Active particles are intrinsically out of equilibrium. They dissipate free energy at the individual particle level to exert forces and to move. A collection of active particles interact and display rich self-organization behaviors absent in equilibrium systems. They are good model systems for cytoskeletal remodeling, collective cell migration and animal flocking. 

I investigate how collective behaviors emerge from self-motility and local interactions among active particles. Using a hydrodynamic theory of active particles, I showed that complex pattern formation of bacterial colonies can be explained by the interplay of logistic growth, crowding effect and alignment interaction. Using computer simulations, I discovered spontaneous aggregation and segregation of active particles induced by confinement and steric repulsion. By explicitly coarse-graining a self-propelled particle model with alignment interaction and rotational inertia, I developed a hydrodynamic theory for collectively turning flocks.

While the dynamics of active particle are being extensively studied, the energetic aspect of these systems remain poorly characterized. My future objective is to explore the impact of energy dissipation on self-organization of active particles.