Coexistence and Criticality in Size-Asymmetric Hard-Core Electrolytes

Liquid-vapor coexistence curves and critical parameters for hard-core 1:1 electrolyte models with diameter ratios λ0ex0ex=0ex0exσ_-/σ₊0ex0ex=0ex0ex1 to 5.7 have been studied by fine-discretization Monte Carlo methods. Normalizing via the length scale σ_±0ex0ex=0ex0ex1/2(σ₊+σ_-), relevant for the low densities in question, both Tc* ( 0ex0ex=0ex0exkBTcσ_±/q²) and ρc* ( 0ex0ex=0ex0exρcσ_±³) decrease rapidly (from 0.05 to 0.03 and 0.08 to 0.04, respectively) as λ increases. These trends, which unequivocally contradict current theories, are closely mirrored by results for tightly tethered dipolar dimers (with Tc* lower by ~0%--11% and ρc* greater by $37%--12%$).