Flow Field–Flow Fractionation for size analysis and characterization of nanoparticles for applications in Life Sciences

Nanotechnologies are rapidly expanding because of the opportunities that the new materials offer in many areas such as the manufacturing industry, food production, processing and preservation, and in the pharmaceutical and cosmetic industry. Size distribution of the nanoparticles determines their properties and is a fundamental parameter that needs to be monitored from the small-scale synthesis up to the bulk production and quality control of nanotech products on the market. A consequence of the increasing number of applications of nanomaterial is that the EU regulatory authorities are introducing the obligation for companies that make use of nanomaterials to acquire analytical platforms for the assessment of the size parameters of the nanomaterials. In this work, Asymmetrical Flow Field-Flow Fractionation (AF4) and Hollow Fiber F4 (HF5), hyphenated with Multiangle Light Scattering (MALS) are presented as tools for a deep functional characterization of nanoparticles. In particular, it is demonstrated the applicability of AF4-MALS for the characterization of liposomes in a wide series of mediums. Afterwards the technique is used to explore the functional features of a liposomal drug vector in terms of its biological and physical interaction with blood serum components: a comprehensive approach to understand the behavior of lipid vesicles in terms of drug release and fusion/interaction with other biological species is described, together with weaknesses and strength of the method. Afterwards the size characterization, size stability, and conjugation of azidothymidine drug molecules with a new generation of metastable drug vectors, the Metal Organic Frameworks, is discussed. Lastly, it is shown the applicability of HF5-ICP-MS for the rapid screening of samples of relevant nanorisk: rather than a deep and comprehensive characterization it this time shown a quick and smart methodology that within few steps provides qualitative information on the content of metallic nanoparticles in tattoo ink samples.

Hydrogeochemical characterization of Seehausen territory - Bremen

The aim of this thesis is to provide a geochemical characterization of the Seehausen territory (a neighborhood) of Bremen, Germany. In this territory it is hosted a landfill of dredged sediments coming both from Bremerhaven (North See) and Bremen harbor (directly on the river Weser). For this reason this work has been focused also on possible impacts of the landfill on the groundwaters (shallow and deep aquifer). The Seehausen landfill uses the dewatering technique to manage the dredged sediments: incoming sediments are put into dewatering fields until they are completely dried (it takes almost a year). Then they are randomly sampled and analyzed: if the pollutants content is acceptable, sediments are treated with other materials and used instead of raw material for embankment, bricks, etc., otherwise they are disposed in the landfill. During this work it has been made a study of the natural geology and hydrogeology of the whole area of interest, especially because it is characterized by ancient natural salt deposits. Then, together with the Geological Survey of Bremen and the Harbor Authority of Bremen there have been identified all useful piezometers for a monitoring net around the landfill. During the sampling campaign there have been collected data of the principal anions and cations, physical parameters and stable water isotopes. Data analysis has been focused particularly on Cl, Na, SO4 and EC because these parameters might be helpful to attribute geochemical trends to the landfill or to a natural background. Furthermore dataloggers have been installed for a month in some piezometers and EC, pressure, dissolved oxygen and temperature data have been collected. Finally there has been made a deep comparison between current and historical data (1996 – 2011) and between old interpolation maps and current ones in order to see time trends of the aquifer geochemistry.

Magnetic spectroscopy and microscopy of functional materials

Heusler intermetallics Mn$_{2}Y$Ga and $X_{2}$MnGa ($X,Y$=Fe, Co, Ni) undergo tetragonal magnetostructural transitions that can result in half metallicity, magnetic shape memory, or the magnetocaloric effect. Understanding the magnetism and magnetic behavior in functional materials is often the most direct route to being able to optimize current materials and design future ones.rnrnSynchrotron soft x-ray magnetic spectromicroscopy techniques are well suited to explore the the competing effects from the magnetization and the lattice parameters in these materials as they provide detailed element-, valence-, and site-specific information on the coupling of crystallographic ordering and electronic structure as well as external parameters like temperature and pressure on the bonding and exchange.rnrnFundamental work preparing the model systems of spintronic, multiferroic, and energy-related compositions is presented for context. The methodology of synchrotron spectroscopy is presented and applied to not only magnetic characterization but also of developing a systematic screening method for future examples of materials exhibiting any of the above effects. rnrnChapters include an introduction to the concepts and materials under consideration (Chapter 1); an overview of sample preparation techniques and results, and the kinds of characterization methods employed (Chapter 2); spectro- and microscopic explorations of $X_2$MnGa/Ge (Chapter 3); spectroscopic investigations of the composition series Mn$_{2}Y$Ga to the logical Mn$_3$Ga endpoint (Chapter 4); and a summary and overview of upcoming work (Chapter 5). Appendices include the results of a “Think Tank” for the Graduate School of Excellence MAINZ (Appendix A) and details of an imaging project now in progress on magnetic reversal and domain wall observation in the classical Heusler material Co$_2$FeSi (Appendix B).

