How resilient is the MR effect to environmental aging? Long-term performance of MREs under natural weathering conditions

Abstract A material's capacity to preserve its stability amidst fluctuating environmental conditions is a vital factor in determining its durability and effectiveness in real-world applications, yet the long-term performance of magnetorheological elastomers (MREs) under prolonged natural weathering remains underexplored. This study introduces a novel investigation into the stability of MREs composed of 30 wt.% silicone rubber and 70 wt.% carbonyl iron particles, exposed to 12 months of natural weathering in a tropical climate, characterized by ultraviolet radiation, temperature swings, humidity, and rainfall, to assess their durability for potential applications such as automotive suspension systems, vibration dampers, and engine mounts. Morphological analysis using Scanning Electron Microscopy exhibited substantial surface deterioration, while the internal structure remained unaffected. Rheological testing, conducted via an oscillatory shear rheometer, demonstrated a progressive increase in the storage modulus with aging, indicative of matrix stiffening due to age-related crosslinking and hardening. The loss modulus also increased, suggesting enhanced energy dissipation linked to matrix changes. While unaged samples displayed solid-like elastic behavior with no crossover between storage and loss moduli, aged samples shifted toward viscous behavior at higher strains, suggesting reduced elasticity. Remarkably, the relative magnetorheological (MR) effect remained stable across all samples, driven by the preserved alignment of magnetic particles under fields up to 0.73 T, even after prolonged weathering. This stability of the MR effect, despite surface degradation and rheological shifts, represents the study's primary contribution, demonstrating MREs' resilience for long-term use in challenging environments. By linking environmental degradation to rheological performance, this work fills a critical knowledge gap, offering valuable insights into the sustained utility of MREs in applications requiring enduring stability.