Dissertations / Theses on the topic 'Molecular diffusion coefficient'

Nous proposons une nouvelle approche pour déterminer le coefficient de diffusion dans des membranes lipidiques se basant sur la formation d'excimères. Alors que les autres modèles statistiques considèrent le système comme un ensemble de points sur un réseau, nous utilisons un modèle à gros grain afin d'étudier des bicouches lipidiques simulées à l'aide du champs de force Martini. Nous déterminons le taux de réaction dépendant du temps à partir des probabilités de survie obtenues a posteriori à l'aide des trajectoires numeriques des bicouches symétriques de DOPC (1,2-Dioleoyl-sn-glycero-3-phosphocholine) et POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) simulées à 283 K et 293 K respectivement. Les dynamiques de collision sont obtenues en distinguant virtuellement les molécules simulées. Les sondes fluorescentes sont supposées semblables aux lipides, et par conséquent, ne modifient pas la dynamique. Nous obtenons une expression générale pour la probabilité de survie en combinant approximation des paires indépendantes et propriétés d'échelle, mais aucune hypothèse n'est faite pour le taux de formation d'excimère. En superposant les intensités d'émission de fluorescence normalisées, déterminées numériquement, aux courbes de titrations expérimentales, nous obtenons deux ensembles de résultats pour le coefficient de diffusion latéral, selon que l'association entre feuillets est autorisée ou pas. Nous utilisons un rayon de capture de 0.5 nm, la distance à partir de laquelle les deux sondes réagissent pour former un excimère. En comparant la dynamique Martini aux expériences de fluorescence, il est possible d'estimer le facteur d'accélération
We propose a novel approach to extract the lateral diffusion coefficient in lipid bilayers using excimer formation. In contrast to previous statistical models that modeled the system as points undergoing jumps from site to site on a lattice, we use coarse-grained molecular dynamics to study lipid bilayers simulated using the Martini force field. We derive time dependent reaction rates from survival probabilities obtained a posteriori from numerically generated trajectories of symmetric DOPC (1,2-Dioleoyl-sn-glycero-3-phosphocholine) and POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) bilayers at 283K and 293K respectively. Collision dynamics are determined by virtually relabeling the simulated molecules. The fluorescent probes are assumed to behave like ordinary membrane lipids and therefore the dynamics remain unaffected. We derive a generalized expression for the survival probability combining independent pairs and size scaling assumptions, but no assumption is made regarding the kinetic rate of the excimer formation process. By fitting the numerically determined normalized fluorescence emission intensities to experimental titration curves, we obtain two sets of results for the lateral diffusion coefficients depending whether interleaflet excimer association is allowed or not. We use a capture radius of 0.5 nm, the distance at which the probes react to form excimers. By relating Martini dynamics to real fluorescence experiments, we estimate the numerical Martini acceleration factor. We also study mixtures of oxidized-non oxidized DOPC and POPC bilayers using a hydroperoxidized model of these lipids for different concentrations of the oxidized component (3.1%, 25% and 50%). Using pair correlation functions, we extract structural information on the systems and determine whether the two components are prone to mixing or not. Finally, we calculate the thermodynamic mixing parameters within the framework of the virial expansion

