Structural Transition of Magnetorheological Fluids in Microgravity

Bennung, Eric Scott
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Magnetorheological (MR) fluids exhibit unique mechanical and rheological properties when subjected to a magnetic field. MR fluids greatly increase their viscosity through rapid formation of chains of dipoles along the direction of the field. Lateral cross-linking of these chains allows the fluid support stress perpendicular to the applied field. Thus, MR fluids undergo a large, fast, and reversible transition from a liquid-like to a solid-like state upon the application of a magnetic field. This provides an excellent basis for a vast number of applications, such as actively controlled dampers and actuators. This thesis presents observations and analysis of experiments performed as part of the InSPACE NASA program. The experiments were performed on the International Space Station (ISS). The InSPACE goal is to understand the long-time three-dimensional aggregation kinetics of MR fluids under steady and pulsed magnetic fields by testing models and hypotheses. This thesis focuses on this evolution of MR aggregates. Studies such as these are complicated on Earth due to the rapid sedimentation induced by gravity. Video microscopy experiments were performed in the ISS microgravity science glovebox. Aggregation kinetics were studied as a function of field- and sample-based parameters. Images gathered from the videos were prepared for data collection with proper image processing parameters. Particle tracking algorithms were then applied to extract quantitative data. Specific data on the kinetics of aggregation comes in the form of the time evolution of the number density of aggregates, the inter-aggregate separation, and the average aggregate size. The data analysis is based on the Smoluchowski equation.