Universality of Ionic Criticality: Size- and Charge-Asymmetric Electrolytes

TL;DR

This study uses grand canonical simulations to investigate the critical behavior of size- and charge-asymmetric electrolytes, confirming Ising universality for certain models and exploring finite-size effects in others.

Contribution

It provides unbiased estimates of critical temperatures and densities for asymmetric electrolyte models, extending understanding of universality classes beyond symmetric cases.

Findings

Ising universality observed for z=1, 2:1, and 3:1 models.

Critical densities are approximately 5% lower than previous estimates.

Finite-size effects complicate analysis for z=3 models.

Abstract

Grand canonical simulations designed to resolve critical universality classes are reported for $z$:1 hard-core electrolyte models with diameter ratios $\lambda {=} a_+/a_- {\lesssim} 6$. For $z {=} 1$ Ising-type behavior prevails. Unbiased estimates of $T_c(\lambda)$ are within 1% of previous (biased) estimates but the critical densities are $\sim $5 % lower. Ising character is also established for the 2:1 and 3:1 equisized models, along with critical amplitudes and improved $T_c$ estimates. For $z {=} 3$, however, strong finite-size effects reduce the confidence level although classical and O$(n {\geq} 3)$ criticality are excluded.