Molecular Dynamics Study Comparing the Enthalpy of Vaporization of Water under Electric Fields in Bulk and Interfacial Systems

Abstract

Understanding how non-ionizing external electric fields influence the phase change properties of water, particularly the enthalpy of vaporization (ΔHvap), remains unsettled in both experimental and molecular dynamics simulation studies. Simulation outcomes can be contradictory, reporting either increases or decreases in ΔHvap. Some of these reported discrepancies may be due to interfacial effects. In this context, the present work isolates the role of the liquid–vapor interface in equilibrium molecular dynamics simulations of water under an external electric field by comparing ΔHvap in bulk and interfacial systems. Simulations were carried out using the TIP4P-Ew water model, applying uniform electric fields (0.05 V/Å and 0.1 V/Å) along both lateral and normal directions. For bulk, ΔHvap increases up to 5% consistent with field-induced polarization and in good agreement with continuum model predictions. In the liquid–vapor configuration, a lateral electric field produces a smaller but measurable increase in ΔHvap of up to ~1%, also attributable to polarization effects. In contrast, a normal field within the investigated range does not induce significant polarization in the liquid–vapor system, leaving ΔHvap unchanged. Surface tension decreases up to 5% for both field orientations.