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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.
51

Solution Assembly of Conjugated Polymers

Bokel, Felicia 01 May 2013 (has links)
This dissertation focuses on the solution-state polymer assembly of conjugated polymers with specific attention to nano- and molecular-scale morphology. Understanding how to control these structures holds potential for applications in polymer-based electronics. Optimization of conjugated polymer morphology was performed with three objectives: 1) segregation of donor and acceptor materials on the nanometer length-scale, 2) achieving molecular-scale ordering in terms of crystallinity within distinct domains, and 3) maximizing the number and quality of well-defined donor/acceptor interfaces. Chapter 1 introduces the development of a mixed solvent method to create crystalline poly(3-hexyl thiophene) (P3HT) fibrils in solution. Chapter 2 describes fibril purification and approaches to robust and functional fibrils, while chapters 3 and 4 demonstrate the formation of hybrid nanocomposite wires of P3HT and cadmium selenide (CdSe) nanoparticles by two methods: 1) co-crystallization of free and P3HT-grafted CdSe for composite nanowires and 2) direct attachment of CdSe nanoparticles at fibril edges to give superhighway structures. These composite structures show great potential in the application of optoelectronic devices, such as the active layer of solar cells. Finally, ultrafast photophysical characterization of these polymers, using time-resolved photoluminescence and transient absorption, was performed to determine the aggregation types present in suspended fibrils and monitor the formation and decay of charged species in fibrils and donor-acceptor systems
52

Organic-inorganic hybrid photovoltaics based on organometal halide perovskites

Lee, Michael M. January 2013 (has links)
This thesis details the development of a novel photovoltaic device based on organometal halide perovskites. The initial focus of this thesis begins with the study of lighttrapping strategies in solid-state dye-sensitised solar cells (detailed in chapter 3). While I report enhancement in device performance through the application of near and far-field light-trapping techniques, I find that improvements remain step-wise due to fundamental limitations currently employed in dye-sensitised solar cell technology— notably, the available light-sensitising materials. I found a promising yet under researched family of materials in the methyl ammonium tri-halide plumbate perovskite (detailed in chapter 4). The perovskite light-sensitiser was applied to the traditional mesoscopic sensitised solar cell device architecture as a replacement to conventional dye yielding world-record breaking photo-conversion e!ciencies for solid-state sensitised solar cells as high as 8.5%. The system was further developed leading to the conception of a novel device architecture, termed the mesoporous superstructured solar cell (MSSC), this new architecture replaces the conventional mesoporous titanium dioxide semiconductor with a porous insulating oxide in aluminium oxide, resulting in very low fundamental losses evidenced through high photo-generated open-circuit voltages of over 1.1 V. This development has delivered striking photo-conversion ef- ficiencies of 10.9% (detailed in chapter 6).
53

Organic-inorganic hybrid graft copolymers of polystyrene and polydimethylsiloxane

