Molecular Dynamics Simulation of the Electrically Induced Spreading of an Ionically Conducting Water Droplet

Abstract

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.

Molecular Investigation of Contact Line Movement in Electrowetted Nanodroplets

“…The periodic boundary condition was given in both x and y directions . The simulation box was sufficiently large so that no periodic artifacts were observed. , The NVT (at different constant temperatures) ensemble was used during the simulation. An additional force ( f = q ( i ) × E ) was exerted by the external electric field on the charged atoms q ( i ).…”

“…Song et al explored the effect of a parallel electric field for a surface having a specific solid–liquid Lennard-Jones parameter of 0.301 kcal/mol, which exhibited a transition from asymmetric to symmetric spreading with an increase in electric field strength. There are prior studies on the impact of introducing ions within the droplet under parallel , and perpendicular electric field, which have elucidated the dependence of droplet shape on ion concentration and specificity. Furthermore, Cao et al went one step further to obtain the dynamics of nanodroplets confined in carbon nanotubes (CNTs).…”

Direct Visualization of the Behavior and Shapes of the Nanoscale Menisci of an Evaporating Water Droplet on a Hydrophilic Nanotextured Surface via High-Resolution Synchrotron X-ray Imaging

“…However, for application in broader research and engineering fields, synchrotron X-ray imaging still has technical limitations such as limited geometrical features of test sections (configuration, dimension, and so on), difficulties of three-dimensional image realization, relatively limited time resolution, and so on. Recently, numerical studies based on Monte Carlo and molecular dynamics simulations have been widely carried out to give an intuition in the physical interpretation of the nanometer-scaled interfacial phenomena, − instead of technically limited experiments. We will study the intuitive relation between computational prediction and experimental results with the assistance of molecular dynamic simulation in the future work.…”

Wetting Behaviors of a Nano-Droplet on a Rough Solid Substrate under Perpendicular Electric Field

“…The size of the substrate is 12 × 1.5 × 12 nm 3 . The atoms of silicon substrate were kept frozen during the molecular dynamic MD simulations to speed up the simulation, as used in the literature [ 21 , 23 , 26 ]. 2000 water molecules were randomly distributed into a spherical nano-droplet with a radius of 2.5 nm.…”

“…The initial distance between the center of the spherical nano-droplet and the substrate surface is 3 nm. A simple point charge/extension (SPC/E) model is chosen for water molecules, which has already been applied successfully to study the wetting phenomena of droplets on solid substrates [ 21 , 22 , 23 , 26 , 27 , 28 , 29 , 30 ]. The intermolecular interactions are calculated as follows.…”