Magnetorheological Elastomers: Electric Properties versus Microstructure

A series of composite materials comprising elastomeric matrix filled with magnetic filler (magnetorheological elastomer) were prepared in two morphological variants, namely with random and organized spatial distribution of filler particles. Orderly arrangement in the latter case was achieved through application of magnetic field throughout curing. Influence of filler concentration and its arrangement in magnetorheological elastomers (isotropic and anisotropic) on electric properties was studied by the means of dc conductivity measurement and dielectric relaxation spectroscopy. Qualitatively different behavior was observed for anisotropic samples with relaxations linked to charge transport along filler clusters. Activation energy of these was extracted from temperature measurements and found to decrease with filler loading as inter-particle distance diminishes. Strongly non-linear character of this decrease was explained by decreasing degree of anisotropy in structured samples with increasing filler loading due to spatial and viscous effects preventing arrangement of filler as regular as in case of low concentrations. This correlation, i.e. between dielectric properties and inner structure of magnetorheological elastomers, is employed for description of such systems inner morphology.