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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Struktur-Eigenschafts-Beziehungen in der Leistungsfähigkeit von phosphorhaltigen Flammschutzmitteln für Polyurethan-Schäume

Lenz, Johannes 02 September 2021 (has links)
Polyisocyanurat (PIR)-Schaumstoffe werden aufgrund ihrer geringen Wärmeleitfähigkeit, der hohen Druckstabilität bei geringer Dichte und der geringen Wasserabsorption in vielen Bereichen eingesetzt. Zu den Anwendungsgebieten zählen Isolierungen und der Gebäudebau. In diesen Anwendungsbereichen ist eine flammhemmende Wirkung der verwendeten Materialien gefordert. PIR-Schäume an sich zählen jedoch zu den leicht entflammbaren Stoffen. Ohne den Einsatz von Flammschutzmitteln wäre somit die vielseitige Anwendung von PIR nicht möglich. In der Industrie wird bislang als „state-of-the-art“-Flammschutzmittel für PIR-Schäume das Additiv Tris(2-chloroisopropyl)phosphat (TCPP) verwendet. Nachteil des TCPPs und aller anderen halogenhaltigen Flammschutzmittel sind die beim Verbrennen freigesetzten korrosiven und toxischen Gase. Aufgrund dieses Gesundheitsaspektes, staatlicher Regulierungen und öko-Zertifizierungen geht der Trend zu halogenfreien Flammschutzmitteln. Zu vielversprechenden Alternativen zählen an dieser Stelle phosphorhaltige Verbindungen. In dieser Arbeit wurde eine Reihe von Phosphonat-basierten Additiven für PIR synthetisiert. Als Grundlage dieser Additive diente das Phosphonat Dibenzo[d,f][1,3,2]dioxa-phosphepin-6-oxid (BPPO). Durch eine Phospha-Michael-Addition des BPPOs an ungesättigte Verbindungen wurden Additive gewonnen, welche der Schaumformulierung zugesetzt werden konnten. Neben ungesättigten Verbindungen wurden auch Aldehyde mit BPPO umgesetzt, wobei dazu die Pudovik-Reaktion genutzt wurde. Hierdurch konnten BPPO-Derivate erzeugt werden, welche OH-Gruppen aufweisen. Diese können durch eine Addition an das Polyisocyanat kovalente Bindungen zum Polymer ausbilden, was ein Herausmigrieren der Additive verhindert. Durch diese beiden Reaktionsmechanismen wurden zwei Gruppen an BPPO-Derivaten synthetisiert, welche bislang noch nicht in der Literatur als Flammschutzmittel beschrieben worden sind. Durch die Addition verschiedener organischer Verbindungen wurde die chemische Struktur dieser BPPO-Derivate systematisch variiert. Durch diese Variation und anschließende Untersuchungen konnten Struktur-Eigenschafts-Beziehungen aufgestellt werden. Nach der erfolgreichen Synthese wurden die P-haltigen Verbindungen in PIR-Schäumen verwendet. Parallel dazu wurden Benchmark-Schäume hergestellt, die Flammschutzmittel aus der Literatur und der Industrie enthielten. Die physikalischen Eigenschaften der so hergestellten Schäume wurden anschließend untersucht. Ebenso wurde das thermische Abbauverhalten sowie das Brandverhalten analysiert. Die Ergebnisse wurden mit denen der Benchmark-Schäume verglichen und liefern einen wesentlichen Beitrag zum Verständnis der grundlegenden Struktur-Eigenschafts-Beziehungen im Flammschutz von Polyurethanen. Wie aus der Literatur bereits bekannt, ist die Wirkungsweise phosphorhaltiger Flammschutzmittel abhängig von der Oxidationszahl des Phosphoratoms. Bei höheren Oxidationszahlen findet die flammhemmende Wirkung in der Festphase und bei niedrigeren Oxidationszahlen in der Gasphase statt. Dieser Trend konnte durch den vergleichenden Einsatz von chemisch ähnlichen Phosphinaten, Phosphonaten und Phosphaten bestätigt werden. Ein weiterer wichtiger Einflussfaktor ist die Bindung des Additivs im Schaum. Des Weiteren konnte in dieser Arbeit gezeigt werden, dass Verbindungen mit aromatischen Gruppen sich positiv auf das Brandverhalten auswirken. Diese Ergebnisse tragen wesentlich zum Verständnis der grundlegenden Struktur-Eigenschafts-Beziehungen beim Flammschutz von Polyurethanen bei. Dies wiederum ermöglicht Vorhersagen über das Verhalten von phosphorhaltigen Additiven im Schaum und deren Auswirkungen auf den Flammschutz. Ebenso ist es möglich, mit den gewonnenen Erkenntnissen bestehende Additive durch die Anpassung ihrer chemischen Struktur zu optimieren oder für ein spezielles Einsatzgebiet neu zu entwickeln. Mit TA-BPPO