In this episode of the Physics World Weekly podcast, we hear from a trio of scientists with a common interest in the physics of droplets. Specifically, Joe Forth, Rob Malinowski and Giorgio Volpe share a fascination with droplets that are “animate” – that is, capable of responding to their surroundings in ways that resemble the behaviour of living organisms.

As they explain in the podcast, systems must tick three boxes to qualify as animate. First, they must be active, able to use energy from their environment to do work and perform tasks. Second, they must be adaptive, able to move between different dynamical states in response to changes to their environment or their own internal states. Finally, they must be autonomous, able to process multiple inputs and choose how to respond to them without intervention from the outside world.

Incorporating all these behaviours into a droplet – or a system of many droplets – is challenging. The boundary between autonomous and non-autonomous systems is proving especially hard to overcome, and Volpe, Malinowski and Forth have a friendly disagreement over whether any droplet-based system has managed it yet.

Crosses disciplinary borders

Part of the challenge, they say, is that the field crosses disciplinary borders. Although Volpe thinks the community of droplet researchers is getting better at finding a common vocabulary for discussions, Forth jokes that it is still the case that “the chemists are scared of physics, the physicists are scared of chemists, everyone is scared of biology”. The potential rewards of overcoming these fears are great, however, with possible future applications of animate droplets ranging from consumer products such as deodorant to oil spill clean-up.

This discussion is based on a Perspective article that Volpe (a professor of soft matter in the chemistry department at University College London, UK), Malinowski (a research fellow in soft matter physics in the same department) and Forth (a colloid scientist and lecturer in the chemistry department at the University of Liverpool, UK) wrote for the journal EPL, which sponsors this episode of the podcast.

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