Mesoscopic theory for size- and charge-asymmetric ionic systems: I. The case of extreme asymmetry

Abstract

A mesoscopic theory for the primitive model of ionic systems is developed for arbitrary size, λ = σ + /σ − , and charge, Z = e + /|e − |, asymmetry. Our theory is an extension of the theory we developed earlier for the restricted primitive model. The case of extreme asymmetries λ → ∞ and Z → ∞ is studied in some detail in a mean-field approximation. The phase diagram and correlation functions are obtained in the asymptotic regime λ → ∞ and Z → ∞, and for infinite dilution of the larger ions (volume fraction n p ∼ 1/Z or less). We find a coexistence between a very dilute 'gas' phase and a crystalline phase in which the macroions form a bcc structure with the lattice constant ≈ 3.6σ + . Such coexistence was observed experimentally in deionized aqueous solutions of highly charged colloidal particles.

Correlation functions in an ionic liquid at coexistence with an ionic crystal: results of the Brazovskii-type field theory

“…[11], and described in more detail in Refs. [25,29,30]. In the WF the field η(x) is approximated by its most probable form for each given field φ(x).…”

Field theory for size- and charge-asymmetric primitive model of ionic systems: Mean-field stability analysis and pretransitional effects

“…Preliminary fieldtheoretic results [8] indicate that when the size and the charge of the cation are several orders of magnitude larger than the size and the charge of the anion, the gas-liquid type phase separation is preempted by a transition between gas and a colloidal crystal for a large range of temperatures, including room temperature [8]. The predictions of Ref.…”

Universality class of the critical point in the restricted primitive model of ionic systems

“…For fixed temperature and chemical potential the probability density that the local densities assume a particular form ρ + (x), ρ − (r) is given by [7,42] p[ρ where…”