Silica-Supported Gold Nanoparticles: Synthesis, Characterization and Reactivity

The main aim of this work was the synthesis and applications of functionalized-silica-supported gold nanoparticles. The silica-anchored functionalities employed, e.g. amine, alkynyl carbamate and sulfide moieties, possess a notable affinity with gold, so that they could be able to capture the gold precursor, to spontaneously reduce it (possibly at room temperature), and to stabilize the resulting gold nanoparticles. These new materials, potentially suitable for heterogeneous catalysis applications, could represent a breakthrough among the “green” synthesis of supported gold nanoparticles, since they would circumvent the addition of extra reducing agent and stabilizers, also allowing concomitant absorption of the active catalyst particles on the support immediately after spontaneous formation of gold nanoparticles. In chapter 4 of this thesis is also presented the work developed during a seven-months Marco Polo fellowship stay at the University of Lille (France), regarding nanoparticles nucleation and growth inside a microfluidic system and the study of the corresponding mechanism by in situ XANES spectroscopy. Finally, studies regarding the reparation and reactivity of gold decorated nanodiamonds are also described. Various methods of characterization have been used, such as ultraviolet-visible spectroscopy (UV-Vis), Transmission Electron Microscopy (TEM), Dynamic Light Scattering (DLS), X-ray Fluorescence (XRF), Field Emission Gun Scanning Electron Microscopy (SEM-FEG), X-ray Photoionization (XPS), X ray Absorption Spectroscopy (XAS).

Synthesis and characterization of temperature- and light-responsive polymers and block copolymers

In summary, thermoresponsive polyacrylamides with various amounts of different photoswitchable side groups, i. e. azobenzene, salicylideneaniline and fulgimide were successfully prepared. As such, in a first step three different chromophores with an amine functionality were synthesized. The synthesis of the stimuli-responsive materials was based on the RAFT polymerization of activated ester acrylates followed by a polymer analogous reaction with different amines. The procedure has been designed to allow the synthesis of well-defined materials with functional groups. All copolymers prepared in this way showed a LCST in aqueous solution. The LCST was in general decreased by increasing the amount of hydrophobic dye incorporated into the thermoresponsive polymer. However, in the case of the fulgimide, the LCST was hardly affected by the chromophore. For azobenzene containing PNIPAM polymers and analogues, higher LCST values were measured after irradiation of the polymer sample solutions with UV-light (Delta LCSTmax = 7.3°C). A reversible light-induced solubility change within a certain temperature range was possible. In contrast to this, irradiated samples of salicylideneaniline containing thermoresponsive copolymers showed an irreversible increase in the LCST (Delta LCSTmax = 13.0°C). Fulgimide chromophores did not influence the LCST of PNIPAM based copolymers after UV-light exposure.rnSimilar to the thermoresponsive polyacrylamides with azobenzene side groups, poly(oligo(ethylene glycol) methyl ether methacrylate) [P(OEGMA)] polymers with azobenzene end groups showed a LCST shift upon UV-irradiation. These polymers were synthesized by RAFT polymerization using a functional chain transfer agent (CTA). For this, PFP-CTA was used as a RAFT-agent for end group functionalization of (thermoresponsive) polymers. In contrast to the statistically arranged copolymers with azobenzene side groups, P(OEGMA) polymers with terminal azobenzene showed a linear increase of the LCST shifts with increasing amount of chromophore (Delta LCSTmax = 4.3°C). Noteworthy, the chemical nature of the end group exhibited a strong influence on the LCST in the case of short thermoresponsive P(OEGMA) polymers.rnThe investigation on temperature- and lightresponsive polymers was transferred onto block copolymers capable to self-assemble into polymeric micelles. Therefore, PEO-b-PNIPAM block copolymers with azobenzene moieties were synthesized successfully. These polymers showed a “smart” behavior in aqueous solution, as the reversible formation and disruption of the micelles could either be controlled by temperature or using light as a stimulus. The usefulness of these materials was demonstrated by encapsulation of a hydrophobic dye in the core of the micelle. Such materials might have a great potential as a model system for several technical or biological applications.rnFinally, double thermoresponsive block copolymers forming micellar structures in a certain temperature range with functional end groups could successfully be synthesized. These “smart materials” based on POEGMA-b-PNIPMAM have been demonstrated to be very promising for a temperature selective immobilization on a protein surface. This might be a suitable concept for further biological applications.rnConcluding, different thermoresponsive copolymers and block copolymers with lightresponsive moieties arranged along the backbone or located at the chain ends were successfully prepared and investigated. By controlling the nature of functional groups and their respective incorporation ratios, the LCST could be dialed in precisely. Further, the LCST of the polymers could be triggered by light. A light-controlled disruption of micellar structures could be shown for functional block copolymers. The importance of end groups of thermoresponsive polymers was demonstrated by a temperature-controlled protein-polymer binding of a terminal biotin-functionalized double thermoresponsive polymer. The synthetic approaches and the material properties presented here should be promising for further research and applications beyond this dissertation.rn