als Additiv konnten zudem bessere Flammschutzeigenschaften erzielt werden als mit dem analogen Derivat des DOPO. Abschließend lässt sich sagen, dass mit BPPO und seinen Derivaten eine wirksame Alternative zu dem bislang verwendeten Triphenylphosphat gefunden wurde. Die erhaltenen Resultate legen eine Anwendung in der Industrie nahe. / Polyisocyanurate (PIR) foams are used in many areas due to their low thermal conductivity, high pressure stability at low density and low water absorption. Applications include insulation, building construction and the automotive industry. In these applications, the materials used, need to have a flame retardant effect. PIR foams themselves are highly flammable materials. Without the use of flame retardants, the versatile application of PIR would not be possible. In industry the additive tris(2-chloroisopropyl)phosphate (TCPP) is currently used as a ”state-of-the-art“flame retardant for PIR foams. The disadvantage of TCPP and all other halogen-containing flame retardants are the corrosive and toxic gases released during combustion. Due to this health aspect, governmental regulations and eco-certifications the trend leads towards halogen-free flame retardants . Promising alternatives at this point include phosphorous-containing compounds. In this work a number of phosphonate-based additives for PIR were synthesized. The phosphonate dibenzo[d,f][1,3,2]dioxa-phosphepine-6-oxide (BPPO) served as the basis for these additives. Additives were obtained by Phospha-Michael addition of BPPO to unsaturated compounds, which could be added to the foam formulation. Besides unsaturated compounds, aldehydes were also reacted with BPPO using the Pudovik reaction. By this means, BPPO derivatives with OH groups could be produced. These can form covalent bonds to the polymer by addition to the polyisocyanate, which prevents the additives from migrating out. By these two reaction mechanisms two groups of BPPO derivatives were synthesized, which have not yet been described as flame retardants in the literature. By adding different organic compounds, the chemical structure of these BPPO derivatives was systematically varied. By this variation and subsequent investigations structure-property relationships could be established. After successful synthesis, the P-containing compounds were used in PIR foams. In parallel, benchmark foams containing flame retardants from literature and industry were produced. The physical properties of the foams produced in this way were then investigated. The thermal degradation behaviour as well as the fire behaviour was also analysed. The results were compared with those of the benchmark foams and provide a significant contribution to the understanding of the basic structure-property relationships in the flame retardancy of polyurethanes. As already known from the literature, the mode of action of phosphorous-containing flame retardants depends on the oxidation number of the phosphorus atom. At higher oxidation numbers the flame retardant effect takes place in the solid phase and at lower oxidation numbers in the gas phase. This trend was confirmed by the comparative use of chemically similar phosphinates, phosphonates and phosphates. Another important influencing factor is the binding of the additive in the foam. Furthermore it could be shown in this work that compounds with aromatic groups have a positive effect on the fire behavior. These results contribute significantly to the understanding of the basic structure-property relationships in flame retardancy of polyurethanes. This in turn allows predictions to be made about the behavior of phosphorus-containing additives in the foam and their effects on flame retardancy. It is also possible to optimize existing additives by adapting their chemical structure, or to develop new additives for a specific application. With TA-BPPO as an additive, it was also possible to achieve better flame retardant properties than with the analogue derivative of DOPO.In conclusion, BPPO and its derivatives are an effective alternative to the triphenyl phosphateused so far. The results obtained suggest an application in industry.
2

