The carbon metabolism in costal sediments is of major importance for the global carbon cycle. Costal sediments are also subjected to physical forcing generating water fluxes above and through the sediments, but how the physical affect the carbon metabolism is currently poorly known. In this study, the effect of advective pore water flow on degradation of organic matter in permeable sandy sediment was investigated in a laboratory study during wintertime. Sediments were collected from both brackish water (Askö) and from a fresh water stream (Getå Stream). In two chamber experiments, with and without advective pore water flow, the degradation of organic matter was measured through carbon dioxide analysis from water and headspace. In Askö sediments mineralization rates ranged from 3.019 - 5.115 mmol C m-2 d-1 and 3.139 mmol C m-2 d-1 with and without advective pore water flow, respectively. Those results correspond with results from earlier studies of carbon mineralization rates in sediment in the North Sea and the Baltic Sea. There were no significant differences between the two groups in the Askö sediment. In Getå Stream sediments mineralization rates ranged between 4.059 mmol C m-2 d-1 and 6.806 mmol C m-2 d-1 with and without advective flow, respectively. The mineralization rates for Getå Stream correspond with earlier studies of carbon mineralization rates in a stream in New Hampshire.

Geomembranes are one of the most widely used geosynthetics in various civil engineering applications. Their primary function is as a barrier to liquid or vapour flow. Smooth Geomembranes are frequently used in combination with different soils, and due to their low surface roughness, are challenging to design to ensure adequate shear strength along the smooth geomembrane-soil interface. It is important to use the appropriate values of interface shear strength parameters in the design of slopes incorporating one or more geomembranes in contact with soils. The parameters are determined by conducting direct shear test on the geomembrane-soil interface. Laboratory tests of interface shear strength for geomembranes and soil are typically carried out with no provision for measurement of pore pressures at the soil/geomembrane interface. <p>This thesis deals with study of smooth geomembrane-soil interfaces, particularly under unsaturated conditions. The various factors that affect the interface shear behaviour are also studied. The tests were conducted using a modified direct shear box with a miniature pore pressure transducer installed adjacent to the surface of the geomembrane. Geomembranesoil interface shear tests were carried out with continuous measurement of suction in close proximity to the interface during the shearing process thus making it possible to analyze test results in terms of effective stresses. The method was found to be suitable for unsaturated soils at low values of matric suction. <p>Results of interface shear tests conducted using this method show that it is quite effective in evaluating interface shear behaviour between a geomembrane and an unsaturated soil. The results suggest that soil suction contributes to shearing resistance at low normal stress values. At lower normal stress values, the interface shear behaviour appears to be governed only by the magnitude of total normal stress. <p> At high normal stresses, the failure mechanism changed from soil particles sliding at the surface of geomembrane to soil particles getting embedded into the geomembrane and plowing trenches along the direction of shear. A plowing failure mechanism resulted in the mobilization of significantly higher shear strength at the geomembrane soil interface. It was found that placement water contents near saturated conditions results in lower effective stresses, a shallower plowing mechanism and lower values of mobilized interface shear strength.

Els materials porosos s'utilitzen àmpliament en moltes branques de la ciència i tecnologia modernes com la catàlisi, la separació de mescles, la purificació de fluids i la fabricació de membranes. Per a que els sòlids porosos puguin aplicar-se amb èxit cal disposar d'una caracterització precisa de la superfície i de les propietats estructurals, així com també una bona comprensió del comportament físico-químic dels fluids dins dels porus. Alguns materials, com les zeolites, tenen estructures poroses ben definides, però d'altres, com els òxids porosos, carbons i vidres de porus controlat, són bastant amorfs. Per això, un tema clau i, sovint, complicat, és la caracterització adequada d'aquests tipus de materials. Durant molts anys, l'adsorció de gasos s'ha emprat per estudiar les propietats de sòlids porosos, degut a que és un mètode ràpid, simple i que proporciona prou informació. Es van desenvolupar molts mètodes per extraure dades sobre la porositat i les propietats de la superfície de materials a partir d'isotermes d'adsorció. En les dues últimes dècades, amb l'ajuda dels ordinadors, cada cop més i més ràpids, l'ús de les tècniques de modelat molecular ha anat guanyant rellevància. En aquest context, l'objectiu general d'aquest treball de tesi és desenvolupar eines a escala molecular emprant la mecànica estadística i aplicant-la a la caracterització de materials adsorbents.Després d'una breu introducció en el tema (capítol 1), en el capítol 2 presentem una revisió de la metodologia bàsica emprada en aquest treball. En el capítol 3 hem implementat la teoria funcional de la densitat de mesures fonamentals o FMT (de l'anglès, Fundamental-Measured density functional theory), publicada per Kierlik i Rosinberg, per descriure l'adsorció de molècules Lennard-Jones en porus cilíndrics. Pel que sabem, aquest és el primer cop que la teoria s'aplica a la geometria cilíndrica. L'exactitud de la teoria en predir isotermes d'adsorció i perfils de densitat de partícules es compara amb simulacions Monte Carlo en el col·lectiu gran canònic per un rang ample de mides de porus. Aquesta comparació mostra que la concordança és molt bona en tots els casos. Addicionalment, s'ha aplicat la teoria a l'adsorció en porus plans per estudiar la influència de la geometria