EAGER: Emergent order of hydrodynamically coupled microrotors

1544196(Vlahovska)

The objective of the proposed research is to investigate theoretically and experimentally a new class of active fluids, that of suspensions of self-rotating particles. Active fluids are fluids that behave in unique ways, because of the presence of active particles that can self-assemble, or can move and pack in different ways, giving different macroscopic properties to the fluid. Certain complex fluids and biofluids fall in this category. Even a flock of birds, or a school of fish, where each moving animal moves on its own, but the motion of all follows a pattern at a much larger scale than the individual, are examples of active fluids.

It is proposed to examine dense suspensions of rotating spheres (rotors). It has very recently been found that in a monolayer of rotors with initially randomly distributed up or down spins, same-spin rotors spontaneously segregate and collectively move in traffic lanes or circulate in large vortices. When the rotor density gets close to maximum packing, the rotors jam into crystals that continuously melt, reassemble, and move. It is proposed to study these phenomena with a combined computational and experimental approach to understand how this collective behavior emerges from the hydrodynamic interactions between the rotors. The numerical simulations are based on the immersed boundary method. The experimental system relies on the Quincke effect, which is the spontaneous spinning of a dielectric sphere in an applied uniform electric field. The proposed research aims to (1) include the electrostatic interactions in the numerical simulations, and (2) investigate the dynamics of a pair and monolayer of Quincke rotors. In addition to advancing basic knowledge, the research will uncover novel dynamic structures that could be exploited for design of `smart' materials responsive to the external environment. The PIs will incorporate the results from this research in graduate courses and will also leverage successful outreach programs at Brown University to communicate the relevance and significance of the work to the general public.