Self-Assembly of Active Particles.

Abstract

Self-assembly of active particles is believed to play an important role in enabling tomorrow's generation of smart materials. As a system is driven out of thermodynamic equilibrium, existing thermodynamic theory fails to predict the system behavior; however, it often exhibits rich and novel behaviors that are not found otherwise and could be leveraged for designing smart materials. In this thesis, by using computer simulation, we investigate the self-assembly behaviors of active particles driven via two different mechanisms: self-propulsion and -rotation, and show that the particle activity, in combination with other design parameters, gives rise to a great diversity of novel structures and dynamics.

In particular, we implement the first 3D model of self-propelled particles interacting via a soft Morse potential and demonstrate how the self-propulsion together with the parameters of interaction potential and thermal noise influence the particles to form a variety of 3D swarming structures. We also report novel behaviors that deviate from equilibrium self-assembly, including swarm coexistence, sensitivity to initial conditions and structure switching. The results, in addition to elucidate general swarming behavior, could motivate further studies in self-assembly of self-propelled, interacting colloids in 3D.

We then perform the first study of self-rotated shaped particles that interacting solely via excluded volume. Each particle is driven by a constant torque in either a clockwise or counter-clockwise direction. In spite of the model simplicity, we observe a wealth of interesting behavior that is otherwise not possible with self-propelled particles or in equilibrium self-assembly. We report phase separation, collective and heterogeneous dynamics, rotating crystals and complex phase behavior. The rich behavior resulted from a minimal model opens up many possibilities for further studies of practical interest.

Lastly, we carry out preliminary, exploratory study of systems of self-rotated particles in confinement. Early experimental results from experimental collaborators confirm some of the findings for bulk systems. In addition, our initial simulations reveal some remarkable, unique dynamics for systems with flexible boundaries and highlights exciting possibilities worth pursuing further.