Thermodynamics of the Screened Coulomb Pair Potential

Abstract

The thermodynamics of a screened Coulomb potential of the Yukawa-type is examined in detail. It is shown that, as a consequence of the screening term, the Gibbs and Helmholtz free energies are not equal. Furthermore, the Gibbs form has an attractive tail. The well-known Derjaguin−Landau−Verwey−Overbeek (DLVO) and the Sogami−Ise theories are compared, and attempts to eliminate the attractive tail are discussed in detail. Parallels are found in the phase transitions in charged colloid systems and the van der Waals gas, with particular emphasis on the “internal pressures” and “excluded volumes”. On the basis of computer simulations, it is concluded that the screened Coulomb interaction is inadequate for describing systems that have many-body interactions. A new interpretation of the stability of void regions within a charged colloid system is presented.