CMSA Active Matter Seminar: Controlling chaotic advection in 2D active nematics

Recent years have seen a surge of interest in active materials, in which energy injected at the microscale gives rise to mesoscale coherent motion. One prominent example is an active 2D "liquid crystal" composed of microtubules in the nematic phase. The activity is generated by molecular motors that consume ATP to generate local shearing between the microtubules. The resulting 2D fluid flow exhibits self-generated mesoscale chaotic dynamics with a characteristic folding and stretching pattern. We analyze this dynamics from the perspective of chaotic advection, in which the fluid can be viewed as "stirred" by topological defects in the nematic order parameter. Typically, these defects move in an irregular, chaotic pattern. We explore conditions, both theoretically and in experiments, under which the topological defects can be coaxed to perform regular periodic motion, thus bringing some degree of order to the chaos.