THE ROLE OF SOLVENT DIPOLE STRUCTURE ON THE CAPACITANCE OF CHARGED INTERFACES

An electrostatic model of solvent (H2O) dipole interactions at charged interfaces is reported. The model of H2O used in the present study has an internal dipole structure characterized by both a dipole moment mu(D) and a finite dipole length d(mu). The electric force acting on an individual molecule in the first monolayer is computed as a function of d,, taking into account both surface charge-dipole and dipole-dipole 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 H2O orientation, is shown to be sensitive to the dipole structural parameters mu(D) and d(mu), demonstrating the necessity of accounting for the charge distribution within the solvent molecule. The results are discussed in terms of existing models of H2O currently used in molecular dynamics and Monte Carlo simulations of interfacial fluid structure.