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Effect of Electrolytes on Room-Temperature Sodium-Sulfur Battery PerformanceDaniel Jacob Reed (12457485) 26 April 2022 (has links)
<p> </p>
<p>Room-temperature sodium-sulfur (RT Na-S) batteries are an emergent new technology that are highly attractive due to their low raw materials cost and large theoretical specific energy. However, many fundamental problems still plague RT Na-S batteries that prevent their progression from the research and development phase to the commercial phase. Sulfur and its final discharge product are insulators, and intermediate polysulfide discharge products are soluble in commonly used liquid electrolytes. As a result, RT Na-S cells exhibit large capacity defects, low coulombic efficiencies, and rapid capacity fading. Additionally, the reactive sodium metal anode can form dendrites during cycling, which reduces capacity and shortens cell life. One way to combat these issues is the judicious selection of electrolyte components. In this study, the effects of monoglyme (G1), diglyme (G2), and tetraglyme (G4) glyme ether electrolyte solvents on RT Na-S cell performance are investigated. Galvanostatic cycling of Na/Na symmetric coin cells reveals that the G2 solvent enable stable cycling at low overpotentials over a wide range of current densities. In contrast, the G1-based cells show evidence of dendritic plating, and G4-based cells are not suitable for use at high current densities. Electrochemical impedance spectroscopy during cycling confirms that the G2 solvent facilitates the formation of a strong, stable SEI on the Na electrode surface. Results from galvanostatic cycling of RT Na-S full coin cells demonstrates that G1-based cells deliver the highest initial specific discharge capacities among the three cell types, but G4-based cells are the most reversible. Infinite charging, the indefinite accrual of charge capacity at the high charge voltage plateau, affects all cell types at different cycle numbers and to different extents. This behavior is linked to the strength of the polysulfide shuttle during charge. Optical microscopy experiments show that G2 and G4 facilitate the formation of the S3•- sulfur radical, which reduces capacity. G1 minimizes the radical formation and thus delivers higher initial specific discharge capacity. In order to fully optimize the electrolyte for RT Na-S cells, future work should study glyme solvent blends, additives, and concentrated salts.</p>
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Optimizing the Discovery and Processability of Biologically Derived Molecular Glass Host Materials for Photonic ApplicationsFlynn, John J. 22 June 2020 (has links)
No description available.
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Étude des cinétiques de réticulation et de la dynamique moléculaire de réseaux silicones : compréhension des mécanismes catalytiques par analyse viscoélastique et RMN / Study of the rosslinking kinetics and the molecular dynamics of silicone networks : description of the catalytic mechanisms by rheology and NMRAutin, Laura 07 December 2012 (has links)
La catalyse de polycondensation des silicones, et notamment des élastomères vulcanisables à froid bicomposants, constitue un enjeu scientifique, environnemental et économique. Le dilaurate de dibutyl étain (DLDBE), classé CMR2, très largement utilisé dans l'industrie du silicone sera prochainement interdit par la nouvelle réglementation REACH. L'objectif de cette étude est donc d'étudier de nouveaux systèmes catalytiques des réactions de polycondensation. L'effet des différents constituants de la formulation (masse molaire du PDMS réactif, concentration en réticulant, concentration en catalyseur) sur la cinétique de réticulation et sur les propriétés finales a été étudié par combinaison des techniques de rhéologie, RMN et taux de gonflement. Principalement, ce travail consiste en l'étude approfondie de deux catalyseurs : une guanidine et un complexe de zinc et les résultats montrent que la construction des réseaux est plus ou moins différente selon la catalyse. En effet, un dérivé de l'étain conduit à une construction en deux étapes d'hydrolyse et de condensation, dont l'hydrolyse est d'abord favorisée. En comparaison, les complexes de zinc tendent à se comporter d'une façon très similaire, bien que l'hydrolyse des alcoxysilanes soit plus importante. Au contraire, une catalyse basique favorise très largement la condensation par rapport à l'hydrolyse. La guanidine réagit très rapidement avec les fonctions silanols. Ensuite, l'hydrolyse des alcoxysilanes se produisant