Crossover behavior in fluids with Coulomb interactions

According to extensive experimental findings, the Ginzburg temperature t<Subscript>G</Subscript> for ionic fluids differs substantially from that of nonionic fluids [W. Schröer, H. Weigärtner, Pure Appl. Chem. <Emphasis Type="Bold">76, 19 (2004)]. A theoretical investigation of this outcome is proposed here by a mean field analysis of the interplay of short and long range interactions on the value of t<Subscript>G</Subscript>. We consider a quite general continuous charge-asymmetric model made of charged hard spheres with additional short-range interactions (without electrostatic interactions the model belongs to the same universality class as the 3D Ising model). The effective Landau-Ginzburg Hamiltonian of the full system near its gas-liquid critical point is derived from which the Ginzburg temperature is calculated as a function of the ionicity. The results obtained in this way for t<Subscript>G</Subscript> are in good qualitative and sufficient quantitative agreement with available experimental data. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 2007