Stockmayer fluid with a shifted dipole. II. Interfacial behavior

Abstract

We investigate the properties of the liquid–vapor interface in the shifted-dipole Stockmayer fluid using molecular dynamics simulations in the canonical ensemble. We study the role of dipole moment strength and the degree of asymmetry on equilibrium interfacial characteristics, including density profiles, polar order, nematic order, interfacial polarization, electric field, and electrostatic potential. In addition, we compute angular distribution functions across the interface to gain insight into how the dipole shift affects the molecular orientation. We find that the shift significantly affects angular distribution functions by altering the polar order while leaving the nematic order relatively unaffected, relative to the reference regular Stockmayer fluid. These results can be explained using an image-dipole construct that has been previously applied to regular Stockmayer fluids. We find remarkable agreement between the simple theory and the simulations in the qualitative shape of the distribution functions for both the liquid and vapor phases in proximity to the interface. Surprisingly, the spontaneous polarization at the interface, and therefore the generated electric field, changes sign as the dipole moment strength increases, leading to an inversion of the sign of the potential difference across the interface.