dans une moindre proportion, le réseau tridimensionnel se construit. Ces travaux ont donc montré que le complexe de zinc étudié est un bon remplaçant du DLDBE / Silicones condensation catalysis, and more especially room temperature vulcanizable compounds, is a very important scientific, environmental and economic issue. The catalysis species, derivated from tin dilaurate, which are now classified as a CMR2 compound (toxic for reproduction), have been widely used in the silicone industry. The new REACH regulation is going to forbid its use very soon. This study aims to work on new catalytic systems. The influence of the components of the formulation on the kinetics and mechanical properties has been study by different methods: rheology, NMR and swelling measurements. More precisely, this work focuses on two catalysts: one guanidine and zinc complexes. Results have shown that the network construction depends on the catalysis. In fact, while using a tin compound, the construction occurs in two steps, in which hydrolysis is the most important. As a comparison, zinc complexes present the same behaviour as tin compounds even though the hydrolysis step is much more important. On the contrary, it’s known that basic catalysis enhances the condensation step. Then, the guanidine quickly reacts with the silanol functions. Then, in a second step, the alkoxysilanes hydrolysis occurs in a smaller proportion. The tridimensional network is getting built. This work mainly showed that zinc complexes can easily replace tin compounds
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Methylammonium Formate as a Mobile Phase Modifier for Reversed Phase Liquid ChromatographyGrossman, Shau 06 August 2008 (has links)
No description available.
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Contamination of Fresh Produce with Human Pathogens in Domestic and Commercial KitchensPaden, Holly Noelle 10 December 2018 (has links)
No description available.
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INVESTIGATION OF SIGN REVERSAL BETWEEN ELECTROMAGNETICALLY INDUCED TRANSPARENCY AND ABSORPTION IN ATOMIC VAPORDay, Amanda N. 19 August 2013 (has links)
No description available.
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Magneto-Transport and Optical Control of Magnetization in Organic Systems: From Polymers to Molecule-based MagnetsBozdag, Kadriye Deniz 30 September 2009 (has links)
No description available.
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Studying the altered reactivity of electrochemical systems in room temperature ionic liquidsErnst, Sven January 2013 (has links)
The work presented in this thesis examines the electrochemical behaviour of a number of species, both surface-bound and in the solution phase, in various room-temperature ionic liquids (RTILs), in order to identify systems which show altered reactivities in room-temperature ionic liquids, compared to that in conventional, molecular, aprotic solvents. The fundamentals of electrochemistry are outlined and an introduction to room-temperature ionic liquids is given, after which the results of six original investigations are presented, as follows; The electrochemical response of surface-bound anthraquinonyl films was investigated as a function of RTIL cation size. The reduction of oxygen to superoxide in the [C<sub>2</sub>mim][NTf<sub>2</sub>] RTIL was studied at different carbon electrodes. The mechanisms of electrodeposition and stripping of Zn(II) onto bulk zinc deposits, on glassy carbon electrodes, in the [C<sub>4</sub>mPyrr][NTf<sub>2</sub>] RTIL were investigated. A novel and successful method for the fabrication of zinc microdisk electrodes was developed and the electrochemical behaviour of these electrodes was investigated. The mechanisms for the electrochemical reductions of some bromo- and nitrobenzenes at platinum microelectrodes were determined in the [C<sub>4</sub>mPyrr][NTf<sub>2</sub>] ionic liquid, in order to identify systems which displayed changed reactivities in RTILs compared to those in molecular aprotic solvents. The altered reactivity of 1-bromo-4-nitrobenzene in the [C<sub>4</sub>mPyrr][NTf<sub>2</sub>] ionic liquid was utilised via electrochemical reduction at zinc microelectrodes in order to form arylzinc compounds. The work presented in this thesis shows that the oft-taken view that the reactivity of a given species in an ionic liquid will mimic that in conventional aprotic solvents is not always the case. Reactivities can be markedly different between RTILs and aprotic solvents and can also be highly dependent on the specific ionic liquid employed.