Sutherland, Aimee Celeste 03 1900 (has links)
Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Hybrid graft copolymers of polystyrene (PSty) and polydimethylsiloxane macromonomers (PDMS) were synthesised. PSty-g-PDMS was synthesised employing the grafting through technique via a conventionally free radical polymerization (FRP) using a polydimethylsiloxane macromonomer. In this series the amount of PDMS incorporated into the copolymer was varied by varying the macromonomer to styrene ratios as well as the length of the PDMS side chain. This allows for the study of the effect that the macromonomer content and the branching length has on the efficiency of the grafting process. A second series of PDMS-g-PSty was also synthesized where the PDMS forms the backbone and the PSty the grafts. Two synthetic techniques were employed for the formation of these polymers. Firstly, the grafting onto approach was used where functional polystyrene prepolymers with either an allyl or vinyl end-groups were synthesised anionically (living anionic polymerization) prior to the coupling of a functional prepolymer using a hydrosilylation reaction with a Karstedt platinum catalyst. This technique was successful and gave insight to the effect of the polystyrene prepolymer graft length has on the grafting efficiency as well as the functional groups needed on the PDMS backbone. Furthermore, the effect of the viscosity (of the PDMS macromonomer) plays on the grafting efficiency was also elucidated. Lastly, the grafting from approach was employed for the formation of PDMS-g-PSty. ATRP, atom transfer radical polymerization, of styrene using a bromoisobutyrate functional PDMS macroinitiator was used for the synthesis of these copolymers. This was accomplished by reacting commercial silane functional PDMS molecules via a hydrosilylation reaction (using a Karstedt catalyst) with allyl-2- bromo-2-methyl-propionate to give a PDMS macroinitiator with bromoisobutyrate functional groups. This will allow for the initiation and growth of polystyrene branches from the PDMS backbone (employing ATRP with a suitable catalyst and ligand). The formation of the endproduct, PDMS-g-PSty, via this route proved to be extremely difficult and largely unsuccessful. Liquid chromatography (LC) at the critical point (LCCC) of polystyrene was used to separate the graft material from homo-polymers which might have formed as well as from the PDMS macromonomer. This technique allows for a very fast chromatographic analysis of the grafting reaction. Under the critical conditions of PSty it was found that the graft copolymer eluted at a lower retention time than the unreacted macromonomer and PSty homopolymer. Two-dimensional chromatography, where LCCC (1st dimension) was coupled to size exclusion chromatography (2nd dimension), was used for the evaluation of the CCD and MMD (molecular mass distribution) of the graft material. LC was furthermore coupled off-line to FTIR and TEM using an LC interface. LCFTIR gave insight to the microstructure of the material, whilst LC-TEM gave insight to the morphological nanostructure of the material. / AFRIKAANSE OPSOMMING: Hibried ent-kopolimere is gesintetiseer uit polistireen (PSty) en polidimetielsiloksaan (PDMS). PSty-g-PDMS is gesintetiseer deur gebruik te maak van die ent-deur tegniek via ‘n konvensionele vrye radikaal polimerisasie proses (VRP). In die reeks is die hoeveelheid PDMS wat geïnkorporeer is, gevarieer deur die hoeveelheid PDMS tot PSty verhouding te verander asook die lengte van die PDMS sytak. Gevolglik het dit toegelaat vir die studie van die effek wat die makromonomeer inhoud, sowel as die taklengte het op die effektiwiteit van die ent-proses. ‘n Tweede reeks is ook gesintetiseer, waar die PDMS die ruggraat vorm van die ko-polimeer, en die stireen die takke vorm van die ko-polimeer. Dus is PDMS-g-PSty gesintetiseer. Twee sintetiese tegnieke is benut vir die vorming van die kopolimere. In die eerste geval is daar van die ent-op tegniek gebruik gemaak waar funksionele polistireen prepolimere met ‘n alliel of ‘n silaan end-groep gesintetiseer is deur gebruik te maak van ‘n anioniese lewendige polimerisasie voor die koppeling van die PDMS makromonomere deur ‘n hidrosililasie proses met ‘n Karstedt platinum katalisator. Die tegniek was suksesvol en het in diepte insig gegee van die effek wat die molekulêre lengte van die polistireen prepolimeer het op die effektiwiteit van die ent-proses, sowel as die minimum hoeveelheid funksionele groepe wat teenwoordig moet wees op die PDMS ruggraat. Verder is die effek wat die viskositeit (van die PDMS makromonomeer) op die ent-proses het, bekend gemaak. Laastens is daar ook van die ent-vanaf tegniek gebruik gemaak vir die vorming van PDMS-g-PSty. AORP, atoom oordrag radikale polimerisasie, van stireen, deur gebruik te maak van ‘n bromoisobutiraat funksionele PDMS makro-inisieerder, is gebruik vir die sintese van die kopolimere. Die makro-inisieerders is bekom deur gebruik te maak van kommersiële silaan funksionele PDMS, en dit is gereageer deur middel van ‘n hidrosililasie proses met alliel-2-bromo- 2-metiel-propionaat. Dit het PDMS makroinisieerders tot gevolg gehad met bromoisobutiraat funksionele groepe. Gevolglik kon stireen takke vanaf die PDMS ruggraat gegroei word deur gebruik te maak van AORP met ‘n geskikte katalisator en ligand. Die vorming van die end-produk, PDMS-g-PSty, deur middel van hierdie roete was onsuksesvol. Vloeistof chromatografie by die kritiese punt van polistireen was gebruik om die ent-produk te skei van die homo-polimere en PDMS makromonomeer. Gevolglik kon die chemiese samestelling van die ent-produk geëvalueer word. Twee-dimensionele chromatografie, waar vloeistof chromatografie by die kritiese punt van polistireen in die eerste vlak gekoppel was aan grootte uitsluitings chromatografie in die tweede vlak, was benut om die chemiese komposisie sowel as die molekul re massa verdeling van die entproduk te verkry. Verder was vloeistof chromatografie indirek aan Fourier-oordrag infrarooi en transmissie elektron mikroskopie (TEM) gekoppel. Eergenoemde het insig gegee tot die mikrostruktuur van die materiaal, terwyl laasgenoemde insig gegee het tot die morfologiese nanostruktuur van die materiaal.
54

