  Recent progress in colloidal science has led to elaborate self-assembled
structures whose complexity raises hopes for elaborating new materials.
However, the throughputs are extremely low and consequently, the chance to
produce materials of industrial interest, for instance, groundbreaking optical
devices, harnessing complete three-dimensional band gaps, is markedly low.
  We discovered a novel hydrodynamic effect that may unlock this bottleneck. It
is based on the dipolar flow interactions that build up when droplets are
slowed down by the microchannel walls along which they are transported. Coupled
with depletion forces, we succeeded to form, via a continuous flow process, at
unprecedented speeds and under exquisite control, a rich ensemble of
monodisperse planar and tridimensional clusters, such as chains, triangles,
diamonds, tetahedrons, heterotrimers, possessing geometrical, chemical, and/or
magnetic anisotropies enabling directional bonding. Continuous productions of
millions of building blocks per second for elaborating new functional materials
can be envisioned.
