Experimental Investigation of the Effect of the Filler Morphology on the Viscoelastic Shear Properties of PDMS-Based Magnetorheological Elastomers

Magnetorheological elastomers (MREs, hereinafter) are a type of smart composite whose basic constituents are a non-magnetic soft elastomeric matrix and ferromagnetic filler particles. The viscoelastic properties of MREs are tunable by an external magnetic field, which provides them with greater functionality than conventional reinforced polymers.Despite the abundant amount of literature studying the complex micromechanics of MREs, the effect of the filler morphology is an aspect that has been recurrently overlooked by researchers. Spherical iron particles have been by far the most frequently used to fabricate MREs since all the theoretical models for this type of material assume that the embedded particles are perfect spheres, which greatly simplifies the equations.In the present study, a multiscale experimental approach has been adopted to investigate the microscopic mechanisms governing the macroscopic viscoelastic behavior of PDMS-silicone-based MREs, with an emphasis on the effect of the filler morphology on both the microstructure and the shear response of the composite. Sixteen different MRE materials have been produced using four different iron powders of varying average particle size, shape and texture. The morphology of the iron particles and the microstructure of the fabricated materials have been analyzed via X-ray computed nanotomography (X-ray nano CT) and scanning electron microscopy (SEM). In addition, the shear moduli of the specimens have been monitored under coupled magneto-mechanical loading via dynamic mechanical analysis (DMA). It has been proven that the morphology of the filler has a significant impact on the mechanical properties of MREs. The particle size affects the strength of the magnetic interparticle interactions, which produce a confining effect on the rubber matrix, while the particle shape and texture have a great influence on the rubber-filler mechanical adhesion