del porus en aquest fenomen. Els resultats indiquen que el confinament de la geometria cilíndrica introdueix diferències significatives en la forma de les isotermes d'adsorció i els perfils de densitat. Aquestes diferències són rellevants a l'hora de caracteritzar materials porosos. Els resultats indiquen que té lloc un comportament per capes en el porus cilíndric més petit que s'ha considerat, mentre que l'adsorció en un porus pla de la mateixa grandària necessita un potencial químic molt més alt per aconseguir una adsorció significant. A mida que el diàmetre del porus augmenta, la influència de la geometria es fa cada cop menys important, encara que es pot observar una certa desviació en la transició de condensació capil·lar. Addicionalment, per porus més amples, obtenim una adsorció multicapa amb condensació capil·lar a potencials químics alts, amb el mateix comportament qualitatiu observat en ambdues geometries. Quan el diàmetre assoleix el límit on els efectes de curvatura ja no són rellevants, el comportament quantitatiu del porus cilíndric es redueix al mateix que el del porus pla. La formació d'una capa fina adsorbent en mides de porus intermèdies i grans sembla correspondre a una transició de fase termodinàmica de segon ordre, per al rang de paràmetres utilitzat i les condicions termodinàmiques estudiades. No obstant, els resultats semblen indicar una interrelació entre aquest comportament i la transició pre-mullada (de la paraula anglesa prewetting) que s'observa en geometries semi-infinites, especialment al voltant del punt final crític de la línia pre-mullada. L'efecte del confinament és molt important en aquest comportament crossover (de pas). De la comparació de càlculs FMT amb resultats de la teoria funcional de la densitat no local, concloem que la FMT és una eina excel·lent per a l'estudi del comportament de fluids en geometries cilíndriques.En el capítol 4 s'explica com hem aplicat la FMT juntament amb un mètode de regularització per estimar la distribució de mides de porus o PSD (de l'anglès, Pore-Size Distribution) de vidres porosos model. Hem escollit aquest material perquè va ser desenvolupat mitjançant tècniques de modelat molecular, i es pot comparar directament amb la teoria utilitzada en aquest treball. Un avantatge addicional d'aquests materials model, enfront els experimentals, és que, en el primer cas, la mida i forma dels porus són ben conegudes, així com també la posició dels àtoms en la superfície, esdevenint així un material perfecte per comprovar l'exactitud dels mètodes de caracterització teòrica disponibles. Com que hi ha diferents solucions de l'equació integral d'adsorció compatibles amb la isoterma d'adsorció experimental, i diversos factors poden amagar els defectes del model molecular, hem realitzat la caracterització d'una forma sistemàtica: primer hem comprovat l'exactitud de la FMT i el model de porus independent per predir les isotermes d'adsorció "experimentals" utilitzant la PSD ja coneguda per als materials. Això s'ha efectuat amb porus individuals plans i cilíndrics. En segon lloc, un cop la isoterma d'adsorció va ser reconstruïda amb èxit, vam invertir la isoterma d'adsorció integral amb un procediment de regularització. L'exactitud del mètode d'inversió s'ha comprovat també abans d'estimar la PSD de materials diferents. En últim lloc, un cop demostrat que el mètode és correcte, l'hem utilitzat per estimar la PSD de quatre materials. També hem estudiat la influència d'escollir alguns valors particulars de paràmetres moleculars per les interaccions fluid-fluid i sòlid-fluid en el comportament adsorbent d'aquests sistemes. Hem obtingut que el model de porus independent és adequat per als quatre materials investigats en aquest treball. La geometria plana sembla representar millor que la geometria cilíndrica el comportament adsorbent global. Pel que fa a la PSD obtinguda amb el nostre procediment, s'observa que les distribucions obtingudes mitjançant la inversió de la integral estan en millor concordança amb les distribucions geomètriques que les calculades amb el mètode Barrett-Joyner-Halenda (BJH). El locus del pic està situat a la mateixa mida de por, i tots ells són unimodals, mentre que les distribucions BJH mostren un màxim localitzat sistemàticament a porus més petits, estimant per sota la PSD del material, i no són unimodals. En quan a la geometria dels porus individuals que formen el material podem dir que, encara que la PSD és més ampla que les geomètriques, l'adsorció que es prediu per un conjunt de porus plans individuals està en un acord quasi quantitatiu amb la isoterma d'adsorció experimental.Finalment, en el capítol 5 exposem com hem caracteritzat tres mostres diferents de g­alúmina, una d'elles sense tractament i les altres dues calcinades en un forn durant unes hores a 823 i 1023K. Per fer-ho hem mesurat isotermes d'adsorció de nitrogen a 77.35K en un equip Micromeretics ASAP 2000. A més, hem aprofitat les PSD's proporcionades pel programari de l'equip emprant el mètode BJH. Hem calculat isotermes teòriques mitjançant l'aproximació FMT. Hem invertit les equacions integrals d'adsorció amb el mètode de regularització i, finalment, hem obtingut les PSD's per les tres mostres d'alúmina, i les corresponents isotermes d'adsorció pels tres materials. D'aquesta forma hem observat la influència de la calcinació de l'alúmina en la seva PSD. A més, hem comprovat l'exactitud del mètode FMT/de regularització de manera sistemàtica. Quan comparem les PSD's obtingudes amb les corresponents distribucions BJH, hem verificat que, en els dos primers casos (alúmina no tractada i alúmina calcinada a 823K), el mètode BJH estima per sota la mida dels porus, proporcionant una PSD desviada cap a mides més petites. En el cas de l'alúmina calcinada a 1,023K, en la que el procés de sinterització produeix que els porus més petits desapareguin, afavorint els més grans, les PSD's del mètode BJH i les PSD's de la FMT/regularització són molt semblants. Amb això es corrobora el fet conegut de que el mètode BJH és força acurat en la regió macroporosa. Finalment, hem predit la isoterma d'adsorció d'un fluid diferent (età) a una