Molecular dynamics simulation of the electrically induced spreading of an ionically conducting water droplet.

Molecular dynamics simulations are applied to study the spreading behavior of a nanosized water droplet that contains freely moving Na(+)/Cl(-) ions subject to an imposed electric field parallel to a solid surface. Results show that the positive and negative ions move relatively freely in response to an applied electric field, whereas polar water molecules realign themselves. These localized behaviors of the ions and the polar molecules are affected by both the applied electric field strength and the ion concentration, which in turn determine the deformation and spreading of the droplet on a solid substrate. The presence of the freely moving ions causes the ion-containing droplet to spread differently from a droplet of pure water. In a weak electric field of 0.05 V/Å, a droplet of a lower ion concentration spreads asymmetrically and the spreading asymmetry is considerably smaller than that associated with a pure water droplet of the same size. In a stronger field of 0.1 V/Å, a droplet of a higher ion concentration spreads symmetrically and completely wets the solid surface whereas a less ionically conducting droplet undergoes an asymmetric-to-symmetric transition in spreading until it reaches equilibrium.