Doutoramento em Engenharia Química
This work focuses diffusivities due to their importance in the design and simulation of rate-controlled processes. Three approaches are followed: phenomenological modeling through the development of predictive macroscopic models, molecular dynamics simulations, and experimental measurement by the chromatographic peak broadening technique. Self-diffusion coefficients of model and real fluids were firstly studied using entropy based scaling laws. Rosenfeld, Dzugutov and Bretonnet expressions were tested using a large database previously compiled, involving 1727 data points. It was shown that they fail in the entire range of density and temperature, and that diffusivity depends not only on residual entropy but also on the size/geometry of the molecule (through a chain size parameter). For these reasons, a new universal correlation using artificial neural networks was proposed, which relates self-diffusivities with residual entropy and chain size parameter. It is valid for both model and real fluids, whether spherical or asymmetrical, polar or non-polar (global AARD = 9.13%). Moreover, a simple analytical expression was devised for spherical systems, and provides only 4.61% of error based uniquely on residual entropy. Three modified hydrodynamic expressions were proposed to accurately estimate tracer diffusivities (D12) in supercritical carbon dioxide (SC-CO2), based on the Wilke-Chang, Scheibel and Lusis-Ratcliff equations. They relate D12 with the ratio between temperature and solvent viscosity (T/η1), and solute molar volume at normal boiling point (Vbp), as in the original models. The introduction of two universal constants reduce the average errors from [11.70– 23.16]% to [8.26–8.51]% for a large database of 150 systems and 4484 data points over wide ranges of temperature and pressure. In an attempt to adopt more reliable solute properties, four improved Stokes- Einstein based models were devised by modifying Wilke-Chang, Scheibel, Lusis-Ratcliff, and Tyn-Calus equations, where Vbp values were substituted by critical volumes. They achieve similar results to the previous approach (AARD = 7.86-8.56%) for an equivalent database. Further statistics confirmed the good and sturdy nature of these models to accurately predict tracer diffusivities in SC-CO2 for any kind of solute. Another predictive model was developed for supercritical systems, combining two terms – background plus singular – to accurately estimate diffusivities not only far but also near the critical point, where asymptotic behavior is observed. The model achieves an average error of 6.20% for a large database, performing equally well for polar and non-polar solutes, and in the whole pressure-temperature plane, while expressions from literature deliver 11.62- 75.17% errors. Molecular dynamics simulations were performed to study the diffusivities of propanone, butanone, 2-pentanone and 3-pentanone in SC-CO2. They were computed using Einstein formula, and their dependence on temperature, pressure (or density), and molecular size was analyzed. A local structural analysis was further accomplished by calculating some radial distribution functions and coordination numbers to disclose and interpret the local environment of CO2 around each group composing ketone molecules. An experimental setup to measure diffusion coefficients by chromatographic peak broadening technique was designed, assembled and tested. Tracer diffusivities of α-pinene in SC-CO2 were determined at 313.15, 323.15 and 333.15 K, and pressures from 175 to 275 bar. The dependency of D12 upon temperature, pressure, solvent density, and hydrodynamic behavior has been examined in detail. Finally, the experimental data were modeled using equations developed in this work and good results were obtained (AARD = 2.48 – 3.56%); well-known expressions from the literature were also considered.
Neste trabalho estudaram-se coeficientes de difusão devido à sua importância no projeto e simulação de processos conduzidos por cinética. Foram seguidas três abordagens: modelação fenomenológica através do desenvolvimento de modelos macroscópicos preditivos, simulações de dinâmica molecular e medição experimental pela técnica cromatográfica de abertura de pico. Os coeficientes de autodifusão foram primeiramente focados, analisando-se leis de redução baseadas na entropia residual. As expressões de Rosenfeld, Dzugutov e Bretonnet foram testadas usando uma extensa base de dados compilada previamente, envolvendo 1727 pontos. Mostrou-se que estas equações falham em toda a gama de densidade e temperatura, e que a difusividade depende não só da entropia residual mas também do tamanho/geometria da molécula (através de um parâmetro que caracteriza o tamanho da cadeia). Por estas razões propôs-se uma correlação universal baseada em redes neuronais, que relaciona os coeficientes de autodifusão com a entropia residual e o parâmetro de tamanho da molécula. Esta é válida para fluidos modelo e reais, quer sejam moléculas esféricas ou não esféricas, polares ou apolares (AARD global = 9.13%). Para além disso, uma expressão analítica simples foi desenvolvida para sistemas esféricos, baseada apenas na entropia residual, dando origem um erro médio de 4.61%, Três expressões hidrodinâmicas modificadas foram propostas para estimar com exatidão difusividades binárias a diluição infinita (D12) em dióxido de carbono supercrítico (SC-CO2), baseadas nas equações de Wilke-Chang, Scheibel e Lusis-Ratcliff. Estas relacionam D12 com a razão entre a temperatura e a viscosidade do solvente (T/η1), e com o volume molar do soluto à temperatura normal de ebulição (Vbp), tal como o fazem os modelos originais. A introdução de duas constantes universais reduziu os erros médios de [11.70–23.16]% para [8.26–8.51]%, calculados para uma extensa base de dados de 150 sistemas e 4484 pontos experimentais, varrendo gamas largas de pressão e temperatura. Com o objetivo de se utilizar propriedades de soluto mais plausíveis, foram propostos quatro modelos baseados na relação de Stokes-Einstein, modificando as equações de Wilke-Chang, Scheibel, Lusis-Ratcliff e Tyn- Calus, onde os valores de Vbp foram substituídos por volumes críticos. Estas fornecem resultados similares aos da abordagem anterior (AARD = 7.86- 8.56%) para uma base de dados equivalente. O cálculo de outras grandezas estatísticas permitiu confirmar a solidez destes modelos para prever difusividades binárias de quaisquer solutos em SC-CO2. Foi proposto outro modelo preditivo para sistemas supercríticos, combinando dois termos – regular e singular – para estimar corretamente difusividades não apenas longe mas também junto ao ponto crítico, onde se sabe existir um comportamento assimptótico de D12. O modelo fornece um erro médio de 6.20% para toda a base de dados, com bom desempenho para solutos polares e não polares em toda a gama pressão-temperatura, enquanto as expressões da literatura atingem erros de 11.62-75.17%. Foram efetuadas simulações de dinâmica molecular para estudar as difusividades de propanona, butanona, 2-pentanona e 3-pentanona em SCCO2. Estas foram calculadas usando a relação de Einstein, e as suas dependências com a temperatura, pressão (ou densidade) e tamanho molecular foram analisadas. Foi ainda conduzida uma análise estrutural local dos sistemas através do cálculo de funções distribuição radial e números de coordenação, para discriminar e interpretar o ambiente local do CO2 em torno de cada grupo que compõe as moléculas de cetona. Foi concebida, instalada e testada uma instalação experimental para medir coeficientes de difusão pelo método cromatográfico de abertura de pico. Foram determinadas difusividades de α-pineno a diluição infinita em SC-CO2 a 313.15, 323.15 e 333.15 K, e pressões entre 175 e 275 bar. Examinou-se em pormenor a dependência de D12 com a temperatura, pressão e densidade do solvente, e o seu comportamento hidrodinâmico. Por fim, os valores experimentais foram modelados usando equações desenvolvidas neste trabalho e obtiveram bons resultados (AARD = 2.48 – 3.56%); foram também consideradas expressões bem conhecidas da literatura.

