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Aus dem Streubild der Kleinwinkelstreuung kann im Allgemeinen, die die Streuvertei-lung erzeugende Struktur nicht eindeutig rekonstruiert werden. Die Ursache dafür wird erörtert und die damit verbundenen Einschränkungen bei der rechnerischen Auswertung der Streukurven an Beispielen veranschaulicht. Dies geschieht an Streukurven, die mit bekannten Größenverteilungen berechnet wurden. Weiterhin wird untersucht, welche Fit- Ansätze sich zur Auswertung der Kleinwinkelstreuexperimente am besten eignen. Als Fit- Ansätze wurden Reihenentwicklungen nach Trigonometrischen- und Polynomfunkti-onen und eine theoretisch motivierte Funktion verwendet. Neben dem entscheidenden Vergleich mit der Streukurve der Ausgangsfunktion werden die Ergebnisse auch den Rechnungen gegenübergestellt, die mit der weit verbreiteten Glatter- Methode erzielt werden.

This work is the result of two separate lines of study into the family of frustrated rare-earth pyrochlores with ferromagnetic interactions. The first is an examination of Yb2Ti2O7 and Ho2Ti2O7 through small angle neutron scattering (SANS) techniques. The sensitivity to anisotropic ferromagnetic correlations of SANS makes it an ideal tool to investigate the anomalous scattering of Yb2Ti2O7 , and to take a closer look into the low Q region of the spin ice Ho2Ti2O7 , where long range dipolar effects modify magnetic scattering. We show that in Yb2Ti2O7 the ferromagnetic order observed by other researchers coexists with short range HHH correlations to 0.03 K. We identify a new feature in Yb2Ti2O7 , a medium range (on the order of 100 ̊A) ferromagnetic correlation which appears to correlate well with the systems heat capacity anomaly. In Ho2Ti2O7 , we observe isotropic magnetic scattering in the low Q region that correlates to the system heat capacity anomaly. The second research project involves the system Ho2Sn2−xTixO7 with x=0,0.5,1,1.5,2. We use SQUID magnetometry and inelastic neutron scattering to examine the effects of B-site disorder on the spin ice system. We find some discrepancies with previous generation instrument results for the crystal electric field (CEF) Hamiltonian, and find results consistent with our previously hypothesized picture of the effects of B-site disorder on the CEF levels. We also observe increased spin dynamics in the disordered compounds, which is consistent with recent theory work predicting a transition to a quantum spin liquid phase in disordered non-kramers spin ice compounds. / Thesis / Master of Science (MSc)

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Dealloying is a corrosion process in which one or more elements are selectively removed from an alloy leading to a 3-dimensional porous structure of the more noble element(s). These porous structures have been known to cause stress corrosion cracking in noble metal alloy systems but more recent interest in using the corrosion process to produce porous metals has developed. Applications for these structures range from high surface area electrodes for biomedical sensors to use as skeletal structures for fundamental studies (e.g. low temperature heat exchangers or sensitivity of surface diffusivity to chemical environment). In this work we will review our current understanding of alloy corrosion including our most recent results demonstrating a more accurate method for calculating alloy critical potential based on potential hold experiments. The critical potentials calculated through the potential hold method were â 0.030VMSE, 0.110VMSE, and 0.175VMSE for Cu80Pt20, Cu75Pt25 Cu71Pt29 respectively. We will present the use of porous metals for making surface diffusivity measurements in the Pt systems as a function of chemical environment. A review of the use of small angle neutron scattering to make accurate measurements of pore size is presented and the sensitivity of pore size to electrolyte, electrolyte composition, applied potential and temperature will be explained. The production of porous Pt with pore sizes ranging from 2-200nm is demonstrated. / Ph. D.

