Untersuchung der Flüssig-Flüssig Phasenübergänge von Lösungen flüssiger Salze mit Imidazolium Kationen

Abstract

Binary solutions of the room temperature ionic liquids (RTIL) C:sub:n:/sub:mim:sup: :/sup:PF:sub:6:/sub::sup:-:/sup: and C:sub:n:/sub:mim:sup: :/sup:BF:sub:4:/sub::sup:-:/sup: (n = 4, 6, 8) have been investigated. Many separation temperatures have been found for solutions with alcohols and water. A systematic dependence of the separation temperature on the chain length of the alcohol or on the side chain length of the imidazolium cation could be observed. Using the RPM-reduced variables, all separation points lie on a straight line, independent on the nature of the RTIL.:p:For further investigations, the critical points and the phase diagrams of the systems C:sub:6:/sub:mim:sup: :/sup:BF:sub:4:/sub::sup:-:/sup:/water, 1-propanol, 1-butanol, 1-pentanol, 1-hexanol, 2-butanol and 2-pentanol have been determined.:p:Viscosity and refractive index measurements of the critical samples indicated clearly Ising-like behaviour. Besides, the composition of the coexisting phases could be estimated using the refractive index data.:p:The analysis of the static light scattering data gave, at first, mean-field critical behaviour, in opposition with the results of the viscosity and refractive index investigations. Another set of measurements indicated a sample heating by the laser beam (the so-called thermal lens effect). Taking into consideration the real temperature in the laser beam, the static light scattering data indicated a critical behaviour between Ising and mean-field. Analysing the dynamic light scattering data critical Ising-like behaviour could be confirmed. Because the amplitude of the autocorrelation function sinks linearly with the reduced temperature, a second process, which is quicker than the time-scale of the correlator, was supposed. Taking both the sample heating and the background intensity into consideration, the analysis of the static light scattering data gave also Ising-like criticality, as expected.