ABSTRACT COMPARISON OF SORPTION CAPACITIES OF HYDROCARBONS ON DIFFERENT SAMPLES OF MCM-41 AYDOGDU, Birsu M. Sc., Department of Chemical Engineering Supervisor: Prof. Dr. Hayrettin Y&Uuml / CEL Co-Supervisor: Prof. Dr. G&uuml / rkan KARAKAS January 2013, 69 pages MCM-41(Mobil Composition Matter-41) is one of the three members of M41S family and has a highly ordered hexagonal honeycomb like structure with a narrow pore size distribution in mesopore range, high surface area, high pore volume and high thermal stability. These features make MCM-41 proper to use for adsorption, catalysis, ion exchange and separation processes. . In this study sorption capacities of C8 aromatics (o-, m-, p-xylene and ethylbenzene at 30 &deg / C, 50 &deg / C and 65 &deg / C) on a MCM-41 sample synthesized in our laboratory were determined gravimetrically by using a commercial automated electro balance system and compared with results obtained in a previous and similar MSc thesis study with a sample of different origin and characteristics / specifically low BET surface area (492 m2/g). MCM-41 sample was synthesized by hydrothermal synthesis method with cetyltrimethylammoniumbromide (CTAMBr as surfactant) and tetraethyl ortosilicate (TEOS as silica source) in basic conditions. This MCM-41 sample was calcined at 540 oC for 8 h and characterized by XRD, nitrogen adsorption at 77 K, TGA, TEM, SEM and SEM-EDX. According to XRD data, main characteristic peak for synthesized MCM-41 was obtained at 2&theta / =2.28&deg / . Three small reflection peaks can be seen at 2&theta / values of 2.59, 4.27&deg / and 4.5&deg / . XRD pattern of the MCM-41, indicated that the desired structure of MCM-41 was successfully synthesized. Surface area, pore volume and average pore diameter were obtained from the nitrogen adsorption data at 77 K as 1154 m2/g, 1.306 cm3/g and 2.75 nm respectively. TGA analysis showed that the 540 oC is proper for the calcination. SEM -EDX analysis gave an oxygen atomic concentration 66.40% and silicon atomic concentration 33.60%. These results showed that the chemical composition of the synthesize material was in almost pure SiO2 form. The adsorbed amount for all isomers at the same pressure decreased as the temperature of the adsorption isotherms increases as expected for physical adsorption. Nitrogen adsorption of MCM-41 in this study showed type IV isotherm with H2 type hysteresis loop according the IUPAC classification. However, for o-,m-, and p-xylene an approximately linear increase in the adsorbed amount as a function of relative pressure was observed from the adsorption isotherms. Except for adsorption isotherms of m-xylene and p-xylene at 65 oC all isotherms of xylenes showed hysteresis loops. Hysteresis loops narrowed down with increasing temperature. p-xylene and m-xylene adsorption isotherms at 65 oC were reversible and did not show any hysteresis loop. Ethylbenzene adsorption isotherms at 30 oC, 50 &deg / C and 65 oC also showed a linear increase in the adsorption amount as a function of relative pressure like xylenes. At 50 &deg / C and 65 oC adsorption isotherms of ethylbenzene were reversible without a hysteresis loop. For all adsorbates volume of adsorbed amounts were calculated on the assumption that they exist as saturated liquids at the isotherm temperature and found to be significantly lower than pore volume obtained from nitrogen adsorption isotherm at 77K. Sorption capacities of these hydrocarbons on MCM-41 were also very low when compared to values found in a previous study which involved a MCM-41 sample of significantly lower surface area ( 492 m2/g ). This may be attributed to structure degradation which requires further investigation.

