BULK AND INTERFACIAL PROPERTIES OF POLAR FLUIDS

Based on a suitable density functional theory for inhomogeneous fluids we investigate both the bulk phase diagram and interfacial structures of polar fluids in general and of Stockmayer fluids in particular. We derive a scheme which allows us to analyze one-component fluids composed of molecules with strong permanent dipole moments which are shown to affect significantly the bulk phase diagram. The results for the bulk phase diagram are in good agreement with published Monte Carlo data. Furthermore we investigate the profiles of the number density and of the orientational order at the liquid-vapor interface as well as the corresponding surface tension. We systematically analyze the dependences of these quantities on the temperature and on the strength of the dipole moment of the molecules. This reveals power laws and, close to criticality, scaling behavior. Our approach, which is reliable even for large dipole moments, allows us to determine separately those contributions to the surface tension which are due to the orientational degrees of freedom.