Interactions of polarizable media in water: A molecular dynamics approach

We investigate the interactions of polarizable solutes in water as a function of the solute permittivity. A generic and computationally efficient simulation methodology for the investigation of systems involving dielectric discontinuities is introduced. We report results for interactions between two polarizable cylindrical solutes of nanometer dimensions, which demonstrate that the interactions between the solutes strongly depend on the solute permittivity ε. For low permittivity, ε∼1-2, the interactions are dominated by surface tension forces whose origin lies in the formation of a vapor cavity between the two hydrophobic solutes. This effect leads to a drying transition, where the intersolute force changes discontinuously at a specific solute-solute separation. We find that a moderate permittivity, ε∼20, enhances the solvation of the polarizable objects inhibiting this drying transition. In the limit of moderately high permittivity, the interactions are dominated by solvation forces. These forces are much larger than those calculated using macroscopic models of dielectrics, which consider water as a continuum dielectric medium. Our results emphasize the importance of including the solvent explicitly to investigate dielectric discontinuities and interactions between polarizable media in water.