Aminoxyl radicals - pure organic materials with tunable magnetic and sensing properties

Stabile Radikale haben in vielen Bereichen der Chemie, Physik, Biologie und Biomedizin ihren Nutzen unter Beweis gestellt. Gerade im letzten Jahrzehnt erlebte diese Substanzklasse vor allem wegen den Anwendungsmöglichkeiten von Nitroxiden als Red-Ox-Sensoren oder magnetischen Materialen ein erneutes Interesse. Das erste Kapitel beschäftigt sich mit der grundlegenden Theorie zur Entwicklung magnetischer Materialien. Des Weiteren sollen anhand einiger Beispiele Radikale im Komplex mit paragmagnetischen Metallen, Biradikale und Polyradikale beschrieben werden. rnrnIm zweiten Kapitel soll auf die Synthese von Hybrid Fluorophore-Nitrononyl-Nitroxid und Iminonitroxidradiale, sowie ihre Charakterisierung über IR, CV, EPR und Röntgenstrukturanalyse eingegangen werden. Mittels UV/Vis-Spektroskopie soll hierbei eine mögliche Anwendung als Red-Ox-Sensoren festgestellt werden. Hierbei werden über anschließende PL Untersuchungen eben diese Sensoreigenschaften der dargestellten Radikale bestätigt werden. Vielmehr noch soll die Möglichkeit von Pyren-Pyrazol-Nitronyl-Nitroxid als NO-Nachweis erläutert werden.rnrnFortschritte sowohl im Design als auch in der Analyse von magnetischen Materialen auf der Basis von Nitroxiden ist Thema des dritten Kapitels. Über ein klassisches Ullmann-Protokoll wurden verschiedene Nitronyl-Nitroxid und Iminonitroxid Biradiale mit unterschiedlichen π-Brücken zwischen den Radikalzentren synthetisiert. Magnetische Messungen belegen einen relativ starken antiferromagnetischen intramolekularen Austausch für den Großteil der untersuchten Biradikale. Hierbei zeigte sich jedoch eine außergewöhnliche hohe Austausch-Kupplung für 3,3‘-Diazatolandiradikale, die nur über die Existenz von starken intermolekularen Wechselwirkungen beschrieben werden kann. Durch Kombination der Röntgenstrukturanalyse mit DFT Berechnungen konnte im Fall des Tolan verbrückten Diradikals 87c die Intra-Dimer-Kupplung auf Jintra = -8,6 K bestimmt werden. Ein direkter Beweis für eine intermolekulare Anlagerung von Jinter ~- 2K konnte über eine Tieftemperatur AC-Messung von 87c erhalten werden. Bezüglich der magnetischen Messung ist das Nitronyl Biradikal 87c ein vielversprechender Kandidat für einen rein organischen eindimensionalen Quantenmagnet.rnrnAbsicht dieser Untersuchungen ist es zu zeigen, dass über die Kombination verschiedener struktureller Elemente die Sensitivität von Nitroxid basierten Sensoren und die intramolekulare Austauschwechselwirkung in π-konjugierten Spinsystemen so eingestellt werden kann, dass es möglich ist Moleküle mit gezielten Sensor- oder Magneteigenschaften zu entwickeln. rn

