Schröer, Wolffram PhD
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Schröer, Wolffram PhD
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Schröer, Wolffram PhD
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Item type:Publication, Untersuchungen des kritischenVerhaltens von Lösungen IonischerFlüssigkeiten mit dembis(trifluormethylsulfonyl)imid Anion(2008-09-19); ; ; 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.doctoral thesis407 144 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Thermodynamische und laserspektroskopische Untersuchungen von Phasenübergängen in ionischen Flüssigkeiten(2006-10-24); ; ; The room temperature ionic liquids (RTIL) trihexyl(tetradecyl)phosphonium chloride and the corresponding bromide are soluble in hydrocarbons. The investigated solutions in heptane, octane, nonane and decane show liquid-liquid phase separation with an upper critical solution point at ambient temperatures.Scaled by the critical data, the phase diagrams show corresponding state behaviour. Notably, the corresponding state phase diagrams are in agreement with that of alcohol solutions of other RTILs and also with the simulation results of the restricted primitive model (RPM). The location of the critical point suggests that the demixing is mainly determined by Coulomb interactions, although the critical temperature and the critical density are below the figures of the RPM prediction. Highly accurate measurements of the phase diagram by refractive index measurements for the investigated critical sample of trihexyl(tetradecyl)phosphonium chloride in n-nonane prove Ising critical behaviour with indications of a crossover to Mean-Field. Viscosity measurements on the critical sample of the same system also show Ising critical behaviour with deviations expected for crossover. Static and dynamic light scattering measurements also prove Ising criticality. Thus the measurements of the critical properties of the ionic solutions in Hydrocarbons consistently showing Ising criticality rule out the possibility of mean-field behaviour, which was proposed because of the long-range nature of the Coulomb interactions.doctoral thesis232 278 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Untersuchungen kritischer Fluktuationen des flüssig-flüssig Phasenübergangs von Mischungen Ionischer Flüssigkeiten in aromatischen Lösungsmitteln und Wasser(2008-09-19); ; ; 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.doctoral thesis232 156 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Lichtstreuung in trüben Flüssigkeiten(2007-12-06); ; ; This work is about evaluation of light scattering experiments. The static and dynamic scattering properties of polystyrene-latex samples and of a critical sample of the system 3-methyl-pyridine/water/NaBr were investigated. The scattering experiments were performed using a 3D-cross-correlation setup.Samples of high to low transmissions were investigated. In highly turbid samples multiply scattered light contributes to the scattering intensities and correlation functions. An evaluation using traditional light scattering theory, valid for transparent samples and single scattering, leads to erroneous results. Therefore it was reasonable to precisely estimate the contribution of multiply scattered light to the scattering intensities and the correlation functions.The first part of this work describes light scattering experiments of latex samples. The detector deficiencies were determined by evaluating the dependence of the amplitudes of the auto correlation functions of the polarized scattered light on the countrates. Thus it was possible to convert the experimental countrates and correlation functions into their ideal counterparts. The contributions of single and multiple scattering to the scattering intensities were calculated from the amplitudes of the 3D-cross-correlation functions. The field correlation functions of the single and of the multiple scattering were determined from the ideal auto correlation functions and the 3D-cross-correlation functions. Monte-Carlo simulations were also applied to estimate the multiple scattering contributions. The simulation results were in good agreement with the experimental data. The influence of the turbidity on the angular dependency of the single scattering volume was analysed and correction functions were presented.The second part of this work deals with Monte-Carlo simulations of the static and dynamic light scattering of the critical sample. These simulations were also in good agreement with the experimental results.doctoral thesis292 267