Rheological properties of magnetorheological elastomer with fountain-like particle chain alignments

Abstract

Magnetorheological elastomer (MRE) consists of magnetic particles known as carbonyl iron (CIPs), which are locked in a silicone-based matrix in various configurations or alignments, depending on the curing process of the MRE. However, current MREs exhibit different properties due to different CIP’s alignments in the MRE. In fact, most previous studies have focused on a specific angle of the aligned particles to achieve the enhanced viscoelastic properties of MRE. Thus, its effect on the MRE’s stiffness is still rather limited in various devices. In addition, the changes in directions of applied shear force could not result in maximum stiffness or MR effect of MRE, since the interaction of the applied force with the material is effective only in one direction of the particle’s chain alignment. Therefore, in this study, an approach of particle’s alignment of CIPs in an MRE namely, fountain-like structure is introduced to produce numerous angles of CIPs arrangement in the MRE. This study began with the development of a mould to produce numerous directions of magnetic flux lines, in order to have a fountain-like structure for the CIPs to be cured accordingly in the MRE during the curing process. The simulation of the fountain-like magnetic flux lines was done via FEMM analysis. Three types of MREs having different curing structures namely isotropic, fountain-like MRE, and inverted fountain-like MRE were fabricated. The rheological properties of these MREs in terms of storage modulus and magnetorheological (MR) effect were measured in an oscillatory shear mode using a rheometer upon input parameters of sweep strains, sweep frequency and sweep magnetic fields. Meanwhile, the micrograph analyses of all MRE samples were done via FESEM. The results revealed that both fountain-like MREs exhibited higher storage modulus than the isotropic MRE, about 0.06 to 0.1 MPa under the absence of magnetic field (off-state condition), and the values were further increased with the applied magnetic field (on-state condition). In particular, storage modulus of fountainlike MRE was higher as compared to inverted fountain-like MRE. However, the MR effect of inverted fountain-like MRE has overridden fountain-like MRE attributed to its lower initial storage modulus. On the other hand, the phenomenon of higher storage modulus in fountain-like MRE is due to the cramped CIPs upon applied shear stress, thus it was stiffer to resist deformation, as compared to inverted fountain-like MRE which was more expanded towards the applied shear stress. The findings show that fountain-like MREs exhibit the utmost response in an oscillatory shear mode application, for both the off- and on-states conditions, which this novel approach has the potential to be used for the in-situ fabrication method of MRE devices.