Síntese e caracterização de hidróxidos duplos lamelares preparados na presença de polímeros orgânicos ou com macromoléculas intercaladas / Synthesis and characterization of layered double hydroxides prepared in the presence of organic polymers or intercalated with macromolecules

Reis, Márcio José dos 30 April 2009 (has links)
Compostos lamelares do tipo da hidrotalcita ou hidróxidos duplos lamelares (HDL), são materiais que possuem notáveis propriedades estruturais, químicas, eletrônicas, iônicas, ópticas e magnéticas. Em função dessas propriedades, os HDL apresentam uma diversidade de aplicações tais como adsorventes e catalisadores. Este trabalho tem por objetivo utilizar polímeros e macromoléculas na preparação e caracterização de HDL, visando melhorar as propriedades texturais dos HDL de MgAl-CO3 preparados em meio contendo polímeros orgânicos ou a intercalação direta de dendrímeros tipo PAMAM de gerações -0,5 e +0,5 em HDL do sistema Zn/Al. Os HDL de MgAl-CO3 foram preparados pela adaptação do método de coprecipitação a pH decrescente, com a presença de polímeros solubilizados no meio, como molde. Os materiais foram caracterizados por difração de Raios X, análise termogravimétrica, espectroscopia no infravermelho e medidas de área superficial por BET. Baseando-se nos resultados obtidos, pode-se concluir que propriedades texturais dos HDL preparados são modificadas, quando na presença de alguns polímeros. Na maioria dos casos, os valores calculados de área superficial específica foram mais elevados, em comparação com aquele obtido para o HDL preparado em meio reacional sem polímero. Isto pode ser explicado pela diminuição do tamanho de partículas e aumento no diâmetro médio de poros dos materiais preparados, provocada pela presença de polímeros no meio reacional. Os HDL intercalados com dendrímeros PAMAM G-0,5 e PAMAM G+0,5 foram preparados por duas rotas diferentes: coprecipitação a pH constante e troca iônica em fase dupla. Os materiais obtidos foram caracterizados por meio de difração de Raios X, análise de termogravimétrica associada à espectrometria de massas e espectroscopia no infravermelho. Utilizando os dois procedimentos de preparação, a intercalação de PAMAM G-0,5 deu origem a HDL com os mesmos espaçamentos basais, concordando com a intercalação dos ânions do dendrímero em um arranjo perpendicular à lamela do HDL, enquanto que para a intercalação do PAMAM G+0,5, espaçamentos basais muito menores do que o tamanho da molécula foram obtidos. A diferença entre a distância interlamelar observada e a esperada pode ser explicada por um arranjo peculiar das moléculas desse dendrímero em uma forma elipsoidal, devido às interações intramoleculares. Espectros no infravermelho confirmam a presença dos dendrímeros nos materiais Zn2Al-PAMAM G-0,5 e Zn2Al-PAMAM G+0,5. Finalmente, a presença destes dendrímeros foi confirmada por análise térmica associada com espectrometria de massas. Os estudos de Raios X com variação de temperatura in situ e as análises termogravimétricas revelaram que o material obtido pela intercalação do PAMAM G+0,5 é termicamente menos estável do que aquele intercalado com PAMAM G-0,5, concordando com a diferença de estabilidade entre os dendrímeros livres. / Hydrotalcite-like lamellar compounds or layered double hydroxides (LDH) are materials that present notable structural, chemical, electronic, ionic, optical and magnetic properties. Depending on these properties, the LDH present a great variety of applications such as adsorbents and catalysts. The aim of this work is to prepare and to characterize MgAl-CO3-LDH prepared in aqueous media containing organic polymer to improve textural properties, and to prepare HDL by intercalation of dendrimer (PAMAM) of generations -0.5 and +0.5 in ZnAl-HDL. MgAl-CO3-HDL samples were prepared by an adaptation of the coprecipitation method at decreasing pH, with the presence of polymers in the aqueous media as template. The materials were characterized by powder X-ray diffraction, termogravimetric analysis, infrared spectroscopy and BET isotherms. Based on the obtained results, it can be concluded that the textural properties of the prepared LDH were modified. The calculated values of specific surface area were higher in most of the cases compared with those obtained by the LDH prepared without polymer due to a decrease of the particle size and an increase in the average pore diameter of the prepared materials due to the presence of polymers. HDL with intercalated (PAMAM) dendrimers G-0.5 and G+0.5 were prepared by two different methods: coprecipitation at constant pH, and ionic exchange in double phase. The obtained materials were characterized by powder X-ray diffraction, thermal gravimetric analysis associated with mass spectrometry, and infrared spectroscopy. X-ray powder diffraction patterns exhibit the characteristic profiles of the lamellar materials with basal spacing depending on the nature of the dendrimer. For both preparation methods, the intercalation of PAMAM G-0.5 gives rise to LDH with basal spacing in agreement with the dendrimer molecules perpendicular to the layer of the host structure, while for PAMAM G+0.5 a basal spacing smaller than the molecule size was obtained. The difference between the obtained and the expected value is explained by an accommodation of the dendrimer molecule in an ellipsoidal shape, due to the intra-molecular interactions. Infrared spectra confirm the presence of dendrimers in the Zn2Al-PAMAM G-0.5 and Zn2Al-PAMAM G+0.5 materials. Finally, thermal analyses associated with mass spectrometry confirm the presence of these dendrimers. Powder X-ray diffraction with in situ temperature variation reveals that the material obtained by the PAMAM G+0.5 intercalation is thermally less stable than that prepared by PAMAM G-0.5 intercalation, in agreement with the difference in the thermal stability of the free dendrimers.
55

