R-3 Repository :: Browsing by Author "Chapman, Walter G"

Browsing by Author "Chapman, Walter G"

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A Systematic Study of Short and Long Range Interactions in Associating Fluids Using Molecular Theory
(2015-12-17) Ahmed, Wael; Chapman, Walter G; Cox, Kenneth R; Tomson, Mason B; Biswal, Sibani L
Parameters needed for the Statistical Associating Fluid Theory (SAFT) equation of state are usually fit to pure component saturated liquid density and vapor pressure. In this thesis, other sources of information such as quantum mechanics, infinite dilution properties, Fourier transform infrared (FT-IR) spectroscopy and molecular dynamic (MD) simulation are used to obtain a unique set of parameters for complex fluids such as water and alcohols. Consequently, the equation of state can be more predictive and the parameters are not anymore system dependent. Moreover, the four vertices of the molecular thermodynamic tetrahedron (phase equilibrium experiments, spectroscopy, MD simulation and molecular theory) are used to study the distribution of hydrogen bonds in water and alcohol containing mixtures. The new sets of physical parameters and the knowledge gained in studying hydrogen bonding are then applied to model water content of sour natural gas mixtures as well as the phase behavior of alcohol + n-alkane and alcohol + water binary systems. Accurate determination of the water content in hydrocarbons is critical for the petroleum industry due to corrosion and hydrate formation problems. Experimental data available in the literature on the water content of n-alkanes (C5 and higher) is widely scattered. The perturbed chain form of the SAFT equation of state (PC-SAFT) was used to accurately correlate water mole fraction in n-alkanes, C1 to C16, which are in equilibrium with liquid water or ice. In addition, a list of experimental data is recommended to the reader based on its agreement with the fundamental equation of state used in this dissertation. The proposed molecular model was then applied to predict water content of pure carbon dioxide (CO2), hydrogen sulfide (H2S), nitrous oxide (N2O), nitrogen (N2) and argon (Ar) systems. The theory application was also extended to model water content of acid gas containing mixtures in equilibrium with an aqueous or a hydrate phase. To model accurately the liquid-liquid equilibrium (LLE) at subcritical conditions, cross association between CO2, H2S and water was included. The hydrate phase was modeled using a modified van der Waals and Platteeuw (vdWP) theory. The agreement between the model predictions and experimental data measured in our lab was found to be good across a wide range of temperatures and pressures. Modeling the phase behavior of liquid water can be quite challenging due to the formation of complex hydrogen bonding network structures at low temperatures. However, alcohols share some similarities with water in terms of structure and physical interactions. As a result, studying alcohol + n-alkane binary systems can provide us with a better understanding of water-alkane interactions. Besides, the application of alcohols in the petroleum and the biodiesel industry is of great importance. As a result, Polar PC-SAFT was used to model short chain 1- alcohol + n-alkane mixtures. The ability of the equation of state to predict accurate activity coefficients at infinite dilution was demonstrated as a function of temperature. Investigations show that the association term in SAFT plays an important role in capturing the right composition dependence of the activity coefficients in comparison to excess Gibbs free energy models (UNIQUAC in this case). Results also show that considering long range polar interactions can significantly improve the fractions of free monomers predicted by PC-SAFT in comparison to spectroscopic data and molecular dynamic (MD) simulations. Additionally, evidence of hydrogen bonding cooperativity in 1-alcohol + n-alkane systems is discussed using spectroscopy, simulation and theory. In general, results demonstrate the theory’s predictive power, limitations of Wertheim’s first order thermodynamic perturbation theory (TPT1) as well as the importance of considering long range polar interactions for better hydrogen bonding thermodynamics. Furthermore, the thermodynamics of hydrogen bonding in 1-alcohol + water binary mixtures is studied using MD simulation and Polar PC-SAFT. The distribution of hydrogen bonds in pure saturated liquid water is computed using TIP4P/2005 and iAMOEBA simulation water models. Results are compared to spectroscopic data available in the literature and to predictions using Polar PC-SAFT. The distribution of hydrogen bonds in pure alcohols is also computed using the OPLS-AA force field. Results are compared to Monte Carlo (MC) simulations available in the literature and to predictions using Polar PC-SAFT. The analysis show that hydrogen bonding in pure alcohols is best predicted using a two-site model within the SAFT framework. On the other hand, simulations show that increasing the concentration of water in the mixture increases the average number of hydrogen bonds formed by an alcohol molecule. As a result, a transition in association scheme occurs at high water concentrations where hydrogen bonding is now better captured using a three site alcohol model within the SAFT framework. The knowledge gained in understanding hydrogen bonding is applied to model the vapor-liquid equilibrium (VLE) and LLE of 1-alcohol + water mixture using Polar PC-SAFT. Predictions are in good agreement with experimental data, thus exhibiting the equation of state predictive power.