Simulation of Smart Materials

The aim of this thesis is the elucidation of structure-properties relationship of molecular semiconductors for electronic devices. This involves the use of a comprehensive set of simulation techniques, ranging from quantum-mechanical to numerical stochastic methods, and also the development of ad-hoc computational tools. In more detail, the research activity regarded two main topics: the study of electronic properties and structural behaviour of liquid crystalline (LC) materials based on functionalised oligo(p-phenyleneethynylene) (OPE), and the investigation on the electric field effect associated to OFET operation on pentacene thin film stability. In this dissertation, a novel family of substituted OPE liquid crystals with applications in stimuli-responsive materials is presented. In more detail, simulations can not only provide evidence for the characterization of the liquid crystalline phases of different OPEs, but elucidate the role of charge transfer states in donor-acceptor LCs containing an endohedral metallofullerene moiety. Such systems can be regarded as promising candidates for organic photovoltaics. Furthermore, exciton dynamics simulations are performed as a way to obtain additional information about the degree of order in OPE columnar phases. Finally, ab initio and molecular mechanics simulations are used to investigate the influence of an applied electric field on pentacene reactivity and stability. The reaction path of pentacene thermal dimerization in the presence of an external electric field is investigated; the results can be related to the fatigue effect observed in OFETs, that show significant performance degradation even in the absence of external agents. In addition to this, the effect of the gate voltage on a pentacene monolayer are simulated, and the results are then compared to X-ray diffraction measurements performed for the first time on operating OFETs.

Studies of degradation of organic solar cell materials using electrical scanning probe microscopy

Intense research is being done in the field of organic photovoltaics in order to synthesize low band-gap organic molecules. These molecules are electron donors which feature in combination with acceptor molecules, typically fullerene derivarntives, forming an active blend. This active blend has phase separated bicontinuous morphology on a nanometer scale. The highest recorded power conversionrnefficiencies for such cells have been 10.6%. Organic semiconductors differ from inorganic ones due to the presence of tightly bonded excitons (electron-hole pairs)resulting from their low dielectric constant (εr ≈2-4). An additional driving force is required to separate such Frenkel excitons since their binding energy (0.3-1 eV) is too large to be dissociated by an electric field alone. This additional driving force arises from the energy difference between the lowest unoccupied molecular orbital (LUMO) of the donor and the acceptor materials. Moreover, the efficiency of the cells also depends on the difference between the highest occupied molecular orbital (HOMO) of the donor and LUMO of the acceptor. Therefore, a precise control and estimation of these energy levels are required. Furthermore any external influences that change the energy levels will cause a degradation of the power conversion efficiency of organic solar cell materials. In particular, the role of photo-induced degradation on the morphology and electrical performance is a major contribution to degradation and needs to be understood on a nanometer scale. Scanning Probe Microscopy (SPM) offers the resolution to image the nanometer scale bicontinuous morphology. In addition SPM can be operated to measure the local contact potential difference (CPD) of materials from which energy levels in the materials can be derived. Thus SPM is an unique method for the characterization of surface morphology, potential changes and conductivity changes under operating conditions. In the present work, I describe investigations of organic photovoltaic materials upon photo-oxidation which is one of the major causes of degradation of these solar cell materials. SPM, Nuclear Magnetic Resonance (NMR) and UV-Vis spectroscopy studies allowed me to identify the chemical reactions occurring inside the active layer upon photo-oxidation. From the measured data, it was possible to deduce the energy levels and explain the various shifts which gave a better understanding of the physics of the device. In addition, I was able to quantify the degradation by correlating the local changes in the CPD and conductivity to the device characteristics, i.e., open circuit voltage and short circuit current. Furthermore, time-resolved electrostatic force microscopy (tr-EFM) allowed us to probe dynamic processes like the charging rate of the individual donor and acceptor domains within the active blend. Upon photo-oxidation, it was observed, that the acceptor molecules got oxidized first preventing the donor polymer from degrading. Work functions of electrodes can be tailored by modifying the interface with monomolecular thin layers of molecules which are made by a chemical reaction in liquids. These modifications in the work function are particularly attractive for opto-electronic devices whose performance depends on the band alignment between the electrodes and the active material. In order to measure the shift in work function on a nanometer scale, I used KPFM in situ, which means in liquids, to follow changes in the work function of Au upon hexadecanethiol adsorption from decane. All the above investigations give us a better understanding of the photo-degradation processes of the active material at the nanoscale. Also, a method to compare various new materials used for organic solar cells for stability is proposed which eliminates the requirement to make fully functional devices saving time and additional engineering efforts.

