Description:

Active matter, both synthetic and biological, demonstrates complex spatiotemporal self-organization and the emergence of collective behavior. Active fluids comprised of autonomous spinning units, injecting energy and angular momentum at the microscopic level, represent a promising platform for active materials design. I will demonstrate a plethora of unexpected and complex collective phenomena revealed in our lab in active liquids formed by rolling colloids realized by either Quincke or magnetic rollers [1, 2]. I will show that concentrated magnetic roller liquids energized by external uniaxial alternating magnetic field self-organize into a state with multiple long-lived vortices in unconfined environment [3, 4]. Spontaneous dynamic local roller densifications trigger the formation of multiple vortices in an open environment with the neighboring vortices more likely to occur with the opposite sense of rotation. In the case of Quincke rollers, the complexity of the accessible dynamic states is dramatically increased when the shape anisotropy of colloidal particles give rise to rollers with activity-controlled curvatures of their trajectories and spontaneous handedness of their motion [2]. By controlling the activity of such Quincke rollers new emergent dynamic phases are revealed, ranging from a gas of spinners to unconfined aster-like vortices and rotating flocks, with either polar or nematic alignment of the particles. I will also demonstrate that activity modulations can be effectively used to induce complex collective response and non-trivial self-organization in active roller liquids (chiral state reversals [5], spontaneous shockwaves).

Speaker: Alexey Snezhko: Argonne National Laboratory

Host: Michelle Driscoll