Untersuchungen des kritischenVerhaltens von Lösungen IonischerFlüssigkeiten mit dembis(trifluormethylsulfonyl)imid Anion

Abstract

Binary mixtures of the ionic liquid 1-methyl-3-octadecylimidazolium bis(trifluoromethylsulfonyl)imide with nonpolar solvents (cyclohexane, methylcyclohexane) were investigated.Liquid-liquid phase transition with an upper critical point was found in both cases.The phase diagrams were determined visually by the 'cloud-point' method and analyzed by a function which presumes Ising critical behavior and a rectilinear diameter of the phase diagram.The corresponding state analysis was carried out. The phase diagrams scaled by the critical data are in agreement with the simulation results for the restrictive primitive model.A series of accurate measurements (refractive index, viscosity, static and dynamic light scattering) were performed on critical samples in order to analyze the critical behavior.The coexistence curves were determined using the minimum deviation method and analyzed in terms of various concentration variables.The critical viscosity was measured. The analysis of the critical enhancement in the viscosity gave Ising-like critical behavior with a crossover to mean field criticality.Static light scattering data was analyzed using the Orstein-Zernike function. The obtained values for the critical exponents were close to the theoretical Ising values.For the cyclohexane system an crossover from Ising to mean field criticality was observed in the region far away from the critical temperature. The diffusion constants were obtained from dynamic light scattering experiments. The analysis confirmed the Ising like criticality.