Il s'agit d'une étude fondamentale de l'influence de l'autoassociation de molécules polyaromatiques pr mesure des coefficients de diffusion rotationnelle à partir des temps de relaxation T1 des carbones protonés. Des molécules comme le fluoranthène, le chrysène ou le benzanthracène sont des rotateurs plans asymétriques ou toupies non symétriques (molécules planes possédant deux axes principaux, par rapport auxquels les moments d'inertie sont différents). La mesure du temps de relaxation dipolaire est directement liée au paramètre caractérisant la réorientation moléculaire, appelée temps de corrélation efficace

Ce travail de thèse a été réalisé, dans le cadre de la convention CIFRE 1538/2010, au sein d'adixen Vacuum Products (aVP) à Annecy (France). Il a été en partie financé par le projet S.P.A.M. (Surface Physics for Advanced Manufacturing). Il s'agit d'un projet ITN financé par le programme Pierre et Marie Curie de la Communauté Européenne rassemblant des partenaires universitaires et industriels dont aVP. L'objectif de ce programme était de contribuer à l'étude et au développement de la lithographie et en particulier la lithographie à ultraviolet extrême (EUVL). Ce travail porte sur la problématique de la contamination moléculaire dans l'industrie des semi-conducteurs ainsi que les besoins de maitrise de contamination pour la photolithographie EUVL. Pour ce faire, des modèles mathématiques de sorption ont été recherchés, testés et validés à l'aide d'une microbalance à quartz (QCM). Cette technique, possédant une très haute sensibilité (au niveau du ng), permet d'étudier les phénomènes de sorption relatifs à tout matériau déposable sur un cristal de quartz mis au contact de différents gaz dont la pression partielle est maitrisée. Par conséquent, le protocole détaillé dans cette thèse peut être utilisé pour d'autres types d'expériences dans toute discipline nécessitant une telle précision. Le déroulement de notre plan d'expérience comprend deux types de matériaux naturellement différents : un polymère (PCBA) d'une part et deux substrats métalliques (SS AISI 304 et CuC1) d'autre part pour lesquels le transfert de masse n'intervient pas de la même manière. Les gaz d'étude ont été sélectionnés pour leur intérêt dans l'industrie des semi-conducteurs (vapeur d'eau, HF). Le résultat de l'interaction des gaz d'étude avec les substrats ciblés est suivi en direct par la QCM, ce qui permet non seulement de valider et/ou améliorer les modèles mathématiques déjà disponibles dans la bibliographie mais aussi de les ajuster aux données obtenues expérimentalement. Nous pouvons ainsi non seulement prévoir le comportement des contaminants à l'équilibre (isothermes) et à l'état transitoire mais aussi réaliser des estimations de sorption à des températures autres que celles retenues pour notre plan d'expérience
This thesis was carried out within the framework of the CIFRE 1538/2010 convention at adixen Vacuum Products (aVP) in Annecy (France). It is has been partly funded by the ITN project SPAM (Surface Physics for Advanced Manufacturing). SPAM is an ITN project funded by the Pierre and Marie Curie program of the European Community bringing together academic institutions and industrial partners including aVP. The objective of this program was to contribute to the study and development of lithography and extreme ultraviolet lithography (EUVL). This work deals with the issues caused by the airborne molecular contamination (AMC) in the semiconductor industry and their control needs in EUVL and the current photolithography. In order to tackle the problem, sorption mathematical models have been investigated and validated using a quartz crystal microbalance (QCM). This technique, which confers a high sensitivity (ng level), allows the study of the sorption phenomena related to any deposable material onto a quartz crystal in contact with different gases whose concentrations are accurately controlled. Consequently, the protocol detailed in this thesis may be used for other types of experiments in any discipline requiring such precision. The conduct of our experimental plan includes two types of naturally different materials: a polymer (PCBA) on the one hand and two metallic substrates (stainless steel AISI 304 and CuC1) on the other hand, for which the matter transfer does not occur in the same manner. Studied gases were selected for their interest in the semiconductor industry (water vapor, HF). The resulting interaction between the studied gases and the targeted substrates is continuously followed by the QCM, which allows not only to validate the mathematical models already proposed by the literature but also to fit the experimentally obtained data. This enables us not only to predict the behavior of the AMC at equilibrium (isotherms) and the transient state but also to provide sorption estimations at temperatures other than those specified in our experimental plan

