Ring-like structures in magnetoactive elastomers based on magnetic hard powder

Abstract

In this study, we report on the experimentally observed phenomenon of ring-like structures formation from chains of magnetic microparticles in magnetoactive elastomers based on magnetic hard powder. In order to find an explanation for the specific macroscopic magnetic properties of composites, microstructural observations on the elastic composite based on a thin layer of magnetic hard particles have been carried out. Particles embedded in such magnetic composites can move inside the matrix with some restrictions and form chain-like structures on being subjected to magnetizing and turn over as first the strength of the external magnetic field decreases and then the polarity of the field switches to opposite. The quantitative parameters of these processes depend on a number of factors including coercivity and remanence of particles, polymer matrix elasticity, and external field intensity. In zero-field, the magnetized particles can assemble into ring-like structures, thus tending to bring the free energy of the overall system to a minimum. The study is primarily aimed to shed a light on understanding the specific magnetic properties of magnetic polymers, such as magnetoactive or magnetorheological elastomers with a magnetic hard filler. Furthermore, the phenomenon of ring-like structures formation can be used for controlled remote patterning of particles in magnetic elastic composite thin films, which is attractive for various applications.

Effects of soft and hard magnetic particles on the mechanical performance of ultra-soft magnetorheological elastomers

“…Under such circumstances, it is essential not only the magnetorheological characterisation, but also the control of the shape of hMRE structures under magnetic fields and the influence of geometrical effects together with multifunctional mechanisms at the microscale. Although some relevant works on soft hMREs have been published [60,67], to the best of the authors' knowledge there is still a gap of knowledge on extremely soft hMREs (stiffness lower than 10 kPa). Such a soft nature of the elastomeric matrix promotes large microstructural deformations within the MRE that can lead to remarkable macrostructural responses.…”