A SIMPLE-MODEL TO INVESTIGATE THE EFFECTS OF NON-COULOMBIC INTERACTIONS ON THE STRUCTURE OF CHARGED INTERFACES

A simple field theoretical model is considered for an electrified inte rface in which the electrolyte solution is in contact with a charged h ard wall. The model for the electrolyte includes Coulombic interaction s, local ideal entropy, functional and specific nonlocal interactions. For the specific nonlocal interactions, the simplest form of the squa re gradient term is selected. The charged hard wall is characterized b y an additional short range potential reduced to the form of a Dirac f unction. An exact relation, analogous to Maxwell relations in thermody namics, is derived describing the effect of the wall specificity on th e electric properties. In the mean held theory, the consistency equati ons for the ionic profiles are solved analytically in the Limit of sma ll charge densities and weak wall potentials. The electric double laye r structure is discussed in terms of two characteristic lengths-Debye length for electrostatics and the characteristic length for the specif ic interaction. We also present and discuss charge and density profile s of ions calculated numerically by it differential equation solver. W ith the results thus obtained we find a behavior much different from t he classical Gouy-Chapman theory. (C) 1998 American Institute of Physi cs.