The nonlinear electrodynamic characteristics and presence of vortex dynamics in pseudo 2-dimensional microbridges make them attractive to design novel passive and active microwave circuits. Before such applications could be feasibly accomplished, a greater understanding of the the these devices are necessary, by a complete DC, microwave and optoelectronic characterization. A cryostat design and construction is discussed including the creation of test beds for DC characterization. Coplanar waveguide (CPW) design methodology is presented and used for the creation of CPWs for microwave characterization. Microbridges and meander lines are also embedded into the CPWs for determining the microwave performance of said devices and for optoelectronic characterizations. Results are compared against accepted results from theory and simulations, introducing vortices as explanations for device behaviour. Feasibility of these devices as single photon detectors is discussed.

A concentric pneumatic nebulizer (CPN) and a custom designed flow focusing nebulizer (FFN) are characterized. As will be shown, the classical Nukiyama-Tanasawa and Rizk-Lefebvre models lead to erroneous size prediction for the concentric nebulizer under typical operating conditions due to its specific design, geometry, dimension and different flow regimes. The models are then modified to improve the agreement with the experimental results. The size prediction of the modified models together with the spray velocity characterization are used to determine the overall nebulizer efficiency and also employed as input to a new Maximum Entropy Principle (MEP) based model to predict joint size-velocity distribution analytically. The new MEP model is exploited to study the local variation of size-velocity distribution in contrast to the classical models where MEP is applied globally to the entire spray cross section. As will be demonstrated, the velocity distribution of the classical MEP models shows poor agreement with experiments for the cases under study. Modifications to the original MEP modeling are proposed to overcome this deficiency. In addition, the new joint size-velocity distribution agrees better with our general understanding of the drag law and yields realistic results.

The Lithium-ion (Li-ion) battery is one of the major topics currently studied as a potential way to help in reducing greenhouse gas emissions. Major car manufacturers are interested in adapting the Li-ion battery in the power trains of Plug-in Hybrid Electric Vehicles (PHEV) to improve fuel efficiency. Materials currently used for Li-ion batteries are LiCoO2 (LCO) and graphite—the first materials successfully integrated by Sony into Li-ion batteries. However, due to the high cost and polluting effect of cobalt (Co), and the low volumetric capacity of graphite, new materials are being sought out. LiFePO4 (LFP) and SnO2 are both good alternatives for the cathode and anode materials in Li-ion batteries. But, to create high-performance batteries, nano-sized carbon-coated particles of LFP and SnO2 are required. The present work attempts to develop a new synthesis method for these materials: organic template-assisted synthesis for three-dimensionally ordered macroporous (3DOM) LFP and porous SnO2. With the newly developed synthesis, highly pure materials were successfully synthesized and tested in Li-ion batteries. The obtained capacity for LFP was 158m Ah/g, which is equivalent to 93% of the theoretical capacity. The obtained capacity for SnO2 was 700 mAh/g, which is equivalent to 90% of the theoretical capacity. Moreover, Hybrid Pulse Power Characterization (HPPC) was used to test LFP and LCO for comparison and feasibility in PHEVs. HPPC is generally used to test the feasibility and capacity fade for PHEVs. It simulates battery use in various driving conditions of PHEVs to study pulse energy consumption and regeneration. In this case, HPPC was conducted on a half-cell battery for the first time to study the phenomena on a single active material, LFP or LCO. Based on the HPPC results, LFP proved to be more practical for use in PHEVs.

Femtosecond time-resolved photoelectron spectroscopy (fsTRPES) experiments have been used to study the photoelectron energy spectra of simple molecules since the 1980’s. Analysis of these spectra provides information about the ultrafast internal conversion dynamics of the parent ions. However, ultraviolet pulses must be used for these pump-probe experiments in order to ionize the molecules. Since current solid state lasers, such as the Ti:sapphire laser, typically produce pulses centered at 800nm, it is necessary to generate UV pulses with nonlinear frequency mixing techniques. I therefore constructed an optical setup to generate the 3rd and 4th harmonics, at 266.7nm and 200nm, respectively, of a Ti:sapphire (Ti:sa) chirped-pulse amplified (CPA) laser system that produces 35fs pulses centered at 800nm. Thin Beta-Barium Borate (β-BaB2O4 or BBO) crystals were chosen to achieve a compromise between short pulse durations and reasonable conversion efficiencies, since ultrashort pulses are quite susceptible to broadening from group velocity dispersion (GVD). Output energies of around 11μJ and 230nJ were measured for the 266.7nm and 200nm pulses, respectively. The transform limits of the 3rd and 4th harmonic pulse lengths were calculated from their measured spectral widths. We found that the 266.7nm bandwidth was large enough to support sub-30fs pulses, and due to cutting at the lower-wavelength end of the 200nm spectrum, we calculated an upper limit of 38fs. The pulses were compressed with pairs of CaF2 prisms to compensate for dispersion introduced by transmissive optics. Two-photon absorption (TPA) intensity autocorrelations revealed fully compressed pulse lengths of 36 ± 2 fs and 42 ± 4 fs for the 3rd and 4th harmonics, respectively.

