Magnetorheological elastomers (MREs) are adaptive composite materials whose mechanical properties can be controlled by an external magnetic field, making them attractive for vibration isolation systems, adaptive structures, and smart engineering applications. Despite their growing use, the durability of MREs under long-term cyclic loading remains poorly understood. This study investigates the degradation behaviour of a silicone-based MRE subjected to purely mechanical, purely magnetic, and combined magneto-mechanical cyclic loading. A custom-designed test rig was developed to simultaneously apply cyclic deformation and magnetic excitation, while the evolution of the complex effective modulus, including its storage and loss components, was monitored over 250,000 loading cycles. The results show that cyclic magnetic loading alone produces degradation comparable to that caused by cyclic mechanical loading, identifying magnetic excitation as a significant damage-driving mechanism. Simultaneous magnetic and mechanical loading results in a pronounced synergistic effect, reducing the effective modulus by more than 50% after 250,000 cycles. An energy-based degradation model and SEM observations supported the observed behaviour. The findings provide new insight into degradation mechanisms in magnetically responsive composites and highlight the importance of considering durability in MRE-based structural and vibration isolation components.

A showcase study in which magnetic particles are investigated as a filler, mainly for the development of solid polymer electrolytes, is presented. The magnetic particles, in the form of polypyrrole (PPy) nanotubes, were decorated with different amounts of magnetite nanoparticles, which can be tuned through synthesis. The particles were dispersed in high molecular weight poly(ethylene oxide) blended with sodium carboxymethyl cellulose, preparing pellets and thin films. An external magnetic field was used to obtain anisotropic thin films, with the differences described in detail. After solid characterization, we show that, depending on the synthesis of composite particles and the fabrication methods of the pellets and films, we can alter various properties─magnetic (Msat ∼ 30-60 emu/g), electric (σionic ∼ 10-7-10-4 S/cm), and mechanical (G' ∼ 8-10 MPa). The presence of the filler improved the shear modulus (∼60 MPa), competing with dendrite propagation while offering improved thermal stability at elevated temperatures (80°C). Depending on the preparation and composition of the filler material, the ionic conductivity always improved with the presence of the PPy/Fe3O4, with a specific sample reaching ∼10-4 S/cm at room temperature. The present work is a new strategy to improve the properties of solid polymer electrolytes and can pave the way for more efficient and more competitive magnetic composites used for energy storage.

This study presents a new class of low-cost composite materials based on a silicone oil suspension containing nickel-based hybrid microparticles in equal volume fractions. Two types of suspensions were prepared using magnetic particles with different compositions. The nickel content of the hybrid microparticles was 78.3 and 83.4 wt% nickel core, respectively, with the rest being a polypyrrole coating composed of nanoparticles and nanotubes. Utilizing a specialized experimental setup, we investigated the influence of nickel concentrations on the electrical conduction properties of the suspensions. The measurements were performed under electric and combined electric and magnetic fields. Our findings demonstrate that the electrical conductivity has a non-linear response with external fields and it can be effectively tuned through the nickel content and the external fields. A model was developed to understand the observed trends. These findings have significant implications for the design and optimization of advanced materials in applications requiring the precise control of electrical properties under varying field conditions.

Understanding processing-induced changes in the polymer composites is of the utmost necessity as it affects the final properties and the reliability of the products. Despite their importance, related investigations are frequently overlooked, especially in the case of magnetorheological elastomers (MREs). In this study, the processinginduced changes were investigated within an isotropic MRE based on a thermoplastic elastomer (TPE) matrix loaded with carbonyl iron (CI) microparticles. Systematic thermomechanical tests in the molten state were used to mimic the processing conditions, revealing the time evolution of the particle/matrix interactions. The interactions manifested as an increase in the viscoelastic properties, which was attributed to the development of a secondary network composed of the confined polymer chains in the vicinity of the CI particles. The restricted mobility improved the reinforcing effect and structural integrity but diminished the field-induced stiffening of the composite, i.e., the magnetorheological effect. The existence of the particle/matrix covalent bonding was postulated and explained based on the coupling reaction between the thermomechanically-induced radicals formed in the polymer chain and the alkoxyl radicals on the surface of the CI particles. The new findings are highly relevant for the further development of reprocessable and recyclable TPE-based MREs, while the robust measuring protocol is deemed to be implementable for studying particle/matrix interactions in diverse composite systems.

