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

Abstract

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.

Bridging from particle to macroscopic scales in uniaxial magnetic gels

“…However, the nature of the mechanical response and other characteristic material properties can strongly depend on the spatial distribution of the magnetic particles within the sample. 1,31,[44][45][46][47][48][49][50][51] Typical particle diameters range from nano-to micrometers and thus involve an intermediate, i.e., mesoscopic length scale. Finally, for rubbery substances, the fact that the materials are elastic mainly results from the entropic properties of the single crosslinked polymer chains and is therefore of molecular microscopic origin.…”

Depolarized light scattering from prolate anisotropic particles: The influence of the particle shape on the field autocorrelation function

“…41 Ferrofluids 42 and ferrogels [43][44][45] (for a recent review see Ref. 46) with magnetic particles provide further prominent examples of smart materials where anisotropic particles are involved.…”

Tunable dynamic response of magnetic gels: Impact of structural properties and magnetic fields

“…This may be exploited in constructing novel damping devices [10] and vibrational absorbers [11]. Several theoretical studies have shown that the internal spatial particle distribution plays a qualitative role for this effect [12][13][14][15]. Furthermore, applying time-dependent external magnetic fields can induce deformations, which makes the materials candidates for the use as soft actuators [5,16,17].…”