Biochar characterization for its environmental and agricultural utilization. Occurrence, distribution and fate of labile organic carbon and polycyclic aromatic hydrocarbons

In this thesis the potential risks associated to the application of biochar in soil as well the stability of biochar were investigated. The study was focused on the potential risks arising from the occurrence of polycyclic aromatic hydrocarbons (PAHs) in biochar. An analytical method was developed for the determination of the 16 USEPA-PAHs in the original biochar and soil containing biochar. The method was successfully validated with a certified reference material for the soil matrix and compared with methods in use in other laboratories during a laboratory exercise within the EU-COST TD1107. The concentration of 16 USEPA-PAHs along with the 15 EU-PAHs, priority hazardous substances in food, was determined in a suite of currently available biochars for agricultural field applications derived from a variety of parent materials and pyrolysis conditions. Biochars analyzed contained the USEPA and some of the EU-PAHs at detectable levels ranging from 1.2 to 19 µg g-1. This method allowed investigating changes in PAH content and distribution in a four years study following biochar addition in soils in a vineyard (CNR-IBIMET). The results showed that biochar addition determined an increase of the amount of PAHs. However, the levels of PAHs in the soil remained within the maximum acceptable concentration for European countries. The vineyard soil performed by CNR-IBIMET was exploited to study the environmental stability of biochar and its impact on soil organic carbon. The stability of biochar was investigated by analytical pyrolysis (Py-GC-MS) and pyrolysis in the presence of hydrogen (HyPy). The findings showed that biochar amendment significantly influence soil stable carbon fraction concentration during the incubation period. Moreover, HyPy and Py-GC-MS were applied to biochars deriving from three different feedstock at two different pyrolysis temperatures. The results evidenced the influence of feedstock type and pyrolysis conditions on the degree of carbonisation.

Development of new analytical procedures aimet at the characterization of artistic samples

In this thesis, new advances in the development of spectroscopic based methods for the characterization of heritage materials have been achieved. As concern FTIR spectroscopy new approaches aimed at exploiting near and far IR region for the characterization of inorganic or organic materials have been tested. Paint cross-section have been analysed by FTIR spectroscopy in the NIR range and an “ad hoc” chemometric approach has been developed for the elaboration of hyperspectral maps. Moreover, a new method for the characterization of calcite based on the use of grinding curves has been set up both in MIR and in FAR region. Indeed, calcite is a material widely applied in cultural heritage, and this spectroscopic approach is an efficient and rapid tool to distinguish between different calcite samples. Different enhanced vibrational techniques for the characterisation of dyed fibres have been tested. First a SEIRA (Surface Enhanced Infra-Red Absorption) protocol has been optimised allowing the analysis of colorant micro-extracts thanks to the enhancement produced by the addition of gold nanoparticles. These preliminary studies permitted to identify a new enhanced FTIR method, named ATR/RAIRS, which allowed to reach lower detection limits. Regarding Raman microscopy, the research followed two lines, which have in common the aim of avoiding the use of colloidal solutions. AgI based supports obtained after deposition on a gold-coated glass slides have been developed and tested spotting colorant solutions. A SERS spectrum can be obtained thanks to the photoreduction, which the laser may induce on the silver salt. Moreover, these supports can be used for the TLC separation of a mixture of colorants and the analyses by means of both Raman/SERS and ATR-RAIRS can be successfully reached. Finally, a photoreduction method for the “on fiber” analysis of colorant without the need of any extraction have been optimised.