This research presents an in-depth exploration of the electrical and magnetic properties of a polypyrrole nanotubes/magnetite nanoparticles (PPyM) material embedded in a silicone oil matrix. A key finding of our study is the dual nature of the composite, i.e. it exhibits a behaviour akin to both electro- and magnetorheological suspensions. This unique duality is evident in its response to varying electric and magnetic field intensities. Our study focuses on examining the electrical properties of the composite, including its dielectric permittivity and dielectric loss factor. Additionally, we conduct an extensive analysis of its rheological behavior, with a particular emphasis on how its viscosity changes in response to electromagnetic stimuli. This property notably underscores the material's dual-responsive nature. Employing a custom experimental design, we integrate the composite into a passive electrical circuit element subjected to alternating electric fields. This methodological approach allows us to precisely measure the material's response in terms of resistance, capacitance, and charge under different field conditions. Our findings reveal substantial changes in the material's electrical conductivity and rheological characteristics, which are significantly influenced by the intensity of the applied fields. These results enhance the understanding of electro-magnetorheological properties of PPyM-based magnetic composites, and also highlight their potential in applications involving smart materials. The distinct electrical, magnetic and rheological modulation capabilities demonstrated by this composite render it as promising candidate for advanced applications. These include sensory technology, actuation systems, and energy storage solutions.

Electrorheological (ER) materials have attracted considerable attention over the decades, owning to their unique ability to rapidly change their rheological properties upon exposure to an electric field. Such feature enables these materials in numerous applications. This paper reviews the general aspects of electrorheological fluids (ERFs), and introduces the most often used ER materials. Liquid carriers are briefly compared and numerous dispersed dielectric particles are represented from both, inorganic and organic categories, along with a wide range of composites. A selection of reviewed ERF particles characteristics (their type, geometry, size, conductivity and ER efficiency) is summarized in tables. Advantages and drawbacks of state-of-the-art ERFs are outlined, along with their general requirements. Additionally, an open living online document is attached and meant to keep a summary of the key characteristics of ER particles covered in future ERF-focused publications and create a rich online resource for the scientific community over time. Fellow researchers are therefore welcomed to contact the authors for their published data to be included (the open living table is to be updated regularly).

This study investigates the fabrication and characterization of innovative electrical devices (EDs) subjected to an alternating electric field in the presence of static electric and magnetic fields. The EDs contain...

In this work, two magnetorheological suspensions composed of polypyrrole nanorods decorated with magnetite nanoparticles and suspended in silicone oil were studied as electrical devices. The electrical devices (EDs) were fabricated in a unique cell using nanotubes with different magnetic and electric properties which can be tailored during synthesis. The electrical effects of the suspensions were studied under static electric and magnetic fields and were superimposed on a medium-frequency electric field. The electrical resistance Rp and the quality factor Qp at the terminals of EDs were extracted and analysed. Additionally, the equivalent electrical capacitances Cp were obtained through a well-established theory and then compared for each ED. Through the electrical and magnetic dipolar approximation model, it was illustrated that the electrical effect induced in a suspension can be three times higher depending on the amount of the magnetite. Thus, by tuning the synthesis parameters, it is possible to obtain EDs with well-defined and unique properties.

