Liquid can turn into solid, physicists show

Updated on: Friday, October 14, 2011

Physicists claim to have for the first time demonstrated in simulations that liquid can turn into solid under high electric field.

A team at the Georgia Institute of Technology has shown that under the influence of sufficiently high electric fields, liquid droplets of certain materials undergo solidification, forming crystallites at temperature and pressure conditions that correspond to liquid droplets at field-free conditions.

This electric-field-induced phase transformation is termed electro-crystallisation, the physicists say.

"We show that with a strong electric field, you can induce a phase transition without altering the thermodynamic parameters," said Prof Uzi Landman, who led the research published in the 'Journal of Physical Chemistry C'.

In these simulations, the team set out first to explore a phenomenon described by Sir Geoffrey Ingram Taylor in 1964 in the course of his study of the effect of lightning on raindrops, expressed as changes in the shape of liquid drops when passing through an electric field.

While liquid drops under field-free conditions are spherical, they alter their shape in response to an applied electric field to become needle-like liquid drops.

Instead of the water droplets used in the almost decade-old laboratory experiments of Taylor, the team focused their study on a 10 nanometre diameter liquid droplet of formamide, which is a material made of small polar molecules each charactered by a dipole moment that is more than twice as large as that of a water molecule.

With the use of molecular dynamics simulations developed at the CCMS, which allow scientists to track the evolution of materials systems with ultra-high resolution in space and time, the physicists explored the response of the formamide nano-droplet to applied electric field of variable strength.

Influenced by a field of less than 0.5V/nm, the spherical droplet elongated only slightly. However, when the strength of the field was raised to a critical value close to 0.5 V/nm, the simulated droplet was found to undergo a shape transition resulting in a needle-like liquid droplet with its long axis measuring about 12 times larger than the perpendicular small axis of the needle-like droplet.

The value of the critical field found in the simulations agrees well with the prediction obtained almost half a decade ago by Taylor from general macroscopic considerations.

Past the shape transition further increase of the applied electric field yielded a slow, gradual increase of the aspect ratio between the long and short axes of needle-like droplet, with the formamide molecules exhibiting liquid diffusional motions, say the physicists.

"Here came the Eureka moment. When the field strength in the simulations was ramped up even further, reaching a value close to 1.5V/nm, the liquid needle underwent a solidification phase transition," Landman said.

Liquid can turn into solid, physicists show

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