In recent years, metal-organic frameworks (MOFs) have been identified as promising adsorbents in a number of industrially relevant, yet challenging, separations, including the removal of propane from propane/propylene mixtures and the separation of mixtures of xylene isomers. The highly tuneable nature of MOFs - wherein structures may be constructed from a variety of diverse building blocks – has resulted in the publication of a staggering number of frameworks incorporating a wide range of network topologies, pore shapes and pore diameters. As a result, there are a huge number of candidate adsorbents to consider for a given separation. Molecular simulation techniques allow the identification of those structural features and characteristics of a MOF which exert the greatest influence on the adsorption and separation of the compounds of interest, providing insights which can both guide the selection and accelerate the development of adsorbents for a specific application. The separation of propane/propylene mixtures via adsorption has typically focused on selective adsorption of the olefin, propylene, via specific olefin-adsorbent interactions. These propylene-selective MOFs result in processes which selectively remove the most abundant species in the process stream and are typically characterised by high heats of adsorption, resulting in large adsorption units and adsorbents which are difficult to regenerate. In this work, the capability of MOFs to selectively adsorb propane over propylene is explored, potentially allowing for the design of smaller and more energy-efficient adsorption units. By studying a range of different MOFs as well as carbon-based model pores, it was found that the low-pressure selectivity of the structure is determined by the strength of the electrostatic interaction between propylene and the framework, while the adsorptive preference at industrially-relevant pressures is dominated by the enhanced packing efficiency of propylene over propane. The confinement of C3 molecules, however, may be employed to negate this entropic advantage and guide the development of materials which selectively adsorb propane over propylene. It has recently been reported that the adsorptive preference of a MOF for one xylene isomer over another may be predicted based solely on the pore size distribution of the structure. In this work, the impact of pore size on selectivity was studied systematically in both one-dimensional model pore systems of varying geometries and analogous published MOF structures. The ability of the framework to discriminate between xylene molecules in these systems was found to be determined primarily by the different packing arrangements available to the different isomers – while small pores were found to favour the slimmest of the isomers, larger pores were found to favour the more compact ortho- isomer. Finally, the adsorption and diffusion of xylene isomers in a more complex MOF, UiO-66(Zr), was studied in depth. Simulations were able to correctly predict the previously-reported preference of the MOF for ortho-xylene (oX). The smaller volume of the oX molecule compared to the other isomers was found to be responsible both for an enhanced entropic contribution and higher guest-host interaction energies. The importance of framework flexibility in the diffusion of xylene isomers in UiO-66(Zr) was also explored, with distortion of the structure in response to interaction with adsorbed molecules found to be essential in allowing xylenes to diffuse through the pore space.

The purpose of the work is to employ molecular simulation to further extend the understanding of Self-Assembled Monolayers (SAMs), especially as it relates to three particular applications: organic-inorganic composite membranes, surface treatments in Micro-Electro-Mechanical Systems (MEMS) and organic-surface-modified Ordered Mesoporous Materials (OMMs). The first focus area for the work is the use of SAMS in organic-inorganic composite membranes for gas separations. These composite membranes, recently proposed in the literature, are based on the chemical derivatization of porous inorganic surfaces with organic oligomers. Our simulations achieve good qualitative agreement with experiment in several respects, including the improvement in the overall selectivity of the membrane and decrease in the permeance when increasing the chain length. The best improvement in the overall solubility selectivity is reached when the chains span throughout the pore. The second application focus is on the use of SAMs as coatings in MEMS devices. The work focuses on the modeling of adhesion issues for SAM coatings at the molecular level. It is shown that as the chain length is increased from 4 to 18 carbon atoms, the adhesion forces between two monolayers at the same separations decreases. The third application focus is on the use of SAMs for tailoring surface and structural properties of OMMs, in particular, porous silicas. A molecular study of structural and surface properties of a silica material with a 5 nm pore size, modified via chemical bonding of organosilanes with a range of sizes (C4, C8 and C18) is presented. Grand canonical MC simulations are employed to obtain nitrogen adsorption isotherms for unmodified and modified MCM-41 material models. Furthermore, the density profiles of alkyl chains and nitrogen molecules are analyzed to clarify the differences in the adsorption mechanisms in unmodified and modified materials. The position of the capillary condensation steps gradually shifted to lower pressure values with the increase in size of the bonded ligands, and this shift was accompanied by a gradual disappearance of the hysteresis loop. As the length of the bonded ligands is increased, a systematic decrease in the pore diameter is observed and the multi-layer adsorption mechanism in modified model materials diminishes.

