Self-assembly and time-dependent control of active and passive triblock Janus colloids

Abstract

We perform Brownian dynamics simulations to explore the self-assembly of a two-dimensional model system of triblock Janus colloids as an example of “patchy” colloids forming complex structures. Previous experiments and simulation studies have shown that such systems are capable of forming a two-dimensional kagome lattice at room temperature. However, it is well established that the crystallization is strongly hampered by the formation of long-lived metastable aggregates. For this reason, recent studies have investigated activity, i.e., self-propulsion of the Janus particles, as a mechanism to accelerate the formation of stable kagome structures [S. A. Mallory and A. Cacciuto, J. Am. Chem. Soc. 141, 2500–2507 (2019)] at selected state points. Here, we extend, first, the investigations of active Janus colloids for a broader range of densities and temperatures. We also characterize in detail the associated nucleation of kagome clusters, as well as their structure in the steady state. Second, to make contact with the equilibrium case, we propose a simple activity time protocol where an initially chosen activity is switched off after a finite time. With this protocol, we not only find kagome structures in a much broader range of densities than in the purely passive case but also obtain a kagome crystallization boundary very close to that proposed in earlier Monte Carlo simulations.