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[en] SOLID SURFACE ROOMTEMPERATURE PHOSPHORIMETRY FOR THE SELETIVE DETERMINATION OF NITROGENATED AND SULPHURATED POLYCICLIC AROMATIC COMPOUNDS INGASOLINE AND SEDIMENT SAMPLE / [pt] UTILIZAÇÃO DA FOSFORIMETRIA NA TEMPERATURA AMBIENTE SUPORTADA EM SUBSTRATO SÓLIDO PARA A DETERMINAÇÃO SELETIVA DE COMPOSTOS POLICÍCLICOS AROMÁTICOS NITROGENADOS E SULFURADOS EM GASOLINA E EM SEDIMENTOCARLOS EDUARDO CARDOSO 27 June 2007 (has links)
[pt] Neste trabalho, métodos analíticos baseados na
fosforimetria na
temperatura ambiente foram desenvolvidos para a
determinação de sete
compostos policíclicos aromáticos (CPA) sulfurados e
nitrogenados presentes do
petróleo. Mais especificamente, o objetivo foi o de
fornecer ferramentas
analíticas que permitissem avaliar e quantificar estes CPA
em gasolina e em
uma amostra ambiental (sedimento). Adicionalmente, a
informação obtida
através da fosforimetria mostrou potencial para permitir
diferenciar amostras (por
exemplo, a identificação de amostras contaminadas) por
meio de perfil em três
dimensões ou curvas de nível. A aplicação de técnica de
varredura sincronizada
e o uso do efeito externo seletivo do átomo pesado
aumentaram o grau de
seletividade e de discriminação entre amostras, pois
induziu fosforescência de
componentes específicos na amostra e melhorou a resolução
espectral dos
resultados. Inicialmente, foi feito um estudo das
características fosforescentes
das substâncias em diferentes condições experimentais,
seguido da
maximização do sinal fosforescente de cada uma das
substâncias nas condições
experimentais mais propícias para observação do sinal
fosforescente. Para tal, o
papel filtro, previamente tratado para redução do sinal de
fundo, foi utilizado
como substrato sólido para imobilização dos analitos,
permitindo a observação
de intensa fosforescência na temperatura ambiente. Os
parâmetros de mérito
das metodologias desenvolvidas para cada um dos analitos
em questão foram
obtidos. As faixas lineares se estenderam entre 1,0 x 10-7
e 5,0 x 10-4 mol L-1,
considerando as concentrações das soluções dos analitos
aplicadas no
substrato. Os coeficientes de determinação (r2) obtidos
ficaram sempre acima de
0,9784. Os limites de detecção absolutos (para 5 µL de
amostra) foram todos na
ordem do ng, mostrando a capacidade para detecção sensível
em termos de
massa efetiva de analito. Os testes de repetibilidade
mostraram valores variando
entre 12 e 18%, o que pode ser considerado satisfatório
para a técnica realizada
em substrato sólido. Também foram conduzidos estudos de
robustez e
reprodutibilidade. Alternativamente, sinais fosforescentes
foram maximizados em
condições experimentais secundárias do ponto de vista da
magnitude de sinal, mas potencialmente relevantes do ponto
de vista da seletividade. Testes de
recuperação indicaram, na maioria dos casos, resultados
bastante satisfatórios
no caso das misturas sintéticas contendo quantidades
eqüimolares de
componentes (nesse caso, foram testadas várias combinações
de analitos e de
interferentes) ou contendo interferentes, em concentrações
cinco vezes maior
que a do analito de interesse. Nos casos mais críticos em
termos de
interferências, recursos instrumentais ou quimiométricos
foram aplicados para
melhorar a seletividade e possibilitar a quantificação. Os
métodos desenvolvidos
foram testados em amostras simuladas de gasolina, em
gasolina comercial e em
uma matriz ambiental (sedimento) fortificadas com os
analitos de interesse. As
recuperações obtidas foram bastante satisfatórias e
compreendidas entre 90% e
117%. Estudos envolvendo varreduras de fosforescência
total (TPS) também
foram realizados, com o intuito de se obter uma impressão
digital característica
para cada um dos analitos. Testes de TPS em gasolina
comercial indicaram a
presença de pelo menos seis dos sete analitos estudados,
devido à obtenção de
perfis espectrais muito semelhantes aos dos padrões.
