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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

Preparation and Study of Electro-Optical Properties of Novel Flexible Substrate Materials

Huang, Kuan-lung 29 July 2008 (has links)
Monomer 4,4¡¦¡¦¡¦¡¦-Difluore-3,3¡¦¡¦¡¦¡¦-bis(trifluoromethyl)-2¡¦¡¦,3¡¦¡¦,5¡¦¡¦,6¡¦¡¦-triphenyl (M4) were converted to novel poly(arylene ether)s by nucleophilic displacement reaction with several bisphenols in this study, then we called them : P-A1, P-A2, P-B1, P-B2. These polymers exhibit weightaverage molecular weight (Mw) between 2.2¡Ñ10^4 to 2.2¡Ñ10^5 g/mol. The molecular weight were investigated and confirmed by Mass and GPC. The molecular structures were investigated and confirmed by NMR and FT-IR.Thermal analysis physics studies with these polymers confirmed by Thermogravimetric analyzer (TGA) and differential scanning calorimetry (DSC). It is indicated that Td 5% of these polymers were 450¢XC ~ 548¢XC in TGA and Tg of these polymers were 303¢XC ~ 324¢XC in DSC.Besides, these polymers not were observed apparent crystallizing point, so we consider that they are not easy crystallized. Therefore, they could make manufacture in higher temperature and have higher thermal stability.In photophysical property of polymeric thin films, we obtained absorption wavelength that was 232nm ~ 300nm in UV-Vis absorption spectra and excitation wavelength that was 362nm ~ 368nm in PL spectra. Furthermore, the transmission spectra of polymeric thin films showed that visible light transparency were up to 83%. Besides, we used Ellipsometer to measure refractive index(n) that is 1.33 ~ 1.49.In drop shape analysis system, contact angles of the polymeric thin films are more than 109.8¢X. They show that the polymer thin films have low polarity and good hydrophobicity. By above material properties of these polymers, they have high thermal stabilities, high optical transparency, low polarity and good hydrophobicity. These good material properties are doing as a plastic substrate of devices or panel display.
2

A Theoretical Study of the Electronic Structures of Tetrahedral Boron-Halogen Complexes

Alshahrani, Sahar 20 May 2019 (has links)
This study addresses the structure and the bonding in the family of tetrahedral boranes. The specific molecules studied are the series B4X4 (X=H, F, Br, Cl, I), the series B4BrCl3, B4Br2Cl2, and B4Br3Cl and tetra-tert-butyl-tetraborane, t-Bu4B4. The research presented herein employs the Hartree-Fock Self Consistent Field (HFSCF), the Moller-Plesset second-order perturbation theory (MP2), and the Density Function Theory (DFT). A variety of basis sets was employed. Our calculations are the first theoretical studies of B4Br4, B4I4, B4BrCl3, B4Br2Cl2, and B4Br3Cl, and are also the first calculations for the D4h structures of any of these molecules, except for B4H4. These results were compared with experimental results, where such comparisons can be made. The most energetically stable structure for all the B4X4 and B4BrnClm molecules has symmetry Td.
3

Os níveis diferenciados de desempenho escolar : analisando estabilidades e mudanças nas concepções e expectativas de professores, familiares e alunos /

Giraldi, Luciana Ponce Bellido. January 2010 (has links)
Orientador: Silvia Regina Ricco Lucato Sigolo / Banca: Maria Regina Guarnieri / Banca: Márcia Cristina Argente Perez / Resumo: A partir de uma perspectiva bioecológica de pesquisa, elaborada por Urie Bronfenbrenner e, apoiada por outros estudiosos, como os trabalhos de Gimeno Sacristán, o objetivo geral deste estudo foi o de analisar concepções e expectativas de professores, alunos e familiares sobre o alto, o médio e o baixo desempenho escolar e considerar a constituição das mesmas em possíveis estabilidades e mudanças no decorrer da experiência escolar de alunos no Ensino Fundamental I. Para isso foi realizada uma pesquisa qualitativa, teórica/prática, numa cidade no interior do Estado de São Paulo, numa escola pública municipal, em uma sala de aula de 2º ano e em uma de 5º ano, cada uma com uma professora responsável. Tais docentes tiveram um papel fundamental ao estudo por aceitarem o convite para participar do mesmo fornecendo informações e, além disso, cada uma indicou seis estudantes, seguindo os critérios préestabelecidos de serem dois alunos de cada grupo: alto, médio e baixo desempenho escolar, total de doze alunos com suas respectivas famílias. Foram realizadas entrevistas com a referida tríade e observações da prática pedagógica em períodos distintos (1º, 2º e 4º bimestre escolar). Os resultados foram organizados em dois momentos: primeiramente foram destacadas concepções gerais sobre funções da escola, papéis sociais, conceito de infância e de aluno. Neste momento, foi possível conhecer o espaço escolar, expondo a rotina dos sujeitos e a realidade da unidade. Na sequência as concepções e expectativas sobre os diferenciados desempenhos escolares foram analisadas trazendo, inicialmente, as categorias gerais de apreciação de cada desempenho contrastadas com vivencias de sujeitos específicos que experienciavam o desempenho discutido. Ao analisar as idéias gerais sobre cada desempenho, verificou que estas não se ajustavam indistintamente a todos os alunos... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Based in a bioecological perspective, developed by Urie Bronfenbrenner and supported by other scholars as the work of Gimeno Sacristán, the main objective of this study is to examine concepts and expectations of teachers, students and families about the high, medium and low performance and consider the constitution of possible stabilities and changes in the course of the school experience of students in elementary school. To achieve this objective, it was conducted a qualitative, theoretical/practical research in a city in the countryside of the State of Sao Paulo. From an invitation to teachers of a school, there had been adherence to search and, from this, a teacher from the second year and another one from the fifth year indicated six students, according to the preestablished criteria of two students from each group: high, medium, and low school performance, total of twelve students with their families. Interviews were conducted with the triad and observations of pedagogical practice in different periods (1, 2 and 4 two-month periods). The results were organized into two phases; firstly were highlighted general conceptions about functions of the school, social roles, concepts of childhood and student. It was possible to know the educational space, exposing the routine of the people and the reality of the unit. Secondly, the ideas and expectations about the different school performances were analyzed, initially considering the general categories of each performance, contrasted with the reality of people who specifically experienced the performance in discussion. It was possible to notice that there have been changes in perceptions of specific people opposed to general ideas, however, essentially, the teacher from second year thought that distinguished school performances were related to the field of linguistic code (mainly), the same was true with the teacher from fifth year... (Complete abstract click electronic access below) / Mestre
4

