The Role of Solvent Dipole Structure on the Capacitance on Charged Interfaces.

An electrostatic model of solvent H20 dipole interactions at charged interfaces is reported. The model of H20 used in the present study has an internal dipole structure characterized by both a dipole moment uD and a finite dipole length du The electric force acting on an individual molecule in the first monolayer is computed as a function of du, taking into account both surface chargedipole and dipoledipole interactions. Inclusion of the finite dimensions of the dipole and hard-core solvent diameter allows a simple and self-consistent method for calculating the interaction between solvent molecules. The capacitance of the charged interface, based on a simplistic two state model of H20 orientation, is shown to be sensitive to the dipole structural parameters uD and du, demonstrating the necessity of accounting for the charge distribution within the solvent molecule. The results are discussed in terms of existing models of H20 currently used in molecular dynamics and Monte Carlo simulations of interfacial fluid structure.