altra temperatura (333K), en un dels materials caracteritzats (alúmina no tractada), amb l'ànim d'establir la robustesa de la PSD obtinguda. La concordança obtinguda mostra que és possible utilitzar aquest mètode de caracterització i extrapolar els resultats a altres condicions, mentre s'empri un nombre suficient de mides de porus per calcular la isoterma desitjada, i els paràmetres d'interacció sòlid-fluid es triïn adequadament. / Los materiales porosos se utilizan en muchas ramas de la ciencia y la tecnología, por ejemplo, se usan como catalizadores, en la separación de mezclas, en la purificación de fluidos, y en la fabricación de membranas. Su aplicación adecuada requiere de la caracterización precisa de sus propiedades superficiales y estructurales, además del conocimiento del comportamiento fisicoquímico de los fluidos cuando se encuentran dentro de los poros. Algunos materiales, como las zeolitas, tienen estructuras porosas bien definidas, pero otros en cambio (óxidos porosos, carbones, vidrios porosos con tamaño controlado) son bastante amorfos. Por lo tanto, una caracterización correcta de los materiales porosos es un área de estudio muy importante, la cual en algunos casos es una tarea sencilla pero en la mayoría no. Durante muchos años la adsorción de gases ha sido empleada para estudiar las propiedades de sólidos porosos, dado que es bastante fácil, simple y se puede obtener mucha información. Se han desarrollado muchos métodos para interpretar los datos experimentales y determinar la porosidad, las propiedades superficiales y la distribución de los tamaños de los poros de los materiales a partir de las isotermas de adsorción. En las dos últimas décadas, con la ayuda de las computadoras cada vez más rápidas, se ha extendido mucho el uso las técnicas de la mecánica estadística para realizar esta tarea. En este contexto, el objetivo general de esta tesis consiste en desarrollar herramientas a escala molecular utilizando la mecánica estadística para la caracterización de materiales adsorbentes.Después de una breve introducción en el tema (capítulo 1), el capítulo 2 está dedicado a hacer una revisión de la metodología básica empleada en este trabajo. En el capítulo 3 hemos implementado la teoría funcional de la densidad de medidas fundamentales (FMT, del inglés Fundamental-Measure density functional theory) de Kierlik y Rosinberg para describir la adsorción de moléculas Lennard-Jones dentro de poros cilíndricos. Hasta donde sabemos, ésta es la primera vez que esta teoría es aplicada a geometría cilíndrica. La exactitud de la teoría en predecir las isotermas de adsorción y los perfiles de la densidad es verificada por comparación con simulaciones Monte Carlo en el colectivo Gran Canónico para un amplio intervalo de tamaños de poros, observándose una buena concordancia en todos los casos. Adicionalmente, la teoría ha sido aplicada a la adsorción en poros planos para estudiar la influencia de los poros en esta propiedad. Los resultados indican que el confinamiento de la geometría cilíndrica introduce diferencias significativas en la forma de las isotermas de adsorción y de los perfiles de la densidad. Estas diferencias son relevantes para la caracterización de los materiales porosos. Nuestros resultados indican que un comportamiento de formación de capa tiene lugar en el poro cilíndrico, mientras que la adsorción en un poro plano del mismo tamaño necesita un potencial químico mucho más alto para alcanzar una adsorción significativa. Cuando el tamaño de poro se incrementa, la influencia de la geometría se vuelve menos importante, pero aún se observa un cierto desplazamiento del lugar en el cual se da la transición de la condensación capilar. Adicionalmente, para poros más anchos, tenemos formación de multicapas con condensación capilar a potenciales químicos altos, observándose el mismo comportamiento cualitativo en ambas geometrías. Cuando el diámetro alcanza el límite en donde los efectos de la curvatura ya no son relevantes, el comportamiento cuantitativo de los poros cilíndricos y de los planos es muy similar. La formación de una fina película adsorbida a tamaños de poro grandes e intermedios parece corresponder a una transición de fase termodinámica de segundo orden, para el intervalo de parámetros usado y a las condiciones termodinámicas estudiadas. Sin embargo, los resultados encontrados parecen indicar que existe una relación entre este comportamiento y el de una transición de pre-mojado observada en geometrías semi-infinitas, especialmente en la vecindad del punto final crítico de la línea de pre-mojado. El efecto del confinamiento es muy importante en este comportamiento de transición. A partir de la comparación de los cálculos hechos con FMT y los hechos con la teoría funcional de la densidad no-local, concluimos que la FMT es una excelente herramienta para el estudio del comportamiento de los fluidos en geometrías cilíndricas confinadas.En el capítulo 4 hemos aplicado la FMT en combinación con un método de regularización para estimar la distribución de tamaños de poros (PSD, del inglés Pore-Size Distribution) de materiales modelo que imitan a los vidrios porosos. Hemos elegido este material en particular porque fue desarrollado con técnicas de modelado molecular, y se puede hacer una comparación directa con la teoría aquí usada. Una ventaja adicional de estos materiales modelo, con respecto a los materiales reales, es que en este caso la forma y tamaño de los poros se conoce exactamente, además de que se sabe la posición de los átomos en la superficie, convirtiéndolo en un material ideal para verificar la exactitud de los métodos de caracterización teóricos disponibles. Dado que existen varias soluciones de la ecuación integral de adsorción compatibles con la isoterma de adsorción experimental, y que varios factores pueden ocultar los defectos del modelo molecular, hemos hecho la caracterización de una manera sistemática: primero hemos probado la exactitud de la FMT y del modelo de poros independientes para predecir las isotermas de adsorción "experimentales" usando la PSD geométrica ya conocida para estos materiales. Esto ha sido hecho tanto