Sir Geoffrey Ingram Taylor in 1964 described the phenomena of liquid drop changing its shape when passing through an electric field. He observed it in the rain drops modifying their outlook when struck upon by lightening.
Exploring the same phenomena, a team of researchers hailing from Georgia Institute of technology, have unveiled another method for solidification of liquids. Demonstrated with the help of simulation, they have explained the solidification of liquid into crystals under the influence of sufficiently high electric fields. They have termed this phase transformation as “electro-crystallization”.
Instead of the spherical liquid drops used by Taylor, the Georgia tech researchers focused their study on a liquid formamide droplet of 10 nanometer radius. Formamide is composed of polar molecules with dipole moment twice as that of a water molecule.
By using simulation tools, the researchers observed the response of formamide droplets to the applied electric field of variable strength. These tools have been developed at the Center of Computational and Material Sciences (CCMS) @ Georgia tech, to track the progression of material systems with ultra-high resolution in space and time. On applying a field with strength slightly higher than that of 0.5 Volts per nanometer, the droplet changed its shape from spherical to needle like with its axis in the direction of applied field. The simulation results were all in agreement with the observations done by Taylor half a century ago.
Further increase in the strength of the field, post elongation, increased the width to height aspect ratio of the droplet like needle, while the molecules of the element showing liquid diffusional movement.
With even further increase in the field strength, diffusional motion of the molecules freeze and the liquid droplet of formamide underwent phase transition culminating into solid crystals. As narrated by one of the researcher; characteristic structure of such crystals was different from those observed in X-ray crystallography determined under zero field conditions years ago.
On subsequently decreasing the strength of applied electric field, crystals gradually reverted back to their liquid form and at zero field strength they turned back into spherical drops.
Further analysis of the phenomena revealed that in addition to the shape change at 0.5V/nm the degree of reorientation of electric dipoles of the molecules increases. After phase transition, these dipoles retain a direction same as that of the applied field. This reorientation is actually responsible for breaking the symmetry and transforming the droplet into a state where it possesses a large net electric dipole otherwise absent in zero fields.
Side by side with the simulations, the researchers formulated an analytical free-energy model for describing the balance between polarization, interfacial tension and dielectric saturation combinations.
This model serves the purpose of providing a theoretical framework for understanding the changes undergone by dielectric dipoles due to the applied electric fields.
Researchers believe that the behavior shown by formamide can be attributed to the large electric dipole moment. The study has uncovered the possibilities of controlling and directing shapes, states (solid and liquid) and properties of certain materials.
In addition to the advancement in understanding material behavior and its microscopic origin, the study may prove critical in the development of applications related to targeted drug delivery, Nano encapsulation, printing of nanostructures as well as in the fields of aerosol science, electrospray propulsion and environmental sciences.
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