Properties of magnetic hybrid materials - a microscopic simulational approach

本课题的目的是利用粒子模拟的方法研究磁性软物质。在之前的资助期内，我们主要集中于研究磁性凝胶的静态特性。除此之外，我们还开发了模拟模型来捕捉凝胶在外部场中变形的不同机制。此外，我们还研究了凝胶中磁性纳米颗粒的空间构型与样品形状之间的相互作用，以及聚合物网络结构的影响。然而，许多关于磁性软物质的实验使用了时间相关的刺激，如交流磁场，并探测动力学。因此，我们开始研究磁性凝胶的动力学性质。特别地，我们研究了通过打开或关闭外场引起的凝胶中的弛豫过程。在最后一个筹资期内，我们将继续这些努力。一方面，我们研究了控制磁性凝胶聚合物网络结构的各种因素，以及它们如何影响其磁变形性能。另一方面，我们将扩展时间依赖性刺激的研究。在这里，我们将重点研究磁性凝胶在交流磁场中的变形响应。这将支持需要振荡驱动的应用的材料设计。此外，我们集中在微流变的球形和各向异性颗粒在聚合物悬浮液。目标是，首先，获得一个更好的理解颗粒-基质耦合；其次，我们的目标是阐明磁性粒子对交流磁场的响应如何改变局部矩阵性质。这涉及到在优先程序中由几个小组进行的各种实验。此外，我们将设计一个嵌入磁性赤铁矿主轴的PNIPAAM凝胶的模拟模型，并将获得的结果与优先程序中进行的实验测量进行比较。第一个重点将是颗粒-基质耦合，其次是凝胶的流变性能。最后，我们将为其他小组使用和发展的理论提供数值数据，例如用于聚合物基质介导的磁性颗粒之间相互作用的DFT计算。

The goal of this project is to study magnetic soft matter by means of particle-based simulations. In the previous funding period we have focussed mainly on the investigation of static properties of magnetic gels. Amongst other things we have developed simulation models that capture the different mechanisms for a gel's deformation in an external field. Furthermore, we have examined the interplay between the spatial configuration of magnetic nanoparticles in the gel and the sample shape, as well as the influence of the polymer network structure. Many experiments on magnetic soft matter, however, use time-dependent stimuli such as AC magnetic fields and probe the dynamics. We therefore have started to investigate the dynamical properties of magnetic gels. In particular, we investigated the relaxation processes in a gel caused by switching an external field on or off. In the last funding period, we will continue these efforts. On one hand, we investigate the various factors that control the polymer network structure of a magnetic gel, and how they affect its magnetodeformational properties. On the other hand, we will extend our work on time-dependent stimuli. Here, we will focus on the deformational response of magnetic gels in AC magnetic fields. This will support the design of materials for applications which require oscillatory actuation. Furthermore we concentrate on the micro-rheology of spherical and anisotropic particles in a polymer suspension. The objective is, first, to gain a better understanding of the particle-matrix coupling; Second, we aim to elucidate on how the local matrix properties can be changed by the magnetic particles response to an AC magnetic field. This relates to various experiments performed by several groups within the priority program. Moreover, we will devise a simulation model for PNIPAAM gels into which magnetic hematite spindles are embedded and compare the obtained results to experimental measurements performed within the priority program. The first focus will be on the particle-matrix coupling, followed by the gel's rheological properties.Lastly, we will provide numerical data for theories used and developed in other groups, e.g. for DFT calculations on polymer matrix mediated interactions between magnetic particles.