L'etude d'un melange ternaire de polymeres en solution semidiluee presente deux modes de relaxation. Mise en evidence par diffusion de lumiere quasi-elastique de deux processus de diffusion: le premier, lent, correspond au mouvement relatif des deux polymeres; le second, rapide, correspond au mouvement cooperatif du reseau physique forme par les deux polymeres

Orientador: Sergio Persio Ravagnani
Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica
Made available in DSpace on 2018-08-07T03:49:14Z (GMT). No. of bitstreams: 1 Trochmann_JoseLuizLino_D.pdf: 1070584 bytes, checksum: 3407aee7ad6d88d9de0a1326aaf3d29d (MD5) Previous issue date: 2006
Resumo: Neste trabalho de tese foi realizado um estudo do potencial de predição de propriedades de transporte em matrizes poliméricas de poli - imidas, utilizando a simulação dinâmica molecular de gases simples como Oxigênio, Nitrogênio e Dióxido de Carbono. A propriedade de transporte de interesse prático, a permeabilidade de uma membrana polimérica a um dado penetrante, envolve a determinação de propriedades de ordem cinética e termodinâmica, respectivamente a determinação do coeficiente de difusão e da solubilidade deste penetrante na matriz polimérica. Atenção especial foi conferida à propriedade cinética, pela predição do coeficiente de autodifusão dos penetrantes. Num procedimento experimental clássico é de vital importância para significância das conclusões derivadas dos experimentos, o uso de amostras de membranas poliméricas adequadamente preparadas quanto à composição química, estrutura física e morfologia. Analogamente, quando se utiliza a simulação molecular para a predição de propriedades, tais como o coeficiente de autodifusão, também é de fundamental relevância para os resultados obtidos, a qualidade dos modelos moleculares das matrizes poliméricas, que serão usados como base. Assim para a preparação de modelos moleculares com o adequado empacotamento, um procedimento para a obtenção de modelos bem equilibrados foi desenvolvido neste trabalho. Os modelos moleculares desenvolvidos foram usados para a obtenção dos valores de massa específica em função da temperatura, e comparados aos valores experimentais disponíveis e quando necessário a, valores preditos por meio da expressão de massa específica em função da temperatura, acima e abaixo da temperatura de transição. A capacidade do modelo molecular desenvolvido em predizer a massa especifica e temperatura de transição vítrea foi usada como critério para a validação da adequação do empacotamento proposto para o referido modelo molecular da matriz polimérica. Os modelos validados de empacotamento, células amorfas, foram utilizados para o cálculo do coeficiente de autodifusão dos gases acima mencionados, através do da simulação dinâmica molecular. A comparação dos coeficientes de autodifusão obtidos das poli-imidas aromáticas e éster imidas, BAAF, 6FDA-ODA, PMDA-ODA e BA-20DA, para os gases O2, N2 e CO2, com os dados experimentais, permitiu concluir a adequação das células amorfas e do esquema de simulação dinâmica molecular para a predição do coeficiente de autodifusão.. A versão preditiva de Vrentas e Duda, baseada na teoria do volume livre, foi utilizada para a predição dos coeficientes de autodifusão da água e do etanol para as poli-imidas acima. , Estes valores, quando comparados com os valores obtidos através da simulação dinâmica molecular mostram a validade de ambas as teorias para a predição da cinética de difusão de penetrantes em matrizes poliméricas complexas
Abstract: In this thesis a study of the predictive potential of the molecular dynamic simulation was performed for transport properties of light gases in polyimide matrix. From de practical point of view permeability is the property of most interest, and involves kinetics as well as thermodynamics properties, diffusion coefficient and solubility of the penetrants molecule in the bulk polymeric matrix, this work will be focus in the former. As important as is in as experimental work, a well prepared polymeric membrane is essential for the significance of the draw conclusions. Therefore a special attention was take in the preparation of the bulk molecular polymeric model, the so called amorphous cell, in order to obtain well-equilibrated molecular packing models for the polyimide matrixes. The amorphous cells were prepared throughout thermodynamic transforms, using one or more of the statistical ensembles and cell specific volume obtained as a function of temperature, this data was compared against the experimental data available, and when necessary to data obtained via predictive methods. The molecular packing model ability to predict the glass transition temperature was used as criteria to validate de amorphous cell, to be used in the molecular dynamic' simulations allow the matrix to be locally flexible and coupled to the classic molecular dynamics simulation. The resulting self diffusion coefficients for the polyimide, BAAF, 6FDA-ODA, PMDA­ODA and BA-20DA for the gases O2, N2 e CO2 were compared to the experimental data. The lack of quality experimental diffusion data available for polyimide membranes for larger penetrants as water and ethanol, showed up as a good opportunity to assess the predictive capability of the molecular dynamic simulation for self diffusion coefficients, considering the relevant technological relevance of polyimide membranes for pervaporation process. The data of self diffusion coefficient produced by the predictive version of free-volume theory after Vrentas and Duda, was compared with the data produced via coupled molecular dynamic simulation for the water and ethanol penetrants, showing the relevance of both theories for the prediction of penetrants kinetic in complex polymeric matrixes
Doutorado
Ciencia e Tecnologia de Materiais
Doutor em Engenharia Química

