Speziation von Plutonium bei der Sorption und Diffusion in Opalinuston

Die vorliegende Arbeit wurde im Rahmen des BMWi-Verbundprojektes Wechselwirkung und Transport von Aktiniden im natürlichen Tongestein unter Berücksichtigung von Huminstoffen und Tonorganika – Wechselwirkung von Neptunium und Plutonium mit natürlichem Tongestein“ durchgeführt. Um die langfristige Sicherheit der nuklearen Endlager beurteilen zu können, muss eine mögliche Migration der radiotoxischen Abfälle in die Umwelt betrachtet werden. Wegen seiner langen Halbwertszeit (24000 a) leistet Pu-239 einen wesentlichen Beitrag zur Radiotoxizität abgebrannter Kernbrennstoffe in einem Endlager. Das redox-sensitive Pu tritt in Lösung unter umweltrelevanten Bedingungen in den Oxidationsstufen +III bis +VI auf und kann nebeneinander in bis zu vier Oxidationsstufen vorliegen. Tonsteinformationen werden als mögliches Wirtsgestein für Endlager hoch-radioaktiver Abfälle betrachtet. Deshalb sind ausführliche Informationen zur Mobilisierung und Immobilisierung des Pu durch/in das Grundwasser aus einem Endlager von besonderer Bedeutung. In dieser Arbeit wurden neue Erkenntnisse über die Wechselwirkung zwischen Pu und dem natürlichen Tongestein Opalinuston (OPA, Mont Terri, Schweiz) mit Hinblick auf die Endlagerung wärmeentwickelnder radioaktiver Abfälle in einem geologischen Tiefenlager gewonnen.rnDer Fokus der Arbeit lag dabei auf der Bestimmung der Speziation von Pu an der Mineraloberfläche nach Sorptions- und Diffusionsprozessen mittels verschiedener synchrotronbasierter Methoden (µ-XRF, µ-XANES/EXAFS, µ-XRD, XANES/EXAFS). rnDie Wechselwirkung zwischen Pu und OPA wurde zunächst in Batch- und Diffusionsexperimenten in Abhängigkeit verschiedener experimenteller Parameter (u.a. pH, Pu-Oxidationsstufe) untersucht. In Sorptionsexperimenten konnte gezeigt werden, dass einige Parameter (z.B. Temperatur, Huminsäure) einen deutlichen Einfluss auf die Sorption von Pu haben.rnDie Speziationsuntersuchungen wurden zum einen an Pulverproben aus Batchexperimenten und zum anderen an OPA-Dünnschliffen bzw. Diffusionsproben in Abhängigkeit verschiedener experimenteller Parameter durchgeführt. Die EXAFS-Messungen an der Pu LIII-Kante der Pulverproben ergaben, dass eine innersphäriche Sorption von Pu(IV) an Tongestein unabhängig von dem Ausgangsoxidationszustand des Plutoniums in Lösung stattgefunden hat. Durch die Kombination der ortsaufgelösten Methoden wurde erstmalig mittels μ-XRF die Verteilung von Pu und anderen in OPA enthaltenen Elementen bestimmt. µ-XANES-Spektren an Pu-Anreicherungen auf OPA-Dünnschliffen und in Diffusionsproben bestätigen, dass das weniger mobile Pu(IV) die dominierende Spezies nach den Sorptions- und Diffusionsprozessen ist. Darüber hinaus wurde zum ersten Mal ein Diffusionsprofil von Pu in OPA mittels µ-XRF gemessen. Die Speziationsuntersuchungen mittels μ-XANES zeigten, dass das eingesetzte Pu(V) entlang seines Diffusionspfades zunehmend zu Pu(IV) reduziert wird. Mit µ-XRD wurde Illit als dominierende Umgebung, in der Pu angereichert wurde, identifiziert und Siderit als eine redoxaktive Phase auftreten kann. Die Ergebnisse dieser Arbeit zeigen, dass die Sicherheit von OPA als Wirtsgestein eines Endlagers hoch-radioaktiver Abfälle positiv zu bewerten ist. rn