Function-led Design of Aerogels: Self-assembly of Alloyed PdNi Hollow Nanospheres for Efficient Electrocatalysis

Cai, Bin, Wen, Dan, Liu, Wei, Herrmann, Anne-Kristin, Benad, Albrecht, Eychmüller, Alexander January 2015 (has links)
Amelioration of the building blocks is a plausible approach to graft aerogels with distinguished properties while preserving the aerogel superiority. However, the incorporation of designated properties into metallic aerogels, especially catalytically beneficial morphologies and transition metal doping, still remains a challenge. Here, we report on the first case of an aerogel electrocatalyst composed entirely of alloyed PdNi hollow nanospheres (HNSs) with controllable chemical composition and shell thickness. The synergy of the transition metal doping, combined with the hollow building blocks and the three dimensional network structure make the PdNi HNS aerogels promising electrocatalysts towards ethanol oxidation, among which the Pd83Ni17 HNS aerogel shows a 5.6-fold enhanced mass activity compared to commercial Pd/C. This work expands the exploitation approach of electrocatalytic properties of aerogels into morphology and composition control of its building blocks.
3

A starPEG-heparin hydrogel model of renal tubulogenesis

Weber, Heather 06 March 2017 (has links)
Currently, the only treatment for end stage renal disease is dialysis or kidney transplantation. These methods contain obvious limitations such as the palliative nature of dialysis treatment and the lack of available organs for transplantation. As a result, there is a dire unmet need for alternative options. Regenerative therapies that focus on stimulating the regrowth of injured tissue can be a promising alternative. A critical step in the development of such therapeutic remedies is obtaining robust models that mimic the complex nature of the human kidney. The proximal tubules are a particular region of interest due to their important role in reabsorption and secretion of the glomerular filtrate and the blood, making them particularly susceptible to nephrotoxicity and renal pathologies. For this reason, the goal of this thesis was to engineer a 3D model of human proximal tubulogenesis that would allow for both developmental and regenerative studies. The ideal assay would mimic the human 3D structure and function of proximal tubules in a tunable, robust matrix that can be easily analyzed in throughput screenings for regenerative medicine and toxicity applications. In this thesis, we show the development, characterization, and application of an in vitro human renal tubulogenesis model using a modular and tunable biohybrid starPEG-heparin hydrogel platform. A range of hydrogel mechanics and compositions were systematically tested to determine the optimal conditions for renal tubulogenesis. The results revealed that only soft hydrogels based on heparin and matrix metalloproteinase (MMP) enzymatically cleavable crosslinkers led to the generation of polarized tubule structures. The generated tubules display polarization markers, extracellular matrix components, and organic anion transport functions which mimic the human renal proximal tubule. To the best of our knowledge, this is the first system where human renal tubulogenesis can be monitored ex vivo from single cells to physiologically sized tubule structures in a 3D tunable matrix. Moreover, it was found that heparin played a role in the polarization of proximal tubule cells in the hydrogel culture. The established starPEG-MMP-heparin based hydrogel model was then tested for its application as a renal tubulogenesis model by the addition of pro and anti-tubulogenic factors. It was found that the addition of growth factors and MMP inhibitors could promote and inhibit tubulogenesis, respectively. This model can be used to modulate tubulogenesis by adjusting the mechanical properties of the hydrogel, growth factor signaling, and the presence of insoluble cues (such as adhesion peptides), potentially providing new insights for regenerative therapy. To examine if the established hydrogel-based renal tubulogenesis model could be applied as a drug toxicity platform, the nephrotoxic, chemotherapeutic drug, cisplatin was incubated with the renal tubule model. The tubular structures showed a dose-dependent drug response resembling the human clinical renal pathology. The injured tubular structures also expressed the early in vivo proximal tubule injury biomarker, kidney injury molecule-1 (KIM-1). In conclusion, a hydrogel-based renal tubulogenesis model was successfully developed, characterized, and applied as a nephrotoxicity assay. Our findings suggest that the established hydrogel-based model can additionally be used for personalized medicine, where a patient’s predisposition to drug-induced renal injury or specific renal regenerative medicine treatments could be examined. This platform provides a novel approach to study human nephrotoxicity and renal regenerative medicine ex vivo, limiting the need for animal models, and potentially paving the way for more reliable preclinical trials.
4

Annual Report 2009 - Institute of Radiochemistry

Bernhard, G., Viehweger, K. January 2010 (has links)
No description available.
5

Hydrides of Alkaline Earth–Tetrel (AeTt) Zintl Phases: Covalent Tt–H Bonds from Silicon to Tin

