Suspensions of particles in a viscous liquid often exhibit unusual behavior in flow. This award will study suspensions of magnetic particles that rotate in an applied magnetic field. The rotation of the particles induces a flow in the surrounding liquid. The investigators have found that an instability in the suspension leads to the formations of loosely-packed aggregates of the particles, which can move away from the rest of the suspension under guidance from the magnetic field. The aggregates stay intact as they move, even though the particles inside an aggregate do not touch each other. This leads to an interesting new way to transport particles through a liquid that could be applied in microfluidic or lab-on-a-chip systems where the small dimensions of the device often limit transport of particulate phases. This award will support experimental studies to study the generation of the aggregates, their motion, and the interactions of the aggregates with obstacles they encounter in the flow. The experiments will be complemented by numerical studies that will help interpret data and explore the mechanisms of aggregate formation and motion.
A model system of magnetic microllers near a wall will be used to explore a new platform for active transport. Numerical simulations will be used to identify conditions under which microroller aggregates are expected to form. Experiments will validate the formation of the aggregates and demonstrate effects of different particle shape on aggregation formation and transport. To simulate flow in a structured environment, microroller transport will be studied in an array of patterned posts in periodic, quasi-periodic, self-similar and disordered patterns. The potential for using the microroller system for transporting colloidal cargos will be investigated. The experiments and simulations of the microroller system form visually appealing demonstrations that will be used in hands on activities for elementary and high school students in the New York area.