Metal--organic frameworks (MOFs) are porous crystalline materials that are synthesized from rigid organic ligands and metal-containing clusters. They are highly tunable as a number of different structures can be made by simply changing the organic ligand and/or metal ion. MOFs are a promising class of materials for many energy-related applications, including H2 storage and CO2 capture and sequestration. Computational studies can provide insights into MOFs and the mechanism of gas sorption and separation. Theoretical studies on existing MOFs are performed to determine what structural characteristics leads to favorable gas sorption mechanisms. The results from these studies can provide insights into designing new MOFs that are tailored for specific applications. In this work, grand canonical Monte Carlo (GCMC) simulations were performed in various MOFs to understand the gas sorption mechanisms and identify the favorable sorption sites in the respective materials. Experimental observables such as sorption isotherms and associated isosteric heat of adsorption, Qst, values can be generated using this method. Outstanding agreement with experimental measurements engenders confidence in a variety of molecular level predictions. Explicit many-body polarization effects were shown to be important for the modeling of gas sorption in highly charged/polar MOFs that contain open-metal sites. Indeed, this was demonstrated through a series of simulation studies in various MOFs with rht topology that contain such sites. Specifically, the inclusion of many-body polarization interactions was essential to reproduce the experimentally observed sorption isotherms and Qst values and capture the binding of sorbate molecules onto the open-metal sites in these MOFs. This work also presents computational studies on a family of pillared square grid that are water-stable and display high CO2 sorption and selectivity. These MOFs are deemed promising for industrial applications and CO2 separations. Simulations in these materials revealed favorable interactions between the CO2 molecules and the SiF62- pillars. Further, the compound with the smallest pore size exhibits the highest selectivity for CO2 as demonstrated through both experimental and theoretical studies. Many other MOFs with intriguing sorption properties are investigated in this work and their sorption mechanisms have been discerned through molecular simulation.

Carbonaceous engine deposits tend to accumulate on most of the inner surfaces of the car engine. The presence of these deposits leads to a deteriorated efficiency of the engine and a number of adverse effects, such as higher propensity of the engine to knock. It has been proposed that selective adsorption of some of the fuel components in the porous deposits (and changing composition of the pre-combustion fuel) could be a contributing mechanism of the diminished efficiency of the engine. This, as well as other mechanisms of the deposits action, crucially depend on the porous structure of the material. Therefore, the aim of this investigation is to develop a method, which is able to accurately characterize the internal porous structure of the engine deposits and predict their adsorption properties at different conditions. This should allow us to assess whether the selective adsorption of fuel components is indeed a plausible contributing mechanism to the diminished performance of the engine. Accurate characterization of the engine deposits faces several difficulties due to their complex porous structure and chemical composition. A widely adopted approach in the characterization of activated carbons, which combines molecular simulation, specifically grand canonical Monte Carlo (GCMC) in slit pores, and experimental adsorption isotherms, is the starting point for the method suggested in this work. In this thesis, we will demonstrate that, by systematic modification of the solid-fluid interaction in the molecular simulation, we are able to correctly account for the chemical structural heterogeneity of the samples used. The new parameters of solid-fluid interaction allow us to extract representative pore size distributions and investigate the adsorption properties under different conditions of temperature and pressure, based on the obtained pore size distribution. Specifically, using the experimental data from a single ethane isotherm at 278K we accurately predict ethane adsorption at other temperatures and in different samples. Additionally, the proposed method is able to predict the adsorption of more complex hydrocarbons, i.e. n-butane and isobutane. The performance of the method is assessed by comparing the simulations results with the experimental adsorption measurements data on the engine deposits samples. Another important capability of the method is that it enables us to generate adsorption predictions of two key components commonly used to represent the combustion properties of the fuel, n-heptane and isooctane. We explore the equilibrium adsorption properties of these components based on the determined pore size distributions of the deposit samples. The results presented in the thesis highlight the importance of the adsorption in the internal porous structure of the engine deposits. The present study reinforces the value of molecular simulation combined with a limited number of experimental measurements, to accurately characterize heterogeneous carbonaceous materials and to make predictions at different conditions with sufficient precision.

