Magneto-optically switchable anisotropic suspensions and gels

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In this project we combine two successful concepts of Soft Matter physics, magnetic fluids and liquid crystals. The goal is the development of a new class of multifunctional materials that are sensitive to magnetic fields and can be used for magneto-optical switching and magneto-mechanical effects. We combine ferrofluids and functionalized magnetic nanoparticles with lyotropic nematic suspensions and thermotropic liquid crystals. Ferromagnetic nanoparticles provide the sensitivity against magnetic fields. Anisometric crystallites or liquid-crystalline mesogens contribute birefringent optical properties. This combination opens the potential for multiple applications. Stabile suspensions were prepared and characterized in the previous application periods of this topical program, in addition we made successful attempts to prepare anisotropic ferrogels. The aim of the planned activities in this project is the investigation of the interactions of magnetic nanoparticles with the localen complex anisotropic matrix in different systems. The focus is laid on the influence of the matrix structure on the magneto-optical and viscoelastic properties of the composites: External magnetic fields cause a self-organization of the magnetic nanoparticles, which in turn reorganize the anisotropci environment (the matrix). The feedback of the matrix determines the structure forming dynamics of the magnetic subphase as well as the optical and mechanical properties. We will investigate three different matrix systems, plate-like and rod-like nonmagnetic particles (pigment crystallites) dispersed in an isotrop liquid medium, organo-gels with thread-like internal structure and organic liquid crystals. A special aspect is the transition from isotropic to anisotropic matrices. The most relevant experimental characterization techniques are magneto-optical switching, measurements of magnetically induced birefringence and dichroism, as well as magnetically induced mechanical torques. These techniques are accompanied by rheological studies, magnetorelaxometry (MRX) and susceptometry (ACS), and other methods in cooperation with other groups within the topical program.