Preparação e caracterização de filmes híbridos orgânico-inorgânicos a base de derivados do politiofeno / Preparation and characterization of organic-inorganic hybrid films based on polythiophene derivatives

Mescoloto, Ariane de França [UNESP] 20 February 2017 (has links)
Submitted by Ariane de França Mescoloto null (rianefm@gmail.com) on 2017-02-25T15:53:15Z No. of bitstreams: 1 Dissertação_Ariane_2017.pdf: 4799231 bytes, checksum: 0e27c8b04f680e6a88f1e66a2df4e016 (MD5) / Approved for entry into archive by LUIZA DE MENEZES ROMANETTO (luizamenezes@reitoria.unesp.br) on 2017-03-07T14:05:43Z (GMT) No. of bitstreams: 1 mescoloto_af_me_araiq.pdf: 4799231 bytes, checksum: 0e27c8b04f680e6a88f1e66a2df4e016 (MD5) / Made available in DSpace on 2017-03-07T14:05:43Z (GMT). No. of bitstreams: 1 mescoloto_af_me_araiq.pdf: 4799231 bytes, checksum: 0e27c8b04f680e6a88f1e66a2df4e016 (MD5) Previous issue date: 2017-02-20 / Materiais híbridos orgânico-inorgânicos, constituídos pela combinação de componentes orgânicos e inorgânicos, são homogêneos, apresentam propriedades diferenciadas que refletem a natureza química dos componentes pelos quais foram formados, e são utilizados em diversas aplicações tecnológicas como catalisadores, sensores eletroquímicos, dispositivos ópticos e revestimentos protetores. Este trabalho foi realizado em duas etapas. Primeiramente, foi realizada a síntese e caracterização de um copolímero derivado do politiofeno, P(HTcoAAT), contendo ácido 3-tiofeno-acético (AAT) e 3-hexiltiofeno (HT), sintetizado via copolimerização oxidativa com cloreto férrico e caracterizado químico-estruturalmente por FTIR e RMN 1H e termicamente por TG/DTG. Em seguida, foram preparados filmes híbridos via sol-gel por spin-coating utilizando três óxidos inorgânicos: óxido de silício, titânio e zinco, os quais foram caracterizados opticamente por Espectroscopia no UV-vis e Fluorescência, e morfologicamente por AFM e MEV, além das caracterizações já citadas anteriormente. Os resultados químico-estruturais obtidos comprovaram a eficiência da metodologia usada para a preparação do copolímero e dos híbridos, permitindo a obtenção de matérias com propriedades ópticas interessantes. / Organic-inorganic hybrid materials, formed from organic and inorganic compounds combination, present specific properties that reflect the chemical nature of each precursor compound, and are used for several technological application such as catalists, electrochemical sensors, optical devices and barrier films. This work comprehends two steps: first of all the synthesis of a copolymer derived from polythiophene, P(HTcoTAA) containing 3-thiophene acetic acid (TAA) and 3-hexylthiophene (HT), it was performed from oxidative copolymerization with ferric chloride, and resulting materials characterized by FTIR and 1H NMR spectroscopy and TG/DTG thermal analyses. Following hybrid films from silicium, titanium and zinc oxides were prepared by sol-gel spin-coating and had its optical and morphological characteristics evaluated by UV-vis and Fluorescence spectroscopy, and AFM and SEM microscopy, besides the other characterization before cited. The obtained chemical-structural results show that the used methodology was efficient to prepare both the copolymer and the hybrids, allowing to materials presenting striking optical properties.
56

