Multiple sulfur isotope fractionations in inorganic aqueous systems

New constraints on isotope fractionation factors in inorganic aqueous sulfur systems based on theoretical and experimental techniques relevant to studies of the sulfur cycle in modern environments and the geologic rock record are presented in this dissertation. These include theoretical estimations of equilibrium isotope fractionation factors utilizing quantum mechanical software and a water cluster model approach for aqueous sulfur compounds that span the entire range of oxidation state for sulfur. These theoretical calculations generally reproduce the available experimental determinations from the literature and provide new constraints where no others are available. These theoretical calculations illustrate in detail the relationship between sulfur bonding environment and the mass dependence associated with equilibrium isotope exchange reactions involving all four isotopes of sulfur. I additionally highlight the effect of isomers of protonated compounds (compounds with the same chemical formula but different structure, where protons are bound to either sulfur or oxygen atoms) on isotope partitioning in the sulfite (S4+) and sulfoxylate (S2+) systems, both of which are key intermediates in oxidation-reduction processes in the sulfur cycle. I demonstrate that isomers containing the highest degree of coordination around sulfur (where protonation occurs on the sulfur atom) have a strong influence on isotopic fractionation factors, and argue that isomerization phenomenon should be considered in models of the sulfur cycle. Additionally, experimental results of the reaction rates and isotope fractionations associated with the chemical oxidation of aqueous sulfide are presented. Sulfide oxidation is a major process in the global sulfur cycle due largely to the sulfide-producing activity of anaerobic microorganisms in organic-rich marine sediments. These experiments reveal relationships between isotope fractionations and reaction rate as a function of both temperature and trace metal (ferrous iron) catalysis that I interpret in the context of the complex mechanism of sulfide oxidation. I also demonstrate that sulfide oxidation is a process associated with a mass dependence that can be described as not conforming to the mass dependence typically associated with equilibrium isotope exchange. This observation has implications for the inclusion of oxidative processes in environmental- and global-scale models of the sulfur cycle based on the mass balance of all four isotopes of sulfur. The contents of this dissertation provide key reference information on isotopic fractionation factors in aqueous sulfur systems that will have far-reaching applicability to studies of the sulfur cycle in a wide variety of natural settings.

Mechanical and Electrical Properties of Single-walled Carbon Nanotubes Synthesized by Chemical Vapor Deposition

Despite the tremendous application potentials of carbon nanotubes (CNTs) proposed by researchers in the last two decades, efficient experimental techniques and methods are still in need for controllable production of CNTs in large scale, and for conclusive characterizations of their properties in order to apply CNTs in high accuracy engineering. In this dissertation, horizontally well-aligned high quality single-walled carbon nanotubes (SWCNTs) have been successfully synthesized on St-cut quartz substrate by chemical vapor deposition (CVD). Effective radial moduli (Eradial) of these straight SWCNTs have been measured by using well-calibrated tapping mode and contact mode atomic force microscopy (AFM). It was found that the measured Eradial decreased from 57 to 9 GPa as the diameter of the SWCNTs increased from 0.92 to 1.91 nm. The experimental results were consistent with the recently reported theoretical simulation data. The method used in this mechanical property test can be easily applied to measure the mechanical properties of other low-dimension nanostructures, such as nanowires and nanodots. The characterized sample is also an ideal platform for electrochemical tests. The electrochemical activities of redox probes Fe(CN)63-/4-, Ru(NH3)63+, Ru(bpy)32+ and protein cytochrome c have been studied on these pristine thin films by using aligned SWCNTs as working electrodes. A simple and high performance electrochemical sensor was fabricated. Flow sensing capability of the device has been tested for detecting neurotransmitter dopamine at physiological conditions with the presence of Bovine serum albumin. Good sensitivity, fast response, high stability and anti-fouling capability were observed. Therefore, the fabricated sensor showed great potential for sensing applications in complicated solution.

