In this study, the behavior of partially saturated coarse-grained soil packings was studied as a function of solid surface composition and aqueous salt concentration. The substrates tested were PTFE and soda lime glass, while the aqueous electrolytes consisted of NaCl and CaCl2 in differing concentrations. In order to gain a fundamental understanding of the unsaturated soils system, the two phase intersections of gas-liquid and solid-liquid were studied. The effect of varying aqueous electrolytes on the gas-liquid interface was analyzed by testing the surface tension while systematically varying the electrolyte concentration, while the effect on the solid/liquid/gas interface was studied by altering the surface hydrophobicity and aqueous solution concentration. In order to extend the analysis to soil fabrics, four ideal coarse gained packings were subdivided into their smallest repeating units. These repeating units, along with the measured dependence of the contact angles and surface tension on salt types, allowed an estimation of the equilibrium behavior of the capillary rise and tensile strength within a uniform coarse-grained fabric.

In this thesis we use density functional theory (DFT) to study the solvent mediated interactions between solvophobic, solvophilic and patchy nanostructures namely rectangular cross section blocks. We calculate both the density profiles and local compressibility around the blocks and the results obtained for our model system provide a means to understanding the basic physics of solvent mediated interactions between nanostructures, and between objects such as proteins in water, that possess hydrophobic and hydrophilic patches. Our results give an improved understanding of the behaviour of liquids around solvophobic objects and solvophobicity (hydrophobicity) in general. Secondly, we look into the physics incorporated in standard mean-field DFT. This is normally derived by making what appears to be a rather drastic approximation for the two body density distribution function: ρ(2)(r,r′) ≈ ρ(r)ρ(r′), where ρ(r) is the one-body density distribution function. We provide a rationale for why the DFT often does better than this approximation would make you expect. Finally, we develop a lattice model to understand the nature of the pattern formation exhibited by certain systems of particles deposited on liquid-air interfaces and in particular the nature of the transitions between the different patterned structures that are observed. This is done using Monte Carlo computer simulations and DFT and links the observed microphase ordering with the micellisation process seen e.g. in surfactant systems.

abstract: Emergent environmental issues, ever-shrinking petroleum reserves, and rising fossil fuel costs continue to spur interest in the development of sustainable biofuels from renewable feed-stocks. Meanwhile, however, the development and viability of biofuel fermentations remain limited by numerous factors such as feedback inhibition and inefficient and generally energy intensive product recovery processes. To circumvent both feedback inhibition and recovery issues, researchers have turned their attention to incorporating energy efficient separation techniques such as adsorption in in situ product recovery (ISPR) approaches. This thesis focused on the characterization of two novel adsorbents for the recovery of alcohol biofuels from model aqueous solutions. First, a hydrophobic silica aerogel was evaluated as a biofuel adsorbent through characterization of equilibrium behavior for conventional second generation biofuels (e.g., ethanol and n-butanol). Longer chain and accordingly more hydrophobic alcohols (i.e., n-butanol and 2-pentanol) were more effectively adsorbed than shorter chain alcohols (i.e., ethanol and i-propanol), suggesting a mechanism of hydrophobic adsorption. Still, the adsorbed alcohol capacity at biologically relevant conditions were low relative to other `model' biofuel adsorbents as a result of poor interfacial contact between the aqueous and sorbent. However, sorbent wettability and adsorption is greatly enhanced at high concentrations of alcohol in the aqueous. Consequently, the sorbent exhibits Type IV adsorption isotherms for all biofuels studied, which results from significant multilayer adsorption at elevated alcohol concentrations in the aqueous. Additionally, sorbent wettability significantly affects the dynamic binding efficiency within a packed adsorption column. Second, mesoporous carbons were evaluated as biofuel adsorbents through characterization of equilibrium and kinetic behavior. Variations in synthetic conditions enabled