Self-assembly of polystyrene microspheres into two-level hierarchical structures

Two-level arrays of colloidal particles have been obtained using the method based on an intermittent, ''stick-slip'' motion of the meniscus during colloidal suspension evaporation. The ethanol suspension of monodisperse polystyrene microspheres of about 1 μm in size was prepared by emulsifier-free emulsion polymerization of styrene with potassium persulphate as an initiator. The resulting structures consist of parallel monolayer stripes of deposited microspheres, repeated with a period of 140-150 μm, and empty spaces between them. The microspheres are packed into a hexagonal structure inside the stripes. Laser diffraction patterns have been demonstrated for both levels of ordering, i.e., for the hexagonal structure at the first level and for the parallel stripes at the second level.