TRANSFER OF SMALL IONS ACROSS THE WATER/1,2-DICHLOROETHANE INTERFACE

Molecular dynamics equilibrium and nonequilibrium simulations are used to examine the mechanism and dynamics of transfer of small ions across the water/1,2-dichloroethane interface. The equilibrium calculations provide information about the potential of mean force governing the ion transfer. We show that a two-dimensional free energy surface, which is a function of both ion position and the degree of solvation by one of the liquids, is necessary for properly describing the transfer process. Extensive nonequilibrium calculations for the transfer of ions from the organic phase to water, as well as from water to the organic phase, under conditions of different external electric fields, are described. These calculations show that the transfer into the aqueous phase is an activated process that is facilitated by surface roughness and that the activation energy is associated with the breakup of interfacial water hydrogen bonds. The transfer into the organic phase involves significant perturbation to the interface structure and dragging of the first hydration shell of the ion into the organic phase.