Les argiles sont utilisées dans de nombreuses applications industrielles pour lesquelles l’étude des interactions entre l’eau et les matériaux argileux sont primordiales. Les mécanismes de rétention et de transport de l'eau et des ions à la surface des argiles peuvent être modélisés à l'échelle atomique grâce à des méthodes classiques comme la Dynamique Moléculaire. Ces méthodes nécessitent de paramétrer au préalable les interactions entre les atomes du système. L'objectif principal de cette étude est d'améliorer la description de ces systèmes via la paramétrisation d'un nouveau champ de force polarisable entièrement basée sur des calculs issus de la méthode de la Théorie de la Fonctionnelle de la Densité. Les propriétés structurales, thermodynamiques et dynamiques de la pyrophyllite, du talc, et de la Na-, Ca-, Sr- et Cs-montmorillonite (sèches et hydratées) ont été bien reproduites. Notamment, la structure des couches tétraédriques et celle des espaces interfoliaires sont en très bon accord avec les données expérimentales
The wide use of clay minerals in industrial applications is partly due to their remarkable properties of water retention at the mineral surface. Retention and transport mechanisms of water molecules and ions at the surface of clays can be modeled at the atomic scale via different classical methods such as molecular dynamics. These methods require to parametrize in advance the interaction between the atoms of the system. The goal of this study is to improve the description of these systems via the parametrization of a new polarizable force field entirely based on density functional theory calculations.The structure, the thermodynamics and the dynamics properties of pyrophyllite, talc and Na-, Ca-, Sr- and Cs-montmorillonite are well reproduced. The atomic structure of sheets and interfoliar space are in good agreement with experimental results

Etude de cette molecule de type rotateur asymetrique en solution dans ch::(2)cl::(2), tetrahydrofurane et diglyne. A l'aide de la theorie de la "relaxation couplee" determination des valeurs des trois constantes de diffusion du solute et des densites spectrales relatives aux mecanismes de relaxation dipole-dipole, intra-et intermoleculaire. Etude de l'influence du taux de deuteriation du solvant sur la relaxation du solute dans le cas de ch::(2)cl::(2). Ecart des densites spectrales par rapport aux previsions theoriques. Test de la validite de plusieurs modeles hydrodynamiques: celui de knauss et evans s'avere le mieux adapte

This master thesis deals with a durability of concrete, which has become the centre of the interests of international scientific insitutes during the last years. The resistence of reinforced concrete depends on the covercrete which the aggresive liquids and gases penetrate through from the environment to reinforcement. According to the ability of the covercrete to penetrate degradative species is possible to tell the durability of concrete constructions. In experimental part we look for the actual state of covercrete, ordinary and high strength, by combination of various experiments. We can find here the test´s results of water and gas permeability and absorbability and sorption of concrete which complete the permeability tests. In final part the impact of different concrete types on durability of reinforced concrete is discussed.

The Sutton Chen and quantum Sutton Chen potentials are used in molecular dynamics simulations to describe the structural, thermodynamical, and transport properties of Pd, Ni and their binary alloys in solid, liquid, and glass phases. Static properties including elastic constants, pair distribution function, static structure factor, and dynamical properties consisting of phonon dispersion relation, diffusion coefficient, and viscosity are computed at various temperatures. The melting temperatures for Pd-Ni system are obtained. The transferability of the potentials is tested by simulating the solid and liquid states. The eutectic concentration Pd0.45Ni0.55 is quenched at four different cooling rates. The system goes into glass formation at fast cooling rates, while it evolves to crystal at slow cooling rate. Comparison of calculated structural and dynamical properties with the available experiments and other calculations shows satisfactory consistency.