Recent efforts toward the commercialization of hydrogen fuel cells, a sustainable energy technology, have led to interest in the effects of industrial processing parameters on the morphology and properties of fuel cell ionomers. The ionomer functions as a solid electrolyte membrane on the order of microns thick and as a thin film on the order of tens of nanometers in the catalyst layer. Industrial manufacture of the membrane and catalyst layer is typically a roll-to-roll process that involves casting a colloidal dispersion of the fuel cell ionomer in predominantly mixed alcohol/water solvent systems onto a backing film or substrate, followed by evaporation of the solvent and annealing of the ionomer at elevated temperatures. The current benchmark fuel cell ionomers are a class of polymers with pendant perfluorinated side chains terminating in sulfonic acid groups, called perflurosulfonic acid ionomers (PFSAs). The purpose of this dissertation is to investigate the effects of industrial processing parameters such as dispersion solvent composition, solvent evaporation temperature, and annealing temperature on fuel cell-relevant properties of PFSA solid electrolyte membranes and model thin films. Particular focus is given to newer-generation PFSAs and the effect of their different chemical structures on the morphology and properties of dispersions, membranes, and thin films. Dipole-dipole interactions between colloidal aggregates modulated by solvent composition were found to significantly influence the viscosity of PFSA dispersions. A framework of PFSA-solvent interactions is developed to predict the onset of dipole-dipole interactions as a function of PFSA chemical structure and solvent composition. Increased steric hindrance of shorter PFSA side chain chemical structures is found to inhibit morphological development, resulting in membranes with poorer wet and dry mechanical properties. A shorter side-chain PFSA is suggested to require higher processing temperatures to achieve performance equivalent to a PFSA with slightly longer side chain. The morphology and properties of model PFSA thin films are demonstrated to decay to quasi-equilibrium values upon physical aging at both low and high relative humidity (RH). Thin film swelling curves are demonstrated to be superposable by implementing an aging time-RH shift factor, allowing for prediction of quasi-equilibration times under given fuel cell operating conditions. / Doctor of Philosophy / Interest in environmentally friendly, sustainable energy sources has led to significant industrial, academic, and governmental efforts to commercialize hydrogen fuel cells. Hydrogen gas is split into protons and electrons in the anode catalyst layer. The electrons flow through an external circuit to produce electricity, while the protons are transported from the catalyst layer through a solid electrolyte membrane to the anode to react with oxygen to form water. A key component of hydrogen fuel cells is an ion-containing polymer called an ionomer that is required for the transport of (1) protons in the solid electrolyte membrane and (2) protons and reactant gases in the catalyst layer. The solid electrolyte membrane and catalyst layer can be industrially produced by a continuous process that involves dispersing the ionomer in a mixed alcohol/water solvent and coating it onto a backing film, followed by evaporation of the solvent and annealing of the ionomer. The present work is an investigation of the effect of industrially-relevant processing parameters on the morphology and properties of a class of ionomers called perfluorosulfonic acid ionomers (PFSAs), which phase separate into hydrophilic domains that serve as transport pathways and hydrophobic domains that impart thermomechanical stability. Practical aspects of the processing and function of PFSAs, including viscosity of the PFSA dispersion, minimum processing temperature to achieve solvent stability, and physical aging of the PFSA during fuel cell operation are shown to be fundamentally related to the PFSA chemical structure and morphology.

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Indiana University-Purdue University Indianapolis (IUPUI) / Large protein molecules are abundant in biological cells but are very difficult to study in physiological conditions due to molecular disorder. For large proteins, most structural information is obtained in crystalline states which can be achieved in certain conditions at very low temperature. X-ray and neutron crystallography methods can then be used for determination of crystalline structures at atomic level. However, in solution at room or physiological temperatures such highly resolved descriptions cannot be obtained except in very few cases. Scattering methods that can be used to study this type of structures at room temperature include small-angle x-ray and neutron scattering. These methods are used here to study two distinct proteins that are both classified as glycoproteins, which are a large class of proteins with diverse biological functions. In this study, two specific plasma glycoproteins were used: Fibrinogen (340 kDa) and Alpha 1-Antitrypsin or A1AT (52 kDa). These proteins have been chosen based on the fact that they have a propensity to form very large molecular aggregates due to their tendency to polymerize. One goal of this project is to show that for such complex structures, a combination of scattering methods that include SAXS, SANS, and DLS can address important structural and interaction questions despite the fact that atomic resolution cannot be obtained as in crystallography. A1AT protein has been shown to have protective roles of lung cells against emphysema, while fibrinogen is a major factor in the blood clotting process. A systematic approach to study these proteins interactions with lipid membranes and other proteins, using contrast-matching small-angle neutron scattering (SANS), small angle x-ray scattering (SAXS) and dynamic light scattering (DLS), is presented here. A series of structural reference points for each protein in solution were determined by performing measurements under osmotic stress controlled by the addition of polyethylene glycol-1,500 MW (PEG 1500) in the samples. Osmotic pressure changes the free energy of the molecular mixture and has consequences on the structure and the interaction of molecular aggregates. In particular, the measured radius of gyration (Rg) for A1AT shows a sharp structural transition when the concentration of PEG 1500 is between 33 wt% and 36 wt%. Similarly, a significant structural change was observed for fibrinogen when the concentration of PEG 1500 was above 40 wt%. This analysis is applied to a study of A1AT interacting with lipid membranes and to a study of fibrinogen polymerization in the presence of the enzyme thrombin, which catalyzes the formation of blood clots. The experimental approach presented here and the applications to specific questions show that an appropriate combination of scattering methods can produce useful information on the behavior and the interactions of large protein systems in physiological conditions despite the lower resolution compared to crystallography.