A multi-methodological approach for the study of polymorphism in organic pigments and pharmaceuticals

The study of polymorphism has an important role in several fields of materials science, because structural differences lead to different physico-chemical properties of the system. This PhD work was dedicated to the investigation of polymorphism in Indigo, Thioindigo and Quinacridone, as case studies among the organic pigments employed as semiconductors, and in Paracetamol, Phenytoin and Nabumetone, chosen among some commonly used API. The aim of the research was to improve the understanding on the structures of bulk crystals and thin films, adopting Raman spectroscopy as the method of choice, while resorting to other experimental techniques to complement the gathered information. Different crystalline polymorphs, in fact, may be conveniently distinguished by their Raman spectra in the region of the lattice phonons (10-150 cm-1), the frequencies of which, probing the inter-molecular interactions, are very sensitive to even slight modifications in the molecular packing. In particular, we have used Confocal Raman Microscopy, which is a powerful, yet simple, technique for the investigation of crystal polymorphism in organic and inorganic materials, being capable of monitoring physical modifications, chemical transformations and phase inhomogeneities in crystal domains at the micrometre scale. In this way, we have investigated bulk crystals and thin film samples obtained with a variety of crystal growth and deposition techniques. Pure polymorphs and samples with phase mixing were found and fully characterized. Raman spectroscopy was complemented mainly by XRD measurements for bulk crystals and by AFM, GIXD and TEM for thin films. Structures and phonons of the investigated polymorphs were computed by DFT methods, and the comparison between theoretical and experimental results was used to assess the relative stability of the polymorphs and to assist the spectroscopic investigation. The Raman measurements were thus found to be able to clarify ambiguities in the phase assignments which otherwise the other methods were unable to solve.

Aging assessment of polyethylene-based insulated low-voltage cables for nuclear applications

This thesis aims at investigating the evolution of physico-chemical and electrical properties relevant to low-voltage power cables for nuclear application when subjected to typical nuclear power plant (NPP) environments i.e., to gamma radiation and high temperature. This research is part of the European Project Horizon 2020 TeaM Cables, which aims at providing a novel methodology for efficient and reliable NPP cable aging management to NPP operators. The analyzed samples consist of both coaxial and twisted pair cables with different polymeric compounds used as primary insulation. Insulating materials are based on the same silane cross-linked polyethylene matrix with different additives and fillers. In order to characterize the material response to the environmental stresses, various experimental techniques have been used. These characterizations range from the microscale chemical response e.g. by FTIR, OIT and DSC, to the macroscale electrical and mechanical behavior. A significant part of this Thesis is given to the correlation of the response to aging among the different measured properties. It has been shown that it could be possible to connect both the chemical and mechanical properties of the investigated XLPE cables with the electrical ones. In particular, the high-frequency dielectric response allows an effective monitoring of both the early periods of aging, controlled by the antioxidant consumption kinetics, and then the subsequent oxidation of the polymer matrix. Therefore, dielectric spectroscopy showed to be capable of assessing the LV cable aging state and, it might be used as an aging marker for cable diagnostic. The last part of the manuscript focuses on the building of a predictive modelling approach of LV cable conditions subjected to radio-chemical aging. It resulted into obtaining a lifetime curve which relates the aging factor to which the cable is subjected to, namely the dose rate, with the limit value of the considered electrical property (tanδ).

Synthesis, characterization and conformational studies of bis-phenothiazine-aryl-boranes

This thesis project presents a work based on the study of a particular class of amino-boranes, called bis-phenothiazine-aryl-boranes. The peculiarity of these compounds is the N-B-N chemical moiety and their complex conformational behaviour, due to the combination of steric hindrance and conjugation of the B-N bond. Our work is focused on two main products with different symmetry: bis-phenothiazine-2-methylnaphthyl-borane (2b) and bis-phenothiazine-anthracenyl-borane (2c). We firstly focused our attention on an effective way of synthesis, by optimizing both reaction conditions and purification. The products and co-products of interest were then characterized with NMR, mass spectroscopy and X-Ray diffraction on single crystals. The products were eventually analysed through conformational studies, by experimental techniques, such as dynamic NMR and EXSY, and by a theorical approach with DFT calculations.

