8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

P1.38Fri 911:10-14:00The lquid-liquid phase transitions in ionic solutionsWolffram Schröer, 1 Jan Köser, 1 Darius Arndt, 1 Vlad Vale, 1 Anna Butka, 1 AbdallahElshwishin, 1 and Bernd Rathke 21 Universität Bremen, Fachbereich Biologie-Chemie, Leobener Str. NWII, , 28359,Bremen, Germany2 Universität Bremen Institut Technische Thermodynamik, Bremen, GermanyThe critical properties of phase transitions of fluids and fluid mixtures are known to agree withthat of the 3d-Ising model. Although mean-field criticality was presumed because of the longrangenature of the Coulomb potential and stated by some measurements of the liquid-liquid phasetransition of ionic solutions, it is now almost certain that the phase transitions in ionic systems alsobelong to the Ising universality class. This is stated by experiments investigating the liquid-liquidphase transition of ionic solutions and simulations on the model systems of charged hard spheres.In this paper we report measurements with mK accuracy of the viscosity, of the coexistence curveand the static and dynamic light scattering of various solutions of ionic liquids including suchin non-polar solvents as alkanes, and arenes, dipolar solvents as aren-halides and solvents withhydrogen bonds as alcohols and water. All data show Ising critical behaviour with indicationsof crossover to mean-field criticality. In variance to theoretical estimates, the crossover is shiftedtowards larger separations from the critical temperature with increasing dielectric permittivity ofthe solvent, thus stating Pitzers observation of such a tendency. In variance to the Ising model thephase diagrams are highly asymmetric. Furthermore, the diameter, which is the mean value of thecompositions in the coexisting phases, is non-linear in variance to the predictions of mean-fieldtheories but also to the observations on noble gases. The asymmetry, which is analysed usingcomplete scaling theory, is found to decrease with increasing dielectric permittivity of the solvent.38