Magnetic field effect and other spectroscopies of organic semiconductor and hybrid organic-inorganic perovskite devices

Sahin Tiras, Kevser 01 August 2018 (has links)
This thesis consists of three main studies: magnetic field effects in thermally activated delayed fluorescent (TADF) organic light emitting diodes (OLEDs), magnetic field effects in bipolar and unipolar polythiophene (P3HT) devices and a study of hybrid organic/inorganic perovskite devices. Spin-dependent transport and recombination processes of spin-pair species have been detected by magnetic field effect (MFE) technique in carbon-based semi- conductor devices. Magneto-electroluminescence (MEL) and magneto-conductivity have been measured as a function of the applied magnetic field, B, in light emitting diodes. TADF materials have been used instead of simple fluorescent materials in OLEDs. We have observed very large magnetic response with TADF materials. The second study is magnetic field effects of regio-regular P3HT based OLED devices. P3HT is a well known semiconducting polymer, and its electrical properties such as magneto-conductance can be affected by an applied magnetic field. P3HT was chosen because it exhibits a sign change in magnetoresistance (MR) as the bias is increased. Unipolar and bipolar devices have been fabricated with different electrode materials to understand which model can be best to explain organic magnetoresistance effect, possibly depending on the operating regime of the device. Transport and luminescence spectroscopies were studied to isolate the different mechanisms and identify their fingerprints. The third study is on hybrid organic-inorganic perovskite devices. With the potential of achieving very high efficiencies and the very low production costs, perovskite solar cells have become commercially attractive. Scanning electron microscopy (SEM) images and absorption spectrum of the films were compared in single-step solution, two-step solution and solution-assisted vapor deposition techniques. Grain size, morphology and thickness parameters of perovskite films were studied within these techniques. Perovskite solar cells were fabricated and their efficiencies were measured.
57

Electrical, thermomechanical and sorption properties of hybrid organic-inorganic systems based on urethane oligomers and silicates

Iurzhenko, Maksym 25 November 2009 (has links) (PDF)
L'objectif de cette recherche est d'établir des mécanismes de formation de la structure des systèmes hybrides organique-inorganique à base des oligomères uréthane et silicates en fonction de la réactivité de la composant organique, d'identifier l'impact de l'organisation structurelle du OIS obtenue sur leurs propriétés électriques et thermomécaniques, de sorption et de l'activité du capteur. La signification pratique des résultats est la détermination de l'impact de la réactivité composant organique sur la structure des systèmes hybrides polymère organique-inorganique avec la possibilité d'obtenir des matériaux avec des propriétés spéciales prévisibles. Les résultats peuvent être utilisés comme base scientifique pour comprendre l'interconnexion de la structure, les propriétés et les moyens de leur régulation en direction de systèmes hybrides polymère organique-inorganique. La sensibilité très élevée pour les différents types de solvants, qui, combiné avec une haute sélectivité, a été révélé pour les systèmes de synthèse, la possibilité de leur utilisation pratique en tant que matières capteur existe.
58

Synthese und kolloidale Eigenschaften neuartiger Blockcopolymere mit beta-Dicarbonyl Einheiten = Synthesis and colloidal properties of a novel type of block copolymers bearing beta-dicarbonyl residues / Synthesis and colloidal properties of a novel type of block copolymers bearing beta-dicarbonyl residues

