MONTE-CARLO SIMULATION OF AN ION-DIPOLE MIXTURE AS A MODEL OF AN ELECTRICAL DOUBLE-LAYER

Canonical Monte Carlo simulations were performed for a nonprimitive mo del of an electrical double layer. The ions and the solvent molecules are modeled as charged and dipolar hard spheres, respectively, while t he electrode as a hard, impenetrable wall carrying uniform surface cha rge. We found that the ion-dipole model gives a reasonable description of the double layer for partially charged ions with small to moderate dipole moments, or equivalently for an ''effective'' dielectric const ant. Density, polarization and mean electrostatic potential profiles a re reported. Strong layering structure, and at higher charges, charge inversion in the second layer were found. With appropriate choices of charge and solvent parameters, states corresponding to the primitive o r the solvent primitive model can be produced, and the results agreed well with literature data. At higher effective charges and dipole mome nts, the dipolar solvent has difficulties in preventing the ions from clustering. More realistic models of water and other solvents are nece ssary to study the double layer. (C) 1998 American Institute of Physic s. [S0021-9606(98)51341-4].