Tailoring viscoelastic damping and magnetic response in high–concentration PDMS–ferrite iron magnetorheological elastomer via irregular particle morphology

This study investigates the structure-property relationships of magnetorheological elastomers (MREs) fabricated with fixed, high filler–loading of 60 wt% water–atomized iron powders dispersed in a polydimethylsiloxane (PDMS) matrix. By maintaining a constant concentration, the influence of particle morphology from sub-rounded, narrowly distributed powders (AP45) to highly angular and polydisperse powders (AP80) was isolated from concentration effects. Particle size analysis (PSA) revealed systematic variations in median size (D50 = 26.3–71.9 μm) and distribution breadth (SPAN = 0.762–2.186), providing a quantitative basis for correlating morphology with functional performance. A critical 15 min vacuum degassing step, followed by a two–stage thermal curing protocol (30/86 °C), minimized voids and ensured mechanically robust composites at high–filler contents. Physicochemical characterization confirmed the presence of soft–magnetic α–ferrite and surface Fe–OH groups that promote filler–matrix interactions. Magnetic and dynamic mechanical analyses revealed a clear morphology-driven trade-off. The compact and uniform AP45 morphology achieved the highest saturation magnetization (M s ≈ 202.02 emu/g), making it optimal for high–responsiveness MR–actuation, whereas the highly irregular AP80 morphology enhanced mechanical–interlocking and interfacial–friction, yielding the highest glassy storage–modulus (E' ≈7.02 × 10 3 MPa) and pronounced secondary relaxations in the tanδ response near −37 °C, indicative of superior intrinsic damping. These findings establish particle morphology as a primary design parameter for application-specific MREs and support the use of cost–effective water-atomized iron powders as alternatives to carbonyl iron.