Mass transfer by molecular diffusion is the basic physical mechanism underlying many important areas of chemical engineering and petroleum engineering. In recent years, the problem of mass transfer by the mechanism of molecular diffusion in oil reservoirs, when a non-equilibrium gas is injected into the reservoir, has become increasingly important. In oil recovery projects, gas is injected into oil reservoirs for different reasons such as maintenance of reservoir pressure and enhanced recovery of oil. In these two cases the rate of dissolution of a gas such as methane in a quiescent body of hydrocarbon oil is controlled primarily by the rate of diffusion of the dissolved gas from the gas-oil interface into the body of the liquid phase. In all the above situations, molecular diffusion of gas into liquid or transfer of dissolved gas between enriched and heavier liquid phase due to differences in compositional gradients between gas and liquid phases is important. The most important property required to determine the rate of mass transfer between the two phases in all these cases is the molecular diffusion coefficient at high pressure and temperature. The present investigation is aimed at a systematic study of the mechanism of molecular diffusion of gases in liquids by measuring the diffusion coefficients of methane in dodecane and in a typical Iranian crude oil up to a pressure of 35 MPa and at several temperatures. All tests are conducted in an accurate high-pressure diffusion cell with "finite-domain" moving boundary behavior. The data acquired is used to assess the predictions of various available correlations for diffusion coefficients. Several liquid hydrocarbon swelling tests comprising dodecane and a typical Iranian crude oil as liquids and methane as gas are performed and swelling heights of liquid as a result of gas molecular diffusion are measured at various temperatures (T=25°C to82°C ) and pressures (P=3.2 to 35 MPa), characterized by a sharp increase in volume followed by gradual increase toward the saturation concentration of methane in the liquid phase. A mathematical model is developed to calculate diffusivities using semi-infinite boundary conditions, hi this model, a variable power profile with time is introduced to allow for the moving interface boundary. The current solutions offer significant improvement over those in previous literature that assume a steady-state interface boundary condition with a parabolic concentration profile. The proposed model offers excellent predictions of experimental data for diffusion coefficients of methane-dodecane and crude oil systems. A computer program using a neural network model is set-up to predict the dimensionless diffusivity for special use with more complex systems such as crude oil reservoir flows in fractures and matrix conditions. The results obtained by this software show about +/- 2% deviation in comparison with the experimental data from the diffusion cell experiments.

Mesure des coefficients d'attenuation des elements de numero atomique 46 a 54 dans le domaine 15 a 45 kev. Determination des parametres de la loi de variation empirique du coefficient d'attenuation en fonction de la longueur d'onde du rayonnement. Determination des facteurs de diffusion anomale vers l'avant, en utilisant la relation de dispersion

A fundamental step in the further developments of comprehensive modelling of the diffusive processes in liquids requires the possibility of obtaining reliable and accurate experimental data of the diffusion and thermodiffusion coefficients of multicomponent liquid systems. In the present work, we perform an experimental investigation of the diffusive properties of binary and ternary liquid systems. Two experimental techniques, the ‘Open Ended Capillary’ technique and the ‘Transient Interferometric Technique’ have been developed. Those techniques have been used for the experimental characterization of several systems composed of 1,2, 3,4-Tetrahydrnaphtalene, Isobutylbenzene and Dodecane at ambient temperature. Those particular species were selected as a simplified multicomponent system modelling the fluids contained in natural crude oils reservoirs.

For each of these techniques, experimental set-ups were designed, implemented and calibrated. The procedures for identifying the ternary diffusion coefficients from the measured compositions fields were studied in details.

The Open Ended Capillary Technique was applied under gravity condition to study isothermal diffusion binary and ternary systems. Difficulties related to a new procedure for interpreting the data collected at short times of the experiments are highlighted and its implication in the generalization of the technique for the study of multicomponent systems is discussed.

The Transient Interferometric Technique was used to perform an experimental study of three binary systems under gravity conditions. It was also applied for the investigation of ternary systems under microgravity condition in the frame of the DSC on SODI experiment, which took place aboard the International Space Station in 2011. The experimental results are reported and the analysis of the accuracy of the technique is presented. The TIT is the first technique ever providing accurate experimental measurements of the complete set of diffusion and thermodiffusion coefficients for ternary liquid systems.

Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished

Solid state lithium ion electrolytes are important to the development of next generation safer and high power density lithium ion batteries. Perovskite-structured LLT is a promising solid electrolyte with high lithium ion conductivity. LLT also serves as a good model system to understand lithium ion diffusion behaviors in solids. In this thesis, molecular dynamics and related atomistic computer simulations were used to study the diffusion behavior and diffusion mechanism in bulk crystal and grain boundary in lithium lanthanum titanate (LLT) solid state electrolytes. The effects of defect concentration on the structure and lithium ion diffusion behaviors in LLT were systematically studied and the lithium ion self-diffusion and diffusion energy barrier were investigated by both dynamic simulations and static calculations using the nudged elastic band (NEB) method. The simulation results show that there exist an optimal vacancy concentration at around x=0.067 at which lithium ions have the highest diffusion coefficient and the lowest diffusion energy barrier. The lowest energy barrier from dynamics simulations was found to be around 0.22 eV, which compared favorably with 0.19 eV from static NEB calculations. It was also found that lithium ions diffuse through bottleneck structures made of oxygen ions, which expand in dimension by 8-10% when lithium ions pass through. By designing perovskite structures with large bottleneck sizes can lead to materials with higher lithium ion conductivities. The structure and diffusion behavior of lithium silicate glasses and their interfaces, due to their importance as a grain boundary phase, with LLT crystals were also investigated by using molecular dynamics simulations. The short and medium range structures of the lithium silicate glasses were characterized and the ceramic/glass interface models were obtained using MD simulations. Lithium ion diffusion behaviors in the glass and across the glass/ceramic interfaces were investigated. It was found that there existed a minor segregation of lithium ions at the glass/crystal interface. Lithium ion diffusion energy barrier at the interface was found to be dominated by the glass phase.

Quercetin, a flavonoid that can be extracted from various plant sources, exhibit interesting bioactivity due to relevant antioxidant or anti-carcinogenic properties. One way of extracting this flavonoid is by solid-liquid extraction using, for example, green solvents like ethanol (EtOH) or ethyl acetate (EtOAc), which are well accepted in the food industry. Diffusivity, D12, is an important property in solid-liquid extraction, since this separation is frequently limited by mass transfer kinetics, which requires the knowledge of D12 for the accurate design and optimization of that unitary operation. The diffusivities, D12, of quercetin in ethyl acetate and ethanol were measured by the chromatographic peak broadening (CPB) method in the temperature range 30-60 °C and pressure range 1-150 bar. The diffusivities in ethanol were measured in the same laboratory by another researcher. The D12 values ranged from 3.985×10-6 to 7.826×10-6 cm2 s-1, in the case of ethanol, and 1.018×10-5 to 1.628×10-5 cm2 s-1 for ethyl acetate. The obtained D12 data followed the expected trends with temperature and pressure, namely, positive and negative derivatives, being the influence of temperature much more significant. In parallel, classical molecular dynamics (MD) simulations were performed using the GROMACS software package to estimate the diffusion coefficient in order to assess the possibility of using this computational technique to generate diffusivities for distinct pressure and temperature conditions. Different parameters sets were adopted to carry out simulations in NVT ensemble, such as the cut-off radius for short-range interactions, number of solvent and solute molecules, and simulation duration, with the objective to verify their influence on the quality of D12 estimates. The optimization of the parameters used in the MD simulations led to D12 values in good agreement with the experimental data for ethanol at 1 bar, with relative deviations less than 6.54 %. It was also shown that it is possible to obtain reliable results at higher pressures after introducing a multiplicative factor on the atoms charges of ethanol. In the case of ethyl acetate, the error at 30 °C and 1 bar was −22.51 %. Since the MD self-diffusivities of ethyl acetate also differ significantly from the experimental data, it is suggested in this work to optimize the force field parameters used to model this solvent. The agreement found between experimental and MD quercetin diffusivities in ethanol demonstrates that it is possible to obtain reliable D12 values by classical MD simulations. Further studies are suggested on the influence of different functional groups and structure of other flavonoids on D12, with a structural analysis using the radial distribution and spatial distribution function.
A quercetina, um flavonoide que pode ser extraído de várias fontes vegetais, apresenta bioatividade interessante, devido às suas boas propriedades antioxidantes ou anti-carcinogénicas. Uma das técnicas de extração deste flavonoide é por extração sólido-líquido, usando, por exemplo, solventes verdes como etanol (EtOH) ou acetato de etilo (EtOAc), utilizados na indústria alimentar. A difusividade, D12, é uma propriedade importante nas extrações sólido-líquido pois, muito frequentemente, estas operações unitárias encontram-se limitadas pela cinética de transferência de massa, sendo assim relevante conhecer o coeficiente de difusão para o projeto e otimização destes processos. As difusividades da quercetina em acetato de etilo e em etanol foram medidas pelo método cromatográfico de abertura de pico (CPB), na gama de temperaturas de 303,15 a 333,15 K e de pressões de 1 a 150 bar. No caso do etanol, os valores de D12 já tinham sido medidos anteriormente, no mesmo laboratório, por outro investigador. Os valores experimentais de D12 da quercetina em etanol encontram-se entre 3,985×10-6 e 7,826×10-6 cm2 s-1, e no caso da quercetina em acetato de etilo entre 1,018×10-5 e 1,628×10-5 cm2·s-1. Os resultados experimentais obtidos seguem as dependências esperadas com a temperatura e pressão, nomeadamente, derivadas positivas e negativas, sendo a variação com a temperatura muito mais expressiva. Paralelamente, foram realizadas simulações de dinâmica molecular (MD) clássica utilizando o software GROMACS para estimar as difusividades e averiguar a possibilidade de utilizar esta técnica computacional para calcular valores de D12 noutras condições de pressão e de temperatura. Com este fim em vista, foram testados diferentes conjuntos de parâmetros em simulações no ensemble NVT, tais como o raio de corte das interações de curto alcance, número de moléculas de solvente e duração da simulação, para analisar a sua influência na exatidão das estimativas. A otimização dos parâmetros usados nas simulações de MD conduziu a valores de D12 em boa concordância com os dados experimentais no caso do etanol a 1 bar, com erro relativo inferior a 6.54 %. Foi ainda demonstrado que a pressões mais elevadas é possível obter valores fiáveis de D12, introduzindo um fator multiplicativo nas cargas dos átomos do etanol. No caso do acetato de etilo, o erro a 30 °C e 1 bar foi −22.51 %. Como os valores do coeficiente de auto-difusão do acetato de etilo, estimados por MD, diferem bastante dos valores experimentais, sugere-se neste trabalho a otimização dos parâmetros do campo de forças utilizado para modelar este solvente. A concordância entre as difusividades da quercetina em etanol medidas e estimadas por MD clássica demonstra que é realmente possível obter valores fiáveis de D12 por esta técnica computacional. Sugerem-se estudos adicionais focados em diferentes grupos funcionais e estruturas de flavonoides, através de análises estruturais usando funções de distribuição radial e de distribuição espacial.
Mestrado em Engenharia Química