Investigation of acceptor dopants in ZrNiSn half-Heusler materials

Thermoelectric generators (TEG) are solid state devices and are able to convert thermal energy directly into electricity and thus could play an important role in waste heat recovery in the near future. Half-Heusler (HH) compounds with the general formula MNiSn (M = Ti, Zr, Hf) built a promising class of materials for these applications because of their high Seebeck coefficients, their environmentally friendliness and their cost advantage over conventional thermoelectric materials.rnrnMuch of the existing literature on HH deals with thermoelectric characterization of n-type MNiSn and p-type MCoSb compounds. Studies on p-type MNiSn-based HHs are far fewer in number. To fabricate high efficient thermoelectric modules based on HH compounds, high performance p-type MNiSn systems need to be developed that are compatible with the existing n-type HH compounds. This thesis explores synthesis strategies for p-type MNiSn based compounds. In particular, the efficacy of transition metals (Sc, La) and main group elements (Al, Ga, In) as acceptor dopants on the Sn-site in ZrNiSn, was investigated by evaluating their thermoelectric performance. The most promising p-type materials could be achieved with transition metal dopants, where the introduction of Sc on the Zr side, yielded the highest Seebeck coefficient in a ternary NiSn-based HH compound up to this date. Hall effect and band gap measurements of this system showed, that the high mobility of minority carrier electrons dominate the transport properties at temperatures above 500 K. It could be shown that this is the reason, why n-type HH are successful TE materials for high temperature applications, and that p-types are subjected to bipolar effects which will lead to diminished thermoelectric efficiencies at high temperatures.rnrnTo complement the experimental investigations on different metal dopants and their influence on the TE properties of HH compounds, numerical solutions to the Boltzmann transport equation were used to predict the optimum carrier concentration where the maximum TE efficiency occurs for p-type HH compounds. The results for p-type samples showed that can not be treated within a simple parabolic band model approach, due to bipolar and multi-band effects.rnrnThe parabolic band model is commonly used for bulk TE materials. It is most accurate when the transport properties are dominated by one single carrier type. Since the transport properties of n-type HH are dominated by only one carrier type (high mobility electrons), it could be shown, that the use of a simple parabolic band model lead to a successful prediction of the optimized carrier concentration and thermoelectric efficiency in n-type HH compounds. rn

Structural characterization of intermediate and metastable phases by electron microscopy

Structure characterization of nanocrystalline intermediates and metastable phases is of primary importance for a deep understanding of synthetic processes undergoing solid-to-solid state phase transitions. Understanding the evolution from the first nucleation stage to the final synthetic product supports not only the optimization of existing processes, but might assist in tailoring new synthetic paths. A systematic investigation of intermediates and metastable phases is hampered because it is impossible to produce large crystals and only in few cases a pure synthetic product can be obtained. Structure investigation by X-ray powder diffraction methods is still challenging on nanoscale, especially when the sample is polyphasic. Electron diffraction has the advantage to collect data from single nanoscopic crystals, but is limited by data incompleteness, dynamical effects and fast deterioration of the sample under the electron beam. Automated diffraction tomography (ADT), a recently developed technique, making possible to collect more complete three-dimensional electron diffraction data and to reduce at the same time dynamical scattering and beam damage, thus allowing to investigate even beam sensitive materials (f.e. hydrated phases and organics). At present, ADT is the only technique able to deliver complete three-dimensional structural information from single nanoscopic grains, independently from other surrounding phases. Thus, ADT is an ideal technique for the study of on-going processes where different phases exist at the same time and undergo several structural transitions. In this study ADT was used as the main technique for structural characterization for three different systems and combined subsequently with other techniques, among which high-resolution transmission electron microscopy (HRTEM), cryo-TEM imaging, X-ray powder diffraction (XRPD) and energy disperse X-ray spectroscopy (EDX).rnAs possible laser host materials, i.e. materials with a broad band emission in the near-infrared region, two unknown phases were investigated in the ternary oxide system M2O-Al2O3-WO3 (M = K, Na). Both phases exhibit low purity as well as non-homogeneous size distribution and particle morphology. The structures solved by ADT are also affected by pseudo-symmetry. rnSodium titanate nanotubes and nanowires are both intermediate products in the synthesis of TiO2 nanorods which are used as additives to colloidal TiO2 film for improving efficiency of dye-sensitized solar cells (DSSC). The structural transition from nantubes to nanowires was investigated in a step by step time-resolved study. Nanowires were discovered to consist of a hitherto unknown phase of sodium titanate. This new phase, typically affected by pervasive defects like mutual layer shift, was structurally determined ab-initio on the basis of ADT data. rnThe third system is related with calcium carbonate nucleation and early crystallization. The first part of this study is dedicated to the extensive investigations of calcium carbonate formation in a step by step analysis, up to the appearance of crystalline individua. The second part is dedicated to the structure determination by ADT of the first-to-form anhydrated phase of CaCO3: vaterite. An exhaustive structure analysis of vaterite had previously been hampered by diffuse scattering, extra periodicities and fast deterioration of the material under electron irradiation. rn