Complexes of polyelectrolytes with defined charge distance and different dendrimer counterions

Complexes of polyelectrolytes with defined charge distance and different dendrimer counterions Magdalena Chelmecka Max Planck Institute for Polymer Research; Ackermannweg 10; D-55128 Mainz ; Tel.: (+49) 06131- 379 – 226 A study of complexes in solution is of interest to investigate whether the formation of well-defined assemblies like in classical surfactant systems is possible. Aim of this thesis is to investigate the electrostatic self-assembly of linear polycations of varying charge distance with “large” counterions of varying architecture. We especially investigate the morphology of objects formed, but also their stability under salt free condition and after low molecular mass salt addition. As polycations, Poly(dialkylimino)-alkylene salts (Ionenes) I65MeBr and I25MeBr were chosen. Ionenes are synthesized via Menschutkin reaction and characterized by standard methods. Counterions are Polyamidoamine (PAMAM) dendrimers of generations G2.5, G5.5, G7.5 with -COONa surface groups and shape-persistent, Polyphenylene dendrimers of generation G1 with surface -COOH groups. A complex interplay of interactions is expected to direct the self assembly via electrostatic interaction, geometric factors, hydrophobic interaction or hydrogen bonds. Methods used for the investigation of complexes are: UV-spectroscopy, pH-metric techniques, dynamic and static light scattering, small angle neutron scattering,  potential measurements and potentiometric titration. Under certain conditions, (i.e. charge ratio of compounds, charge density of ionene and dendrimer also concentration of sample) polyelectrolyte systems composed of ionenes and dendrimers build complexes in solution. System compounds are typical polyelectrolytes, but structures which they build behave not usual for typical polyelectrolytes. In a one diffusion mode regime aggregates of about 100 nm hydrodynamic radius have been found. Such aggregates are core-shell or anisotropic core shell structures in the case of ionenes/PAMAM dendrimers complexes. These complexes are stable even at high ionic strength. In case of ionenes with poly(phenylene) dendrimers, hard sphere-like objects or spherical objects with hairy-like surface have been found in a one diffusion mode regime. Their stability at high ionic strength is lower. For the ionenes/poly(phenylene) dendrimers systems one transition point has been found from one to two diffusion processes, towards increasing ionene concentration, i.e. for the samples with fixed dendrimer concentration towards increasing ionic strength. For the diffusion profile of ionene/PAMAM dendrimers in most cases two transition regimes are observed. One at very low ionene concentration, the second one at high ionene concentrations, which again means for the samples with fixed dendrimer concentration, also at higher ionic strength. Both two mode regimes are separated by the one mode regime. As was confirmed experimentally, the one diffusion mode regime is caused by the motion of well defined assemblies. The two diffusion mode regimes are caused by the movement of different sized species in solution, large aggregates and middle-size aggregates (oligoaggregates). The location and also the number of transition points in the diffusion profiles is dependent on the ionene to dendrimer charge ratio, charge density of the compounds and concentration. No influence of the molecular mass of the ionene has been found. The aggregates are found to be charged on the surface, however this surface charge does not significantly influence the diffusion properties of the system.

