Controlling Material Properties With an Electric Field

Researchers from the Georgia Institute of Technology have turned a liquid into a solid solely by applying an electric field – without changing the temperature or pressure. 

Different atoms are able to attract electrons to different degrees, which means that even in a non-charged molecule, like water, there’s what’s called a dipole moment. This means that the chemical bonds making up the molecule are slightly more negative in one direction than in another, which will make the molecule as a whole have a certain electrical polarity. This is why an electric field will make molecules like this arrange in a certain way, depending on the strength of the field. 

From Science Daily:

Physicists have demonstrated in simulations that under the influence of sufficiently high electric fields, liquid droplets of certain materials will 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 electrocrystallization.

This line of study originated in the 60’s when a scientist saw that lightning caused rain drops to change shape. This modern experiment used a 10 nanometre-wide droplet of a more polar molecule called formamide.

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 — oriented along the direction of the applied field — measuring about 12 times larger than the perpendicular (cross-sectional) small axis of the needle-like droplet…

“Here came the Eureka moment,” said Landman. “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, exhibited by freezing of the diffusional motion, and culminating in the formation of a formamide single crystal characterized by a structure that differs from that of the x-ray crystallographic one determined years ago under zero-field conditions. Now, who ordered that?” he added.

Further analysis has shown that the crystallization transition involved arrangement of the molecules into a particular spatial ordered lattice, which optimizes the interactions between the positive and negative ends of the dipoles of neighboring molecules, resulting in minimization of the free energy of the resulting rigid crystalline needle. When the electric field applied to the droplet was subsequently decreased, the crystalline needle remelted and at zero-field the liquid droplet reverted to a spherical shape…

Along with the fundamental interest in understanding the microscopic origins of materials behavior, this may lead to development of applications of field-induced materials control in diverse areas, ranging from targeted drug delivery, nanoencapsulation, printing of nanostructures and surface patterning, to aerosol science, electrospray propulsion and environmental science.

If this is a completely novel discovery, then it’s a pretty big one, but I imagine this kind of phenomenon had at least been hypothesized in the past. In any case it’s an interesting, different way of manipulating materials, and I’m sure it’ll have useful applications, although I get the sense that it might not be in any way we laypeople would understand. 

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