Translational and rotational diffusion coefficients in nanofluids from polarized dynamic light scattering

Nanofluids representing nanometer-sized solid particles dispersed in liquids are of interest in many fields of process and energy engineering, e.g., heat transfer, catalysis, and the design of functionalized materials [1]. The physical, chemical, optical, and electronic properties of nanofluids are strongly driven by the size, shape, surface potential, and concentration of the nanoparticles. For the analysis of diffusive processes in nanofluids allowing access to, e.g., particle size and its distribution, dynamic light scattering (DLS) is the state-of-the-art technique. It is based on the analysis of microscopic fluctuations originating from the random thermal movement of particles in the continuous liquid phase at macroscopic thermodynamic equilibrium. For anisotropic particles or particle aggregates, besides translational diffusion also rotational diffusion occurs. To obtain the sum of the orientation-averaged translational (DT) and rotational (DR) diffusivities by depolarized DLS [2], a homodyne detection scheme is usually applied which can hardly be fulfilled in the experimental realization. Furthermore, the experiments are restricted to limited ranges for temperature, particle concentration, and viscosity

Regionale Arbeitsmarktindikatoren für 1987 und 1988

"Der Beitrag führt eine Reihe von Indikatoren zur unterschiedlichen regionalen Entwicklung von Produktivität und Wachstum, aber auch zu Detailstrukturen von Beschäftigung und Arbeitslosigkeit an. Trotz einer längeren Wachstumsphase (von 1983 bis 1987 ist das reale Bruttoinlandsprodukt insgesamt um 9,4 % gestiegen) sind die Herausforderungen an die regionale Arbeitsmarktpolitik heute keineswegs geringer - im Gegenteil. Seit 1982 ist ein anhaltend hohes Niveau der Arbeitslosigkeit zu verzeichnen. Besorgniserregend ist die ungleiche Entwicklung in den einzelnen Regionen und damit im Zusammenhang vor allem die Strukturkrise im Stahl-, Kohle- und Agrarbereich. Gegenwärtig liegt die Beschäftigtenzahl deutlich über dem letzten Tiefstand von 1983/84. An dieser erfreulichen Entwicklung konnten allerdings nicht alle Regionen gleichermaßen teilhaben: Beschäftigungsgewinne auf der einen Seite (vor allem in Bayern, Baden-Württemberg, aber auch in Rheinland-Pfalz, Schleswig-Holstein und Hessen), Arbeitsplatzabbau bzw. ein relatives Zurückbleiben in anderen Regionen (insbesondere in Nordrhein-Westfalen, Saarland und den Stadtstaaten). Während in einzelnen Arbeitsamtsbezirken auch über die Rezession hinweg erhebliche Beschäftigungsgewinne verbucht werden konnten (z.B. in Waiblingen, Landshut oder Freising über +10 %), mußten vor allem die sogenannten alten Industriestandorte weitere Einbrüche hinnehmen (z.B. Duisburg -13 %). Die Hauptlast der Branchenkrisen tragen eben jene Regionen, von deren Standortpotentialen die Gesamtwirtschaft in mehr als drei Jahrzehnten profitierte." (Autorenreferat)Arbeitsmarktindikatoren, regionale Faktoren, Wirtschaftswachstum, Produktivität, Beschäftigung, Arbeitslosigkeit

Extremely low vapor‐pressure data as access to PC‐SAFT parameter estimation for ionic liquids and modeling of precursor solubility in ionic liquids

Precursor solubility is a crucial factor in industrial applications, dominating the outcome of reactions and purification steps. The outcome and success of thermodynamic modelling of this industrially important property with equations of states, such as Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT), vastly depends on the quality of the pure-component parameters. The pure-component parameters for low-volatile compounds such as ionic liquids (ILs) have been commonly estimated using mixture properties, e. g. the osmotic pressure of aqueous solutions. This leads to parameters that depend on the solvent, and transferability to other mixtures often causes poor modeling results. Mixture-independent experimental properties would be a more suitable basis for the parameter estimation offering a way to universal parameter sets. Model parameters for ILs are available in the literature [10.1016/j.fluid.2012.05.029], but they were estimated using pure-IL density data. The present work focuses on a step towards a more universal estimation strategy that includes new experimental vapor-pressure data of the pure IL. ILs exhibit an almost negligible vapor pressure in magnitude of usually 10−5 Pa even at elevated temperatures. In this work, such vapor-pressure data of a series of 1-ethyl-3-methyl-imidazolium-based [C2mim]-ILs with various IL-anions (e. g. tetrafluoroborate [BF4]−, hexafluorophosphate [PF6]−, bis(trifluoromethylsulfonyl)imide [NTf2]−) were experimentally determined and subsequently used for PC-SAFT parameter estimation. The so-determined parameters were used to predict experimental molecular precursor solubility in ILs and infinitely diluted activity coefficients of various solvents in ILs. The parameters were further compared to modeling results using classical parametrization methods (use of liquid-density data only for the molecular PC-SAFT and the ion-based electrolyte PC-SAFT). As a result, the modeled precursor solubilities using the new approach are much more precise than using the classical parametrization methods, and required binary parameters were found to be much smaller (if needed). In sum, including the pure-component vapor-pressure data of ILs opens the door towards parameter estimation that is not biased by mixture data. This procedure might be suitable also for polymers and for all kind of ionic species but needs extension to ion-specific parametrization in the long term