Synthesis, characterization and formulation of a cathode active material: Copper nitroprusside

Nowadays, rechargeable Li-ion batteries play an important role in portable consumer devices. Formulation of such batteries is improvable by researching new cathodic materials that present higher performances of cyclability and negligible efficiency loss over cycles. Goal of this work was to investigate a new cathodic material, copper nitroprusside, which presents a porous 3D framework. Synthesis was carried out by a low-cost and scalable co-precipitation method. Subsequently, the product was characterized by means of different techniques, such as TGA, XRF, CHN elemental analysis, XRD, Mössbauer spectroscopy and cyclic voltammetry. Electrochemical tests were finally performed both in coin cells and by using in situ cells: on one hand, coin cells allowed different formulations to be easily tested, on the other operando cycling led a deeper insight to insertion process and both chemical and physical changes. Results of several tests highlighted a non-reversible electrochemical behavior of the material and a rapid capacity fading over time. Moreover, operando techniques report that amorphisation occurs during the discharge.

Novel materials for direct X-ray detectors based on semiconducting organic polymers

Conventional inorganic materials for x-ray radiation sensors suffer from several drawbacks, including their inability to cover large curved areas, me- chanical sti ffness, lack of tissue-equivalence and toxicity. Semiconducting organic polymers represent an alternative and have been employed as di- rect photoconversion material in organic diodes. In contrast to inorganic detector materials, polymers allow low-cost and large area fabrication by sol- vent based methods. In addition their processing is compliant with fexible low-temperature substrates. Flexible and large-area detectors are needed for dosimetry in medical radiotherapy and security applications. The objective of my thesis is to achieve optimized organic polymer diodes for fexible, di- rect x-ray detectors. To this end polymer diodes based on two different semi- conducting polymers, polyvinylcarbazole (PVK) and poly(9,9-dioctyluorene) (PFO) have been fabricated. The diodes show state-of-the-art rectifying be- haviour and hole transport mobilities comparable to reference materials. In order to improve the X-ray stopping power, high-Z nanoparticle Bi2O3 or WO3 where added to realize a polymer-nanoparticle composite with opti- mized properities. X-ray detector characterization resulted in sensitivties of up to 14 uC/Gy/cm2 for PVK when diodes were operated in reverse. Addition of nanoparticles could further improve the performance and a maximum sensitivy of 19 uC/Gy/cm2 was obtained for the PFO diodes. Compared to the pure PFO diode this corresponds to a five-fold increase and thus highlights the potentiality of nanoparticles for polymer detector design. In- terestingly the pure polymer diodes showed an order of magnitude increase in sensitivity when operated in forward regime. The increase was attributed to a different detection mechanism based on the modulation of the diodes conductivity.

Experimental characterization of carbon-fiber-reinforced polymer laminates

The goal of this thesis is to make static tensile test on four Carbon Fiber Reinforced Polymer laminates, in such a way as to obtain the ultimate tensile strength of these laminates; in particular, the laminates analyzed were produced by Hand Lay-up technology. Testing these laminates we have a reference point on which to compare other laminates and in particular CFRP laminate produced by RTM technology.