Rich Self-Assembly Behavior of Magnetic Colloids with Radially Shifted Dipoles

Anisotropic potentials in Janus particles provide additional freedom to control particle aggregation into clusters with different sizes and morphologies. In order to study the process of aggregation on magnetic Janus colloids dynamically –nucleation and growth–Brownian dynamic simulations of a dilute suspension of magnetic spherical Janus colloids with their magnetic dipole moments shifted radially towards the surface of the particle were performed. Different aggregation modes were found depending on the dipolar shift(s)—the ratio between the displacement of the dipole and the particle radius—and the dipolar coupling constant (λ) —the ratio between the magnetic dipole-dipole and Brownian forces, were the λ regimens is a strong factor in the stability of the cluster. Each structure phase of the colloids was depended on the combination of s and λ, which was used to build a "phase" diagram showing unique behavior for each region on the dynamical process of aggregation. In low λ regime, the particles aggregate and disaggregate resulting in short-live clusters at small s, while at high s the particles aggregate in permanent triplets. On the other hand, in high λ regime, building blocks –triplets and quadruplets with unique orientational ordering depended of s– were formed during the nucleation process. The different building blocks form larger structures, such as single-chain, ring-like, island-like, worm-like, and double-chain aggregates.