Untersuchungen kritischer Fluktuationen des flüssig-flüssig Phasenübergangs von Mischungen Ionischer Flüssigkeiten in aromatischen Lösungsmitteln und Wasser

Abstract

Critical fluctuations of ionic solutions with a liquid-liquid phase transition are investigated. The phase diagrams of six binary solutions containing ionicliquids were obtained with the cloud-point method and show an upper critical solution point. The investigated systems are 1-dodecyl-3-methyl-imidazolium chloride in benzene, toluene, o-xylol, tetralin; 1-tetradecyl-3-methyl-imidazolium chloride in CCl4 and 1-pentyl-3-methyl-imidazolium trifluoromethanesulfonate in water. With the exception of the water system, the critical points are in accordance with the predictions by the restricted primitive model (RPM). An important observation was the replacement of the upper critical solution point with a lower critical solution point in case of the system 1-pentyl-3-methyl-imidazolium trifluoromethanesulfonate/water, if RPM variables are used.This is a clear distinction between protic and aprotic solutions.Two systems were chosen for critical behavior investigations: 1-dodecyl-3-methylimidazolium chloride/benzene and 1-pentyl-3-methyl-imidazolium trifluoromethanesulfonate/water.For the critical concentration of the system 1-dodecyl-3-methyl-imidazolium chloride/water, the critical analysis with the refractive index measurements was not possible due to the fact that the concentration dependency of the refractive index in the two phase region was to small. The coexistence curve of the system 1-pentyl-3-methyl-imidazolium trifluoromethanesulfonate/water was analyzed in terms of different composition variables and resulted Ising critical behavior.Viscosity measurements of the two solutions were also carried out and yield an enhancement as expected for Ising criticality with a crossover to regular behaviour.The regular background is obtained by interpolation from the measurements at non-critical concentrations.Analyzing the static and dynamic light scattering data for the two systems critical Ising-like behavior could be again confirmed. In the case of the water solution the multiple scattering is relevant in the wider vicinity of the critical point and was corrected for by a Monte Carlo simulation method.Light scattering measurements in the two phase region of the critical solution 1-pentyl-3-methyl-imidazolium trifluoromethanesulfonate/water were also accomplished and gave as in the one phase region Ising critical behavior.