Brownian motion of droplets induced by thermal noise

Brownian motion (BM) is pivotal in natural science for the stochastic motion of microscopic droplets. In this study, we investigate BM driven by thermal composition noise at sub-micro scales, where inter-molecular diffusion and surface tension both are significant. To address BM of microscopic droplets, we develop two stochastic multi-phase-field models coupled with the full Navier-Stokes equation, namely Allen-Cahn-Navier-Stokes (ACNS) and Cahn-Hilliard-Navier-Stokes (CHNS). Both models are validated against capillary wave theory; the Einstein's relation for the Brownian coefficient at thermodynamic equilibrium is recovered. Moreover, by adjusting the co-action of the diffusion, Marangoni effect, and viscous friction, two non-equilibrium phenomena are observed. (I) The droplet motion transits from the Brownian to Ballistic with increasing Marangoni effect which is emanated from the energy dissipation mechanism distinct from the conventional fluctuation-dissipation theorem. (II) The deterministic droplet motion is triggered by the noise induced non-uniform velocity field which leads to a novel droplet coalescence mechanism associated with the thermal noise

Regionale Lohnstrukturen

"Das in einer Region erzielbare Einkommen ist eine der wichtigsten Diagnose- und Zielvariablen der regionalen Struktur- und Arbeitsmarktpolitik. Im folgenden werden einige neuere empirische Befunde zur regionalen Lohnstruktur vorgestellt, die eine Fortführung der Diskussion zu diesem vielschichtigen Thema auf eine sachlich breitere Basis stellen können. Im Vordergrund der Analyse steht die Frage nach dem Lohngefälle zwischen den Regionen, innerhalb der Regionen und der Entwicklung dieser regionalen Lohnstrukturen. Die Ergebnisse zeigen einen durchschnittlichen Bruttojahreslohn, der doch um einiges unter den Angaben liegt, die auf der Basis "zusammengesetzter" Teilstatistiken ermittelt wurden: Der Jahresverdienst lag 1984 z.B. bei 29.161 DM (für Männer bei ca. 34.400 DM, für Frauen bei 21.300 DM brutto; nur ein Teil dieser Lohndifferenz von über 60 % ist auf Teilzeiteffekte zurückzuführen). Die Streuung der Durchschnittsverdienste über die Regionen sind wesentlich größer, als es bisherige Untersuchungen vermuten ließen; Die höchsten Jahresverdienste werden in dienstleistungsorientierten Industrieregionen erzielt, die niedrigsten in ländlich geprägten Gebieten. Dabei ergeben sich Unterschiede in den regionalen Durchschnittsverdiensten, die in den Extremen im Verhältnis 1:2 oder gar darüber hinaus streuen. Auch bei den Tagessätzen treten erhebliche Differenzen auf. Der durchschnittliche Wert von Wolfsburg oder Düsseldorf liegt z.B. um 65 Prozent über dem von Cham, Freyung-Grafenau oder Pirmasens (ähnliches gilt für die Unterschiede in den Branchen)." (Autorenreferat)Lohnstruktur, regionale Verteilung

Computational investigation of ionic liquids

Ionic liquids have been extensively studied over the past few decades to take advantage of their fine-tunable physicochemical properties. Due to the high cost of synthesis as well as a large number of ion combinations, it is beneficial to investigate them using computational chemistry methods. At the same time, it is also challenging to find a suitable computational approach that captures the whole variety of different types of interactions present in ionic liquids. In this work, we have compared the performance of PBE, M06-L, SCAN, SCAN0, and B2PLYP density functionals when describing ionic liquids. DLPNO-CCSD(T) method extrapolated to the complete basis set limit is used as a reference. In addition,we have constructed a density functional theory-based model to evaluate the electrochemical stability and viscosity of ionic liquids. This simple yet efficient model correlates the macroscopic properties to our computational results