tuning of specific surface area and pore morphology of adsorbents. The adsorbed alcohol capacity increased with elevated specific surface area of the adsorbents. While their adsorption capacity is comparable to polymeric adsorbents of similar surface area, pore morphology and structure of mesoporous carbons greatly influenced adsorption rates. Multiple cycles of adsorbent regeneration rendered no impact on adsorption equilibrium or kinetics. The high chemical and thermal stability of mesoporous carbons provide potential significant advantages over other commonly examined biofuel adsorbents. Correspondingly, mesoporous carbons should be further studied for biofuel ISPR applications. / Dissertation/Thesis / M.S. Chemical Engineering 2011

Submitted by Milena Kowalczuk Manosso Amorim (milenamanosso@gmail.com) on 2018-09-10T23:00:08Z No. of bitstreams: 1 versão repositorio 10-09.pdf: 2679208 bytes, checksum: 1f7039ea349763e1a7142ce20ee9a3de (MD5) / Approved for entry into archive by Lucilene Cordeiro da Silva Messias null (lubiblio@bauru.unesp.br) on 2018-09-11T16:47:09Z (GMT) No. of bitstreams: 1 amorim_mkm_me_bauru.pdf: 2679208 bytes, checksum: 1f7039ea349763e1a7142ce20ee9a3de (MD5) / Made available in DSpace on 2018-09-11T16:47:09Z (GMT). No. of bitstreams: 1 amorim_mkm_me_bauru.pdf: 2679208 bytes, checksum: 1f7039ea349763e1a7142ce20ee9a3de (MD5) Previous issue date: 2018-07-27 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Este trabalho investiga os efeitos de tratamento a plasma frio em polímeros convencionais, polipropileno e poliestireno, e em filme amorfo do tipo a-C-H, produzido através de Deposição Química de Vapor Assistida por Plasma (PECVD). Após etapas preliminares de escolha de gás e tempo a serem utilizados, as amostras foram tratadas em plasma de hexafluoreto de enxofre (SF6) em cinco diferentes potências e cinco diferentes pressões, totalizando 25 condições para cada substrato. As superfícies foram caracterizadas por goniometria, perfilometria, Espectroscopia de Infravermelho com Transformada de Fourier (FTIR), Microscopia Eletrônica de Varredura (MEV), Espectroscopia de Raios-X por Energia Dispersiva (EDS) e Espectroscopia de Fotoelétrons Excitados por Raios-X (XPS). Assim, foram examinados ângulo de contato, rugosidade, estrutura química, morfologia, composição química e composição química da superfície, respectivamente. O tratamento com SF6 aumenta a característica hidrofóbica dos três materiais, possivelmente devido à incorporação de flúor nas superfícies. A combinação de potência e pressão que promoveu aumento mais significativo em ϴ variou para cada material: 80 W e 80 mTorr para o filme amorfo, aumentando de 60,6° para 111,1° nestas condições, 20 W e 40 mTorr para o polipropileno, aumentando de 81,8° para 119° e 100 W e 60 mTorr para o poliestireno, aumentando de 74° para 95°. As análises por XPS indicaram a presença de flúor após os tratamentos com plasmas de SF6, mostrando um aumento da razão F/C de 0 para todas as amostras não tratadas para 0,03 para o filme amorfo tratado, 0,14 para o polipropileno tratado, e 0,60 para o poliestireno tratado. / The present work investigates the effects of plasma treatment on conventional polymers, polypropylene and polystyrene, and on amorphous hydrogenated carbon, a-C-H, obtained by Plasma Enhanced Chemical Vapour Deposition, (PECVD). After preliminary studies to establish the plasma gas and treatment times, samples were treated in sulphur hexafluoride (SF6) plasmas at five different powers and five different pressures. Surfaces were characterized by goniometry, profilometry, Fourier Transform Infrared Spectrometry, Scanning Electron Microscopy (SEM), EnergyDispersive X-ray Spectroscopy (EDS) and X-Ray Photoelectron Spectroscopy (XPS). Thus, contact angle, roughness, chemical structure, morphology, chemical composition and surface chemical composition were examined. Results show that SF6 treatments increase the hydrophobicity of the three substrates, possibly due to the surface incorporation of fluorine. The power and pressure combinations that caused the greatest improvements in ϴ were as follows: 80 W and 80 mTorr for the amorphous film, resulting in an increase from 60.6° to 111.11°; 20 W and 40 mTorr for polypropylene, resulting in an increase from 81,8° to 119°; 100 W and 60 mTorr for polystyrene, resulting in an increase from 74° to 95°. The presence of fluorine following the SF6 plasma treatments was confirmed by the XPS analyses, which showed that F/C increased from 0 for all the untreated samples to 0,03 on treated amorphous films, to 0,14 on treated polypropylene, and to 0,60 on treated polystyrene.