con los poros cilíndricos como con los planos. En segundo lugar, una vez que la isoterma de adsorción fue reconstruida, invertimos la isoterma integral de adsorción con un procedimiento de regularización. La exactitud del método de inversión ha sido verificado antes de estimar la PSD de los diferentes materiales. Finalmente, una vez que se ha establecido que el método es correcto, lo usamos para estimar las PSD's de estos cuatro materiales. Hemos estudiado también la influencia de elegir diferentes valores de los parámetros moleculares para la interacción fluido-fluido y para la sólido-fluido en el comportamiento de adsorción en estos sistemas. Los resultados indican que el modelo de poros independientes es adecuado para los cuatro materiales aquí investigados. La geometría plana parece representar el comportamiento de adsorción global mejor que la cilíndrica. En cuanto a lo que las PSD's obtenidas con nuestro procedimiento se refiere, las distribuciones resultantes a través de la inversión de la integral presentan una mejor concordancia con las distribuciones geométricas que las calculadas con el método Barrett-Joyner-Halenda (BJH). El máximo del pico está localizado en el mismo tamaño de poro, y las distribuciones son unimodales, mientras que las BJH's muestran un máximo sistemáticamente localizado a poros más pequeños, subestimando las PSD's del material, y éstas no son unimodales. Respecto a la geometría de los poros individuales que conforman el material, se puede decir, a pesar de que las PSD's son más dispersas que las geométricas, que la adsorción predicha por una colección de poros planos individuales tiene una concordancia casi cuantitativa con la isoterma de adsorción experimental.Finalmente, en el capítulo 5 hemos caracterizado tres muestras diferentes de g­alúmina, una de ellas sin ningún tratamiento, y las otras dos calcinadas en un horno durante varias horas a 823 y a 1,023K. Para ello hemos medido isotermas de adsorción de nitrógeno a 77.35K en un equipo Micromeritics ASAP 2000. Adicionalmente, hemos usado las PSD's calculadas con el método BJH que proporciona el software del mismo equipo experimental para comparar. Hemos calculado las isotermas teóricas utilizando la FMT. Hemos invertido las ecuaciones integrales de adsorción con el método de regularización y, finalmente, hemos obtenido las PSD's para las tres muestras de alúmina, y las correspondientes isotermas de adsorción. De esta manera hemos podido observar la influencia de la calcinación de la alúmina en su PSD. Más aún, hemos probado la exactitud del método combinado FMT/Regularización de una manera sistemática. Cuando hemos comparado las PSD's obtenidas con las correspondientes BJH's, hemos verificado que en los dos primeros casos (alúmina sin tratamiento y alúmina calcinada a 823K) el método BJH subestima el tamaño de los poros, dando PSD's desplazadas a tamaños de poros más pequeños. En el caso de la alúmina calcinada a 1,023K, en la cual el proceso de sinterización ha producido la desaparición de los poros más pequeños en beneficio de los grandes, las PSD's BJH y las PSD's FMT/Regularización son muy similares. Con esto corroboramos el hecho conocido de que el método BJH es bastante exacto en la región de los macroporos. Para terminar, hemos predicho la isoterma de adsorción de un fluido diferente (etano) a una temperatura también diferente (333K) en uno de los materiales caracterizados (alúmina sin tratar) con la idea de comprobar sí la PSD obtenida es transferible a otras condiciones o no. La concordancia observada muestra que es posible usar este método de caracterización y extrapolar los resultados a otras condiciones, procurando que se utilice un número suficiente de tamaños de poro diferentes para calcular la isoterma deseada, y se elijan bien los parámetros de interacción sólido-fluido. / Porous materials are widely used in many branches of modern science and technology, such as catalysis, separation of mixtures, purification of fluids and fabrication of membranes. A successful application of porous solids requires a precise characterization of their surface and structural properties, as well as a good understanding of the physical and chemical behavior of fluids inside the pores. Some materials, such as zeolites, have well defined porous structures, but others, such as porous oxides, carbons and controlled-porous glasses, are quite amorphous. Therefore, a proper characterization of this kind of materials is an important topic, and more often than not, a complicated one. For many years, gas adsorption has been used to study properties of porous solids, since it is fast, simple and informative. Many methods were developed to extract information about porosity and surface properties of materials from adsorption isotherm data. In the last two decades, with the aid of the increasingly faster computers, the use of molecular modeling techniques has been gaining relevance. In this context, the general objective of this thesis is to develop tools at the molecular level using statistical mechanics for the characterization of adsorbent materials.After a brief introduction on the topic (chapter 1), chapter 2 is devoted to a review of the basic methodology employed in this work. In chapter 3 we have implemented the Fundamental-Measure density functional theory (FMT) due to Kierlik and Rosinberg to describe the adsorption of Lennard-Jones molecules in cylindrical pores. To our best knowledge, this is the first time that this theory is applied to a cylindrical geometry. The accuracy of the theory in predicting adsorption isotherms and density profiles is checked by comparison with Grand Canonical Monte Carlo simulations for a wide range of pore sizes, showing very good agreement in all cases. In addition, the theory has been applied to the adsorption in slit-like pores to study the influence of the pore geometry on this property. The results indicate that the confinement of the cylindrical geometry introduces significant differences in the shape of the adsorption isotherms and density profiles. These differences are relevant for the characterization of porous materials. Our results