Pessot Giorgio, Schümann Malte, Gundermann Thomas, Odenbach Stefan, Löwen Hartmut, Menzel Andreas M
Institut für Theoretische Physik II: Weiche Materie, Heinrich-Heine-Universität Düsseldorf, D-40225 Düsseldorf, Germany.
J Phys Condens Matter. 2018 Mar 28;30(12):125101. doi: 10.1088/1361-648X/aaaeaa.
Ferrogels and magnetorheological elastomers are composite materials obtained by embedding magnetic particles of mesoscopic size in a crosslinked polymeric matrix. They combine the reversible elastic deformability of polymeric materials with the high responsivity of ferrofluids to external magnetic fields. These materials stand out, for example, for significant magnetostriction as well as a pronounced increase of the elastic moduli in the presence of external magnetic fields. By means of x-ray micro-computed tomography, the position and size of each magnetic particle can be measured with a high degree of accuracy. We here use data extracted from real magnetoelastic samples as input for coarse-grained dipole-spring modeling and calculations to investigate internal restructuring, stiffening, and changes in the normal modes spectrum. More precisely, we assign to each particle a dipole moment proportional to its volume and set a randomized network of springs between them that mimics the behavior of the polymeric elastic matrix. Extending our previously developed methods, we compute the resulting structural changes in the systems as well as the frequency-dependent elastic moduli when magnetic interactions are turned on. Particularly, with increasing magnetization, we observe the formation of chain-like aggregates. Interestingly, the static elastic moduli can first show a slight decrease with growing amplitude of the magnetic interactions, before a pronounced increase appears upon the chain formation. The change of the dynamic moduli with increasing magnetization depends on the frequency and can even feature nonmonotonic behavior. Overall, we demonstrate how theory and experiments can complement each other to learn more about the dynamic behavior of this interesting class of materials.
铁凝胶和磁流变弹性体是通过将介观尺寸的磁性颗粒嵌入交联聚合物基体中而获得的复合材料。它们将聚合材料的可逆弹性变形能力与铁磁流体对外加磁场的高响应性结合在一起。例如，这些材料因显著的磁致伸缩以及在外加磁场存在下弹性模量的显著增加而脱颖而出。借助X射线微计算机断层扫描，可以高精度地测量每个磁性颗粒的位置和大小。我们在此使用从实际磁弹性样品中提取的数据作为粗粒度偶极 - 弹簧建模和计算的输入，以研究内部结构重组、硬化以及正常模式谱的变化。更确切地说，我们为每个颗粒赋予一个与其体积成比例的偶极矩，并在它们之间设置一个随机的弹簧网络，以模拟聚合物弹性基体的行为。扩展我们之前开发的方法，我们计算当开启磁相互作用时系统中产生的结构变化以及频率相关的弹性模量。特别地，随着磁化强度的增加，我们观察到链状聚集体的形成。有趣的是，静态弹性模量在链形成之前，随着磁相互作用幅度的增加可能首先略有下降，然后才会出现显著增加。动态模量随磁化强度增加的变化取决于频率，甚至可能呈现非单调行为。总体而言，我们展示了理论和实验如何相互补充，以更多地了解这类有趣材料的动态行为。
