Solvent dependence of the rheological properties in hydrogel magnetorheological plastomer

Chemically crosslinked hydrogel magnetorheological (MR) plastomer (MRP) embedded with carbonyl iron particles (CIPs) exhibits excellent magnetic performance (MR effect) in the presence of external stimuli especially magnetic field. However, oxidation and desiccation in hydrogel MRP due to a large amount of water content as a dispersing phase would limit its usage for long‐term applications, especially in industrial engineering. In this study, different solvents such as dimethyl sulfoxide (DMSO) are also used to prepare polyvinyl alcohol (PVA) hydrogel MRP. Thus, to understand the dynamic viscoelastic properties of hydrogel MRP, three different samples with different solvents: water, DMSO, and their binary mixtures (DMSO/water) were prepared and systematically carried out using the oscillatory shear. The outcomes demonstrate that the PVA hydrogel MRP prepared from precursor gel with water shows the highest MR effect of 15,544% among the PVA hydrogel MRPs. However, the samples exhibit less stability and tend to oxidise after a month. Meanwhile, the samples with binary mixtures (DMSO/water) show an acceptable MR effect of 11,024% with good stability and no CIPs oxidation. Otherwise, the sample with DMSO has the lowest MR effect of 7049% and less stable compared to the binary solvent samples. This confirms that the utilisation of DMSO as a new solvent affects the rheological properties and stability of the samples

Enhancement of isotropic magnetorheological elastomer properties by silicone oil

This article focused on the influence of additional silicone oil as an plasticizer additive in a magnetorheological elastomer (MRE) upon its rheological properties. Here, a silicone rubber is used as a base material of the MRE with CIPs act as the filler. Silicone oil (SO) as a plasticizer is added to the base ingredients to improve the viscosity and dispersion of magnetic particles and enhance the MRE properties. Various tests comprised of magnetic, morphology, and rheology tests were conducted for MRE characterization purpose. The results showed that the addition of SO on the MRE had increased 19% of magnetic properties compared to non-SO based MRE. Dispersion of magnetic particles is improved by the addition of SO as observed through Low Vacuum Scanning Electron Microscope (LVSEM). In rheology test, both absolute and relative MR effects were increased by 0.3 MPa and 343%, respectively, with the incorporation of 15 wt% SO. The introduction of SO has proven to resolve the agglomeration issues in isotropic MRE which degrade performances of MRE application devices and systems

Frequency-dependent on the magnetorheological effect of magnetorheological plastomer

A low cross-linked magnetic polymer matrix also known as magnetorheological plastomer (MR plastomer) containing micron-sized carbonyl iron particles (CIPs) is a new kind of MR materials. MR plastomer can be prepared by two main methods which are physically and chemically crosslinking. However, the study on the dynamic properties of involving chemically crosslinked MR plastomer particularly the viscoelastic properties especially frequency-dependent are not systematically investigated. Therefore, in this study, the effect of the frequency on the MR effect and damping performance of chemically crosslinking MR plastomer under oscillatory modes condition were analysed. The magnetic particles namely CIPs were inserted into a plasticine-like polymer matrix causing the materials to exhibit an MR effect in response to an external magnetic field. Polymer base matrix was prepared using poly-vinyl alcohol (PVA), and boric acid (BA) was used as a cross-linking agent for chemically crosslinked MR plastomer. The MR plastomer samples were prepared using 70 wt% of CIPs as magnetic particles. The samples were tested using a rheometer with different test frequencies, which are 1, 5, and 10 Hz at the on-state condition. The experimental results revealed that the frequency has a significant correlation with the MR effect of samples where the MR effect of the sample decreased with the increment of test frequency. The MR effect for each sample at 1, 5, and 10 Hz are 6793, 5049, and 3131% respectively. In contrast, for the frequency sweep test, the storage modulus of the sample showed an increasing trend with the increment of test current, while the loss factor revealed an opposite result. The results proved that this kind of MR materials has the potential to be used in various of applications like soft actuator, vibration absorber, and force sensor

Effect of corroded plate-like iron particles on the rheological properties of magnetorheological elastomer

Prior studies have shown that the storage modulus and MR effect of MR materials were mainly determined by the performance of magnetic particles. However, there is still doubt for its utilization in a long-term operation under various external loads and conditions. In MREs, even though the magnetic particles are embedded in an elastomeric matrix and not exposed to the air, corrosion agents however such as moisture and oxygen can penetrate the structure phase and alter their properties. This corrosion phenomenon can significantly affect the performance of MRE devices. In this work, the effect of corroded plate-like carbonyl iron particles (CIPs) on the properties of magnetorheological elastomer (MRE) is investigated. The CIPs are corroded via accelerated corrosion test in various concentrations of diluted hydrochloric acid; particularly 0.5, 1.0 and 1.5 vol.% HCl. The morphology of non-corroded and corroded plate-like CIPs are characterized via SEM prior to fabrication of MREs. The rheological properties of MREs are tested using a rheometer under varying applied currents and frequencies. The results from SEM images show that the sample of non-corroded plate-like CIPs has a smooth surface structure while the corroded plate-like CIPs looked rougher on its surface structure. The storage modulus of MRE is increased with the increased of frequencies but decreased with MRE containing higher corrosion rates. Similarly, the MR effect are decreased from 90.6% for MRE containing of non-corroded plate-like CIP, to 87%, 81.8%, and 71.8%, respectively with increasing of corrosion rate plate-like CIPs in MRE. The obtained results demonstrate that higher purity of the CIPs, the greater the impact on storage modulus and MR effect of MRE. Hence, significant finding of this research is related to the purity of CIPs that play an important role to ensure the continuous reliable performance of MRE devices for long-term applications