Testes adicionais
mostraram a capacidade de identificar contaminações
(misturas) na gasolina
pela adição de diesel e de querosene. / [en] In this work, analytical methods based on room-temperature
phosphorimetry were developed aiming the quantification of
seven polycyclic
aromatic compounds (PAC) containing sulfur and nitrogen
present in petroleum.
More specifically, the goal was to obtain analytical tool
to allow the evaluation
and the quantification of these PCA in sediment and
gasoline. In addition, the
phosphorimetric information displayed potential for the
discrimination of samples
(for instance, the identification of contaminated samples)
by means of three
dimension plots or level curves. The application of
synchronized sweeping
technique and the use of the selective external heavy atom
effect had increased
the degree of selectivity and discrimination between
samples, since it induces
phosphorescence from specific components of the sample and
improved the
spectral resolution of the results. Initially, a study of
the phosphorescent
characteristics of the compounds in different experimental
conditions was made,
followed of the signal maximization in the most
appropriate experimental
conditions for the observation of phosphorescence. Filter
paper, previously
treated for background reduction, was employed as solid
substrate for the
immobilization of analytes. The analytical figures of
merit for each one of the
methods had been obtained. The linear range varied between
1,0 x 10-7 mol L-1
and 5,0 x 10-4 mol L-1, taking into consideration the
concentration of the solutions
spotted on the substrate. The determination coefficient
values (r2) were always
above of 0.9784. The absolute limits of detection (5 µL
sample) were in ng order,
showing the sensitivity of the developed methods. The
repeatability tests had
enabled values varying between 12 and 18%, which can be
considered
satisfactory for solid substrate technique. Robustness and
reproducibility studies
were also carried out. Additionally, secondary
experimental conditions, in terms
of signal magnitude, were optimized since these could be
relevant from the
selective point of view. Recovery tests indicated, in most
of the cases,
satisfactory results for synthetic mixtures containing
equimolar quantities of
components (in these cases, several analyte/interferent
combinations were tested) and containing interferents in
concentrations five times higher than the
one of the analytes. In the most critical cases in terms
of interferences,
instrumental or quimiometric approaches had been applied
to improve selectivity
and make the quantification possible. The developed
methods had been tested in
simulated gasoline samples, commercial gasoline and in a
sediment sample
fortified with the analytes of interest. The obtained
recoveries had been
considered satisfactory and within 90 and 117%. Total
phosphorescence
scanning (TPS) studies had been also carried out in order
to get the
characteristic fingerprint for each one of the compounds
of interest. TPS tests in
gasoline had indicated the presence of six out of seven of
the studied analytes,
since very similar fingerprints were obtained. Additional
tests had demonstrated
the capability of this procedure to detect gasoline
contaminations with diesel or
kerosene.