This project considers the diffusion of water molecules through a cellular medium in which the cells are modeled by square compartments placed symmetrically in a square domain. We assume the diffusion process is governed by the 2D diffusion equations and the solution is provided by implementing the Crank-Nicolson scheme. These results are verified and illustrated to agree well with the finite element method using the Comsol Multiphysics package. The model is used to compute the values of the apparent diffusion coefficient, (ADC) which is a measure that is derived from diffusion weighted MRI data and can be used to identify, e.g., regions of ischemia in the brain. With our model, it is possible to examine how the value of the apparent diffusion coefficient is affected whenever the extracellular space is varied. We observe that the average distance that the water molecules travel in a definite time is highly dependent on the geometrical properties of the cellular media.
UOIT

abstract: The cell is a dense environment composes of proteins, nucleic acids, as well as other small molecules, which are constantly bombarding each other and interacting. These interactions and the diffusive motions are driven by internal thermal fluctuations. Upon collision, molecules can interact and form complexes. It is of interest to learn kinetic parameters such as reaction rates of one molecule converting to different species or two molecules colliding and form a new species as well as to learn diffusion coefficients. Several experimental measurements can probe diffusion coefficients at the single-molecule and bulk level. The target of this thesis is on single-molecule methods, which can assess diffusion coefficients at the individual molecular level. For instance, super resolution methods like stochastic optical reconstruction microscopy (STORM) and photo activated localization microscopy (PALM), have a high spatial resolution with the cost of lower temporal resolution. Also, there is a different group of methods, such as MINFLUX, multi-detector tracking, which can track a single molecule with high spatio-temporal resolution. The problem with these methods is that they are only applicable to very diluted samples since they need to ensure existence of a single molecule in the region of interest (ROI). In this thesis, the goal is to have the best of both worlds by achieving high spatio-temporal resolutions without being limited to a few molecules. To do so, one needs to refocus on fluorescence correlation spectroscopy (FCS) as a method that applies to both in vivo and in vitro systems with a high temporal resolution and relies on multiple molecules traversing a confocal volume for an extended period of time. The difficulty here is that the interpretation of the signal leads to different estimates for the kinetic parameters such as diffusion coefficients based on a different number of molecules we consider in the model. It is for this reason that the focus of this thesis is now on using Bayesian nonparametrics (BNPs) as a way to solve this model selection problem and extract kinetic parameters such as diffusion coefficients at the single-molecule level from a few photons, and thus with the highest temporal resolution as possible.
Dissertation/Thesis
Source code related to chapter 3
Source code related to chapter 4
Doctoral Dissertation Physics 2020