Particle Coarse-Graining

We explore coarse-graining for particulate systems.

Rotationally driven active matter

Particles driven to motion self-organize like schools of fish, flocks of birds, or bacteria. Research efforts to create matter from such ‘active’ particles involves biopolymers and self-propelled colloids. In general, one distinguishes active matter with an internal energy source from that set into motion by an external field. Our work in this field focuses on particles that interact mechanically like gears and transfer energy input from rotation to translation. We observed phase separation of gears driven in opposite direction and super-diffusive motion along interfaces. Experiments with 3d-printed vibrots confirm the simulation predictions. We demonstrated the existence of self-organizing stable vortices called rotelles.

Rotationally Active
(Left) Mechanism of repulsion of oppositely rotating spinning gears. This is an emergent force. (Middle) Snapshot with vectors indicating short-term translation. (Right) Design of colloidal cells with an active, flexible boundary.

Phase behavior of polyhedral particles

Predicting structure from the attributes of a material’s building blocks is a central goal for materials science. Isolating the role of building block shape provides insight into the ordering of molecules and the crystallization of colloids, nanoparticles, proteins, and viruses. We have been systematically investigating the self-assembly of convex polyhedra. Our results demonstrate a remarkably high propensity for self-assembly and structural diversity. Notable discoveries are the discovery of a quasicrystal from tetrahedra and many more liquid crystals, plastic crystals, and crystals.

Polyhedra Complexity
(Left) Dodecagonal quasicrystal from tetrahedra. (Middle) Summary (or zoology) of hard polyhedral phase behavior. (Right) Three examplary snapshots from simulation outcomes.