Effects of an Applied Electric Field on the Vapor−Liquid Equilibria of Water, Methanol, and Dimethyl Ether

Thermodynamic Study of the Electric Field Effect on Liquid-Vapor Mixture at Equilibrium: An Analysis on a Water-Ethanol Mixture

In this paper, the effect of electric fields on phase equilibria through polarization is investigated. A relation is derived for the chemical potential of a system, where the electric field is localized over a liquid phase mixture in equilibrium with a vapor phase mixture. This relation is then applied to a water-ethanol mixture to explore the effect of polarization-based electric fields on the liquid phase composition. It is observed that the quadratic dependence on electric field strength produces little effect below field strengths of approx. 10 MV/m. However, above this field strength, the mole fraction of water in the liquid phase grows rapidly, increasing by a factor of 8 for a water vapor phase fraction of 0.2 and a field strength of 500 MV/m, which approaches the dielectric breakdown strength of water. Nonetheless, this field strength could be achievable with microfluidic experimental setups.

Liquid-vapor interface of the Stockmayer fluid in a uniform external field

The effect of a uniform (nonspatially varying) external field on the liquid-vapor interface of the Stockmayer fluid (Lennard-Jones particles embedded with a point dipole) has been investigated by molecular-dynamics simulations. The long-ranged parts of both the dipole and Lennard-Jones interactions are treated using an Ewald summation, which removes the effects of the cutoff. The direction of the field shifts the critical point and interfacial properties in different directions. For an external field parallel to the interface, the critical temperature increases, while for a field applied perpendicular to the interface, it decreases. The effects of the field on surface tension and interfacial width are also investigated. For zero field, dipoles near the liquid-vapor interface show a weak orientation parallel to the interface. For fields parallel to the interface, ordering in the liquid phase is greater than the vapor, while for fields perpendicular to the interface, the opposite is true.

Nanoscale lubrication of ionic surfaces controlled via a strong electric field

Frictional forces arise whenever objects around us are set in motion. Controlling them in a rational manner means gaining leverage over mechanical energy losses and wear. This paper presents a way of manipulating nanoscale friction by means of in situ lubrication and interfacial electrochemistry. Water lubricant is directionally condensed from the vapor phase at a moving metal-ionic crystal interface by a strong confined electric field, thereby allowing friction to be tuned up or down via an applied bias. The electric potential polarity and ionic solid solubility are shown to strongly influence friction between the atomic force microscope (AFM) tip and salt surface. An increase in friction is associated with the AFM tip digging into the surface, whereas reducing friction does not influence its topography. No current flows during friction variation, which excludes Joule heating and associated electrical energy losses. The demonstrated novel effect can be of significant technological importance for controlling friction in nano- and micro-electromechanical systems.

Phase diagram of water under an applied electric field

Simulations are used to investigate for the first time the anisotropy of the dielectric response and the effects of an applied electric field E(ex) on the phase diagram of water. In the presence of electric fields ice II disappears from the phase diagram. When E(ex) is applied in the direction perpendicular to the ac crystallographic plane the melting temperatures of ices III and V increase whereas that of ice Ih is hardly affected. Ice III also disappears as a stable phase when E(ex) is applied in the direction perpendicular to the ab plane. E(ex) increases by a small amount the critical temperature and reduces slightly the temperature of the maximum density of liquid water. The presence E(ex) modifies all phase transitions of water but its effect on solid-solid and solid-fluid transitions seems to be more important and different depending on the direction of E(ex).

Electric-field-induced condensation: an extension of the Kelvin equation

The Kelvin equation relates the vapor pressure of a volatile liquid to the curvature of the liquid surface. It describes phenomena such as capillary condensation, capillary adhesion, nucleation, and the adsorption of vapors into porous media. Here we propose an extension of the Kelvin equation, which takes into account changes of the vapor pressure due to electric fields. The presence of electric fields reduces the saturation vapor pressure and leads to field-induced condensation. Field-induced condensation can explain the presence of water bridges in scanning probe nanolithographic methods such as anodic oxidation.