indicate that a layering behavior takes place in the smallest cylindrical pore considered, while the adsorption in a planar pore of the same size needs a much higher chemical potential to achieve a significant adsorption. As the pore size increases, the influence of the geometry becomes less important, although a certain shift in the capillary condensation transition can still be observed. Additionally, for wider pores, we obtain multilayer adsorption with capillary condensation at high chemical potentials, with the same qualitative behavior observed for both geometries. When the diameter size reaches the limit where the curvature effects are not of further relevance, the cylindrical pores reduce to the same quantitative behavior of the slit-like pores. The formation of a thin adsorbed layer at intermediate and large pore sizes seems to correspond to a second order thermodynamic phase transition, for the range of parameters used and the thermodynamic conditions studied. However, the results found seem to indicate some relationship between this behavior and the prewetting transition observed in semi-infinite geometries, especially in the vicinity of the critical end point of the prewetting line. The effect of the confinement is very important in this crossover behavior. From the comparison of Fundamental-Measure density functional theory calculations versus non-local density functional theory results, we conclude that the FMT is an excellent tool for the study of the behavior of fluids in confined cylindrical geometries.In chapter 4 we have applied the FMT in conjunction with a regularization method to estimate the pore-size distribution (PSD) of model porous glasses. We have chosen this particular material because it was developed with molecular modeling techniques, and a direct comparison can be made with the theory used here. An additional advantage of these model materials, versus experimental ones, is that in this case the size and shape of the pores is well known, as well as the position of the atoms in the surface, making it a perfect material to check the accuracy of the theoretical characterization methods available. Since there are several solutions of the adsorption integral equation compatible with the experimental adsorption isotherm, and several factors can hide defects of the molecular model, we have done the characterization in a systematic manner: we have first checked the accuracy of the FMT and the independent pore model for predicting the "experimental" adsorption isotherms using the geometrical PSD already known for the materials. This has been done with individual cylindrical and slit-like pores. Secondly, once the adsorption isotherm was successfully reconstructed, we inverted the integral adsorption isotherm with a regularization procedure. The accuracy of the inversion method has also been checked before estimating the PSD of the different materials. Finally, once the method has been proved to be correct, we used it to estimate the PSD of four materials. We have also studied the influence of choosing different values of molecular parameters for the fluid-fluid and the solid-fluid interaction on the adsorption behavior of these systems. We have obtained that the independent pore model is adequate for the four materials investigated here. The slit-like geometry seems to represent the overall adsorption behavior better than the cylindrical geometry. As far as the PSD obtained with our procedure is concerned, the distributions obtained by inversion of the integral are in better agreement with the geometrical distributions than the ones calculated with the Barrett-Joyner-Halenda (BJH) method. The locus of the peak is at the same pore size, and all of them are unimodal, while the BJH distributions show a maximum systematically located at smaller pores, underestimating the PSD of the material, and they are not unimodal. Regarding the geometry of the individual pores that form the material, we can say that, although the PSD is broader than the geometrical ones, the adsorption predicted by a collection of individual slit-like pores is in almost quantitative agreement with the "experimental" adsorption isotherm.Finally, in chapter 5 we have characterized three different samples of g­alumina, one of them without treatment and the others two calcined in a furnace during several hours at 823 and 1,023K. For this we have measured adsorption isotherms of nitrogen at 77.35K in a Micromeritics ASAP 2000 apparatus. Additionally, we have used the PSD's provided by the software of the experimental equipment using the BJH method. We have calculated theoretical isotherms by the FMT approach. We have inverted the adsorption integral equations with the regularization method and, finally, we have obtained the PSD's for our three samples of alumina, and the corresponding adsorption isotherms. In this way we have observed the influence of the calcination of alumina on its PSD. Moreover, we have tested the accuracy of the FMT/Regularization method in a systematic way. When we compared the PSD's obtained with the corresponding BJH distributions, we verified that in the two first cases (untreated alumina and alumina calcined at 823K) the BJH method underestimated the size of the pores, giving PSD's shifted to smaller sizes. In the case of alumina calcined at 1,023K, in which the sintering process has produced the disappearance of the smallest pores, favoring the wider ones, the BJH PSD's and the FMT/regularization PSD's perform very similar. With this, we corroborated the known fact that the BJH method is quite accurate in the macroporous region. Finally, we have predicted an adsorption isotherm of a different fluid (ethane) at a different temperature (333K) in one of the characterized materials (untreated alumina) with the aim of establishing the robustness of the PSD obtained. The agreement obtained shows that it is possible to use this characterization method and extrapolate the results at other conditions, provided that a enough number of different pore sizes are used to calculate the desirable isotherm, and the solid-fluid interaction parameters are well chosen.

