Magnetic susceptibility and response time of isotropic and structured magnetorheological elastomers

The response time of magnetorheological elastomers (MREs) depends on the complex interplay of multiple factors. In this study we investigate the response times of silicone rubber based elastomers containing magnetically soft fillers (iron and magnetite) with isotropic, and two types of anisotropic particle structures. The response times of the elastomers were extracted as the characteristic time constant from the time domain dynamic susceptibility response to ramp excitation in the weak field limit (H< 10 kAm(-1)). The MREs with both types of filler materials in all particle configurations showed a positive susceptibility response, while an inverse proportionality was observed between the response times and the slope of the ramp excitation in all cases. The dynamics of the structural change is found to be highly sensitive to the type of the filler material, and the anisotropy of the microstructure. The response times of the iron loaded MREs varied from (4.0 +/- 0.3) ms up to (60.5 +/- 2.3) ms. The magnetite loaded MREs displayed faster response (between (1.2 +/- 0.1) ms and (12.1 +/- 1.8) ms), which is attributed to the cross-linking inhibitor effect of the magnetite particles. The anisotropic particle structure also favors a decreased response time, however the remanence of the particles can modify the structural effect.