Le faible coût du glycérol sur le marché a conduit à des études approfondies sur la conversion du glycérol en dérivés à valeur ajoutée. Ce travail se concentre sur l'estérification catalytique du glycérol, avec l'acide oléique, réaction d’intérêt industriel en raison de la grande valeur commerciale des produits obtenus. Dans ce travail, un nouveau catalyseur acide hétérogène présentant une surface hydrophobe a été développé sur le support ZrO2-SiO2 car un catalyseur acide solide tolérant à l'eau est essentiel pour les réactions d'estérification en milieu biphasique produisant de l'eau. Le catalyseur synthétisé (ZrO2-SiO2-Me&Et-PhSO3H) a été préparé par silication et modification de surface en utilisant du triméthoxyméthylsilane (TMMS) et du 2-(4- chlorosulfonylphényl) éthyltriméthoxysilane. La morphologie de surface, les propriétés physicochimiques et texturales, l'acidité et l'hydrophobicité ont été caractérisées. Le mécanisme de modification de la surface du catalyseur est proposé en fonction des résultats de caractérisation complets. Une nouvelle technique pour contrôler le niveau d'acidité et d'hydrophobicité du catalyseur conçu est décrite dans ce travail. L'acidité et l'hydrophobicité du catalyseur ont été réglées en contrôlant la quantité d'agents de modification de surface. Il a pu être montré que l'hydrophobicité du catalyseur était diminuée à mesure que son acidité augmentait. Le catalyseur ZrO2-SiO2-Me & Et-PhSO3H_70 avec 70% molaire de TMMS et 0,62 mmol/g d'acidité est le catalyseur optimal pour l'estérification du glycérol avec l'acide oléique. Enoutre, le rôle de l'hydrophobicité dans la réaction catalytique a été étudié ici. Ce travail a montré qu'à acidité constante du catalyseur, le catalyseur le plus hydrophobe présentait un meilleur rendement. La conversion en utilisant le catalyseur préparé (ZrO2-SiO2-Me et EtPhSO3H_70) est de 88,2% avec une sélectivité en monooléate de glycérol de 53,5% et une sélectivité en dioléate de glycérol de 40,0% (sélectivité combinée de 94% en monooléate et dioléate de glycérol) pour un rapport équimolaire d'acide oléique/glycérol, une température de réaction de 160°C, une concentration massique du catalyseur de 5% par rapport à la masse d’acide oléique introduit, en conditions de réaction sans solvant et avec un temps de réaction de 8 h. Ce travail révèle que l'hydrophobicité et le volume des pores du catalyseur conçu affectent significativement la sélectivité en produit. De plus, les performances du catalyseur hydrophobe ZrO2-SiO2-Me&Et- PhSO3H_70, ont été comparées à celles de la zircone sulfatée (SO42-/ZrO2) et des catalyseurs commerciaux (Amberlyst 15 et Aquivion). Les résultats de corrélation ont montré que le volume moyen des pores (taille des pores) influençait la sélectivité du produit lorsque le catalyseur ZrO2- SiO2-Me&Et-PhSO3H_70 était comparé à trois catalyseurs SO42-/ZrO2 développés à partir de différents précurseurs de zirconium. Ainsi, le catalyseur à volume de pores le plus élevé est favorable à la production de dioléate de glycérol dans des conditions réactionnelles identiques. On peut conclure que le volume et la taille des pores peuvent être utilisés pour contrôler la sélectivité en produit. En outre, cette étude a également révélé que la propriété d'hydrophobicité améliorait la vitesse de réaction initiale. / The low market value of glycerol has led to extensive investigations on glycerol conversion to value-added derivatives. This work focuses on industrially important catalytic esterification of glycerol with oleic acid due to the high commercial value of the resulting products. In this work, a novel heterogeneous acid catalyst featuring hydrophobic surface was developed on ZrO2-SiO2 support as water tolerant solid acid catalyst is vital for biphasic esterification reactions producing water. The synthesized catalyst (ZrO2-SiO2-Me&Et-PhSO3H) was prepared through silication and surface modification using trimethoxymethylsilane (TMMS) and 2-(4-chlorosulfonylphenyl) ethyltrimethoxysilane. The surface morphology, physiochemical and textural properties, acidity and hydrophobicity were characterized. The mechanism of the catalyst surface modification is thereof proposed according to comprehensive characterization results. A novel technique to control acidity and hydrophobicity level of the designed catalyst is disclosed in this work. The acidity and hydrophobicity of the catalyst were tuned by controlling the