Molecular dynamics (MD) simulations find their applications in fundamental understanding of molecular level mechanisms of physical processes. This assists in tuning the key features affecting the development of the novel hybrid materials. A certain application demanding the need for a desired function can be cherished through the hybrids with a blend of new properties by a combination of pure materials. However, to run MD simulations, an accurate representation of the interatomic potentials i.e. force-fields (FF) models remain a crucial aspect. This thesis intricately explores the fusion of MD simulations, uncertainty quantification, and data-driven methodologies to accelerate the computational design of innovative materials and models across the following interconnected chapters. Beginning with the development of force fields for atomic-level systems and coarse-grained models for FCC metals, the study progresses into exploring the intricate interfacial interactions between 2D materials like graphene, MoS2, and water. Current state-of-the-art model development faces the challenge of high dimensional input parameters' model and unknown robustness of developed model. The utilization of advanced optimization techniques such as particle swarm optimization (PSO) integrated with MD enhances the accuracy and precision of FF models. Moreover, the bayesian uncertainty quantification (BUQ) assists FF model development researchers in estimating the robustness of the model. Furthermore, the complex structure and dynamics of water confined between and around sheets was unraveled using 3D Convolutional Neural Networks (3D-CNN). Specifically, through classification and regression models, water molecule ordering/disordering and atomic density profiles were accurately predicted, thereby elucidating nuanced interplays between sheet compositions and confined water molecules. To further the computational design of hybrid materials, this thesis delves into designing and investigating polymer composites with functionalized MOFs shedding light on crucial factors governing their compatibility and performance. Therefore, this report includes the study of structure and dynamics of functionalized MOF in the polymer matrix. Additionally, it investigates the biomedical potential of porous MOFs as drug delivery vehicles (DDVs). Often overlooked is the pivotal role of solvents (used in MOF synthesis or found in relevant body fluids) in the drug adsorption and release process. This report underscores the solvent's impact on drug adsorption within MOFs by comparing results in its presence and absence. Building on these findings, the study delves into the effects of MOF functionalization on tuning the drug adsorption and release process. It further explores how different physical and chemical properties influence drug adsorption within MOFs. Furthermore, the research explores the potential of functionalized MOFs for improved carbon capture, considering their application in energy-related contexts. By harnessing machine learning and deep learning, the thesis introduces innovative pathways for material property prediction and design, emphasizing the pivotal fusion of computational methodologies with data-driven approaches to advance molecular-level understanding and propel future material design endeavors. / Doctor of Philosophy / Envision a world where scientific exploration reaches the microscopic scale, powered by advanced computational tools. In this frontier of materials science, researchers employ sophisticated computer simulations to delve into the intricate properties of materials, particularly focusing on Metal-Organic Frameworks (MOFs). These MOFs, equivalent to microscopic molecular sponges, exhibit remarkable abilities to capture gases or hold medicinal drug compounds. This thesis meticulously studies MOFs alongside materials like graphene, Boron Nitride and Molybdenum disulfide, investigating their interactions with water with unprecedented precision. Through these detailed explorations and the fusion of cutting-edge technologies, we aim to unlock a future featuring enhanced drug delivery systems, improved energy storage solutions, and innovative energy applications.

No description available.

