Magnetically induced particle dynamics and particulate structure formation in viscous and viscoelastic media – theoretical-numerical investigations

• Applicant: Professor Dr. Andreas Menzel
• Subject Area: Fluid Mechanics
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 511114185

Magnetic gels and elastomers consist of magnetic or magnetizable colloidal particles embedded in a soft, elastic, polymeric medium. They show fascinating properties. For instance, significant changes in their elastic stiffness result when exposed to external magnetic fields, as well as magnetically induced mechanical actuation. Such features strongly depend on the spatial arrangement of the embedded particles that are permanently fixed by the surrounding elastic medium. Anisotropic particle elements such as chain-like aggregates can be realized by applying strong external magnetic fields during fabrication. Our goal is to analyze and to understand the dynamics of such processes of particulate structure formation. Here, the interplay between anisotropic magnetic and hydrodynamic interactions between the particles becomes important. When being displaced, each particle sets the surrounding medium into motion, which affects the configuration of all other particles. We intend to put special emphasis on the influence of the additional viscoelasticity of the surrounding medium. The transition from a viscoelastic fluid-like to an elastic environment during the course of the particle dynamics is considered as well. Further parameters to be varied are the particle concentration, the strength of the magnetic field, the particle shape, as well as polydispersity of the particle shape and size. To realize our endeavor, we need to implement a numerical approach that couples the particle motion to the dynamics of the surrounding viscoelastic medium and allows a mutual approach of the particles basically into contact. We shall perform our investigations in close scientific exchange with the other groups of the Research Unit, who specialize on particle-scale and time-resolved measurements on corresponding experimental systems, who fabricate and analyze corresponding macroscopic samples, who focus on scale-bridging simulations, and who generate and evaluate learning and teaching materials to convey our contents at schools. Our scope is to develop methods to realize most advantageous particulate structures during actual sample preparation, leading to optimized macroscopic properties of the materials, and to communicate our results to a broad public in outreach activities. Beyond this topical context, our project is further relevant within a much more general framework. Overall, we contribute to the understanding of the collective dynamics of discrete particulate inclusions in viscoelastic environments. One example of significant current interest is given by the self-propulsion of active microswimmers. The dynamics of such objects can be qualitatively modified by the viscoelasticity of the surrounding medium already on the single-particle level.

• DFG Programme: Research Units
• Subproject of: FOR 5599: From production processes of structured magnetic elastomers to their macroscopic material behavior
• International Connection: Japan
• Cooperation Partner: Professor Dr. Takeaki Araki