amount of surface modification agents. It was found that the hydrophobicity of the catalyst decreased as its acidity increased. ZrO2-SiO2-Me&Et-PhSO3H_70 catalyst with 70 mol% of TMMS and 0.62 mmol/g acidity is the optimal catalyst for glycerol esterification with oleic acid. Furthermore, the role of hydrophobicity in catalytic reaction was investigated herein. It was found that at constant catalyst acidity, the more hydrophobic catalyst showed better yield. The conversion using the designed catalyst (ZrO2-SiO2-Me&EtPhSO3H_70) is 88.2% with 53.5% glycerol monooleate selectivity and 40.0% glycerol dioleate selectivity (combined 94% selectivity of glycerol monooleate and dioleate) at equimolar oleic acid-to-glycerol ratio, 160 oC, reaction temperature, 5 wt% catalyst concentration with respect to weight of oleic acid, solvent-less reaction conditions and 8 h reaction time. This work reveals that the hydrophobicity and the pore volume of the designed catalyst significantly affect the product selectivity. In addition, the performance of the hydrophobic designed ZrO2-SiO2-Me&Et-PhSO3H_70 catalyst was used to benchmark with catalytic activity of sulfated zirconia (SO42-/ZrO2) and commercial catalysts (Amberlyst 15 and Aquivion). The correlation results showed that the average pore volume (pore size) influenced the product selectivity when ZrO2-SiO2-Me&Et-PhSO3H_70 catalyst was compared to three SO42-/ZrO2 catalysts that were developed from different zirconium precursors. Whereby, the higher pore volume catalyst is favourable to glycerol dioleate production at identical reaction conditions. It can be concluded that pore volume and size can be used to control the product selectivity. In addition, this study also revealed that hydrophobicity characteristic facilitated initial reaction rate effectively.

Neste trabalho, duas preparações de lipase imobilizada (EC 3.1.1.3), tipo B (CALB) de Candida antarctica, foram comparadas como biocatalisadores na síntese de ésteres metílicos. CALB imobilizada comercialmente (Novozym 435 - CALB-435) e CALB imobilizada em esferas de estireno-divinilbenzeno (CALB-MCI) foram testadas para as reações de transesterificação. Um delineamento composto central rotacional (DDCR) e metodologia de superfície de resposta (MSR) foram utilizados para otimizar a relação razão molar álcool:óleo, teor de enzimas, e a água adicionada nas reações. As duas preparações de enzimas mostraram diferentes condições ótimas para a produção de ésteres metílicos, com a taxa inicial da reação de 51,47 mmol L-1 h-1 para CALB-435, e 57 mmol L-1 h-1 para CALB-MCI. O estudo do tempo de reação indicou que em 72 h foi possível obter conversões próximas a 100 % para ambos os derivados. Um alto rendimento de conversão foi obtido sob as condições otimizadas, indicando que a RSM pode ser usada para descrever adequadamente a relação entre os parâmetros de reação e da resposta (teor de ésteres metílicos). Sobre a estabilidade operacional durante as experiências de reutilização, ambos preparados enzimáticos mantiveram 70 % de sua atividade inicial após oito bateladas, sugerindo sua aplicabilidade na produção de biodiesel. / In this work two preparations of immobilized lipase (EC 3.1.1.3), type B (CALB) from Candida antarctica, were compared as biocatalysts in the synthesis of esters. Commercial Novozym 435 (CALB-435) and CALB immobilized on styrene-divinylbenzene beads (CALB-MCI) were tested for the transesterification reactions. Central composite design rotational (DCCR) and response surface methodology (RSM) were used to optimize the substrate molar ratio, enzyme content, and the added water. The two enzyme preparations have shown different optimal conditions for the production of methyl esters, with initial rates of reaction 51.47 mmol L-1 h-1 for CALB-435, and 57 mmol L-1 h-1 for CALB-MCI. The study of reaction time indicated that in 72 h it was possible to obtain conversions close to 100 % for both derivatives. A high yield conversion was obtained under the optimized conditions, indicating that RSM can be used to adequately describe the relationship between the reaction parameters and the response (yield conversion) in lipase-catalyzed biodiesel synthesis. Over the operational stability during experiments of batch reuse, both prepared enzymatic maintained 70 % of their initial activity after eight batches, suggesting their potential for economical application on biodiesel production.

