Imagine being able to herd self-propelled particles through a maze built from the particles themselves. Joakim Stenhammar and colleagues have undertaken simulations designed to do just that — showing that light-controlled motile particles can be manipulated into active rectification devices.
By exploiting the fact that motile particles accumulate in regions where they move more slowly, the authors simulated patterns of high and low particle density using illumination to influence the particles' speed. Chevron-shaped light patterns coaxed the particles to form funnel-like obstructions, taking inspiration from a rectifier that uses micropatterned obstacles to manipulate self-propelled particles. The efficiency of the device was around 1.6, compared with 2.8 in its microfabricated analogue. An alternative sawtooth-shaped design bumped this efficiency up to 2.
The beauty of the proposed device rests with its simplicity: the light imparts only scalar information on the microswimmers, and dispenses with the need for micropatterning — sculpting programmable dynamics out of an otherwise unstructured particle soup.
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Klopper, A. Guided by the light. Nature Phys 12, 376 (2016). https://doi.org/10.1038/nphys3764
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DOI: https://doi.org/10.1038/nphys3764