Elaboration de latex nanostructurés à base de poly(chlorure de vinylidène) par polymérisation en émulsion / Elaboration of poly(vinylidene chloride)-based nanostructured latexes by emulsion polymerization

Garnier, Jérôme 30 October 2012 (has links)
Les emballages alimentaires et pharmaceutiques doivent de nos jours répondre à de nombreux critères : ils doivent non seulement préserver le produit emballé, mais également être inoffensifs, économes en énergie et jetables. Les polymères barrières ont permis de répondre à ces besoins, en offrant des alternatives à des matériaux plus demandeurs en énergie et plus lourds tels que le verre ou les métaux, tout en conservant une faible perméabilité à l’eau et/ou à l’oxygène. Parmi la grande variété de polymères barrières existants, les copolymères du poly(chlorure de vinylidène) (PVDC) offrent une protection plus complète aux contaminants extérieurs, grâce à leurs faibles perméabilités à l’eau et à l’oxygène. Cependant, les films de PVDC sont sujets à des processus de dégradation ayant lieu lors du thermoformage ou sous exposition aux rayonnements UV. Ces effets sont encore plus prononcés dans le cas de films obtenus à partir de latex, dû à des quantités plus importantes d’additifs qui accentueraient les phénomènes de dégradation du polymère. Par conséquent, la synthèse de latex à base de PVDC pour des applications en tant que films barrières aux stabilités thermique et UV améliorées revêt un grand intérêt. Des latex composites à base de PVDC ont tout d’abord été synthétisés en présence de latex semences à fonctionnalité époxy en vue d’améliorer la stabilité thermique du polymère. En effet, les groupements époxy jouent le rôle de stabilisants thermiques en piégeant le chlorure d’hydrogène, dégagé lors du thermoformage et présentant un effet catalytique indirect sur le processus de dégradation du polymère. Dans une première étape, des latex semences à fonctionnalité époxy ont été synthétisés par copolymérisation en émulsion du methacrylate de glycidyle (GMA) et du methacrylate de butyle (BMA). Lors d’une seconde étape, la copolymérisation en émulsion ensemencée du chlorure de vinylidene et de l’acrylate de méthyle a été effectuée en présence des semences de poly(GMA-co-BMA). Des analyses thermogravimétriques effectuées sur les échantillons composites ont mis en évidence le rôle de stabilisant thermique joué par les fonctions époxy. La seconde partie du projet concerne la synthèse de latex hybrides à base d’oxyde de cérium (CeO2) afin d’améliorer la résistance du PVDC aux rayonnements UV. Les nanoparticules d’oxyde de cérium sont en effet attrayantes en tant que stabilisants UV en raison de leur haute absorption des rayonnements UV et d'une faible activité photocatalytique. Cependant, étant donné l’incompatibilité intrinsèque entre les phases inorganique et organique, la synthèse de latex hybrides requiert souvent une étape préliminaire de modification de surface des particules minérales. Le greffage d’alcoxysilanes a d’abord été entrepris sur des particules d’oxyde de cérium afin d’encourager la réaction de polymérisation à leur surface. Des observations par cryo-Microscopie Electronique à Transmission (cryo-MET) effectuées sur les latex hybrides obtenus par cette stratégie ont montré que le greffage d’alcoxysilanes ne permettait pas d’améliorer efficacement la compatibilité entre les phases inorganique et polymère. Enfin, des macro-agents RAFT amphiphatiques ont été employés comme agents comptabilisant réactifs afin de promouvoir la réaction de polymérisation à la surface de l’oxyde de cérium. Des oligomères RAFT ont été obtenus par des réactions de co- ou terpolymérisation en présence d’un agent de contrôle RAFT. Après caractérisation de l’adsorption des macro-agents RAFT à la surface de l’oxyde de cérium, les particules modifiées ont été utilisées dans des réactions de polymérisation en émulsion. Les observations des latex hybrides par cryo-MET ont confirmé l’efficacité de la méthode