Neste trabalho propomos uma investigação através de simulações de dinâmica molecular da água em contato com superfícies hidrofóbicas e hidrofílicas, tanto dentro de nanotubos funcionalizados quanto em membranas bi-dimensionais para dessalinização. No caso da água em contato com superfícies hidrofóbicas e hidrofílicas de nanotubos nós encontramos uma quebra na relação de Stokes-Einstein para a difusão e a viscosidade da água. Essa quebra ocorre para os menores nanotubos − em que pelo menos duas camadas de água formam-se, condição para deslizamento de camadas necessária para o cálculo da viscosidade. O mecanismo por trás deste comportamento é ditado pela estrutura da água confinada. Esse resultado indica que algumas das características observadas para a água dentro de nanotubos hidrofóbicos, como nanotubos de carbono na natureza, são únicas. Encontramos uma grande dependência da dinâmica e estrutura da água confinada com as características polares do nanotubo, principalmente para nanotubos com diâmetros menores que 1 nm. Ao variarmos a temperatura do sistema, observamos ainda uma forte dependência da estruturação das moléculas de água com a temperatura, a ponto de apresentar transições entre estados mais e menos ocupados Nossos resultados de dinâmica molecular também mostram que membranas contendo nanoporos com sítios hidrofílicos entre regiões hidrofóbicas podem apresentar grande fluxo de água e reduzido transporte de íons, o que torna esses materiais excelentes candidatos para sistemas de dessalinização e limpeza de metais pesados. Ao acrescentarmos um químico floculante (cloreto de ferro) à água salgada, encontramos resultados ainda melhores para a rejeição de sal pelas membranas nanoporosas. Todos esses resultados demonstram a importância do estudo das propriedades hidrofóbicas e hidrofílicas em interfaces aquosas. Em todos os casos, encontramos uma dependência inerente das propriedades de transporte da água com a característica polar da superfície de contato. / In this work we have proposed an investigation through molecular dynamics (MD) simulations of the water behavior at hydrophobic and hydrophilic surfaces in both functionalyzed nanotubes and two-dimensional nanpores. In the case of water at hydrophobic and hydrophilic nanotube surfaces, we have found a breakdown of the Stokes-Einstein relation for diffusion and viscosity of water confined in narrow hydrophobic nanopores. The mechanism underlying this behavior is dictated by the structure of water under confinement. This result indicates that some of the features observed for water inside hydrophobic carbon nanotubes cannot be observed in other nanopores. We have also found an important dependence of the water dynamics with the polar character of the nanotube, mostly for small diameters. By varying the temperature, both the dynamics and the water structuration are affected, presenting transitions between dense-packed and low-density states. Our results also shows that nanoporous membranes, with hydrophilic sites sandwiched between hydrophobic regions, can present an important flux of water molecules and reduced ion transportation, making these structures promising for desalination processes. By adding a flocculant ingredient (ferric chloride) to the salt water, we found even larger ion rejection rates. All the results point out the importance of studying hydrophilic and hydrophobic interfaces for water transport. In all the cases, we have found an ubiquitous dependence of water dynamic properties on the surface polarity.