An investigation into complex inorganic materials with Mössbauer spectroscopy

Mössbauer Spektroskopie ist ein unverzichtbares Instrument für die Bestimmung von Oxidationszuständen und für die Analyse von lokalen Ordnungsphänomenen von Mössbauer aktiven Atomen. Weil es sich um eine lokale Methode handelt können sowohl kristalline als auch amorphe Materialien untersucht werden. Die Kombination von lokaler Prüfung mit Mössbauer Spektroskopie und globaler Untersuchung z.B. mit Röntgendiffraktometrie ermöglicht die Studie von Ordnungseffekten von statistisch besetzten Positionen in einer geordneten Matrix. Das wurde hier eingesetzt um die lokale Umgebung in zwei Serien von Heuslerverbindungen, Co2-xFe1+xSi and Co2Mn1-xFexAl zu untersuchen. Für die Co2Mn1-xFexAl Serie wurde eine L21 geordnete Phase in einer insgesamt B2 geordneten Probe detektiert. Ein Wechsel von der AlCu2Mn zu der CuHg2Ti Struktur wurde für die Co2-xFe1+xSi Proben gefunden. Die Transformation von einem Glas zu einem keramischen Material wurde mit 119Sn Mössbauer Spektroskopie untersucht. Die höhere Ordnung in der Keramik wurde von einer kleiner werdenden Mössbauerlinienbreite begleitet. Demzufolge geben die Modifikationen der Sn Umgebungen klar die Transformation des gesamten Materials wieder. Ist die lokale Umgebung von unregelmäßig auftretenden Atomen in einer amorphen Matrix von Interesse, sind lokal prüfende Methoden die zuverlässigsten Methoden die zur Verfügung stehen. In dieser Arbeit wurde 119Sn Mössbauer Spektroskopie eingesetzt um die Oxidationszustände, die lokalen Umgebungen und relativen Intensitäten von Zinn Atomen in einer Silikatmatrix zu bestimmen. Modifikationen dieser Parameter als Funktion von Prozess bestimmenden Parametern wie der Sauerstoffpartialdruck, die Temperatur, die Behandlungsdauer und der Abkühlprozess genauso wie der SnO2 Gehalt sind von Interesse, weil durch Reduktions- und Diffusionsprozesse Änderungen des Koordinations- und des Oxidationszustands der Zinnatome auftreten. Da diese Änderungen in der Glasmatrix verursachen, die das fertige Produkt im industriellen Fertigungsprozess ruinieren können sind diese feinen Veränderungen sehr wichtig. Wenigstens zwei Mössbauerlinien korrespondierend mit zwei verschiedenen Umgebungen für Sn2+ und Sn4+ sind für eine Analyse mit ausreichender Qualität notwendig. Durch Vergleich von den bestimmten Hyperfein Parametern mit den Parametern von Modelsubstanzen werden lokale Umgebungen der Zinnatome entworfen. Für Sn2+ werden zwei auf einer trigonalen Pyramide basierende Umgebungen mit variierender Anzahl von bindenden und nicht-bindenden Sauerstoffatomen formuliert. Für Sn4+ wurde eine tetraedrische und eine oktaedrische Umgebung postuliert. Die relativen Intensitäten der vier Mössbauerlinien wurden um ein Diffusions- und Reaktionsmodell zu entwickeln und um einen Satz von Diffusions- und Transferkoeffizienten zu bestimmen eingesetzt. Die bestimmten Diffusionskoeffizienten stimmen mit den Literaturdaten überein. Der Massentransferkoeffizient ist kleiner als der bestimmte Wert, aber immer noch in der gleichen Größenordnung. Im Gegensatz zu den Erwartungen ist der präsentierte Diffusionskoeffizient für Sn4+ bestimmt als der von Sn2+. Das wiederum kann durch Berücksichtigung von Elektronhoppingprozessen erklärt werden.

Computer simulations of two-dimensional colloidal crystals under confinement and shear

In this thesis we are presenting a broadly based computer simulation study of two-dimensional colloidal crystals under different external conditions. In order to fully understand the phenomena which occur when the system is being compressed or when the walls are being sheared, it proved necessary to study also the basic motion of the particles and the diffusion processes which occur in the case without these external forces. In the first part of this thesis we investigate the structural transition in the number of rows which occurs when the crystal is being compressed by placing the structured walls closer together. Previous attempts to locate this transition were impeded by huge hysteresis effects. We were able to determine the transition point with higher precision by applying both the Schmid-Schilling thermodynamic integration method and the phase switch Monte Carlo method in order to determine the free energies. These simulations showed not only that the phase switch method can successfully be applied to systems with a few thousand particles and a soft crystalline structure with a superimposed pattern of defects, but also that this method is way more efficient than a thermodynamic integration when free energy differences are to be calculated. Additionally, the phase switch method enabled us to distinguish between several energetically very similar structures and to determine which one of them was actually stable. Another aspect considered in the first result chapter of this thesis is the ensemble inequivalence which can be observed when the structural transition is studied in the NpT and in the NVT ensemble. The second part of this work deals with the basic motion occurring in colloidal crystals confined by structured walls. Several cases are compared where the walls are placed in different positions, thereby introducing an incommensurability into the crystalline structure. Also the movement of the solitons, which are created in the course of the structural transition, is investigated. Furthermore, we will present results showing that not only the well-known mechanism of vacancies and interstitial particles leads to diffusion in our model system, but that also cooperative ring rotation phenomena occur. In this part and the following we applied Langevin dynamics simulations. In the last chapter of this work we will present results on the effect of shear on the colloidal crystal. The shear was implemented by moving the walls with constant velocity. We have observed shear banding and, depending on the shear velocity, that the inner part of the crystal breaks into several domains with different orientations. At very high shear velocities holes are created in the structure, which originate close to the walls, but also diffuse into the inner part of the crystal.