Hydrogels are polymeric materials that have three-dimensional polymeric networks, which are able to absorb and retain a large amount of water within their structures without being dissolved. Among the synthetic hydrogel, poly(2-hydroxylethyl methacrylate) (poly(HEMA)) has been of great interest because of its excellent biocompatibility with the three-dimensional networks. Therefore, poly(HEMA) hydrogels have been widely used in many areas, especially in biomedical and pharmaceutical areas, for such applications as packing materials in chromatography, sorbents in controlled release and drug delivery, implanting materials in tissue engineering. However, the applications of poly(HEMA) are still limited because of its weak mechanical strength and network properties. Therefore, in recent decades, the challenge of how to modify and control the polymer properties and how to build highly porous structures in it has received considerable attention because these modifications could significantly improve the performance of poly(HEMA) hydrogels for more favorable applications. Although HEMA and its polymers have been studied for more than 40 years, few reports about the preparation of micro-/nano-porous poly(HEMA) hydrogel particles and the requirements of their applications have risen. Furthermore, how to control the porous structures and the properties of HEMA copolymers have not been well understood. Accordingly, the objectives of this research were to investigate the synthesis of the porous copolymeric particles of HEMA with various comonomers (MMA, St and NVP), to characterize the porous structures and particle morphology, to simulate the synthesis process and porous characteristics, to explore the effects of the polymer compositions and the porous structures on the swelling properties, and to apply the resultant polymeric particles in the controlled release of the hydrophilic model drug. In the present studies, HEMA was copolymerized with three different comonomers, methyl methacrylate (MMA), styrene (St) and N-vinyl-2-pyrrolidone (NVP), respectively, to prepare highly porous particles crosslinked using ethylene glycol dimethacrylate (EGDMA) in the presence of 1-octanol used as a porogen by means of suspension copolymerization in an aqueous phase initiated by 2,2-azobisisobutyronitrile (AIBN). Nano-pores were observed in the present studies. The pore size and the swelling properties of these particles can be successfully controlled by changing comonomers or adjusting the crosslinker and porogen concentration. The results indicate that lower crosslinker or porogen concentration favors generating smaller pores, whereas a higher concentration of a hydrophilic comonomer, higher crosslinker concentration and higher porogen volume ratio promote the generation of larger pores. In addition, the effects of the porous structures and the network properties on the swelling properties were explored. The swelling capacity of the porous particles is reduced with an increase in the EGDMA molar concentration. However, higher porosity in the particles and higher amount of hydrophilic comonomer result in a higher swelling capacity of the particles. The gel formation and the porous characteristics of HEMA/comonomer/EGDMA systems were simulated using the mathematical models combining the reaction kinetics and the thermodynamics. It was found that the model over-predicted the experimental results of the porosity because the pores and the networks are shrunk or collapsed during the porogen removal. Therefore, the model predicts the maximum porosity that the polymeric particles can reach. If the hydrophobic contents are higher, the model gives better prediction of the porosity. It is concluded that the microporous structures of HEMA related hydrogels could be controlled by a properly designed process based on the knowledge gained via this research. The output of this research helps with a better understanding for industrial production of micro-porous hydrogels and their applications.

This research addresses a number of fundamental issues concerning convective mass transfer across fluid-fluid interfaces in porous media. Mass transfer to/from distributed sinks/sources is considered for i) the slow dissolution of liquid filaments of a wetting non-aqueous phase liquid (NAPL) held in the corners of angular pores or throats and ii) the fate of gas bubbles generated during the flow of a supersaturated aqueous phase in porous media. 1. Effects of the stability of NAPL films on wetting NAPL dissolution Wettability profoundly affects the distribution of residual NAPL contaminants in natural soils. Under conditions of preferential NAPL wettability, NAPL is retained within small pores and in the form of thick films (liquid filaments) along the corners and crevices of the pore walls. NAPL films in pore corners provide capillary continuity between NAPL-filled pores, dramatically influencing the behaviour of NAPL dissolution to the flowing aqueous phase by convection and diffusion. A pore network model is developed to explore the dissolution behaviour of wetting NAPL in porous media. The effects of initial NAPL distribution and NAPL film stability on dissolution behaviour are studied using the simulator. NAPL phase loses continuity and splits into disconnected clusters of NAPL-filled pores due to rupture of NAPL films. Quasi-state drainage and fingering of the aqueous phase into NAPL-filled pores is treated as an invasion percolation process and a stepwise procedure is adopted for the solution of flow and solute concentration fields. NAPL film stability is shown to critically affect the rate of mass transfer as such that stable NAPL films provide for more rapid dissolution. The network simulator reproduces the essential physics of wetting NAPL dissolution in porous media and explains the concentration-tailing behaviour observed in experiments, suggesting also new possibilities for experimental investigation. 