Synthesis and characterization of multifunctional hybrid materials: Tuning the mechanical and magnetic properties of hydrogels

铁氧体将凝胶或聚合物基质的特性与磁流体的磁性结合在一起。水凝胶经常被用作基质材料，因为它们可以被水膨胀。由于许多水凝胶对外界刺激如温度、pH或光有反应，这些凝胶也被称为响应性水凝胶。与磁性纳米粒子结合，可以用交流磁场加热杂化凝胶，从而调整凝胶的机械性能。在这最后一个阶段，重点将集中在磁性微凝胶和宏凝胶的合成上，以及在磁场及其对基质的影响下对它们的表征。对于这种多响应性水凝胶，选择特定的磁性粒子种类对于期望的应用是至关重要的。具有聚-N-异丙基丙烯酰胺基质的微凝胶和大分子凝胶将被合成，其中包含由磁铁矿或钴铁氧体组成的磁芯。基质的温度依赖行为将通过动态光散射进行研究。此外，还将重点研究饱和和磁弛豫行为来表征磁性。特别是对于硬磁材料，磁芯周围会引入空穴，使磁芯能够自由旋转。通过这种方式，磁芯应该能够通过施加交流磁场来加热基质，该磁场诱导相变到热响应矩阵的坍塌状态。我们将研究粒子在这些空穴中旋转的自由程度。为了更好地控制基质的热敏性能，将引入不同的基质材料，这些基质材料将通过直接在颗粒表面进行受控自由基聚合来合成。用这种方法可以生产出非常薄且可重复使用的微凝胶壳。通过将这些微凝胶颗粒交联到宏凝胶上，可以在凝胶中获得更高的磁性含量。这样，磁芯(形状、大小、材料)和基质的磁性可以相互调整，以实现通过磁场调节机械性能的能力。

Ferrogels combine the properties of a gel- or polymer matrix with the magnetic properties of a ferrofluid. Hydrogels are often used as matrix materials as they can be swollen with water. Since many hydrogels respond to external stimuli like temperature, pH or light these gels are also named responsive hydrogels. In combination with magnetic nanopartilces the hybridgels can be heated up by an AC magnetic field and thus the mechanical properties of the gel can be adjusted. In this last period the focus will be set on the synthesis on magnetic micro- and macrogels and additional their characterization under the influence of a magnetic field and its effect on the matrix. For such multiresponsive hydrogels the choice of the specific magnetic particle species is crucial for the desired application. Micro- and macrogels with a poly-N-isopropyl acrylamide matrix will be synthesized containing a magnetic core consisting of either magnetite or cobalt ferrite. The temperature dependent behavior of the matrix will be investigated via dynamic light scattering. Additional the magnetic properties will be characterized focusing on the saturation and magnetic relaxation behaviour. Especially for hard magnetic materials cavities will be introduced around the core, so the magnetic cores are able to rotate freely. By this the magnetic core should be enabled to heat up the matrix by applying an AC magnetic field that induces a phase transition into the collapsed state of the thermoresponsive matrix. We will investigate how freely the particles are able to rotate within these cavities. To achieve a better control over the thermoresponsive properties of the matrix different matrix materials will be introduced which will be synthesized by a controlled radical polymerization directly on the surface of the particles. By this method very thin and reproducible microgel shells can be produce. By crosslinking these microgel particles to a macrogel, even higher magnetic content within the marogel can be achieved. With this the magnetic properties of the core (shape, size, material) and the matrix can be tailored to each other, to achieve the ability to tune the mechanical properties by magnetic fields.