pour l’obtention de structures hybrides. Cette stratégie semble ainsi la plus prometteuse pour la synthèse de latex hybrides CeO2/PVDC pour des applications en tant que films barrières présentant une stabilité UV améliorée. / Food and pharmaceutical packages should nowadays fulfill a wide range of requirements : not only should they preserve the packed products from external polluting agents, but they must also be innocuous, more energy-efficient and disposable. Barrier polymers have enabled to meet these criteria, by offering alternatives to more energy-consuming and heavier materials like glass or metals, while maintaining a low permeability to water and/or oxygen. Among the large variety of barrier polymers, poly(vinylidene chloride) (PVDC) copolymers provide a more complete protection to external contaminants, due to their extremely low permeabilities towards water and oxygen. Nonetheless, PVDC films still suffer from limitations as far as their thermal and UV stabilities are concerned. This effect is even more pronounced in the case of films obtained from latexes, due to the presence of higher amounts of additives that could take part in the polymer degradation. Therefore, the synthesis of PVDC-based latexes for use as waterborne barrier films with improved thermal and UV stabilities are of great importance. PVDC-based composite latexes were first synthesized from epoxy-functionalized seed latexes in order to enhance the polymer thermal stability. Given that hydrogen chloride displays an indirect catalytic effect on the polymer degradation, epoxy groups were indeed expected to act as thermal stabilizers by scavenging the HCl released by the polymer under thermal stress. In a first step, epoxy-functionalized seed latexes were synthesized via the emulsion copolymerization of glycidyl methacrylate (GMA) and butyl methacrylate (BMA). In a second step, the seeded emulsion copolymerization of vinylidene chloride and methyl acrylate was carried out in the presence of poly(GMA-co-BMA) seed latexes. Thermogravimetric analyses carried out on the resulting composite samples evidenced the thermal stabilization provided by epoxy groups. The second part of the project focused on the synthesis of cerium oxide-based hybrid latexes so as to improve the stability of PVDC to UV radiation. Cerium oxide (CeO2) nanoparticles are indeed very attractive as UV-stabilizers due to their high absorption of radiation in the UV range and a low photocatalytic activity. However, due to the intrinsic incompatibility between inorganic and polymer phases, the synthesis of inorganic-organic hybrid latexes often requires a preliminary step of modification of the mineral particles surface. The grafting of alkoxysilanes onto nanoceria was first attempted in order to promote the polymerization reaction at the surface of the inorganic particles. Cryo-Transmission Electron Microscopy (cryo-TEM) observations of hybrid latexes obtained via this route showed that this strategy was unsuccessful at improving the compatibility between the inorganic and polymer phases. Amphiphatic macro-RAFT agents were finally considered as reactive compatibilizing agents to direct the polymerization towards the cerium oxide surface. RAFT oligomers were first obtained by co- or terpolymerization reactions in the presence of a RAFT controlling agent. After characterizing the adsorption of amphiphatic macro-RAFT agents at the surface of nanoceria, surface-modified cerium oxide particles were then engaged in reactions of emulsion polymerization reactions. In most cases, cryo-TEM observations carried out on the resulting latexes confirmed the efficiency of the amphiphatic macro-RAFT agent route for the synthesis of hybrid structures. Therefore this route appeared so far to be the most promising for the synthesis of CeO2/PVDC hybrid latexes for use as waterborne barrier films with improved UV-stability.
5

Condensados em redes ópticas periódicas / Condensates in periodic optical lattices