Investigations on the stability and ecotoxicity of selected ionic liquid cations and anions

The field of ionic liquids (ILs) is rapidly growing and several applications have already been discussed or applied. For a long time, such substances were announced to be green . This was solely based on their low vapor pressure and the accompanying enhanced operational safety. This general term was refined when first evaluations on the ecotoxicity and biodegradability of ILs were published, indicating a certain environmental hazard for representatives. Within this thesis investigation on hydrolytic stability, biodegradation potential and ecotoxicological properties were extended to anions and cations which have not yet been studied. This includes three cyano based and three (per)fluorinated anions, five ammonium and several pyrrolidinium, morpholinium, piperidinium, imidazolium and pyridinium cations, as well as a first assessment for bivalent cations. An analytical method based on ion chromatography was developed for all of these compounds in order to monitor the degree of degradation. The studies presented here contribute to the hazard assessment of ILs and support their design with reduced hazard. The investigated anions showed considerable drawbacks since none of them was degraded via hydrolysis or microorganisms and the perfluorinated ones were especially toxic to aquatic organisms. The dicationic ILs seem to be an effective alternative. Their outstanding physico-chemical properties, specifically, the high thermal stability combined with a lower toxicity relative to monocationic analogues are already a step towards safer chemicals while fulfilling the application related profile. However, their biodegradability still needs to be improved. Here, ammonium and pyrrolidinium based ILs are preferable because they are readily biodegradable. This reveals the feasibility to design ILs with reduced hazard potential. However, this work represents an initial hazard assessment and further studies, e.g. long-term toxicity tests of ILs in order to determine chronic effects, are required for concluding evaluations

Oberflächenzusammensetzung und Anreicherungseffekte in Mischungen funktionalisierter und nicht-funktionalisierter Ionischer Flüssigkeiten

This thesis focuses on the surface investigations of neat ionic liquids (ILs) and of binary IL mixtures, particularly mixtures involving functionalized imidazolium-based cations. The investigations are performed by means of angle-resolved X-ray photoelectron spectroscopy (ARXPS), a surface-sensitive ultra-high vacuum (UHV) technique, accessing the first 7 to 9 nm under 0° emission and the topmost 1 to 1.5 nm under 80° emission. Intensity changes of the IL signals with the emission angle directly reflect surface enrichment and depletion of ions as well as molecular orientation effects in the outermost surface layer.Diese Dissertation befasst sich mit der Oberflächenuntersuchung reiner Ionischer Flüssigkeiten (engl. ionic liquids, ILs) und deren binären Mischungen, die funktionalisierte Imidazolium-basierte Kationen enthalten. Die Untersuchungen werden mittels winkelaufgelöster Röntgenphotoelektronenspektroskopie (engl. angle-resolved X-ray photoelectron spectroscopy, ARXPS), einer oberflächenempfindlichen Messmethode im Ultrahochvakuum, durchgeführt. Dies ermöglicht unter einem Emissionswinkel von 0° die ersten 7 bis 9 nm sowie unter 80° die äußersten 1 bis 1,5 nm einer Probe zu untersuchen. Der Vergleich der unter 0° und 80° detektierten IL-Signalintensitäten lässt direkte Rückschlüsse auf Oberflächenanreicherung und -abreicherung von Ionen zu und gibt Informationen über molekulare Orientierungseffekte in der äußersten Oberflächenschicht

Tetracyanidoborates with triply charged rare earth metal cations and their optical properties

A new group of tetracyanidoborates - tetracyanidoborates with trivalent rare earth metal cations - was synthesized. The rare earth tetracyanidoborates form isostructural groups, e.g. [LRE(H2O)5][B(CN)4]3•0.5 H2O, with LRE3+ = La, Ce, Pr, Nd, Sm, Eu, Gd and [HRE(H2O)7][B(CN)4]3 with HRE3+ = Tb, Dy, Ho, Er, Tm, Yb, Lu and Y. These tetracyanidoborates exhibit rare earth cation specific luminescence properties which are improved by the tetracyanidoborate anion. Therefore, the tetracyanidoborates with trivalent rare earth metal cations could have possible applications in phosphors