Electrical conductive adhesives (ECAs) containing silver filler and polyaniline co-filler were characterized for their electro-mechanical properties. Polyaniline is a conductive polymer and has a moderate conductivity in between those of the silver and epoxy. Incorporation of polyaniline (μm sized) in silver-epoxy facilitated the electrical conduction in ECAs and reduced the percolation threshold- a minimum volume of filler necessary to initiate the conduction. It also prevented the localization of charge carriers due to aggregation of silver filler particles. ‘Bridging effect’ was observed due to addition polyaniline in which the polyaniline enhanced the tunneling of electrons over the silver filler particles. We have investigated the polyaniline co-fillers as a promising alternative way to tune the mechanical and electrical properties of the ECAs and have provided a detailed analysis of the electro-mechanical properties of silver-epoxy (Ag-epoxy) and silver-polyaniline-epoxy (Ag-PANI-epoxy) system in both partially-cured/ viscoelastic and fully-cured states. Analysis of electro-mechanical properties of silver-epoxy and silver-polyaniline-epoxy also provided the insights into electrical contact resistance of ECAs under compressive force. Electro-mechanical properties of ECAs were measured ‘in-situ’ using micro-indentation technique. We also synthesized the electrically conductive and highly crystalline nanotubes of polyaniline by mini-emulsion polymerization of aniline. The motivation behind the synthesis of polyaniline was to propose a potential filler/co-filler for replacement of metallic filler in ECAs. Electrical conductivity of polyaniline nanotubes was tuned by in-situ doping using hydrochloric acid as a dopant. Increase in dopant caused the polyaniline crystallite to grow along (400) plane. Optical, structural, electrical and thermal properties of polyaniline nanotubes are reported with varying amount of dopant. We fabricated the flexible electrically conductive coating of polyaniline tubes with uniform dispersion of polyaniline. Electrical performance of as-synthesized flexible coating is also revealed.

The effects of Ca and Ce on the precipitation behaviour and microstructural characteristics of Mg-Zn based alloys are investigated by comprehensive multi-scale characterization and analysis. The elements Ca and Ce are chosen for their potential to enhance (a) precipitation hardening and (b) alloy texture and ductility, and are examined at both alloying and microalloying (< 0.5 wt%) levels. When added individually to Mg-Zn, Ca is found to enhance precipitation, but Ce produces a generally adverse effect on the hardening response. A pre-ageing strategy is proposed to alleviate this negative effect of Ce. The highlight of this work is the double microalloying addition of Ce-Ca to Mg-Zn, as this combination and quantity proves to be the most effective at increasing the age-hardening response, and enhancing microstructural characteristics for improved ductility. Transmission electron microscopy analysis reveals the hardening increase to originate from a refined precipitate microstructure, and the formation of fine-scale basal plate precipitates. These fine precipitates form during early ageing as monolayer GP zones consisting of Ca and Zn. The formation of these GP zones is facilitated by the atomic size difference between those two solutes, and their observed tendency to co-cluster. The monolayer GP zones evolve to multi-layered forms in the peak-aged condition. These precipitates are observed to be uniformly distributed, even where apparent precipitate-free zones are observed for the Mg-Zn type phases in the grain boundary regions. Notably, the size of these precipitate-free zones for the Mg-Zn phases is also reduced in the Ce-Ca microalloyed samples, compared to the binary alloy. The Ce-Ca microalloying additions also promote grain refinement and a weakening of the basal textures, typical of conventional Mg-based alloys, compared to both Mg-Zn and Mg-Zn-Ce. As a result, the tensile behaviour of the alloys with Ce-Ca is similarly enhanced. Considering both the precipitation hardening capability and microstructural characteristics, it is concluded that the double microalloying additions of Ce-Ca can be considered as a new alloy design strategy to successfully achieve improvement in both the strength and ductility of Mg-Zn alloys.

