Magnetically tunable surface properties of soft magnetoactive elastomers

• Applicant: Professor Dr. Mikhail Chamonine
• Subject Area: Synthesis and Properties of Functional Materials ; Materials in Sintering Processes and Generative Manufacturing Processes ; Statistical Physics, Nonlinear Dynamics, Complex Systems, Soft and Fluid Matter, Biological Physics
• Term: from 2020 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 437391117

In magnetoactive elastomers (MAEs), the microstructure of the magnetizable filler (arrangement of micrometer-sized filler particles) can be significantly changed in external magnetic fields if the matrix is soft. This restructuring of the filler is noticeable on the free surface of an MAE sample and the corresponding changes of surface properties (e.g. wettability or adhesion) can be useful for a wide range of applications, e.g. liquid manipulation in microfluidic devices or magnetically controllable cell culture substrates etc.. The primary goal of this project is to investigate magnetic field induced surface changes (e.g. its topography) of MAE materials and establish the general relationships between physicochemical properties of constitutive components of a composite material (i.e. matrix and filler, including their interfaces) and the resulting modifications of surface properties (e.g. wettability or spread reflection) in magnetic fields. The apparent macroscopic surface characteristics are determined by the microscopic properties of constitutive components of a composite material near its surface to be systematically varied. By doing so, a predictive design of the magnetic field responsive MAE surface should be enabled. The main work load of the present project will be systematic and thorough characterization (various surface microscopy methods, optical profilometry, surface scattering techniques, etc.) of magnetic field induced surface changes of MAE and determination of the correlation between surface properties of the composite materials and bulk (magnetorheological and magnetic properties, composition of the filler etc.) properties of their constitutive components. The matrices will be polydimethylsiloxane-based. The filler composition will comprise micrometer-sized soft-magnetic (iron) and/or hard-magnetic (NdFeB) particles of variable size and morphology (spheres, flakes) enhanced by ultrafine (nano-) and fine magnetic particles (e.g. spinel ferrites). The surface properties of particles will be tuned, e.g. for increasing their hydrophobicity or functionalization. The experimental results will be compared with conclusions of recent mesoscopic theoretical approaches in order to verify their validity and identify their limits. To emphasize the structure-property-function relationships, the measurements will be performed in the context of three possible application areas of MAE materials with external magnetic field control: i) tunable surface wetting, ii) erasable and reconfigurable diffractive optical elements, and iii) tunable alignment layers for liquid crystals. The latter application will be used to detect the relaxation behavior of the microscopic filler in the layers adjacent to the surface after switching off the external field. Long-term observations of material performance will be made in order to make conclusions about the aging/degradation of functional surface properties and the underlying physicochemical mechanisms of it.

• DFG Programme: Research Grants
• International Connection: Hungary, Slovenia
• Cooperation Partners: Professorin Dr. Irena Drevensek Olenik; Professor Dr. Darko Makovec; Dr. Péter Salamon