RESTRICTED PRIMITIVE MODEL OF AN IONIC SOLUTION CONFINED TO A PLANE

A model system of electrolytes, the three-dimensional restricted primi tive model (RPM), is investigated for the case where the charged hard spheres are constraint to move on a two-dimensional surface. The prope rties of the thermodynamic states corresponding to the gas and liquid phases have been determined by computer simulation for a wide range of densities and temperatures. The simulations provide results for the e quation of state, internal energy, and correlation functions of the 3D RPM confined to 2D, and allow a characterization of the local order o f the charged spheres as a function of density and temperature. The mo st striking aspect of this order is the organization, at low, although supercritical, temperature and low to moderate densities, of the sphe res into ''clusters'' where linear arrangements or chains of alternati vely positive and negative charges dominate. The domain of validity of the hypernetted chain integral equation. is investigated. The critica l temperature of the gas-liquid transition is located with precision b y means of a finite size,scaling analysis of the simulation results in the critical region. With regard to the critical behavior of the 2D R PM, the limitations on system sizes which could be studied do not allo w to conclude more than possible compatibility with the 2D Ising unive rsality class. (C) 1998 American institute of Physics. [S0021-9646(98) 70241-7].