Self-Assembly of Gears at a Fluid/Air Interface

This paper describes a dynamic systema system that develops order only when dissipating energycomprising millimeter to centimeter scale gears that self-assemble into a simple machine at a fluid/air interface. The gears are driven externally and indirectly by magnetic interactions; they are made of poly(dimethylsiloxane) (PDMS) or magnetically doped PDMS, and fabricated by soft lithography. Transfer of torque between gears can take place through three different mechanisms: mechanical interaction, hydrodynamic shear, and capillarity/overlap of menisci. Interplay between these forces allows interactions and motions that are not possible with conventional systems of gears.