Gallium droplet shape-shifting

A droplet of the metal gallium shifts shape to a regular beat. Credit: Z. Yu et al./Phys. Rev. Lett.

Physics

How to coax liquid metal to shimmy to a beat

‘Gallium heart’ can be slowed or accelerated by electric current.

A drop of liquid gallium can throb with a regular rhythm like a beating heart.

Interest has surged in ‘smart fluids’, which can be moved by electric or magnetic fields and integrated into computer circuits. To make such a fluid, Xiaolin Wang at the University of Wollongong in Australia and his colleagues placed droplets of liquid gallium inside a ring-shaped electrode in an electrolyte bath. The setup was on an incline, so that the droplet rested against the inside of the electrode.

The researchers applied electric current to the apparatus, oxidizing the gallium and reducing its surface tension. That caused the droplet to expand horizontally into a pancake shape and propel itself away from the ring. When the gallium’s contact with the ring was broken, it regained its spherical form and moved down the incline to start the cycle again.

By adjusting the current, the team could change the frequency of this ‘heartbeat’.