Superelastic stress–strain behavior in ferrogels with different types of magneto-elastic coupling

Abstract

Colloidal magnetic particles embedded in an elastic polymer matrix constitute a smart material called a ferrogel. It responds to an applied external magnetic field by changes in elastic properties, which can be exploited for various applications such as dampers, vibration absorbers, or actuators. Under appropriate conditions, the stress-strain behavior of a ferrogel can display a fascinating feature: superelasticity, the capability to reversibly deform by a huge amount while barely altering the applied load. In previous work, using numerical simulations, we investigated this behavior assuming that the magnetic moments carried by the embedded particles can freely reorient to minimize their magnetic interaction energy. Here, we extend the analysis to ferrogels where restoring torques by the surrounding matrix hinder rotations towards a magnetically favored configuration. For example, the particles can be chemically cross-linked into the polymer matrix and the magnetic moments can be fixed to the particle axes. We demonstrate that these systems still feature a superelastic regime. As before, the nonlinear stress-strain behavior can be reversibly tailored during operation by external magnetic fields. Yet, the different coupling of the magnetic moments causes different types of response to external stimuli. For instance, an external magnetic field applied parallel to the stretching axis hardly affects the superelastic regime but stiffens the system beyond it. Other smart materials featuring superelasticity, e.g. metallic shape-memory alloys, have already found widespread applications. Our soft polymer systems offer many additional advantages such as a typically higher deformability and enhanced biocompatibility combined with high tunability.

Review on the advancements of magnetic gels: towards multifunctional magnetic liposome-hydrogel composites for biomedical applications

“…The pointlike dipole interaction can be used as an approximation of the interaction between particles, though it has to be extended to consider the coupling between soft particles under a magnetic field, as the magnetization of the adjacent particle influences the force (attractive or repulsive) between the particles [84]. Further, soft sphere potentials for the excluded volume of the particle are commonly used in molecular dynamics, such as the repulsive Weeks-Chandler-Andersen potential, that does not impose a strict bound to the minimum centre-to-centre distance (the distance is a result of the balancing of the relevant forces) [85][86][87], and is of high importance in the study of magnetic gels/ferrogels [88][89][90]. On the other hand, the hard spheres are commonly used in Monte Carlo simulations, to evaluate the ground state configurations of assembled nanoparticle structures [87,91,92].…”

Magnetically Tunable Vibration Transmissibility for Polyurethane Magnetic Elastomers

“…Magnetic elastomer is a stimulus-responsive soft material, and consists of polymeric matrices and magnetic particles. The viscoelastic property can be altered by the application of magnetic fields, and it has been widely studied experimentally and theoretically [1,2,3,4,5]. We have studied, thus far, the effect of magnetic fields on the viscoelastic property of magnetic elastomers, and have developed various types of magnetic elastomers [6,7,8,9].…”

Novel MRE/CFRP sandwich structures for adaptive vibration control

“…Applying a magnetic field to such a kind of MRE, internal magnetodipolar forces can cause changes in static and dynamic properties [17][18][19][20][21][22][23][24]. Structurally, during synthesis, these forces can lead to a rearrangement of the particles towards chain-like aggregates oriented parallel to the direction of the applied magnetic field [25][26][27][28].…”