2. Convective Mass Transfer across Fluid Interfaces in Straight Angular Pores Steady convective mass transfer to or from fluid interfaces in pores of angular cross-section is theoretically investigated. The model incorporates the essential physics of capillarity and solute mass transfer by convection and diffusion in corner fluid filaments. The geometry of the corner filaments, characterized by the fluid-fluid contact angle, the corner half-angle and the interface meniscus curvature, is accounted for. Boundary conditions of zero surface shear (‘perfect-slip’) and infinite surface shear (‘no-slip’) at the fluid-fluid interface are considered. The governing equations for laminar flow within the corner filament and convective diffusion to or from the fluid-fluid interface are solved using finite-element methods. Flow computations are verified by comparing the dimensionless resistance factor and hydraulic conductance of corner filaments against recent numerical solutions by Patzek and Kristensen [2001]. Novel results are obtained for the average effluent concentration as a function of flow geometry and pore-scale Peclet number. These results are correlated to a characteristic corner length and local pore-scale Peclet number using empirical equations appropriate for implementation in pore network models. Finally, a previously published “2D-slit” approximation to the problem at hand is checked and found to be in considerable error. 3. Bubble evolution driven by solute diffusion during the process of supersaturated carbonated water flooding In situ bubble growth in porous media is simulated using a pore network model that idealizes the pore space as a lattice of cubic chambers connected by square tubes. Evolution of the gas phase from nucleation sites is driven by the solute mass transfer from the flowing supersaturated water solution to the bubble clusters. Effects of viscous aqueous phase flow and convective diffusion in pore corners are explicitly accounted for. Growth of bubble clusters is characterised by a pattern of quasi-static drainage and fingering in the gas phase, an invasion percolation process controlled by capillary and gravitational forces. A stepwise solution procedure is followed to determine the aqueous flow field and the solute concentration field in the model by solving the conservation equations. Mobilization of bubbles driven by buoyancy forces is also studied. Results of bubble growth pattern, relative permeability and macroscopic mass transfer coefficient are obtained under different gas saturations and aqueous flow conditions.

Hydrogels are polymeric materials that have three-dimensional polymeric networks, which are able to absorb and retain a large amount of water within their structures without being dissolved. Among the synthetic hydrogel, poly(2-hydroxylethyl methacrylate) (poly(HEMA)) has been of great interest because of its excellent biocompatibility with the three-dimensional networks. Therefore, poly(HEMA) hydrogels have been widely used in many areas, especially in biomedical and pharmaceutical areas, for such applications as packing materials in chromatography, sorbents in controlled release and drug delivery, implanting materials in tissue engineering. However, the applications of poly(HEMA) are still limited because of its weak mechanical strength and network properties. Therefore, in recent decades, the challenge of how to modify and control the polymer properties and how to build highly porous structures in it has received considerable attention because these modifications could significantly improve the performance of poly(HEMA) hydrogels for more favorable applications. Although HEMA and its polymers have been studied for more than 40 years, few reports about the preparation of micro-/nano-porous poly(HEMA) hydrogel particles and the requirements of their applications have risen. Furthermore, how to control the porous structures and the properties of HEMA copolymers have not been well understood. Accordingly, the objectives of this research were to investigate the synthesis of the porous copolymeric particles of HEMA with various comonomers (MMA, St and NVP), to characterize the porous structures and particle morphology, to simulate the synthesis process and porous characteristics, to explore the effects of the polymer compositions and the porous structures on the swelling properties, and to apply the resultant polymeric particles in the controlled release of the hydrophilic model drug. In the present studies, HEMA was copolymerized with three different comonomers, methyl methacrylate (MMA), styrene (St) and N-vinyl-2-pyrrolidone (NVP), respectively, to prepare highly porous particles crosslinked using ethylene glycol dimethacrylate (EGDMA) in the presence of 1-octanol used as a porogen by means of suspension copolymerization in an aqueous phase initiated by 2,2-azobisisobutyronitrile (AIBN). Nano-pores were observed in the present studies. The pore size and the swelling properties of these particles can be successfully controlled by changing comonomers or adjusting the crosslinker and porogen concentration. The results indicate that lower crosslinker or porogen concentration favors generating smaller pores, whereas a higher concentration of a hydrophilic comonomer, higher crosslinker concentration and higher porogen volume ratio promote the generation of larger pores. In addition, the effects of the porous structures and the network properties on the swelling properties were explored. The swelling capacity of the porous particles is reduced with an increase in the EGDMA molar concentration. However, higher porosity in the particles and higher amount of hydrophilic comonomer result in a higher swelling capacity of the particles. The gel formation and the porous characteristics of HEMA/comonomer/EGDMA systems were simulated using the mathematical models combining the reaction kinetics and the thermodynamics. It was found that the model over-predicted the experimental results of the porosity because the pores and the networks are shrunk or collapsed during the porogen removal. Therefore, the model predicts the maximum porosity that the polymeric particles can reach. If the hydrophobic contents are higher, the model gives better prediction of the porosity. It is concluded that the microporous structures of HEMA related hydrogels could be controlled by a properly designed process based on the knowledge gained via this research. The output of this research helps with a better understanding for industrial production of micro-porous hydrogels and their applications.

