Machine Design

Turning liquids to solids using electric fields: electrocrystallization

Georgia Institute of Technology

Physicists at the Georgia Institute of Technology have used computer simulations to show that sufficiently strong electric fields can solidify liquids into crystals at temperatures and pressures under which the material should otherwise remain liquid. The process is termed electrocrystallization, and was first described by Geofrey Taylor in 1964 while studying the effects of lightning on raindrops.

The simulations used molecular-dynamics software developed at Georgia Tech. It let the scientist examine the behavior of a 10-nm diameter drop of formamide, a material consisting of polar molecules with a dipole moment more than twice as large as that of water. The simulation revealed that an electric field of less than 0.5 V/nm made the spherical drop elongate slightly. When the field approached 0.5 V/nm, the sphere transformed into a needlelike structure with an aspect ratio of 12, with the long dimension oriented along the direction of the field.

Higher fields brought higher and higher aspect ratios. And when the field was 1.5 V/nm, the simulation showed the droplet solidified into a single formamide crystal. Ramping the field down led to the crystalline needle melting, eventually returning to a spherical shape. Researchers theorize that the transformation to a crystal arose from the molecules arranging themselves into a lattice, which increased the interactions between the positive and negative ends of neighboring molecules’ dipoles. This minimized the free energy in the droplet and caused solidification.

Further research will uncover more about the microscopic origin of material behavior and could lead to field-controlled drug delivery, printing of nanostructures, and aerosols.

© 2011 Penton Media, Inc.

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