<p>Premelting is the formation of a thin, thermodynamically stable, liquid-like film at an interface for temperatures below the equilibrium melting temperature. Using a Monte Carlo technique, the underlying short range structural forces for premelting at the grain boundary can be directly calculated. This technique is applied to a (i) Σ9 ⟨115⟩ 120^o twist boundary and a (ii) Σ9 ⟨011⟩ {411} symmetric tilt boundary in an embedded atom model of Aluminum-Magnesium alloy. Both grain boundaries exhibit disordered structures near the melting point that depend on the concentration of Magnesium. The behavior is described quantitatively with sharp interface thermodynamics, involving an interfacial free energy that depends on width of the grain boundary, referred to as the disjoining potential. The disjoining potential calculated for boundary (i) displays a decreasing exponential dependence on width of the grain boundary, while the disjoining potential of (ii) features a weak attractive minimum. This work is discussed in relation to a previous study using pure Nickel, results of which can be useful to the theoretical study of thermodynamic forces underlying grain boundary premelting in an alloy.</p> / Master of Science (MSc)

Orientadores: Munir Salomão Skaf, Vitor Rafael Coluci / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-26T20:42:42Z (GMT). No. of bitstreams: 1 Faro_TatianaMellodaCosta_D.pdf: 8054394 bytes, checksum: ce0d79df42ce453ffc39b51bf0ad1094 (MD5) Previous issue date: 2015 / Resumo: Atualmente, a economia mundial depende do uso de combustíveis fósseis para a geração de energia. Esse modelo apresenta problemas ambientais graves, uma vez que o petróleo é um material não-renovável e muito poluente. O gás hidrogênio apresenta-se como uma alternativa promissora para substituir os combustíveis utilizados atualmente devido a um conjunto de características positivas: ele é atóxico, tem uma alta densidade energética gravimétrica e gera apenas água como produto de sua combustão. Apesar de tais vantagens, ele ainda não é utilizado comercialmente em larga escala. O maior empecilho tecnológico para que o hidrogênio possa substituir os combustíveis fósseis está no seu armazenamento. Existem diversas propostas para armazenar o hidrogênio, como tanques contendo o hidrogênio nas formas de gás pressurizado ou de líquido, além de sistemas sólidos que permitam a sua adsorção. Todavia, nenhum sistema construído até então foi capaz de armazenar o hidrogênio de forma tão barata, segura e eficaz quanto seria necessário. Nanoestruturas de carbono são vistas como uma boa alternativa para construir dispositivos de armazenamento de hidrogênio baseados na fisissorção. Os nanopapiros de carbono, formados por folhas de grafeno enroladas no formato de um papiro, são considerados particularmente promissores para armazenar o hidrogênio, uma vez que possuem uma alta área superficial, extremidades abertas e distâncias intercamadas facilmente controláveis. Na primeira etapa deste trabalho, realizamos simulações de Dinâmica Molecular (MD) para estudar a dinâmica e a estabilidade de diversos nanopapiros em função de alguns dos seus parâmetros estruturais. Posteriormente, aplicamos o método de Monte Carlo Grand-Canônico (GCMC) para estudar o processo de adsorção de hidrogênio em nanopapiros selecionados, de forma a caracterizar quantitativamente e qualitativamente as fases adsorvidas / Abstract: Presently, the world economy depends on the use of fossil fuels to generate energy. This model presents serious environmental problems, since petroleum is a non-renewable and very pollutant material. Hydrogen gas presents itself as a promising alternative to substitute the fuels currently used due to a few positive characteristics: it is non-toxic, possesses a high gravimetric energetic density and only generates water as a combustion byproduct. In spite of all these advantages, hydrogen still isn't used commercially in a large scale. The biggest technological drawback for hydrogen to substitute fossil fuels is in its storage. There are many proposed ways to store hydrogen, such as tanks containing highly pressurized or liquid hydrogen, or solid systems that allow its adsorption. However, no system built up to the date had been able to store hydrogen as cheap, safe and efficiently as necessary. Carbon nanostructures are seen as a good alternative to build hydrogen storage devices based on physisorption. Carbon nanoscrolls, formed by graphene sheets scrolled in a papirus-like shape, are considered as particularly promising adsorption materials, since they possess a high surface area, open edges and easily controllable interlayer distances. In the first step of this work, we made Molecular Dynamics (MD) simulations to study the dynamics and the stability of several nanoscrolls as a function of their structural parameters. Subsequently, we used the Grand-Canonical Monte Carlo (GCMC) method to study the hydrogen adsorption process in selected nanoscrolls, as to characterize the adsorbed phases quantitatively and qualitatively / Doutorado / Físico-Química / Doutora em Ciências

