PNNL

Abstract

The result of transferring a polarizable iodide anion across the H2O-CCl4 liquid/liquid interface was investigated. The computed transfer free energy profile or potential of mean force exhibits a minimum near the Gibbs dividing surface, and its characteristics are similar to those of found in a corresponding water vapor/liquid interface study involving a smaller minimum free energy. Molecular dynamics simulations also were carried out to compare the concentrations of NaCl, NaBr, and NaI at H2O-vapor and H2O-CCl4 interfaces. While the concentration of bromide and iodide ions were lower at the H2O-CCl4 interface when compared to the H2O-vapor interface, the chloride ion concentrations were similar at both interfaces. Analysis of the solvation structures of iodide and chloride ions revealed that the more polarizable iodide ion was less solvated than the chloride ion at the interface. This characteristic brought the iodide ion in greater contact with CCl4 than the chloride ion, resulting in repulsive interactions with CCl4, which reduced its propensity for the interface. This work was performed at the Pacific Northwest National Laboratory (PNNL) and was supported by the Division of Chemical Sciences, Office of Basic Energy Sciences, U.S. Department of Energy (DOE). PNNL is operated by Battelle for the DOE. The DOE Division of Chemical Sciences and the Scientific Computing Staff, Office of Science provided computer resources at the National Energy Research Supercomputer Center (Berkeley, California) that supported this research.