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 ha s an internal dipole structure characterized by both a dipole moment m u(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-dipol e interactions. Inclusion of the finite dimensions of the dipole and h ard-core solvent diameter allows a simple and self-consistent method f or calculating the interaction between solvent molecules. The capacita nce of the charged interface, based on a simplistic two-state model of H2O orientation, is shown to be sensitive to the dipole structural pa rameters mu(D) and d(mu), demonstrating the necessity of accounting fo r the charge distribution within the solvent molecule. The results are discussed in terms of existing models of H2O currently used in molecu lar dynamics and Monte Carlo simulations of interfacial fluid structur e.