Soft hybrid magnetorheological elastomer: Gap bridging between MR fluid and MR elastomer

Two major branches of the magnetorheological (MR) materials are MR fluids and MR elastomers. The MR fluids largely suffer from the sedimentation problem. On the other hand, MR elastomers conquer the sedimentation problem but have a lower MR effect. A magnetic field is required when an anisotropic configuration of the magnetic particles in the MR elastomer is desired. In this paper, we present a gap bridging material between MR fluids and MR elastomers, which may overcome the sedimentation problem of MR fluid as well as exhibits the anisotropic MR effect but avoids the need of a magnetic field during the crosslinking process as required for the fabrication of conventional anisotropic MR elastomer. A soft hybrid MR elastomer has been developed by forming a core-shell structure. The core consists of a mixture of magnetic particles and a carrier medium. Two types of carrier media have been adopted, named as fluid core and solid core. The shell is made from an elastomer. The investigation was performed to understand the effect of the concentration of magnetic particles in both liquid and solids cores as well as the effect of viscosity of the carrier fluid in the liquid core. The magnetorheological study revealed that the high viscosity carrier fluid is not as good as a low viscosity carrier fluid for the shear stress enhancement. However, for the core-shell soft hybrid MR elastomers, MR effect exhibited by the high viscosity carrier fluid core ( > 1000 Pa.s) was found to be as good as the low viscosity carrier fluid core. The high viscosity carrier fluid also overcomes the sedimentation problem of MR fluids and also exhibits a remarkable MR effect even in a moderately strong magnetic field. Similarly, it also exhibits the anisotropic MR effect when the direction of the applied magnetic field is changed, however, no magnetic field was applied during the crosslinking as typically required for conventional anisotropic MR elastomers. Such core-shell soft hybrid MR elastomers with high viscosity fluid core potentially bridge the gap between MR fluids and MR elastomers and open a new door of MR materials' applications that might have not been achieved by the exclusive utilization of the previous MR materials.