Matsushita, Eduardo Toshio Domingues 06 August 2007 (has links)
Utilizamos o modelo de Bose-Hubbard para estudar as estabilidades dinâmica e termodinâmica dos condensados numa rede óptica periódica circular. O nosso principal objetivo foi investigar a existência de condensados metaestáveis no sistema. Deduzimos e resolvemos a equação de Gross-Pitaevskii e, a partir da análise das soluções, foi possível mostrar que o sistema se condensa em estados com momento modular bem definido. Esses estados formam uma base que diagonaliza o termo que descreve o tunelamento atômico no hamiltoniano de Bose-Hubbard. No contexto da teoria de Bogoliubov deduzimos para cada condensado, o hamiltoniano efetivo cuja diagonalização determina o espectro das excitações coletivas do sistema. Identificamos corretamente o modo de energia zero, conseqüência da violação da conservação do número de átomos, e verificamos que este possui momento modular igual ao do condensado. No estudo da estabilidade vimos que todos os condensados com momento modular nos 2º e 3º quadrantes são termodinamicamente instáveis e as respectivas condições de estabilidade dinâmica dependem dos parâmetros de controle do sistema. Por outro lado os condensados com momento modular nos 1º e 4º quadrantes são todos dinamicamente estáveis enquanto que, nesse caso, é a estabilidade termodinâmica que depende dos parâmetros de controle do sistema. Nessa análise verificamos que o condensado com momento modular zero, que corresponde ao mínimo global da energia, é sempre estável. Determinamos exatamente o intervalo nos parâmetros de controle a partir do qual podemos encontrar condensados metaestáveis no sistema. Examinamos como a competição entre as intensidades dos termos de tunelamento e repulsão local afeta a estabilidade dos condensados. Essa competição define dois regimes distintos: Rabi, onde a coerência entre estados localizados nos sítios é mantida, e Fock, onde não há mais essa coerência e a aplicabilidade da aproximação de Bogoliubov é questionável. / We use the Bose-Hubbard model to study the dynamical and thermodynamical stabilities of condensates in a circular periodic optical lattice. Our main goal was to investigate the existence of metastable condensates in the system. We derive and solve the Gross-Pitaevskii equation, and from the analysis of the solutions it was possible to show that the system condenses in states with well-defined modular momentum. These states constitute a basis that diagonalizes the term of the Bose-Hubbard Hamiltonian which describes the dynamics of atomic tunneling. In the framework of Bogoliubov theory we determine, for each condensate, the effective Hamiltonian whose diagonalization give us the collective excitation spectrum of the system. We show that the mode associated to a zero eigenvalue, which is a consequence of the violation of atoms number conservation, has the same modular momentum of the condensate. The condensates with modular momentum in the 2nd and 3rd quadrants are all thermodynamically unstable whereas the dynamical stability depends on the control parameters. On the other hand, the condensates with modular momentum in the 1st and 4th quadrants are all dynamically stable whereas the thermodynamical stability depends on the control parameters. Our analysis shows that the condensate with modular momentum zero, which corresponds to a global minimum of energy, is always stable independently of the control parameters. We determine, exactly, the range on the control parameters where it is possible to detect metastability in the system. We have studied how the competition between the intensities of the tunneling and local interaction terms affects the stability of the condensates. This competition defines two distinct regimes: Rabi, where the coherence between states localized in the sites is achieved, and Fock, where this coherence is not achieved and the validity of Bogoliubov approximation is questionable.
6

Os níveis diferenciados de desempenho escolar: analisando estabilidades e mudanças nas concepções e expectativas de professores, familiares e alunos

Giraldi, Luciana Ponce Bellido [UNESP] 13 August 2010 (has links) (PDF)
Made available in DSpace on 2014-06-11T19:24:34Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-08-13Bitstream added on 2014-06-13T19:31:15Z : No. of bitstreams: 1 giraldi_ipb_me_arafcl.pdf: 1208852 bytes, checksum: ed1655bd8de9870a452a086fc019c537 (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / A partir de uma perspectiva bioecológica de pesquisa, elaborada por Urie Bronfenbrenner e, apoiada por outros estudiosos, como os trabalhos de Gimeno Sacristán, o objetivo geral deste estudo foi o de analisar concepções e expectativas de professores, alunos e familiares sobre o alto, o médio e o baixo desempenho escolar e considerar a constituição das mesmas em possíveis estabilidades e mudanças no decorrer da experiência escolar de alunos no Ensino Fundamental I. Para isso foi realizada uma pesquisa qualitativa, teórica/prática, numa cidade no interior do Estado de São Paulo, numa escola pública municipal, em uma sala de aula de 2º ano e em uma de 5º ano, cada uma com uma professora responsável. Tais docentes tiveram um papel fundamental ao estudo por aceitarem o convite para participar do mesmo fornecendo informações e, além disso, cada uma indicou seis estudantes, seguindo os critérios préestabelecidos de serem dois alunos de cada grupo: alto, médio e baixo desempenho escolar, total de doze alunos com suas respectivas famílias. Foram realizadas entrevistas com a referida tríade e observações da prática pedagógica em períodos distintos (1º, 2º e 4º bimestre escolar). Os resultados foram organizados em dois momentos: primeiramente foram destacadas concepções gerais sobre funções da escola, papéis sociais, conceito de infância e de aluno. Neste momento, foi possível conhecer o espaço escolar, expondo a rotina dos sujeitos e a realidade da unidade. Na sequência as concepções e expectativas sobre os diferenciados desempenhos escolares foram analisadas trazendo, inicialmente, as categorias gerais de apreciação de cada desempenho contrastadas com vivencias de sujeitos específicos que experienciavam o desempenho discutido. Ao analisar as idéias gerais sobre cada desempenho, verificou que estas não se ajustavam indistintamente a todos os alunos... / Based in a bioecological perspective, developed by Urie Bronfenbrenner and supported by other scholars as the work of Gimeno Sacristán, the main objective of this study is to examine concepts and expectations of teachers, students and families about the high, medium and low performance and consider the constitution of possible stabilities and changes in the course of the school experience of students in elementary school. To achieve this objective, it was conducted a qualitative, theoretical/practical research in a city in the countryside of the State of Sao Paulo. From an invitation to teachers of a school, there had been adherence to search and, from this, a teacher from the second year and another one from the fifth year indicated six students, according to the preestablished criteria of two students from each group: high, medium, and low school performance, total of twelve students with their families. Interviews were conducted with the triad and observations of pedagogical practice in different periods (1, 2 and 4 two-month periods). The results were organized into two phases; firstly were highlighted general conceptions about functions of the school, social roles, concepts of childhood and student. It was possible to know the educational space, exposing the routine of the people and the reality of the unit. Secondly, the ideas and expectations about the different school performances were analyzed, initially considering the general categories of each performance, contrasted with the reality of people who specifically experienced the performance in discussion. It was possible to notice that there have been changes in perceptions of specific people opposed to general ideas, however, essentially, the teacher from second year thought that distinguished school performances were related to the field of linguistic code (mainly), the same was true with the teacher from fifth year... (Complete abstract click electronic access below)
7