Synthesis and characterization of fluorescent atropoisomeric bis-arylboryl-carbazoles

This thesis project presents a work based on the study of bis-arylboryl-carbazoles a particular class of aminoboranes. The peculiarity of these compounds is the -B=N+ chemical moiety and their conformational behaviour coming from the combination of steric constrain and conjugation of the B-N bond. Our work is focused on three products: 9-(mesityl(naphthalen-1-yl)boraneyl)-9H-carbazole 1a, 9-(mesityl(2-methylnaphthalen-1-yl)boraneyl)-9H-carbazole 1b and 9-(anthracen-9-yl(mesityl)boraneyl)-9H-carbazole 1c. We firstly focused our attention on the synthesis optimizing conditions. Then the products were synthetized and characterized with NMR. The products were eventually analysed through conformational studies, by a theoretical approach with DFT calculations and by experimental techniques, such as standard kinetic and EXSY. In the end of this work the products were characterized through fluorescence studies both by DFT, TD-DFT calculations and experimentally by emission spectroscopy.

Nanomechanical characterization of soft bioelectronic interfaces via modeling-informed atomic force microscopy

The field of bioelectronics involves the use of electrodes to exchange electrical signals with biological systems for diagnostic and therapeutic purposes in biomedical devices and healthcare applications. However, the mechanical compatibility of implantable devices with the human body has been a challenge, particularly with long-term implantation into target organs. Current rigid bioelectronics can trigger inflammatory responses and cause unstable device functions due to the mechanical mismatch with the surrounding soft tissue. Recent advances in flexible and stretchable electronics have shown promise in making bioelectronic interfaces more biocompatible. To fully achieve this goal, material science and engineering of soft electronic devices must be combined with quantitative characterization and modeling tools to understand the mechanical issues at the interface between electronic technology and biological tissue. Local mechanical characterization is crucial to understand the activation of failure mechanisms and optimizing the devices. Experimental techniques for testing mechanical properties at the nanoscale are emerging, and the Atomic Force Microscope (AFM) is a good candidate for in situ local mechanical characterization of soft bioelectronic interfaces. In this work, in situ experimental techniques with solely AFM supported by interpretive models for the characterization of planar and three-dimensional devices suitable for in vivo and in vitro biomedical experimentations are reported. The combination of the proposed models and experimental techniques provides access to the local mechanical properties of soft bioelectronic interfaces. The study investigates the nanomechanics of hard thin gold films on soft polymeric substrates (Poly(dimethylsiloxane) PDMS) and 3D inkjet-printed micropillars under different deformation states. The proposed characterization methods provide a rapid and precise determination of mechanical properties, thus giving the possibility to parametrize the microfabrication steps and investigate their impact on the final device.

Characterization Of Single Use Reactor Used For The Manufacturing Of Formulated Products Within The Pharmaceutical Industry

Mixing is a fundamental unit operation in the pharmaceutical industry to ensure consistent product quality across different batches. It is usually carried out in mechanically stirred tanks, with a large variety of designs according to the process requirements. A key aspect of pharmaceutical manufacturing is the extensive and meticulous cleaning of the vessels between runs to prevent the risk of contamination. Single-use reactors represent an increasing trend in the industry since they do not require cleaning and sterilization, reducing the need for utilities such as steam to sterilize equipment and the time between production batches. In contrast to traditional stainless steel vessels, single-use reactors consist of a plastic bag used as a vessel and disposed of after use. This thesis aims to characterize the fluid dynamics features and the mixing performance of a commercially available single-use reactor. The characterization employs a combination of various experimental techniques. The analysis starts with the visual observation of the liquid behavior inside the vessel, focusing on the vortex shape evolution at different impeller speeds. The power consumption is then measured using a torque meter to quantify the power number. Particle Image Velocimetry (PIV) is employed to investigate local fluid dynamics properties such as mean flow field and mean and rms velocity profiles. The same experimental setup of PIV is exploited for another optical measurement technique, the Planar Laser-Induced Fluorescence (PLIF). The PLIF measurements complete the characterization of the reactor with the qualitative visualization of the turbulent flow and the quantitative assessment of the system performance through the mixing time. The results confirm good mixing performances for the single-use reactor over the investigated impeller speeds and reveal that the filling volume plays a significant role in the fluid dynamics of the system.

