Phase coexistence in polydisperse charged hard-sphere fluids: mean spherical approximation.

Area of Science:

• Physical Chemistry
• Statistical Mechanics
• Thermodynamics

Background:

• Charged hard sphere mixtures are complex systems with challenging thermodynamic property calculations.
• The mean spherical approximation provides an analytic solution for such mixtures.

Purpose of the Study:

• To demonstrate that polydisperse fluid mixtures of charged hard spheres belong to the class of truncatable free energy models.
• To simplify the analysis of phase coexistence in these systems.

Main Methods:

• Utilizing the analytic solution of the mean spherical approximation for multicomponent charged hard spheres.
• Mapping infinite equations for phase coexistence to a finite system of nonlinear equations in generalized moments.
• Calculating phase diagrams (cloud/shadow curves, binodals) and analyzing coexisting phase distribution functions.

Main Results:

• Polydisperse charged hard sphere mixtures are identified as truncatable free energy models.
• The formalism allows for the representation of thermodynamic properties using a finite number of moments.
• Full phase diagrams and detailed distributions of coexisting phases were calculated for specific systems.

Conclusions:

• The truncatable free energy model approach offers a powerful simplification for understanding phase behavior in polydisperse charged hard sphere mixtures.
• This method provides a computationally tractable way to determine thermodynamic properties and phase diagrams.