Macroscopic synthesis of self-assembled dissipative structures

This paper describes the preparation and manipulation of several coexisting , dynamically self-assembled aggregates of millimeter-sized, magnetized dis ks floating at a liquid-air interface and spinning under the influence of a rotating external magnetic field. Local minima in the in-plane energy prof ile of these disks are created by positioning ferromagnetic needles above t he plane of the interface: these needles concentrate the magnetic field loc ally in that plane, Spinning disks assemble in the local minima, and the po sitions and geometries of their aggregates can be manipulated spatially by changing the positions of the needles. Fragmentation and fusion of aggregat es in response to changes in the magnetic fields are described.