L'adsorption de CO dans la faujasite échangée au CuI et au Na+ a été modélisée à l'aide des approches quantiques (DFT) et classiques (Monte Carlo). Grâce à l'approche DFT, la surface d'énergie potentielle de la faujasite a été explorée. Différents types d'interactions de CO avec les cations ont été identifiés, pour chacune les effets induits par l'adsorption de CO aux niveaux structural et énergétique ont été analysés, et le calcul de la fréquence de vibration de CO a été réalisé. Grâce aux valeurs obtenues, une nouvelle attribution des spectres d'adsorption de CO dans CuY et NaY a été établie. D'un autre côté, grâce aux simulations Monte Carlo dans l'ensemble Grand Canonique, les propriétés d'adsorption (isothermes et enthalpies) de la faujasite vis-à-vis de CO ont été modélisées, et le mécanisme microscopique d'adsorption de CO a été établi. La mise en œuvre de ces simulations a nécessité de paramétrer un nouveau champ de force destiné à décrire les interactions CO/faujasite et CO/CO. / CO adsorption in CuI and Na+ exchanged faujasite has been modeled by mean of quantum (DFT) and classical (Monte Carlo) approaches. By mean of the DFT calculations, faujasite potential energy surface has been explored. Different types of CO interactions with the cations have been highlighted, for each one of them CO adsorption effects on the structural and energetic parameters have been analyzed, and calculations of the CO stretching frequency have been performed. Thanks to our calculated values, a new attribution of CO adsorption spectra in CuY and NaY has been established. On another side, by mean of Monte Carlo simulations in the Grand Canonical ensemble, faujasite adsorption properties regarding CO (isotherms and enthalpies) have been modeled, and the CO adsorption mechanism has been established at the microscopic level. The implementation of these simulations has required the derivation of a new force field describing the CO/faujasite and CO/CO interactions.

La simulación molecular presenta la ventaja de ofrecer un marco teórico importante para predecir propiedades termodinámicas y de transporte de fluidos con aplicaciones industriales. En este trabajo, se explotó está ventaja para predecir el equilibrio líquido vapor de agua, compuestos aromáticos y sus mezclas a condiciones tanto sub- como supercríticas. Se realizó una comparación de diferentes potenciales intermoleculares conocidos mediante el cálculo de propiedades termodinámicas de sistemas puros que sirvió de punto de partida para llevar a cabo una optimización de parámetros transferibles para un potencial intermolecular de agua y compuestos aromáticos. En el caso de agua, se llevo a cabo el análisis y evaluación de propiedades termodinámicas de un modelo simple de agua. En este modelo, las contribuciones electrostáticas se aproximan mediante interacciones de corto alcance en vez de las típicas fuerzas de Coulomb de largo alcance. En general, se han encontrado grandes desviaciones con respecto a los datos experimentales, tal como un valor de temperatura crítica de 360K, valor 50% alejado del valor experimental. Debido a que estos resultados nos indican la importancia de incluir las fuerzas de Coulomb en el modelo molecular empleado para reproducir correctamente las propiedades de agua, el trabajo de investigación se ha enfocado en la optimización de los parámetros de los potenciales TIP4P y SPC/E. Los resultados obtenidos muestran que es posible encontrar una mejor aproximación al punto crítico experimental a partir de la optimización del modelo SPC/E. Sin embargo, el buen acuerdo con los experimentos del modelo original a condiciones ambiente se pierde usando los parámetros del modelo optimizado. Por otro lado, la estimación de propiedades de compuestos aromáticos esta de acuerdo con los datos experimentales permitiendo la reproducción de la densidad de líquido saturado, presión de saturación y entalpía de vaporización para compuestos puros. Finalmente, en el caso de mezclas se ha aplicado el conjunto de parámetros obtenidos para aromáticos. Las propiedades termodinámicas de la mezcla binaria aromático-aromático y aromático agua son analizadas en un amplio rango de temperaturas y presiones. Las desviaciones encontradas entre los valores calculados y los experimentales sugieren aplicar un mejor método de optimización para sistemas puros o por otro lado, promover un potencial de interacción intermolecular más sofisticado. Las estimaciones a condiciones cercanas al punto crítico están en buen acuerdo con los datos experimentales. / La simulació