Auer, Henry, Guehne, Robin, Bertmer, Marko, Weber, Sebastian, Wenderoth, Patrick, Hansen, Thomas Christian, Haase, Jürgen, Kohlmann, Holger 28 February 2019 (has links)
Zintl phases form hydrides either by incorporating hydride anions (interstitial hydrides) or by covalent bonding of H to the polyanion (polyanionic hydrides), which yields a variety of different compositions and bonding situations. Hydrides (deuterides) of SrGe, BaSi, and BaSn were prepared by hydrogenation (deuteration) of the CrB-type Zintl phases AeTt and characterized by laboratory X-ray, synchrotron, and neutron diffraction, NMR spectroscopy, and quantum-chemical calculations. SrGeD4/3–x and BaSnD4/3–x show condensed boatlike six-membered rings of Tt atoms, formed by joining three of the zigzag chains contained in the Zintl phase. These new polyanionic motifs are terminated by covalently bound H atoms with d(Ge–D) = 1.521(9) Å and d(Sn–D) = 1.858(8) Å. Additional hydride anions are located in Ae4 tetrahedra; thus, the features of both interstitial hydrides and polyanionic hydrides are represented. BaSiD2–x retains the zigzag Si chain as in the parent Zintl phase, but in the hydride (deuteride), it is terminated by H (D) atoms, thus forming a linear (SiD) chain with d(Si–D) = 1.641(5) Å.
6

In situ hydrogenation of the Zintl phase SrGe

Auer, Henry, Wallacher, Dirk, Hansen, Thomas Christian, Kohlmann, Holger 28 February 2019 (has links)
Hydrides (deuterides) of the CrB-type Zintl phases AeTt (Ae = alkaline earth; Tt = tetrel) show interesting bonding properties with novel polyanions. In SrGeD4/3–x (γ phase), three zigzag chains of Ge atoms are condensed and terminated by covalently bound D atoms. A combination of in situ techniques (thermal analysis and synchrotron and neutron powder diffraction) revealed the existence of two further hydride (deuteride) phases with lower H (D) content (called α and β phases). Both are structurally related to the parent Zintl phase SrGe and to the ZrNiH structure type containing variable amounts of H (D) in Sr4 tetrahedra. For α-SrGeDy, the highest D content y = 0.29 was found at 575(2) K under 5.0(1) MPa of D2 pressure, and β-SrGeDy shows a homogeneity range of 0.47 < y < 0.63. Upon decomposition of SrGeD4/3–x (γ-SrGeDy), tetrahedral Sr4 voids stay filled, while the Ge-bound D4 site loses D. When reaching the lower D content limit, SrGeD4/3–x (γ phase) with 0.10 < x < 0.17, decomposes to the β phase. All three hydrides (deuterides) of SrGe show variable H (D) content.
7

Tetrasubstituierte Calix[4]arene mit gemischten Donorgruppen als selektive Liganden für Seltenerdelemente

Glasneck, Florian 19 April 2022 (has links)
folgt
8

Upconverting luminescent nanoparticles for bioimaging applications

Nsubuga, Anne 14 June 2019 (has links)
The synthesis and surface modification of upconverting nanoparticles (UCNPs) composed of a host lattice NaYF4 doped with sensitizers (Yb3+, Nd3+) and luminescent emitters (Er3+) were investigated for potential integration in biological applications.The fascination of NaYF4: Nd3+, Yb3+, Er3+ upconverting nanoparticles derives from their capacity to be excited in the biologically transparent window (650-950 nm) enabling deep tissue penetration. In particular, the ability to convert near infrared radiation into visible light (upconversion), which prevents autofluorescence and over-heating effect of biological tissues.In biological applications especially in vivo, morphology and size of the nanoparticles plays a crucial role in determination of cellular responses and fate in living organism. Heterogeneously sized nanoparticles, in contrast to uniform ones, might be distributed unevenly in the organism causing undesirable toxic side effects. Therefore, precise control of the nanoparticle size, distribution, and reproducibility were main tasks in the first part of this work. Colloidal upconverting nanoparticles were synthesized using coprecipitation method. Synthetic parameters such as reaction temperature (280-320 °C), and time (5-30 min) were used to tailor the nanoparticle morphology, crystal phase (cubic or hexagonal) and particle size (sub-10 - 20 nm). Integration of these nanoparticles in biological applications requires dispersibility in aqueous media. Hence hydrophobic UCNPs were surface-modified with low molecular weight ligands including O-phospho-L-threonine, alendronic acid, and PEG-phosphate ligands to generate water-dispersible UCNPs. Furthermore, in this work, photocrosslinking of diacetylenes is presented as an effective way to create robust UCNPs with a crosslinked shell. Finally, the protein corona formation on UCNPs coated with charged, zwitterionic and nearly neutral ligands was investigated. The composition of protein binding to UCNP is notably influenced by the surface charges of the UCNPs. Overall, the results obtained in the frame of this work show that the NaYF4: Nd3+, Yb3+, Er3+ UCNPS have the potential to replace conventional fluorophores in bioimaging applications due to their remarkable optical properties, as well as the derivatization flexibility of their surface
9