Condensados em redes ópticas periódicas / Condensates in periodic optical lattices

Eduardo Toshio Domingues Matsushita 06 August 2007 (has links)
Utilizamos o modelo de Bose-Hubbard para estudar as estabilidades dinâmica e termodinâmica dos condensados numa rede óptica periódica circular. O nosso principal objetivo foi investigar a existência de condensados metaestáveis no sistema. Deduzimos e resolvemos a equação de Gross-Pitaevskii e, a partir da análise das soluções, foi possível mostrar que o sistema se condensa em estados com momento modular bem definido. Esses estados formam uma base que diagonaliza o termo que descreve o tunelamento atômico no hamiltoniano de Bose-Hubbard. No contexto da teoria de Bogoliubov deduzimos para cada condensado, o hamiltoniano efetivo cuja diagonalização determina o espectro das excitações coletivas do sistema. Identificamos corretamente o modo de energia zero, conseqüência da violação da conservação do número de átomos, e verificamos que este possui momento modular igual ao do condensado. No estudo da estabilidade vimos que todos os condensados com momento modular nos 2º e 3º quadrantes são termodinamicamente instáveis e as respectivas condições de estabilidade dinâmica dependem dos parâmetros de controle do sistema. Por outro lado os condensados com momento modular nos 1º e 4º quadrantes são todos dinamicamente estáveis enquanto que, nesse caso, é a estabilidade termodinâmica que depende dos parâmetros de controle do sistema. Nessa análise verificamos que o condensado com momento modular zero, que corresponde ao mínimo global da energia, é sempre estável. Determinamos exatamente o intervalo nos parâmetros de controle a partir do qual podemos encontrar condensados metaestáveis no sistema. Examinamos como a competição entre as intensidades dos termos de tunelamento e repulsão local afeta a estabilidade dos condensados. Essa competição define dois regimes distintos: Rabi, onde a coerência entre estados localizados nos sítios é mantida, e Fock, onde não há mais essa coerência e a aplicabilidade da aproximação de Bogoliubov é questionável. / We use the Bose-Hubbard model to study the dynamical and thermodynamical stabilities of condensates in a circular periodic optical lattice. Our main goal was to investigate the existence of metastable condensates in the system. We derive and solve the Gross-Pitaevskii equation, and from the analysis of the solutions it was possible to show that the system condenses in states with well-defined modular momentum. These states constitute a basis that diagonalizes the term of the Bose-Hubbard Hamiltonian which describes the dynamics of atomic tunneling. In the framework of Bogoliubov theory we determine, for each condensate, the effective Hamiltonian whose diagonalization give us the collective excitation spectrum of the system. We show that the mode associated to a zero eigenvalue, which is a consequence of the violation of atoms number conservation, has the same modular momentum of the condensate. The condensates with modular momentum in the 2nd and 3rd quadrants are all thermodynamically unstable whereas the dynamical stability depends on the control parameters. On the other hand, the condensates with modular momentum in the 1st and 4th quadrants are all dynamically stable whereas the thermodynamical stability depends on the control parameters. Our analysis shows that the condensate with modular momentum zero, which corresponds to a global minimum of energy, is always stable independently of the control parameters. We determine, exactly, the range on the control parameters where it is possible to detect metastability in the system. We have studied how the competition between the intensities of the tunneling and local interaction terms affects the stability of the condensates. This competition defines two distinct regimes: Rabi, where the coherence between states localized in the sites is achieved, and Fock, where this coherence is not achieved and the validity of Bogoliubov approximation is questionable.
8

Développement de solutions innovantes d'électrolytes pour sécuriser les accumulateurs lithium-ion / Development of innovative electrolytes for safer lithium-ion batteries