Tropfenbasierte Multiphasen – Mikroreaktionstechnologie in organisch-chemischer Synthese

In der vorliegenden Doktorarbeit werden neue, mikrofluidische Verfahren, zur Durchführung chemischer Reaktionen in mehrphasigen Systemen präsentiert. rnDas Einschließen von Reaktionspartnern in einzelne Segmente, deren Volumina im Bereich von Mikro- bis Femtoliter liegen und die dadurch erzeugten enormen, spezifischen Oberflächen, ermöglichen Massentransportprozesse über die Phasengrenzfläche zwischen einzelnen Segmenten, drastisch zu intensivieren. Aufgrund geringer räumlicher Ausdehnungen einzelner Kompartimente und durch vorherrschende, zirkulierende Strömungen in den einzelnen Abschnitten, sind Diffusions- und Konvektionsprozesse in diesen rasch, sodass an der Grenzfläche gebildete, reaktive Intermediate in sehr kurzen Zeitintervallen umgesetzt werden können. rnrn

Diffusion of laser polarized gases in MRI

The use of Magnetic Resonance Imaging (MRI) as a diagnostic tool is increasingly employing functional contrast agents to study or contrast entire mechanisms. Contrast agents in MRI can be classified in two categories. One type of contrast agents alters the NMR signal of the protons in its surrounding, e.g. lowers the T1 relaxation time. The other type enhances the Nuclear Magnetic Resonance (NMR) signal of specific nuclei. For hyperpolarized gases the NMR signal is improved up to several orders of magnitude. However, gases have a high diffusivity which strongly influences the NMR signal strength, hence the resolution and appearance of the images. The most interesting question in spatially resolved experiments is of course the achievable resolution and contrast by controlling the diffusivity of the gas. The influence of such diffusive processes scales with the diffusion coefficient, the strength of the magnetic field gradients and the timings used in the experiment. Diffusion may not only limit the MRI resolution, but also distort the line shape of MR images for samples, which contain boundaries or diffusion barriers within the sampled space. In addition, due to the large polarization in gaseous 3He and 129Xe, spin diffusion (different from particle diffusion) could play a role in MRI experiments. It is demonstrated that for low temperatures some corrections to the NMR measured diffusion coefficient have to be done, which depend on quantum exchange effects for indistinguishable particles. Physically, if these effects can not change the spin current, they can do it indirectly by modifying the velocity distribution of the different spin states separately, so that the subsequent collisions between atoms and therefore the diffusion coefficient can eventually be affected. A detailed study of the hyperpolarized gas diffusion coefficient is presented, demonstrating the absence of spin diffusion (different from particle diffusion) influence in MRI at clinical conditions. A novel procedure is proposed to control the diffusion coefficient of gases in MRI by admixture of inert buffer gases. The experimental measured diffusion agrees with theoretical simulations. Therefore, the molecular mass and concentration enter as additional parameters into the equations that describe structural contrast. This allows for setting a structural threshold up to which structures contribute to the image. For MRI of the lung this allows for images of very small structural elements (alveoli) only, or in the other extreme, all airways can be displayed with minimal signal loss due to diffusion.

