Magnetomechanical response of bilayered magnetic elastomers

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One of the central appealing properties of magnetic gels and elastomers is that their elastic moduli can reversibly be adjusted from outside by applying magnetic fields. The impact of the internal magnetic particle distribution on this effect has been outlined and analyzed theoretically. In most cases, however, affine sample deformations are studied and often regular particle arrangements are considered. Here we challenge these two major simplifications by a systematic approach using a minimal dipole-spring model. Starting from different regular lattices, we take into account increasingly randomized structures, until we finally investigate an irregular texture taken from a real experimental sample. On the one hand, we find that the elastic tunability qualitatively depends on the structural properties, here in two spatial dimensions. On the other hand, we demonstrate that the assumption of affine deformations leads to increasingly erroneous results the more realistic the particle distribution becomes. Understanding the consequences of the assumptions made in the modeling process is important on our way to support an improved design of these fascinating materials.

Section: Dipole-spring Minimal Modelmentioning

confidence: 99%

Structural control of elastic moduli in ferrogels and the importance of non-affine deformations

Pessot

Cremer

Borin

et al. 2014

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“…The core feature of these materials is their magnetomechanical coupling [31][32][33], i.e. the way magnetic effects such as the response to an external magnetic field couple to the overall mechanical properties (e.g.…”

Section: Introductionmentioning

confidence: 99%

“…strain or elastic moduli) and vice versa. As was recently shown, such coupling is responsible for surprising properties such as * Electronic address: giorgpess@thphy.uni-duesseldorf.de † Electronic address: hlowen@thphy.uni-duesseldorf.de ‡ Electronic address: menzel@thphy.uni-duesseldorf.de superelasticity [34], a characteristic buckling of chains of particles under a perpendicular external magnetic field [35], qualitative reversal of the strain response [32], volume changes due to mesoscopic wrapping effects [36], or tunability of the electrical resistance [37]. There are several key factors that can influence the magnetomechanical coupling: the magnetic particle concentration [1,38,39], the stiffness of the gel [40], or whether the magnetic moments of the particles can freely reorient or must instead rotate synchronously with the whole particle [2,41].…”

Section: Introductionmentioning

confidence: 99%

Dynamic elastic moduli in magnetic gels: Normal modes and linear response

Pessot

Löwen

Menzel

2016

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In the perspective of developing smart hybrid materials with customized features, ferrogels and magnetorheological elastomers allow a synergy of elasticity and magnetism. The interplay between elastic and magnetic properties gives rise to a unique reversible control of the material behavior by applying an external magnetic field. Albeit few works have been performed on the time-dependent properties so far, understanding the dynamic behavior is the key to model many practical situations, e.g., applications as vibration absorbers. Here we present a way to calculate the frequency-dependent elastic moduli based on the decomposition of the linear response to an external stress in normal modes. We use a minimal three-dimensional dipole-spring model to theoretically describe the magnetic and elastic interactions on the mesoscopic level. Specifically, the magnetic particles carry permanent magnetic dipole moments and are spatially arranged in a prescribed way, before they are linked by elastic springs. An external magnetic field aligns the magnetic moments. On the one hand, we study regular lattice-like particle arrangements to compare with previous results in the literature. On the other hand, we calculate the dynamic elastic moduli for irregular, more realistic particle distributions. Our approach measures the tunability of the linear dynamic response as a function of the particle arrangement, the system orientation with respect to the external magnetic field, as well as the magnitude of the magnetic interaction between the particles. The strength of the present approach is that it explicitly connects the relaxational modes of the system with the rheological properties as well as with the internal rearrangement of the particles in the sample, providing new insight into the dynamics of these remarkable materials.

“…1,[23][24][25][26][27] Consequently, the possibility of constructing externally tunable damping devices 28 or vibration absorbers 23 has been outlined. Also, the deformations of the materials in external magnetic fields have been investigated [29][30][31][32][33][34] and their use as soft actuators 1,35 and as magnetic sensors [36][37][38] has been pointed out.…”

Section: Introductionmentioning

confidence: 99%

Bridging from particle to macroscopic scales in uniaxial magnetic gels

Menzel

2014

Connecting the different length scales of characterization is an important, but often very tedious task for soft matter systems. Here, we carry out such a procedure for the theoretical description of anisotropic uniaxial magnetic gels. The so-far undetermined material parameters in a symmetry-based macroscopic hydrodynamic-like description are determined starting from a simplified mesoscopic particle-resolved model. This mesoscopic approach considers chain-like aggregates of magnetic particles embedded in an elastic matrix. Our procedure provides an illustrative background to the formal symmetry-based macroscopic description. There are presently other activities to connect such mesoscopic models as ours with more microscopic polymer-resolved approaches; together with these activities, our study complements a first attempt of scale-bridging from the microscopic to the macroscopic level in the characterization of magnetic gels.