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.

Routing messages between pairs of nodes is one of the most fundamental tasks in any distributed computing system. An Interval Routing Scheme (IRS) is a well-known, space-efficient routing strategy for routing messages in a network. In this scheme, each node of the network is assigned an integer label and each link at each node is labeled with an interval. The interval assigned to a link l at a node v indicates the set of destination addresses of the messages which should be forwarded through l at v. When studying interval routing schemes, there are two main problems to be considered: a) Which classes of networks do support a specific routing scheme? b) Assuming that a given network supports IRS, how good are the paths traversed by messages? The first problem is known as the characterization problem and has been studied for several types of IRS. In this thesis, we study the characterization problem for various schemes in which the labels assigned to the vertices are d-ary integer tuples (d-dimensional IRS) and the label assigned to each link of the network is a list of d 1-dimensional intervals. This is known as Multi-dimensional IRS (MIRS) and is an extension of the the original IRS. We completely characterize the class of network which support MIRS for linear (which has no cyclic intervals) and strict (which has no intervals assigned to a link at a node v containing the label of v) MIRS. In real networks usually the costs of links may vary over time (dynamic cost links). We also give a complete characterization for the class of networks which support a certain type of MIRS which routes all messages on shortest paths in a network with dynamic cost links. The main criterion used to measure the quality of routing (the second problem) is the length of routing paths. In this thesis we also investigate this problem for MIRS and prove two lower bounds on the length of the longest routing path. These are the only known general results for MIRS. Finally, we study the relationship between various types of MIRS and the problem of drawing a hypergraph. Using some of our results we prove a tight bound on the number of dimensions of the space needed to draw a hypergraph.

Quantum information processing has been the subject of countless discoveries since the early 1990's. It is believed to be the way of the future for computation: using quantum systems permits one to perform computation exponentially faster than on a regular classical computer. Unfortunately, quantum systems that not isolated do not behave well. They tend to lose their quantum nature due to the presence of the environment. If key information is known about the noise present in the system, methods such as quantum error correction have been developed in order to reduce the errors introduced by the environment during a given quantum computation. In order to harness the quantum world and implement the theoretical ideas of quantum information processing and quantum error correction, it is imperative to understand and quantify the noise present in the quantum processor and benchmark the quality of the control over the qubits. Usual techniques to estimate the noise or the control are based on quantum process tomography (QPT), which, unfortunately, demands an exponential amount of resources. This thesis presents work towards the characterization of noisy processes in an efficient manner. The protocols are developed from a purely abstract setting with no system-dependent variables. To circumvent the exponential nature of quantum process tomography, three different efficient protocols are proposed and experimentally verified. The first protocol uses the idea of quantum error correction to extract relevant parameters about a given noise model, namely the correlation between the dephasing of two qubits. Following that is a protocol using randomization and symmetrization to extract the probability that a given number of qubits are simultaneously corrupted in a quantum memory, regardless of the specifics of the error and which qubits are affected. Finally, a last protocol, still using randomization ideas, is developed to estimate the average fidelity per computational gates for single and multi qubit systems. Even though liquid state NMR is argued to be unsuitable for scalable quantum information processing, it remains the best test-bed system to experimentally implement, verify and develop protocols aimed at increasing the control over general quantum information processors. For this reason, all the protocols described in this thesis have been implemented in liquid state NMR, which then led to further development of control and analysis techniques.