Chancelier, Léa 24 October 2014 (has links)
Les batteries lithium-ion dominent le marché des appareils nomades et celui des véhicules électriques. Néanmoins elles posent des problèmes de sécurité liés à leur électrolyte, contenant des carbonates inflammables et volatils. Pour sécuriser ces systèmes, les liquides ioniques (LI) sont étudiés comme électrolytes alternatifs. Ce sont des sels liquides à température ambiante, réputés stables thermiquement et non inflammables. Ce caractère sécuritaire des LI, souvent avancé, est pourtant peu étayé par des expériences probantes. Les travaux de cette thèse visent à comprendre le comportement de ces LI en situations abusives, telles qu'un échauffement de la batterie, un feu ou une surcharge. Les températures de décomposition de LI contenant les cations imidazolium ou pyrrolidinium différemment substitués et l'anion bis(trifluoromethanesulfonyl)imide ont été déterminées par analyse thermogravimétrique (ATG). Une analyse critique des données (de la littérature et de nos mesures) a permis de définir une procédure optimisée, pour obtenir des résultats reproductibles et comparables. Des électrolytes constitués de mélanges de carbonates ou de LI et de sels de lithium ont été analysés par ATG dynamique et isotherme, et leurs produits de décomposition ont été identifiés. Leur comportement au feu a été testé par la mesure des chaleurs de combustion, des délais d'inflammation et l'identification des gaz générés. Des tests de cyclage électrochimique ont été menés avec ces mêmes électrolytes dans des systèmes lithium-ion constitués des électrodes Li4Ti5O12 et LiNi1/3Mn1/3Co1/3O2. L'évolution des électrolytes et des surfaces des électrodes en situation de surcharge a été examinée / Lithium-ion batteries are dominating both the nomad device and electric vehicle markets. However they raise safety concerns related to their electrolyte, which consists of flammable and volatile carbonate mixtures and toxic salts. The replacement of the latter by ionic liquids (IL), liquid salts claimed to be thermally stable and non-flammable, could provide a safer alternative. Yet this often claimed feature has been poorly examined by experiments. The work of this thesis investigates IL behaviour under abuse conditions such as overheating, fire or overcharge. Decomposition temperatures of IL based on differently substituted imidazolium or pyrrolidinium cations and the bis(trifluoromethanesulfonyl)imide anion were determined by thermogravimetric analysis (TGA). A critical study of gathered data (from literature and our work) led to the determination of an optimised procedure to obtain reproducible and comparable results. Electrolytes based on carbonates mixtures or IL and containing lithium salt were studied by dynamic and isothermal TGA, and their decomposition products were identified. Their combustion behaviour was also tested by measuring heats of combustion and ignition delays. Emitted gases were analysed and quantified. Electrochemical cycling tests were carried out with these electrolytes in lithium-ion systems based on Li4Ti5O12 and LiNi1/3Mn1/3Co1/3O2 electrodes. The evolution of the electrolytes and electrodes surface was also examined under overcharge
9