Geomembranes are one of the most widely used geosynthetics in various civil engineering applications. Their primary function is as a barrier to liquid or vapour flow. Smooth Geomembranes are frequently used in combination with different soils, and due to their low surface roughness, are challenging to design to ensure adequate shear strength along the smooth geomembrane-soil interface. It is important to use the appropriate values of interface shear strength parameters in the design of slopes incorporating one or more geomembranes in contact with soils. The parameters are determined by conducting direct shear test on the geomembrane-soil interface. Laboratory tests of interface shear strength for geomembranes and soil are typically carried out with no provision for measurement of pore pressures at the soil/geomembrane interface. <p>This thesis deals with study of smooth geomembrane-soil interfaces, particularly under unsaturated conditions. The various factors that affect the interface shear behaviour are also studied. The tests were conducted using a modified direct shear box with a miniature pore pressure transducer installed adjacent to the surface of the geomembrane. Geomembranesoil interface shear tests were carried out with continuous measurement of suction in close proximity to the interface during the shearing process thus making it possible to analyze test results in terms of effective stresses. The method was found to be suitable for unsaturated soils at low values of matric suction. <p>Results of interface shear tests conducted using this method show that it is quite effective in evaluating interface shear behaviour between a geomembrane and an unsaturated soil. The results suggest that soil suction contributes to shearing resistance at low normal stress values. At lower normal stress values, the interface shear behaviour appears to be governed only by the magnitude of total normal stress. <p> At high normal stresses, the failure mechanism changed from soil particles sliding at the surface of geomembrane to soil particles getting embedded into the geomembrane and plowing trenches along the direction of shear. A plowing failure mechanism resulted in the mobilization of significantly higher shear strength at the geomembrane soil interface. It was found that placement water contents near saturated conditions results in lower effective stresses, a shallower plowing mechanism and lower values of mobilized interface shear strength.

The pore diameter of a catalyst support controls the diffusion of reactant molecules to the catalytic active sites; thus, affecting the rates and conversions of the hydrotreating reactions. Desirable textural properties of SBA-15 makes it a potential alternative to the conventionally used γ-Al2O3 support due to the fact that its pore size can be manipulated via controlling the synthesis parameters, while maintaining relatively high surface area. Larger pore diameter SBA-15 supports may facilitate the diffusion of bulky molecules as that of the asphaltenes present in the heavy petroleum fractions, making it a potential catalyst support for hydrotreating operations. Considering the very sour nature of Canadas bitumen with high sulfur contents in the range of 2-6 wt %, the appreciably high sulfur contents particularly present in Athabasca derived heavy gas oils (about 4 wt % sulfur), the rising demand for cleaner fuels, and also the increasing stringency on environmental standards, the need for novel and improved hydrotreating catalysts cannot be overemphasized. By varying the molar ratio of hexane to ammonium fluoride, the pore channels of SBA-15 could be varied. Controlling the pore diameter of these supports via micelle swelling facilitated the production of larger pore diameter SBA-15-supported catalysts. In this project, four mesoporous silica SBA-15 catalyst supports with pore diameters in the range of 5-20 nm were synthesized in the preliminary phase using hexane as the micelle swelling agent and subsequently utilized for the loading of 2 wt.% Fe and 15 wt.% W catalyst metals, respectively. The hexagonal mesoscopic structure of these materials were characterized using powder small-angle X-ray scattering (SAXS), N2 adsorption-desorption isotherms, TEM and SEM images. Powder XRD analysis evidenced inhomogeneous metal dispersion on the largest pore diameter catalyst. An optimum pore diameter of 10 nm was found for Cat-B and subsequently used to obtain the optimum Fe and W loadings required to achieve the best hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) activities. The optimum catalyst was found to be Cat-H with metal loadings of 3 wt.% Fe and 30 wt.% W. At these loadings and temperatures of 375°C, 388°C, and 400°C, HDS activities of 53.4%, 64.1%, and 73.3% with corresponding HDN activities of 21.9%, 26.2%, and 38.3%, respectively, were recorded. Catalytic performance evaluations conducted on equal mass loading using a reference commercial γ-Al2O3-supported FeW catalyst offered HDS activities of 69.3%, 80.4%, and 89.1%, with corresponding HDN activities of 16.4%, 32.4%, and 49.3% at the same temperatures studied. However, no significant changes in HDS and HDN activities were observed for similar evaluations on volume percent metals loading basis. Kinetic studies performed with the optimum FeW/SBA-15 catalyst suggested activation energies of 147.2 and 150.6 kJ/mol for HDS and HDN, respectively, by the Langmuir-Hinshelwoods model. Similar results were predicted by the Power Law and Multi-parameter models for HDS (129.6 and 126.7 kJ/mol, respectively), which does not conclusively make the latter model clearly stand out as the best. Data fitting by the Power Law suggested reaction orders of 2 and 1.5 for HDS and HDN, which seem to be consistent for the hydrotreatment of heavy gas oil. Finally, a long-term deactivation study spanning a period of 60 days time-on-stream showed the optimum catalyst to be stable under hydrotreating experiments conducted in a downward flow micro-trickle bed reactor at temperature, pressure, liquid hourly space velocity (LHSV), and gas/oil ratio of 375400˚C, 8.8 MPa, 1h-1, and 600 mL/mL (at STP), respectively.

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