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

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