Synthesis, Conformation and Glycosidic Bond Stabilities of Septanoside Sugars

Dey, Supriya January 2014 (has links) (PDF)
Seven-membered cyclic sugars, namely, septanoses and septanosides, are less commonly known sugar homologues. Synthesis of septanoses arise an interest due to their configurational and conformational features and the attendant possibilities to explore their chemical and biological properties. Septanosides derivatives, mostly, deoxy-septanosides were synthesized, by many synthetic methodologies, such as, Knoevengal condensation, ring-closing metathesis, Bayer-Villeger oxidation and ring-expansion of 1,2-cyclopropanted glycals as key steps. Apart from septanosyl monosaccharides, septanoside containing di- and tri-saccharides were also performed using glycosylation and ring expansions. Another area of sustained interest is the studies of the stabilities of glycosidic bonds. Acid- and enzyme-catalyzed hydrolysis of glycosidic bond were investigated intensely in the case of pyranosides and furanosides. The explanation of the hydrolysis of such stereomeric sugars were rationalized on the basis of stereoelectronic effects, such as, (i) antiperiplanarity; (ii) synperiplanarity of lone-pair of electrons involed in the hydrolysis process; (iii) steric effects; (iv) field and hyperconjugative effects; (v) conformational effects; (vi) disarming torsional effects and (vii) substituent effects. Chapter 1 of the thesis describes a survey of (i) synthesis of deoxy-septanosides and septanoside-containing di-and tri-saccharides and (ii) acid-catalyzed hydrolysis of glycopyranosides. In a programme, it was desired to identify a new methodology for the synthesis of 2-deoxy-2-C-septanosides. Synthesis of various septanosides from 2-hydroxy glycals, namely, oxyglycals, involves intermediates, such as, vinyl halide (III) and diketone (IV) (Scheme 1). These intermediates were identified as precursors for the synthesis of desired 2-deoxy-2-C-septanosides. Scheme 1 reactions, namely, Heck, Suzuki and Sonogashira reaction for the formation of hither-to unknown septanoside, branching out at C-2. Heck coupling and Suzuki coupling reaction of bromo-oxepine was performed using activated alkenes, acrylates and substituted boronic acid, respectively, in presence of Pd(OAc)2, to furnish 2-deoxy-2-C-alkyl/aryl septanoside derivatives (Scheme 2). Scheme 2 2-deoxy-2-C-alkynyl septanoside derivatives (Scheme 3). Scheme 3 BnO OOMe BnO OOMePd(PPh3)2Cl2,CuIBr BnO R BnO DMF:THF:Et3N(3:2:1)BnO OBn 98 oC, 72 h BnO OBn R=Ph,SiMe3,C6H13 One of the 2-deoxy-2-C-alkyl septanoside derivative was converted to the corresponding protecting-group free 2-deoxy-2-C-alkyl septanoside, using hydrogenolysis (Pd/C, H2) and NaBH4-mediated reduction. Chapter 2 presents details of the synthesis of 2-deoxy-2-C-alkyl/aryl/alkynyl septanoside derivatives from a bromo-oxepine. Continuing the efforts to extend the ring-opening of oxyglycal derived gem-dihalo-1,2¬cyclopropanted sugar, a Lewis acid-catalyzed ring-opening was considered important. The presence of an additional substituent in C-2 of oxyglycal switches reactivity as compared to glycals. For example, ring-opening of glycal derived gem-dihalo-1,2-cyclopropane generates 2-C-branched pyranoside, whereas corresponding oxyglycal generates oxepines even when both the reactions were performed under a mild basic condition, illustrating a sufficient reactivity difference between a glycal and an oxyglycal. Thus, ring-opening reaction of gem-dichloro-1,2-cyclopropanted oxyglycal in the presence of a Lewis acid, hither-to unknown, was examined. In this event, it was found that ring-opening reaction led to chloro-oxepine derivatives in the presence of AgOAc, using alcohol as nucleophiles. Primary, secondary, unsaturated and aromatic alcohols were used in the ring-opening reaction. The ring-opening reaction was stereoselective and only α-anomer was obtained in a good yield in each case (Scheme 5). The counter-anion also reacted in an instance, so as to furnish O-acetyl chloro-oxepine during the ring-opening reaction. Scheme 5 The course of the reaction in the absence of alcohol led to afford only the O-acetyl chloro-oxepine (Scheme 6). Scheme 6 It became pertinent to compare the result this work with that of AgOAc-catalyzed ring-opening of glycal derived gem-dihalo-1,2-cyclopropanated sugar, which led to C-furanoside derivative, as reported by Harvey and co-workers. The sequence of reactions involved were protonation of the endo-cyclic oxygen, followed by ring-opening to generate resonance stabilized allylic ion, which rearranged to C-furanoside. In contrast, oxyglycal derived gem-dihalo-1,2-cyclopropane studied herein led to chloro-oxepine exclusively, without subsequent rearrangement. Ring-opening of glucal derived gem-dihalo-1,2-cyclopropanated sugars, followed by cyclization to C-furanoside were likely to have occurred, due to isomerisation of less-substituted endo-cyclic double bond at C2-C3 of oxepine to C1-C2 unsaturated vinyl ether. Such a reaction was related closely to the acid-catalyzed rearrangement in less-substituted oxepine systems. On the other hand, gem-dichloro-1,2¬cyclopropanated oxyglycal derived chloro-oxepine did not undergo such an isomerisation, possibly due to unsaturation being present at highly substituted C2-C3 carbons (Scheme 7). Thus, the presence of an additional oxy-substituent at C-2 in oxyglycal derived cyclopropane derivative plays a major role to control the reactivity, as compared to glycal derived cyclopropane derivatives. Scheme 7 without undergoing further reactions, was confirmed further by the following reactions: (i) RuCl3¬NaIO4 mediated oxidation; (ii) NaBH4 reduction and (iii) Pd/C mediated hydrogenolysis (Scheme 8). Scheme 8 1,2-cyclopropane to exclusive formation of chloro-oxepine in the presence of AgOAc. It was planned further to synthesize a 1,7-linked-α-D-diseptanoside, through the oxyglycal route. Ring-opening of oxyglycal derived gem-dihalo-1,2-cyclopropanated derivative with 6¬hydroxy glycal led to 1,7-α-linked disaccharide unit. The following reactions were performed in order to synthesize 