Capacitance of thin dipolar fluid films

Abstract

It is shown that for certain simple fluids the free energy is a functional of the local number density and local polarisation only. For such a fluid, a formula for the dielectric constant in terms of the direct correlation function is obtained. The theory is applied to a fluid of hard-sphere dipoles described in the mean spherical approximation. It is shown that the result obtained for the dielectric constant agrees with that obtained earlier by Wertheim. The capacitances of thin films of the fluid are also obtained. At the higher bulk fluid densities measurable effects appear in films many molecular diameters thick.