Ising criticality ionic fluids

BiCl3 is, however, little conducting in the liquid phase, and it resembles nonionic rather than ionic fluids. This may warn that specific interactions may destroy the peculiar effects of ionic criticality. Likewise, water (Tc = 647 K) shows Ising behavior [61]. At the critical point, autoprotolysis of water is enhanced by three orders of magnitude relative to ambient conditions [62]. 

One of the few attempts to tackle the problem of ionic criticality more quantitatively was made by Hafskjold and Stell in 1982 [36], and was later taken up by H0ye and Stell [17, 302, 303]. Based on a comparative analysis of the correlation functions for nonionic and ionic fluids, these authors asserted that the critical point of the RPM is Ising-like. To this end, they argued that the density-density correlation function hpp(r) and the associated direct correlation function cpp(r) obey essentially the same OZ equation and closure as that of a single-component, nonionic fluid. It was assumed that this analogy suffices to ensure that the critical exponents are Ising-like. 

Crossover. Generally, crossover from an Ising-like asymptotic behavior to mean-field behavior further away from the critical point [86, 87] may be expected. Such a behavior is also expected for nonionic fluids, but occurs so far away, that conditions close to mean-field behavior are never reached. Reports about crossover [88] and the finding of mean field criticality [14—16] suggest that in ionic systems the temperature distance of the crossover regime from the... 

The two-term crossover Landau model has been successfully applied to the description of the near-critical thermodynamic properties of various systems, that are physically very different the 3-dimensional lattice gas (Ising model) [25], one-component fluids near the vapor-liquid critical point [3, 20], binary liquid mixtures near the consolute point [20, 26], aqueous and nonaqueous ionic solutions [20, 27, 28], and polymer solutions [24]. 

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