Highly ordered size-dispersive packings of polydisperse microgel spheres

Dilute suspensions of polydisperse polystyrene microgels in the size range of 5-50 nm in organic solvents were evaporated under controlled conditions, and the resulting two-dimensional packing structures were investigated. The particles form highly ordered structures, as revealed by electron microscopy. The ordering process is understood as a unique self-organization process, in which differences in the particle size and the polydispersity of the particles are a main driving force. The structures follow the rules of hyperbolic geometry and are named "Zenon"-packing, indicating that the two-dimensional structures without translational invariance can still be understood as a special form of a regular lattice. A systematic variation of the solvent quality and the surface tension of the suspension shows that the ordering essentially is based upon size-dispersive van der Waals attractions between the microgels.