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

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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.