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

Authors: 
Córdova-Figueroa, U. M., University of Puerto Rico at Mayagüez
Rivera-Rivera, L. Y., University of Michigan
DeLaCruz-Araujo, R. A., University of Puerto Rico - Mayagüez
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.