1,7-linked-α-diseptanoside 2: (i) cyclopropanation of the glycal double bond; (ii) ring opening of the gem-dihalo cyclopropane; (iii) RuO4 mediated oxidation; (iv) NaBH4 reduction and (v) hydrogenolysis using Pd/C, H2 (Scheme 9). Similar methodology was used for the synthesis of monoseptanoside, namely, n-pentyl-D-glycero-D-galacto-septanoside. Scheme 9 1 Oxyglycal route was also used for the synthesis of 2-chloro-2-deoxy septanoside 3, using hydrogenolysis (Pd/C, H2) and NaBH4 mediated reduction of chloro-oxepine (Scheme 10). Scheme 10 A kinetic study of the hydrolytic stabilities of mono-and diseptanoside was undertaken using an acid-catalysis, in a subsequent investigation. In the course of studies, it was observed that glycosidic bond in the reducing-end hydrolyzed twice faster than that at the non-reducing end, whereas glycosidic bond in monosaccharide 1 hydrolyzed 1.5 times faster than of reducing-end glycosidic bond in diseptanoside 2. Further, it was found that the replacement of the C-2 hydroxyl group by a chloride group reduced the rate of hydrolysis (Table 1). Table 1. First order rate constants and thermodynamic parameters for the acid-catalyzed hydrolysis of glycosidic bond in septanosides 1, 2 and 3. Compound Rate of hydrolysis ΔH# ΔS# ΔG# (kobs) (104 s-1) (kcal/mol) (cal/mol K) (kcal/mol) 35 oC 45 oC 85 oC 90 oC a non-reducing end of 2. A computational study was conducted, in order to gain further insight into the hydrolysis, using B3LYP/6-311G* level theory in the Gaussian 09 program packages. Calculations using the PCM solvent model with water as the solvent showed that the orientation of hydroxylmethyl group plays an important role. In the case of 1, the gg conformer was calculated stable by 2.12 kcal/mol, as compared, to tg-conformer. In the gg conformation, the optimal positioning of the dipole C7-O7 stabilized the oxo-carbonium ion in the transition state (Figure 1). Also, hydroxyl group at C4 stabilized the transition state, through non-covalent interaction (Figure 1). The transition state for the hydrolysis of 1 was found to present activation barrier (∆G#) of 19.9 kcal/mol, which was in good agreement with value for 1 (∆G# = 23.26 kcal/mol), as calculated from Erying plot (Table 1). On the other hand, inductive effect of the chloride group, as well as, the tg-orientation of the hydroxymethyl group appeared to contribute to the slower rate of the hydrolysis. Figure 1. gg- and tg-conformations in the ground state of 1. Chapter 4 describes synthesis of 1,7-linked-α-D-diseptanoside, 2-chloro-2-deoxy septanoside and their acid-catalyzed hydrolysis studies. Solid-state and solution phase conformation of septanosides are rare at present even when solid-state structures of pyranoside and furanosides are known commonly, that provide rich information of covalent and non-covalent interactions. In this context, single crystal X-ray structural analysis of septanosides, namely, n-pentyl-2-chloro-2-deoxy-α-D-manno-sept-3-uloside 4 and p-bromo phenyl 4,5,7-tri-O-benzyl-β-D-glycero-D-talo-septanoside 5 were analyzed. It was observed that the solid-state structure of 4 adopted twist-chair conformation, namely, 5,6TC3,4, whereas 5 adopted O,1TC2,3 conformation (Figure 2). An analysis of non-covalent interactions revealed that a dense network of O−H···O and C−H···O stabilized the crystal lattice of 4, whereas O−H···O and C−H···π stabilized the crystal lattice of 5. Chapter 5 describes the detailed analysis of X-ray crystal structure of two septanoside derivatives including non-covalent interactions responsible for the stabilization of crystal lattice. Figure 2. ORTEP of 4 and 5 with displacement ellipsoids, at a 10 % and 50 % probability level. In summary, the thesis established the following major results: (i) synthesis of 2-deoxy-2-C¬alkyl/aryl septanoside from a bromo-oxepine, using organometallic C-C bond forming reactions; (ii) the ring-opening reaction of oxyglycal derived gem-dihalo-1,2-cyclopropane in the presence of AgOAc and the effect of additional C-2 oxy-substituent in the reactivity, in comparison to glycal; (iii) an oxyglycal route for the synthesis of 1,7-linked-α-D-diseptanoside, 2-chloro-2-deoxy septanoside and their acid-catalyzed hydrolysis studies and (iv) solid-state X-ray crystal structural analysis and computational analysis of the conformation and non-covalent interactions associated with the stabilization of crystal lattice. Overall, the studies presented in the thesis provide a new insight into the synthesis, acid-catalyzed hydrolysis and solid-state structural analysis of septanoside derivatives.
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THE EFFECT OF MOLECULAR DESIGN ON SPIN DENSITY LOCALIZATION AND RADICAL-INITIATED DEGRADATION OF CONJUGATED RADICAL CATIONS

Kaelon Athena Jenkins (16613448) 19 July 2023 (has links)
<p> Radical species are essential in modern chemistry. In addition to fundamental chemistry, their unique chemical bonding and distinct physicochemical features serve critical functions in materials science in the form of organic electronics. Due to their high reactivity, radicals of the main group element are often transient. In recent years, remarkably stable radicals are often stabilized by π-delocalization, sterically demanding side groups, carbenes, and weakly coordinating anions. The impacts of modifications such as electron-donating, electron-withdrawing, and end-capping on the spin density distribution and thermodynamic and kinetic stability of archetypal radical-driven processes such as dimerization are not well understood. This dissertation aims to track the perturbation of spin density from EDG and EWG modifications, provide mechanistic insight into the radical-initiated reactions of conjugated radical cations, and establish correlations between molecular design and thermochemical properties and their resulting kinetic stability by computationally evaluating these characteristics against experimental data. The disclosed connections give useful new recommendations for the rational design of thermodynamically and kinetically stable novel materials.</p>

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