Krasia, Theodora January 2003 (has links)
The present work is dealing with the first synthesis and characterisation of amphiphilic diblock copolymers bearing b-dicarbonyl (acetoacetoxy) chelating residues. Polymers were obtained by Group Transfer Polymerisation (GTP)/acetoacetylation and controlled radical polymerisation techniques (RAFT).<br><br>Different micellar morphologies of poly(n-butyl methacrylate)-block-poly[2-(acetoacetoxy)ethyl methacrylate] (pBuMA-b-pAEMA) were observed in cyclohexane as a selective solvent. Depending on the block length ratio, either spherical, elliptical, or cylindrical micelles were formed. The density of the polymer chains at the core/corona interface is considerably higher as compared to any other strongly segregating system reported in the literature. It is demonstrated that there are H-bond interactions existing between acetoacetoxy groups, which increase the incompatibility between block segments. In addition, such interactions lead to the formation of secondary structures (such as b-sheets or globular structures) and larger superstructures in the micrometer length scale.<br><br>Block copolymers were also used to solubilise metal ion salts of different geometries and oxidation states in organic media, in which are otherwise insoluble. Sterically stabilised colloidal hybrid materials are formed, i.e. monodisperse micelles having the metal ion salt incorporated in their core upon complexation with the ligating pAEMA block, whereas pBuMA forms the solvating corona responsible for stabilisation in solution. Systematic studies show that the aggregation behaviour is dependent on different factors, such as the tautomeric form of the beta-dicarbonyl ligand (keto/enol) as well as the nature and amount of added metal ion salt.
59

Development Of Organic-inorganic Composite Membranes For Fuel Cell Applications

Erdener, Hulya 01 July 2007 (has links) (PDF)
Hydrogen is considered to be the most promising energy carrier of the 21st century due to its high energy density and sustainability. The chemical energy of hydrogen can be directly converted into electricity by means of electrochemical devices called fuel cells. Proton exchange membrane fuel cells (PEMFC) are the most preferred type of fuel cells due to their low operating temperatures enabling fast and easy start-ups and quick responses to load changes. One of the most important components of a PEMFC is the proton conducting membrane. The current membrane technology is based on perfluorosulfonic acid membranes and the most common one being Nafion. Although these membranes have good thermal and chemical stability, mechanical strength and high proton conductivities, they tend to dehydrate very fast at high temperatures and low relative humidity leading to poor fuel cell performances. Moreover, the high manufacturing cost of these membranes limits the mass-production of PEMFC&amp / #8217 / s in near future. The aim of this study is to develop alternative PEMFC membranes that have sufficient thermal and chemical stability, mechanical strength and comparable proton conductivity and fuel cell performances with Nafion membranes at relatively low cost. In this context, organic-inorganic composite membranes and blends were developed. A relatively cheap and commercially available polymer, polyether ether ketone, (PEEK), was chosen as the membrane matrix for its high thermal and mechanical stability and improvable proton conductivity via post-sulfonation. The proton conductivity of SPEEK membrane (at DS 68%) was 0.06 S/cm at 60&deg / C, and this conductivity was further increased to 0.13 S/cm with the introduction of zeolite beta crystals as inorganic fillers. The conductivity of a SPEEK blend (25wt% SPES-75wt% SPEEK) membrane was 0.08 S/cm at 90&deg / C. In PEMFC performance tests, 397 mA/cm2 was obtained for SPEEK membrane (DS 56%) at 0.6V for a H2/O2 PEMFC working at 1 atm and 80&deg / C. This result is promising when compared to the performance of Nafion 112&reg / of 660mA/cm2 under same conditions. These results are welcomed since the target for commercially viable alternate membranes are reached.
60

Matériaux hybrides organiques-inorganiques la photonique / Organic-inorganic hybrids for green photonics : solid state lighting applications