Dendrimere als vielseitige, nano-skalige Objekte für biomimetische, biomedizinische und katalytische Fragestellungen

Appelhans, Dietmar, Voit, Brigitte 29 August 2007 (has links)
With their three-dimensional macromolecular structure and shape, and with their tuneable properties in both the inner and outer spheres, dendrimers are ideal model compounds in the nanometre range between 1 and 10 nm. The possibility to combine different properties within one macromolecule destines them for use in various high-end research fields such as medicine, pharmacy, biology, supramolecular chemistry, nanotechnology and material sciences. On the basis of their high end-group density and a compact, highly branched molecular structure, dendrimers are successfully investigated as carrier systems for active substances and metal ions (e.g. contrast agents for the visualisation of blood vessels), as templates for metal nanoparticles, as artificial enzymes with defined functions, and as materials for catalysis. / Dendrimere sind aufgrund ihrer dreidimensionalen Makromolekülstruktur und -form und ihrer steuerbaren Eigenschaften sowohl an der Oberfläche als auch im Molekülinneren ideale Modellverbindungen im Nanometerbereich – sie sind zwischen 1 und 10 nm groß –, die vorzugsweise in der Medizin, Pharmazie, Biologie, Supramolekularen Chemie, Nanotechnologie und den Materialwissenschaften eingesetzt werden. Aufgrund ihrer hohen Endgruppendichte und der kompakten, stark verzweigten Molekülform werden Dendrimere unter anderem als Trägermaterialien und Transportsysteme für Wirkstoffe und Metallionen, zum Beispiel als Kontrastmittel zur Visualisierung von Organen und Blutgefäßen, als Template für metallische Nanopartikel, zur Erzeugung künstlicher Enzymfunktionen und in der Katalyse erfolgreich untersucht.
10

On Design for Electrochemical Energy Storage Materials

Sakaushi, Ken 19 December 2013 (has links)
In this dissertation, diverse strategic designs of energy storage materials were explored. The main aims were: affordability and high-performances. I) on eco-efficient synthesis of 1D intercalation compounds was described; a low-temperature aqueous solution synthesis of nanostructured 1D (molybdenum trioxide) MoO3 was developed. Subsequent self-assembly of the fibers to form large-scale freestanding films in paper-like structure was achieved without any assistance of organic compounds. Indeed, the whole processes, from synthesis to assembly of obtained materials, do not require toxic organic solvents. As an example of the application of our synthesized materials, 1D MoO3, having the width in 50−100 nm, with the length in micro scale, and with thickness in ~10 nm, and the macroscopic oxide papers consisting of 1D MoO3 and carbon materials were applied as the cathode and anode to lithium-ion batteries, respectively. As a cathode material, the 1D MoO3 showed a high rate capability with a stable cycle performance up to 20 A/g due to a short Li+ diffusion path along [101] and less grain boundaries which were achieved by the precise nanostructure control. As an anode material, the composite paper showed the first specific discharge capacity of 800 mAh/g. These findings above indicate not only an affordable, eco-efficient synthesis and assembly of nanomaterials but also show a new attractive strategy towards a possible whole aqueous process for a large-scale fabrication of freestanding oxide papers without any toxic organic solvent. II) a new energy storage principle using polymeric frameworks was investigated. The new energy storage concept can deliver both high power and high energy. This is because of the novel energy storage nature of designed artificial polymeric frameworks which is different from classical energy storage mechanisms. The main novel discovery was as follows; since CTF-1 is linear stepwise p- and n-dopable polymer, therefore, this framework can store energy as a cathode in the wide working potential with both cation below 3 V versus Li/Li+ and anion above 3 V versus Li/Li+ by Faradaic reaction. Due to this feature, CTF-1 can store high specific capacity of 540 mAh/g. As the result the new energy storage concept which can deliver both high power and high energy was discovered by using a novel polymeric cathode. Unlike typical organic electrodes in sodium battery systems, the CTF-1 has a high specific power of 10 kW/kg, specific energy of 500 Wh/kg, and over 7,000 cycle life retaining 80 % of its initial capacity in half-cells. Indeed, all-organic energy storage devices based on CTF-1 suggested a possibility towards an extremely affordable energy storage device. Recent research on such artificial polymeric frameworks suggests their huge variability to utilize different functional structures which could even further increase power and energy even further when using different starting monomers. This would significantly extend the possibilities of electrical energy storage devices for a sustainable society based on our result. From this point of view, our research strategy which combined the experimental and theoretical study would be a model for further development of this field.

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