Ergodicity and regularity of invariant measure for branching Markov processes with immigration

In this thesis we consider systems of finitely many particles moving on paths given by a strong Markov process and undergoing branching and reproduction at random times. The branching rate of a particle, its number of offspring and their spatial distribution are allowed to depend on the particle's position and possibly on the configuration of coexisting particles. In addition there is immigration of new particles, with the rate of immigration and the distribution of immigrants possibly depending on the configuration of pre-existing particles as well. In the first two chapters of this work, we concentrate on the case that the joint motion of particles is governed by a diffusion with interacting components. The resulting process of particle configurations was studied by E. Löcherbach (2002, 2004) and is known as a branching diffusion with immigration (BDI). Chapter 1 contains a detailed introduction of the basic model assumptions, in particular an assumption of ergodicity which guarantees that the BDI process is positive Harris recurrent with finite invariant measure on the configuration space. This object and a closely related quantity, namely the invariant occupation measure on the single-particle space, are investigated in Chapter 2 where we study the problem of the existence of Lebesgue-densities with nice regularity properties. For example, it turns out that the existence of a continuous density for the invariant measure depends on the mechanism by which newborn particles are distributed in space, namely whether branching particles reproduce at their death position or their offspring are distributed according to an absolutely continuous transition kernel. In Chapter 3, we assume that the quantities defining the model depend only on the spatial position but not on the configuration of coexisting particles. In this framework (which was considered by Höpfner and Löcherbach (2005) in the special case that branching particles reproduce at their death position), the particle motions are independent, and we can allow for more general Markov processes instead of diffusions. The resulting configuration process is a branching Markov process in the sense introduced by Ikeda, Nagasawa and Watanabe (1968), complemented by an immigration mechanism. Generalizing results obtained by Höpfner and Löcherbach (2005), we give sufficient conditions for ergodicity in the sense of positive recurrence of the configuration process and finiteness of the invariant occupation measure in the case of general particle motions and offspring distributions.

Plasmonic nanoparticles as sensors : a novel approach to quantify adsorption and diffusion kinetics

Biosensors find wide application in clinical diagnostics, bioprocess control and environmental monitoring. They should not only show high specificity and reproducibility but also a high sensitivity and stability of the signal. Therefore, I introduce a novel sensor technology based on plasmonic nanoparticles which overcomes both of these limitations. Plasmonic nanoparticles exhibit strong absorption and scattering in the visible and near-infrared spectral range. The plasmon resonance, the collective coherent oscillation mode of the conduction band electrons against the positively charged ionic lattice, is sensitive to the local environment of the particle. I monitor these changes in the resonance wavelength by a new dark-field spectroscopy technique. Due to a strong light source and a highly sensitive detector a temporal resolution in the microsecond regime is possible in combination with a high spectral stability. This opens a window to investigate dynamics on the molecular level and to gain knowledge about fundamental biological processes.rnFirst, I investigate adsorption at the non-equilibrium as well as at the equilibrium state. I show the temporal evolution of single adsorption events of fibrinogen on the surface of the sensor on a millisecond timescale. Fibrinogen is a blood plasma protein with a unique shape that plays a central role in blood coagulation and is always involved in cell-biomaterial interactions. Further, I monitor equilibrium coverage fluctuations of sodium dodecyl sulfate and demonstrate a new approach to quantify the characteristic rate constants which is independent of mass transfer interference and long term drifts of the measured signal. This method has been investigated theoretically by Monte-Carlo simulations but so far there has been no sensor technology with a sufficient signal-to-noise ratio.rnSecond, I apply plasmonic nanoparticles as sensors for the determination of diffusion coefficients. Thereby, the sensing volume of a single, immobilized nanorod is used as detection volume. When a diffusing particle enters the detection volume a shift in the resonance wavelength is introduced. As no labeling of the analyte is necessary the hydrodynamic radius and thus the diffusion properties are not altered and can be studied in their natural form. In comparison to the conventional Fluorescence Correlation Spectroscopy technique a volume reduction by a factor of 5000-10000 is reached.