Castro Teixeira Freitas, Vânia Patricia 21 December 2016 (has links)
Ce travail a pour objet de synthétiser de nouveaux matériaux hybrides organiques-inorganiques, de types silsesquioxanes pontants. La structure locale et les propriétés de luminescence sont caractérisées en vue d’applications potentielles dans le domaine de la photonique durable comme les concentrateurs solaires.Dans ce contexte, trois familles distinctes de matériaux sont synthétisées, basées sur six précurseurs pouvant s’auto-assembler à travers des liaisons hydrogènes et dont les parties sililées peuvent être poly-condensées lors de la réaction sol-gel. Ces précurseurs diffèrent par leur sous structure organique i.e. 1) structure linéaire où la partie organique est basée sur le groupement malonamide (P2-m et P4-m); 2) structure linéaire dans laquelle un aromatique sépare deux groupements amide et/ou thioamide (P(UU), P(UT) and P(TT)) et 3) une structure à trois embranchements dont la partie organique est basée sur des groupements amides (t-UPTES (5000)).Les deux hybrides organiques inorganiques (M2-m et M4-m) résultant de l’hydrolyse condensation des précurseurs P2-m et P4-m sont synthétisés en présence de lanthanides. On étudie l’impact de la présence d’un ou deux groupes malonamides sur la structure locale et les propriétés de photoluminescence.Les hybrides organiques-inorganiques (H(UU), H(UT) and H(TT)) sont obtenus par hydrolyse condensation des précurseurs des précurseurs (P(UU), P(UT) and P(TT)). Des composés organiques modèles des trois sous structurels organiques sont également synthétisés. L’impact de la substitution du groupement urée par le groupement thio-urée sur la structure locale des modèles et des hybrides est étudié par spectroscopie vibrationnelle. Les mécanismes de compressions et les propriétés optiques des matériaux sont ensuite analysés à la lumière des différents types de liaisons hydrogènes (urée-urée, urée-thio-urée et thio-urée--thio-urée) mises en évidence dans ces composés.es hybrides basés sur les précurseurs t-UPTES(5000) sont synthétisés selon différentes stratégies. En changeant la concentration de HCl et d’eau ou en effectuant la synthèse dans un environnement contrôlé, on montre une amélioration des propriétés optiques de ce système, en particulier, le rendement quantique absolu et le coefficient d’absorption. De plus, les mécanismes de recombinaison responsables de l’émission sont étudiés à travers la comparaison entre les propriétés de luminescence des modèles organiques et inorganiques.Finalement, de par leur affinité pour les ions lanthanides les précurseurs P2-m and P4-m ont été dopés par des ions Eu3+. La structure locale des hybrides correspondants montre une coordination entre l’hybride et l’hôte. Grâce à un rendement quantique de luminescence très élevé pour ces matériaux, des concentrateurs solaires luminescents peuvent être développés présentant un maximum de rendement quantique absolu de 0.60+/-0.06 et un rendement de conversion optique de 12.3% dans la région spectrale (300-380 nm). / The present work aims to synthesize new organic-inorganic hybrid materials, bridge silsesquioxanes type, and characterize the local structure and photoluminescence properties overlooking potential applications in the area of sustainable photonics, namely, in solid-state lighting as luminescent solar concentrators.In this context, three distinct families of materials based on six precursors which differ in their structural organization are synthesized, i.e. precursors with structure: 1) linear where the organic component is based on malonamide group (P2-m and P4-m); 2) linear which is added an aromatic ring whose organic part is based on amide and/or thioamide (P(UU), P(UT) and P(TT)) and 3) tri-branched which the organic component is based on amide group (t-UPTES (5000)).Two organic-inorganic hybrids (M2-m and M4-m) which results from hydrolysis and condensation of the precursors P2-m and P4-m are synthetized. The role of the presence of one or two malonamide groups is studied in terms of local structure and photoluminescence properties.Three organic-inorganic hybrids (H(UU), H(UT) and H(TT)) based on (P(UU), P(UT) and P(TT)) aresynthesized and structurally characterized aiming to study the role of the hydrogen bond in the self-assembling of these materials. The presence of different types of hydrogen bonds (bifurcated, linear and cyclic) induces different conformations which affect the physical properties (mechanical and optical) of the materials.Hybrids based on t-UPTES(5000) precursor are synthesized based on different synthesis strategies. Changing the concentration of HCl and water content as well as the synthesis in a controlled environment allow the improvement of the optical properties of this system, in particular, the absolute quantum yield and the absorption coefficient. In addition, it is studied the recombination mechanisms responsible for the emission through the comparison between the corresponding photoluminescence properties of the organic and inorganic models.Finally, due to the structural simplicity of the precursors and affinity with lanthanide ions, P2-m and P4-m precursors are doped with Eu3+. The local structure of the corresponding hybrids shows local coordination between the ion and host. Efficient materials concerning the quantum yield values lead to the development of luminescent solar concentrators with a maximum absolute quantum yield of 0.600.06 and optical conversion efficiency in the absorption spectral region (300-380 nm) of 12.3%.

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