Neste trabalho, duas preparações de lipase imobilizada (EC 3.1.1.3), tipo B (CALB) de Candida antarctica, foram comparadas como biocatalisadores na síntese de ésteres metílicos. CALB imobilizada comercialmente (Novozym 435 - CALB-435) e CALB imobilizada em esferas de estireno-divinilbenzeno (CALB-MCI) foram testadas para as reações de transesterificação. Um delineamento composto central rotacional (DDCR) e metodologia de superfície de resposta (MSR) foram utilizados para otimizar a relação razão molar álcool:óleo, teor de enzimas, e a água adicionada nas reações. As duas preparações de enzimas mostraram diferentes condições ótimas para a produção de ésteres metílicos, com a taxa inicial da reação de 51,47 mmol L-1 h-1 para CALB-435, e 57 mmol L-1 h-1 para CALB-MCI. O estudo do tempo de reação indicou que em 72 h foi possível obter conversões próximas a 100 % para ambos os derivados. Um alto rendimento de conversão foi obtido sob as condições otimizadas, indicando que a RSM pode ser usada para descrever adequadamente a relação entre os parâmetros de reação e da resposta (teor de ésteres metílicos). Sobre a estabilidade operacional durante as experiências de reutilização, ambos preparados enzimáticos mantiveram 70 % de sua atividade inicial após oito bateladas, sugerindo sua aplicabilidade na produção de biodiesel. / In this work two preparations of immobilized lipase (EC 3.1.1.3), type B (CALB) from Candida antarctica, were compared as biocatalysts in the synthesis of esters. Commercial Novozym 435 (CALB-435) and CALB immobilized on styrene-divinylbenzene beads (CALB-MCI) were tested for the transesterification reactions. Central composite design rotational (DCCR) and response surface methodology (RSM) were used to optimize the substrate molar ratio, enzyme content, and the added water. The two enzyme preparations have shown different optimal conditions for the production of methyl esters, with initial rates of reaction 51.47 mmol L-1 h-1 for CALB-435, and 57 mmol L-1 h-1 for CALB-MCI. The study of reaction time indicated that in 72 h it was possible to obtain conversions close to 100 % for both derivatives. A high yield conversion was obtained under the optimized conditions, indicating that RSM can be used to adequately describe the relationship between the reaction parameters and the response (yield conversion) in lipase-catalyzed biodiesel synthesis. Over the operational stability during experiments of batch reuse, both prepared enzymatic maintained 70 % of their initial activity after eight batches, suggesting their potential for economical application on biodiesel production.

Neste trabalho propomos uma investigação através de simulações de dinâmica molecular da água em contato com superfícies hidrofóbicas e hidrofílicas, tanto dentro de nanotubos funcionalizados quanto em membranas bi-dimensionais para dessalinização. No caso da água em contato com superfícies hidrofóbicas e hidrofílicas de nanotubos nós encontramos uma quebra na relação de Stokes-Einstein para a difusão e a viscosidade da água. Essa quebra ocorre para os menores nanotubos − em que pelo menos duas camadas de água formam-se, condição para deslizamento de camadas necessária para o cálculo da viscosidade. O mecanismo por trás deste comportamento é ditado pela estrutura da água confinada. Esse resultado indica que algumas das características observadas para a água dentro de nanotubos hidrofóbicos, como nanotubos de carbono na natureza, são únicas. Encontramos uma grande dependência da dinâmica e estrutura da água confinada com as características polares do nanotubo, principalmente para nanotubos com diâmetros menores que 1 nm. Ao variarmos a temperatura do sistema, observamos ainda uma forte dependência da estruturação das moléculas de água com a temperatura, a ponto de apresentar transições entre estados mais e menos ocupados Nossos resultados de dinâmica molecular também mostram que membranas contendo nanoporos com sítios hidrofílicos entre regiões hidrofóbicas podem apresentar grande fluxo de água e reduzido transporte de íons, o que torna esses materiais excelentes candidatos para sistemas de dessalinização e limpeza de metais pesados. Ao acrescentarmos um químico floculante (cloreto de ferro) à água salgada, encontramos resultados ainda melhores para a rejeição de sal pelas membranas nanoporosas. Todos esses resultados demonstram a importância do estudo das propriedades hidrofóbicas e hidrofílicas em interfaces aquosas. Em todos os casos, encontramos uma dependência inerente das propriedades de transporte da água com a característica polar da superfície de contato. / In this work we have proposed an investigation through molecular dynamics (MD) simulations of the water behavior at hydrophobic and hydrophilic surfaces in both functionalyzed nanotubes and two-dimensional nanpores. In the case of water at hydrophobic and hydrophilic nanotube surfaces, we have found a breakdown of the Stokes-Einstein relation for diffusion and viscosity of water confined in narrow hydrophobic nanopores. The mechanism underlying this behavior is dictated by the structure of water under confinement. This result indicates that some of the features observed for water inside hydrophobic carbon nanotubes cannot be observed in other nanopores. We have also found an important dependence of the water dynamics with the polar character of the nanotube, mostly for small diameters. By varying the temperature, both the dynamics and the water structuration are affected, presenting transitions between dense-packed and low-density states. Our results also shows that nanoporous membranes, with hydrophilic sites sandwiched between hydrophobic regions, can present an important flux of water molecules and reduced ion transportation, making these structures promising for desalination processes. By adding a flocculant ingredient (ferric chloride) to the salt water, we found even larger ion rejection rates. All the results point out the importance of studying hydrophilic and hydrophobic interfaces for water transport. In all the cases, we have found an ubiquitous dependence of water dynamic properties on the surface polarity.

