How Multivalency controls Ionic Criticality

TL;DR

This paper investigates how multivalency affects the critical temperature and density of ionic fluids, revealing that increased valency lowers critical temperature while increasing density, with implications for understanding ionic phase behavior.

Contribution

It provides a detailed analysis of multivalent ionic fluids using models that incorporate ion clustering, solvation, and excluded volume effects, challenging some existing theoretical predictions.

Findings

Critical temperature decreases with increasing valency z.

Critical density increases steeply with z.

Most ions are bound in clusters near the critical point.

Abstract

To understand how multivalency influences the reduced critical temperatures, Tce (z), and densities, roce (z), of z : 1 ionic fluids, we study equisized hard-sphere models with z = 1-3. Following Debye, Hueckel and Bjerrum, association into ion clusters is treated with, also, ionic solvation and excluded volume. In good accord with simulations but contradicting integral-equation and field theories, Tce falls when z increases while roce rises steeply: that 80-90% of the ions are bound in clusters near T_c serves to explain these trends. For z \neq 1 interphase Galvani potentials arise and are evaluated.