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[en] SOLID SURFACE ROOM-TEMPERATURE PHOSPHORIMETRY (SSRTP) FOR THE DETERMINATION OF TWO BETA-CARBOLINES DERIVATIVES (HARMANE E HARMINE) / [pt] FOSFORIMETRIA NA TEMPERATURA AMBIENTE E EM SUBSTRATO SÓLIDO (FTASS) PARA A DETERMINAÇÃO DE DOIS DERIVADOS DA BETA-CARBOLINA (HARMANE E HARMINE)FLAVIA FERREIRA DE CARVALHO MARQUES 01 August 2005 (has links)
[pt] Neste trabalho foi avaliado o uso da Fosforimetria na
Temperatura
Ambiente em Substrato Sólido (FTASS) como técnica analítica
aplicável na
determinação de dois derivados da β-carbolina (harmane e
harmine). Como
suporte sólido foi utilizado o papel de filtro de baixo
sinal de fundo. As
características fosforescentes dos analitos foram estudadas
em função de
diversos parâmetros experimentais, que foram posteriormente
otimizados
visando a maximização do sinal fosforescente. Estes
parâmetros foram: efeito de
íons de átomos pesados; uso de surfactante como modificador
de superfície; pH
e volume de tampão; sistema de solventes e irradiação
prévia das β-carbolinas
com UV. As melhores situações para ambos os analitos foram
obtidas em pH
natural com a adição de Tl+ e em pH básico na presença de
Ag+. Após a
otimização das condições experimentais relevantes, os
parâmetros analíticos de
mérito foram obtidos. Para o harmane, faixas lineares
dinâmicas (a partir do
limite de quantificação, LQ) de 0,39 - 456 ng (Ag+/pH=12) e
de 8,10 - 911 ng
(Tl+/pH=7,7) foram obtidas. Para o harmine, a faixa linear
dinâmica, partindo do
LQ, foi de 0,59 - 1244 ng (dividido em duas faixas
distintas) quando Ag+/pH=9 foi
empregado. Com o uso de Tl+/pH=5,1, a faixa obtida foi de
0,53 a 249 ng. A
precisão do método para as duas substâncias ficou dentro do
esperado para
esta técnica. Também foi estudado o potencial interferente
de algumas
substâncias (AZT, talidomida e outros) e da matriz urina. O
desempenho do
método foi testado através de testes de recuperação em
formulações
farmacêuticas simuladas e em urina enriquecida com o(s)
analito(s), sendo as
recuperações encontradas dentro da faixa recomendada de 90
a 110 %. Estudos
envolvendo a determinação seletiva em misturas contendo
ambos os derivados
da β-carbolina mostraram a viabilidade da determinação
seletiva de harmine na
presença de harmane usando apenas um ajuste de pH. / [en] In the present work a Solid Surface Room-Temperature
Phosphorimetry
(SSRTP) based analytical method was developed aiming the
determination of
two â-carbolines derivatives (harmane and harmine). A low
background filter
paper was employed as solid support. The phosforimetric
characteristics of the
analytes were studied as function of several parameter,
afterwards optimized
aiming the maximization of phosphorescence. Among the
studied parameters
were the effect of heavy atom ions; the use of surfactants
as substrate surface
modifier; pH and volume of buffer; solvent system and the
previuos UV irradiation
of the analytes. The best results for both analytes were
achieved using Tl+ in
natural pH and using Ag+ in basic pH. After optimization of
the relevant
experimental conditions, the analytical figures of merit
were obtained. For
harmane, linear dynamic ranges (starting from the limit of
quantification, LQ) from
0.39 to 456 ng (Ag+/pH=12) and from 8.10 to 911 ng
(Tl+/pH=7.7) were achieved.
For harmine, the linear dynamic ranges, stating from LQ,
were from 0.59 to 1244
ng (divided in two linear ranges) when Ag+/pH=9 was used.
When Tl+/pH=5.1
was employed, linear ranges were from 0.53 to 249 ng. The
precision of the
method was in accordance with the values expected for this
technique. The
potential interferent effect of some substances (AZT,
thalidomide and others) as
well as the effect of urine matrix were also studied. The
performance of the
method was evaluated by recovery tests using simulated
pharmaceutical
formulations and analyte spiked urine samples. In both
cases, recoveries within
the recomended range (from 90 to 110 %) were achieved.
Studies involving the
selective determination of â-carbolines derivatives have
indicated that the
determination of harmine in the presence of harmane is
feasable only by a simple
sample pH adjustment.
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