Flocking behaviour seen among visually equipped particles

Microscopic artificial entities, known as Janus particles, when invested with a form of sight, exhibit spontaneous flocking and crowding behaviour similar to that shown by birds, fish and humans.

The finding, the result of experiments conducted by a team led by physicist François Lavergne from University of Konstanz, Germany, has implications for understanding crowd behaviour, and for the development of autonomous robots.

Janus particles, created more than two decades ago, are items typically only a couple of hundred nanometres across that are coated with two materials producing opposing effects. For instance, one half might attract water, while the other repels it.

For this work, Lavergne and colleagues applied a substance that imbued Janus particles with a version of sight – a way to detect other Janus particles – within particular narrow or broad fields.

The Janus entities are members of a class of materials known as active Brownian particles (APBs), of great interest to roboticists and physicists alike. APBs are small enough to behave like molecules trapped in gas or liquid – that is, when not subject to any external forces they undergo Brownian motion, the sort of random drifting and colliding that ensures that after a given period of time they are randomly distributed through the space available to them.

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