear stress resistance, and increased yield strength, with performance ranking filamentary > rough > spherical. The viscoelastic behaviour of MRFs is strongly influenced by particle morphology, carrier fluid, and applied magnetic field. Filamentary particles produce the highest moduli and the broadest linear viscoelastic regions, while HDES - based MRFs consistently outperform engine oil-based systems in structural stability and field responsiveness. Strain amplitude, magnetosweep, and frequency - dependent measurements reveal tunable microstructures, highlighting the critical role of particle shape and carrier fluid in optimizing both dynamic and static performance. These findings demonstrate that HDES - based MRFs offer a high - performance, environmentally benign platform for advanced engineering applications.