Conductive polypyrrole nanotubes were synthesized with a two-step one-pot synthesis. During synthesis, the nanotubes were decorated with magnetite nanoparticles at different concentrations granting them magnetic properties. The characterization of the tubes revealed differences from the theoretical reactions. A bidisperse magnetorheological fluid (MRF) was prepared by mixing the composite polypyrrole nanotubes/magnetite nanoparticles with commercial carbonyl iron spherical microparticles in silicone oil. The rheological properties of the bidisperse system were studied under the presence of magnetic field at room and elevated temperature. An enhancement of the MR effect with the presence of the nanotubes was observed when compared with a standard MRF consisted only of magnetic microparticles. Due to the faster magnetic saturation of the nanotubes, this enhancement is exceptionally high at low magnetic fields. The stability of the system is studied under dynamic conditions where it is revealed that the nanotubes keep the standard particles well dispersed with the sedimentation improving by more than 50%.

Hybrid organic/inorganic conducting and magnetic composites of core–shell type have been prepared by in-situ coating of nickel microparticles with polypyrrole. Three series of syntheses have been made. In the first, pyrrole was oxidised with ammonium peroxydisulfate in water in the presence of various amounts of nickel and the composites contained up to 83 wt% of this metal. The second series used 0.1 M sulfuric acid as a reaction medium. Finally, the composites with polypyrrole nanotubes were prepared in water in the presence of structure-guiding methyl orange dye. The nanotubes have always been accompanied by the globular morphology. FTIR and Raman spectroscopies confirmed the formation of polypyrrole. The resistivity of composite powders of the order of tens to hundreds Ω cm was monitored as a function of pressure up to 10 MPa. The resistivity of composites slightly increased with increasing content of nickel. This apparent paradox is explained by the coating of nickel particles with polypyrrole, which prevents their contact and subsequent generation of metallic conducting pathways. Electrical properties were practically independent of the way of composite preparation or nickel content and were controlled by the polypyrrole phase. On the contrary, magnetic properties were determined exclusively by nickel content. The composites were used as a solid phase to prepare a magnetorheological fluid. The test showed better performance when compared with a different nickel system reported earlier.

Hybrid conductive paint pigments composed of zinc ferrites (ZF) and polyaniline (PANI) were analysed as both a potential electro-active and corrosion-protective paint from the electrorheological (ER) point of view. The particles were characterised using scanning electron microscopy and X-ray diffraction spec-troscopy. These hybrid conductive particles are used as pigments suitable for applications in paints which was confirmed by determining the consumption of linseed oil, the specific conductivity of aqueous extracts and the density of the tested pigments according to the relevant standardized methods. The chemical stability of particles was evaluated by means of durability tests in aggressive environment showing excellent results for the coated particles. Both ZF/PANI particles and pure ZF were dispersed in silicone oil and their ER behaviour was analysed through controlled shear rate and dynamic oscillatory tests. The ER performance of the pure ZF and the composite ZF/PANI suspensions were compared, show-ing promising results and enhanced ER performance and attention-worthy ER efficiency of the later (in particular, the ER efficiency of the coated particles exceeded 105 % at 0.01 s-1). Lastly, the results were further validated via dielectric spectroscopy. Thus, the ZF/PANI particles have the potential to be applied as a hybrid ER fluid and an electro-active paint.(c) 2022 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.

Despite the vast amount of studies based on magnetorheological elastomers (MREs), a very limited number of investigations have been initiated on their reprocessing. This paper presents a new type of recyclable MRE which is composed of thermoplastic polyurethane (TPU) and carbonyl iron particles (CI). The chosen TPU can be processed using injection moulding (IM), followed by several reprocessing cycles while preserving its properties. Numerous types of injection moulded and reprocessed MREs have been prepared for various particle concentrations. The effect of thermo-mechanical degradation on the recycled MREs has been investigated while simulating the reprocessing procedure. An apparent decrease in molecular weight was observed for all the examined matrices during the reprocessing cycles. These changes are attributed to the intermolecular bonding between the hydroxyl groups on the surface of the CI particles and the matrix which is studied in depth. The effect of reprocessing and the presence of magnetic particles is evaluated via tensile test, magnetorheology and piezoresistivity. These characterization techniques prove that the properties of our MREs are preserved at an acceptable level despite using 100% of recyclates while in real applications only up to 30% of recycled material is generally used.