molecular presenta l'avantatge d'oferir un marc teòric important per a cercar propietats termodinàmiques i de transport de fluids amb aplicacions industrials. En aquest treball es va explotar aquesta avantatge per predir l'equilibri líquid vapor d'aigua, components aromàtics i les seves mescles, tant a condicions sub com supercrítiques. Es va realitzar una comparació de diferents potencials intermoleculars, coneguts mitjançant el càlcul de propietats termodinàmiques de sistemes purs, que ha servit de punt de sortida per portar a terme una optimització de paràmetres transferibles per a un potencial intermolecular de propietats termodinàmiques d'un model simple d'aigua. En aquest model, les contribucions electrostàtiques s'aproximen mitjançant interaccions de curt abast en lloc de les típiques forces de Coulomb de llarg abast. En general, s'ha trobat grans desviacions respecte a les dades experimentals, tal com un valor de temperatura crítica de 360K, valor 50% allunyat del valor experimental. Degut a que aquests resultats ens indiquen la importància d'incloure les forces de Coulomb en el model molecular emprat per reproduir correctament les propietats d'aigua, el treball d'investigació s'ha enfocat en l'optimització dels paràmetres dels potencials TIP4P i SPC/E. Els resultats obtinguts mostren que és possible trobar una millor aproximació al punt crític experimental a partir de l'optimització del model SPC/E. No obstant, el bon acord amb els experiments del model original a condicions ambientals es perden usant els paràmetres del model optimitzat. Per altre banda, l'estimació de propietats de compostos aromàtics esta d'acord amb les dades experimentals permetent la reproducció de la densitat de líquid saturat, pressió de saturació i entalpia de vaporització per a compostos purs mitjançant el potencial AUA-Aromátics proposat. Finalment, en el cas de mescles s'ha aplicat el conjunt de paràmetres obtinguts per aromàtics. Les propietats termodinàmiques de la mescla binària aromàtic-aromàtic i aromàtic-aigua són analitzades en un ample rang de temperatures i pressions. Les desviacions trobades entre els valors calculats i els experimentals suggereixen aplicar un millor mètode d'optimització per a sistemes purs o, per altre banda, promoure un potencial d'interacció intermolecular més sofisticat. Les estimacions en condicions properes al punt crític tenen un bon acord amb les dades experimentals. / Molecular simulation presents the advantage of providing a unified theoretical framework to model fluid properties for industrial applications. In this work we exploit this advantage to predict thermodynamic properties of pure water and aromatics and their mixtures at sub- and supercritical conditions. A comprehensive comparison of different intermolecular potentials has been carried out in order to analyze model predictions for pure component properties. In addition, an optimization of transferable parameters has been performed for an intermolecular potential for aromatics and water. In the case of water, an analysis and evaluation of the thermodynamic properties of a simple model has been performed. In this model, the electrostatic contributions are approximated by short-range interactions instead of the typical long-range Coulombic forces. On the whole, we found huge deviations with experimental data, such as a critical temperature value of 360K, 50% far away from the experimental value. Since, these calculations indicate the importance of including the electrostatic contribution in order to correctly model water, we also focus on reproducing critical properties from an optimization of the well known TIP4P and SPC/E water model parameters. Results obtained show that a better approximation to the critical point prediction is possible from the optimization of the SPC/E parameters, however, the good agreement with experiments for the original model at room conditions vanishes using the optimized parameters. On the other hand, thermodynamic property estimations of aromatic molecules are in good agreement with experimental data and we are able to reproduce saturation liquid densities, saturation pressures, vaporization enthalpies and liquid structure for pure compounds. Finally, in the case of mixtures, we applied the optimized set of parameters obtained for aromatics. The thermodynamic properties of binary aromatic-aromatic and aromatic water mixtures are analyzed over a wide range of temperatures and pressures. Deviations between the predicted and experimental values are found at low temperatures and high densities suggesting that a better optimization process needs to be performed for the pure systems or a more sophisticated intermolecular interaction potential is needed. Nevertheless, the estimations close to critical conditions are in good agreement with experimental data.