(379b) Aggregation and Fragmentation of Active Superparamagnetic Colloidal Chains

Active colloids are excellent candidates for developing reconfigurable soft materials due to their potential to form tunable structures dictated by the relative competition between particle-particle interactions (e.g. magnetic) and the propulsive strength of the particles. In this work, we perform Brownian dynamics simulation of a dilute suspension of active superparamagnetic colloids under a strong magnetic field and analyze their aggregation and fragmentation process in light of these competing mechanisms. Differences in the mean cluster size of chain-like structures are observed depending on the Péclet number Pe—the ratio between self-propulsion and Brownian forces—and the nondimensional magnetic interaction strength λ—the ratio between the magnetic dipole-dipole and Brownian forces. The interplay between self-propulsion and superparamagnetic forces shows that the aggregation process of these systems is best described by the ratio Pe/λ. At small Pe/λ an enhanced aggregation rate is observed in the nucleation process, followed by a power-law behavior for the growth process with exponents in the range typically observed for passive magnetic particles. At intermediate Pe/λ, an enhanced aggregation rate is also observed in the nucleation process while in the growth process the system reaches a steady state mean chain size. In this regime, the steady state mean chain size follows a power-law. Finally, no aggregation occurs when Pe/λ is much greater than 1. This study shows that a propulsion force can serve as an actuator in applications where an accurate control over the colloidal structures and rate of aggregation is required.