Certains procédés d'électrolyse industriels, comme ceux de production de fluor et d'aluminium, génèrent du gaz sur des électrodes peu mouillées par l'électrolyte. Dans ces procédés, la convection est en grande partie induite par le mouvement des bulles. Le temps de résidence du gaz n'étant pas maitrisé, la modélisation de ces électrolyses se heurte à de nombreux défis. Ce travail propose un état des connaissances nécessaires à la modélisation de ce type de cellules. Après avoir mis au point une méthode permettant de réaliser des électrodes fortement hydrophobes, nous avons étudié le dégagement gazeux que celles-ci produisent. Nous avons observé que les bulles qui s'y forment croissent par coalescence et ce phénomène affecte la vitesse de croissance et la taille au détachement. Par la suite, nous avons démontré qu'en localisant le dépôt hydrophobe il est possible d'obtenir une population de bulles dont le nombre, la taille et la position sont maitrisés. Nous avons constaté que l'émission acoustique est un outil efficace pour mesurer, sans observation visuelle, la taille et la vitesse d'ascension des bulles produites par électrolyse. La fréquence la plus énergétique du spectre des salves d'émission acoustique des cellules d'électrolyse produisant du gaz permet, quand la fraction volumique de gaz est faible, de mesurer la taille de toutes les bulles dans la cellule. Quand les bulles sont nombreuses et denses, cette même fréquence est liée aux dimensions de la cellule, à la densité de courant, à la taille des bulles et à la fraction volumique en gaz dans le panache. Nous avons proposé une explication à cette observation basée sur l'hypothèse d'un couplage acoustique des bulles. En l'absence d'agitation vigoureuse, l'activité acoustique d'une cellule d'électrolyse produisant des bulles traduit l'importance du transport de matière aux électrodes. La mesure de la répartition de la densité de courant par la méthode des électrodes segmentées dans une cellule en convection libre a été réalisée. Cette étude a été menée dans le but de tester un outil de simulation numérique des cellules d'électrolyse produisant du gaz. L'effet de la mouillabilité de l'électrode sur la répartition du courant a été évalué. / Molten salts electrochemical processes, like fluorine and aluminium production processes produce bubbles on electrodes slightly wetted by an electrolyte. In those cells, the electrolyte convection is mainly induced by the motion of bubbles. Then, the residence time of gas is not under control and the modelling of such electrolysis still faces many challenges. This work begins with a collection of the information required to model gas-producing cells. We developed an electrochemical composite coating technique to achieve the production of highly hydrophobic electrodes. Then we studied the gas evolution obtained with these electrodes, we observed that coalescences determines the bubbles growth rate and sizes at detachment. When the hydrophobic deposit is local, it is possible to obtain a bubble population whose number, size and position are controlled. We found that the acoustic emission is an effective tool to measure the size and rising speed of bubbles produced by electrolysis without having to observe them visually. When the volume fraction of gas is low, the most energetic frequency of the spectrum of acoustic emission bursts allows measuring the size of all bubbles in the cell. When bubbles are numerous, the most energetic frequency of the acoustic emission spectrum is related to the dimensions of the cell, current density, sizes of the bubbles and gas volume fraction in the plume. We have proposed an explanation for this observation based on the assumption of an acoustic coupling of the bubbles. When bubbles are produced, the acoustic activity of an electrolysis cell is correlated with the mass transport at electrodes. We propose a set of measurements of the distribution of current density at the electrodes in a cell with electrolyte free convection. These measurements have been carried out to benchmark a numerical simulation tool. The effect of the wettability of the electrode on the current distribution was evaluated.