Abstract
Phase separation and criticality are analyzed in charge-asymmetric ionic fluids of equisized hard spheres by generalizing the Debye-Hückel approach combined with ionic association, cluster solvation by charged ions, and hard-core interactions, following lines developed by Fisher and Levin for the case (i.e., the restricted primitive model). Explicit analytical calculations for and systems account for ionic association into dimers, trimers, and tetramers and subsequent multipolar cluster solvation. The reduced critical temperatures, (normalized by ), decrease with charge asymmetry, while the critical densities increase rapidly with . The results compare favorably with simulations and represent a distinct improvement over all current theories such as the mean spherical approximation, symmetric Poisson-Boltzmann theory, etc. For , the interphase Galvani (or absolute electrostatic) potential difference, , between coexisting liquid and vapor phases is calculated and found to vanish as when —with, since our approximations are classical, . Above , the compressibility maxima and so-called -inflection loci (which aid the fast and accurate determination of the critical parameters) are found to exhibit a strong dependence.
7 More- Received 30 June 2005
DOI:https://doi.org/10.1103/PhysRevE.72.041501
©2005 American Physical Society