Mechanical properties of multifunctional magnetic microgel particles

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The project addresses the magneto-mechanical properties of multifunctional hybrid polymer microgel particles. The diameter of the polymer microgel particles can be adjusted in a range between 300 nm - 2 micrometer. They contain magnetic nanoparticles (MNP) with a diameter up to 20 nm, obtained from other groups in the SPP (Schmitt, Behrens). The gel is based on the thermoreponsive polymer Poly(N-isopropyl-acrylamide) (PNIPAM). The further addition of commoners allows tuning the pH sensitivity. One challenge is the control of the coupling between the MNP and polymer matrix in order to tailor the deformation and mechanical changes of the whole microgel induced by a magnetic field. For the optimization of the uptake of magnetic particles and for the control of their mobility the meshsize will be adjusted with respect to the size of the magnetic particles by the amount of crosslinker. The direct coupling of the MNP will be tailored by electrostatic interaction and hydrogen bonding via the addition of charged comonomers and later by colvalent binding. The uptake of MNP will be realized with different strategies, partially also directly in a homogeneous magnetic field. The deformation of the gel particles will be studied by small angle neutron scattering (SANS) measurements (Prevost, Gradzielski)Another part of the project addresses the effect of confinement on the magnetic sensitivity of the microgel particles. Therefore the particles will be adsorbed at a planar surface (wafer). In addition this configuration serves also for studies of mechanical and actuator properties. Within the project a magnetic environment for AFM measurements will be developed. Finally a gradient non-uniform magnetic field perpendicular and a homogeneous field parallel to the planar surface will be available. The influence of the orientation on the viscoelastic behavior and the deformation will be studied. We want to understand the gel properties for the later development of novel materials for e.g. actuatoric. Therefore, a global goal is to bridge the gap between different length scales from the molecular level over the mesoscopic to microscopic lengths and to compare the results with the ones for macroscopic gels from other groups (Schmidt). The experimental results will be compared with the outcome of respective simulations (Holm) and DDFT calculations (Löwen). The hydrogel microparticles will be offered as soft pH and temperature sensitive matrix to several projects within the SPP (Richter, Odenbach, Auernhammer, Hütten). The gel properties like charge density and sign and dye-labeling can be adjusted for each individual task. In the first period we will address the magnetic field as an external field. A long-term goal is to profit from the responsive character (temperature and pH) of the polymer matrix to switch the coupling between the MNP and the polymer matrix.