Experimental analysis of optimization techniques on the road passenger transportation problem

Analyzing the state of the art in a given field in order to tackle a new problem is always a mandatory task. Literature provides surveys based on summaries of previous studies, which are often based on theoretical descriptions of the methods. An engineer, however, requires some evidence from experimental evaluations in order to make the appropriate decision when selecting a technique for a problem. This is what we have done in this paper: experimentally analyzed a set of representative state-of-the-art techniques in the problem we are dealing with, namely, the road passenger transportation problem. This is an optimization problem in which drivers should be assigned to transport services, fulfilling some constraints and minimizing some function cost. The experimental results have provided us with good knowledge of the properties of several methods, such as modeling expressiveness, anytime behavior, computational time, memory requirements, parameters, and free downloadable tools. Based on our experience, we are able to choose a technique to solve our problem. We hope that this analysis is also helpful for other engineers facing a similar problem

Experimental assessment of environmental decay effects in masonry via non destructive diagnostic techniques and mechanical tests

Environmental decay in porous masonry materials, such as brick and mortar, is a widespread problem concerning both new and historic masonry structures. The decay mechanisms are quite complex dependng upon several interconnected parameters and from the interaction with the specific micro-climate. Materials undergo aesthetical and substantial changes in character but while many studies have been carried out, the mechanical aspect has been largely understudied while it bears true importance from the structural viewpoint. A quantitative assessment of the masonry material degradation and how it affects the load-bearing capacity of masonry structures appears missing. The research work carried out, limiting the attention to brick masonry addresses this issue through an experimental laboratory approach via different integrated testing procedures, both non-destructive and mechanical, together with monitoring methods. Attention was focused on transport of moisture and salts and on the damaging effects caused by the crystallization of two different salts, sodium chloride and sodium sulphate. Many series of masonry specimens, very different in size and purposes were used to track the damage process since its beginning and to monitor its evolution over a number of years Athe same time suitable testing techniques, non-destructive, mini-invasive, analytical, of monitoring, were validated for these purposes. The specimens were exposed to different aggressive agents (in terms of type of salt, of brine concentration, of artificial vs. open-air natural ageing, …), tested by different means (qualitative vs. quantitative, non destructive vs. mechanical testing, punctual vs. wide areas, …), and had different size (1-, 2-, 3-header thick walls, full-scale walls vs. small size specimens, brick columns and triplets vs. small walls, masonry specimens vs. single units of brick and mortar prisms, …). Different advanced testing methods and novel monitoring techniques were applied in an integrated holistic approach, for quantitative assessment of masonry health state.

Experimental characterization of cement–bentonite interaction using core infiltration techniques and 4D computed tomography

Deep geological storage of radioactive waste foresees cementitious materials as reinforcement of tunnels and as backfill. Bentonite is proposed to enclose spent fuel drums, and as drift seals. The emplacement of cementitious material next to clay material generates an enormous chemical gradient in pore water composition that drives diffusive solute transport. Laboratory studies and reactive transport modeling predict significant mineral alteration at and near interfaces, mainly resulting in a decrease of porosity in bentonite. The goal of this project is to characterize and quantify the cement/bentonite skin effects spatially and temporally in laboratory experiments. A newly developed mobile X-ray transparent core infiltration device was used, which allows performing X-ray computed tomography (CT) periodically without interrupting a running experiment. A pre-saturated cylindrical MX-80 bentonite sample (1920 kg/m3 average wet density) is subjected to a confining pressure as a constant total pressure boundary condition. The infiltration of a hyperalkaline (pH 13.4), artificial OPC (ordinary Portland cement) pore water into the bentonite plug alters the mineral assemblage over time as an advancing reaction front. The related changes in X-ray attenuation values are related to changes in phase densities, porosity and local bulk density and are tracked over time periodically by non-destructive CT scans.