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

TL;DR

This study investigates how the internal magnetic particle distribution and deformation assumptions affect the elastic moduli tunability of ferrogels, revealing that realistic structures and non-affine deformations significantly influence their mechanical response.

Contribution

It introduces a systematic minimal dipole-spring model to analyze the effects of structural randomness and non-affine deformations on elastic moduli in ferrogels.

Findings

Elastic tunability depends on structural properties.

Affine deformation assumptions become inaccurate with realistic structures.

Non-affine deformations are crucial for accurate modeling.

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.