All-Conjugated Block Copolymers for Organic Photovoltaic Applications
(2014-12-03) Smith, Kendall Allen; Verduzco, Rafael; Chapman, Walter G; Hartgerink, Jeffrey D
Conventional inorganic solar technologies are expensive due to the high cost of processing, while organic materials have significant cost advantages in the raw materials and ease of processing. Unfortunately, organic devices suffer from low efficiency due to difficulty in transporting charges to the electrodes. Typical devices mix the donor and acceptor components and anneal them to allow for phase separation. However, because the phase separation is uncontrolled, domains may be larger than optimal and isolated domains can be formed reducing efficiency. All-conjugated block copolymers have the potential to improve efficiency by creating an ordered structure with controlled domains and continuous pathways through self-assembly. In this work, the relationships between structure, optoelectronic properties, and processing conditions for these materials are systematically investigated using two routes to obtain the materials. In one route, functionalized catalysts are used to initiate controlled polymerizations of two different polymers. These well functionalized precursors are then joined together using copper catalyzed azide alkyne click chemistry. In a second route, a sequential polymerization route is employed where one polymer is synthesized with a well-defined end-group. The polymer is then used as a macroreagent to end-cap a Suzuki polycondensation reaction, yielding materials with direct conjugation between the blocks. The first route yields well-defined materials, whereas the second can access a broader variety of polymers. For all these materials, processing conditions are varied and the morphology of the all-conjugated block copolymers are analyzed by a combination of grazing-incidence X-ray scattering, neutron scattering and reflectivity, atomic force microscopy, and transmission electron microscopy. Materials are found to self-assemble into thermodynamically stable structures with well-defined length scales. It is found that crystallization of either block is predominant in all block copolymers studied, but at intermediate ratios crystallization of both blocks is observed. Processing conditions such as casting temperature, annealing duration, and speed of quenching to room temperature are found to have important effects on thin film crystallinity and orientation of the π-π stacking direction of polymer crystallites. By varying the annealing duration and quenching speed, crystallization of either or both block can be obtained.
Complex fluids at interfaces and interfaces of complex fluids
(2015-02-02) Nouri Dariani, Mariam; Chapman, Walter G; Wong, Michael S; Yakonson, Boris I; Veatch, Sarah L
The present thesis deals with two independent projects and is consequently divided into two parts. The first part details a computational study of the fluid structure of ring-shaped molecules and their positional and orientational molecular organizations in different degrees of confinement, while the second part concerns an experimental study of phase behavior and interfacial phenomena in confined colloid-polymer systems. In the first part, ring-shaped molecules are studied using Monte Carlo simulation techniques in one, two and three dimensions. The model used to describe ring-shaped molecules is composed of hard-spheres linked together to form planar rigid rings. For rings of various sizes and for a wide range of densities, positional and orientational orderings are reported in forms of pair distribution functions of the ring centers and correlation functions of the ring normal orientations. Special emphasis is given to understand structural formation at interfaces, i.e., the structure and orderings of these molecules when they are confined to two dimensions. In a plane but the rings themselves are free to rotate around all axes, nematic ordering is observed at sufficiently high densities. In the second part, phase equilibria of confined aqueous colloid-polymer systems are studied experimentally using fluorescence microscopy. Aqueous mixtures of fluorescent polystyrene spheres and polyacrylamide are confined between a glass slide and a coverslip. The phase diagram is determined as a function of the colloidal and polymer concentrations. Liquid-liquid phase coexistence between a colloid-rich phase and a polymer-rich phase occurs at intermediate polymer concentrations, while liquid-solid phase coexistence between a polymer-rich liquid and a colloid-rich solid is observed at high polymer concentrations. Interfacial thickness and tension of the interface between these coexisting phases are measured using image analysis techniques. It is also observed that the colloid-rich solid and liquid domains coarsen mainly by Ostwald ripening.
Microstructure and Interfacial Properties of Aqueous Mixtures
(2014-11-07) Ballal, Deepti; Chapman, Walter G; Biswal, Sibani L; Kolomeisky, Anatoly B
Understanding the properties of aqueous mixtures has important implications in applications ranging from enhanced oil recovery to biochemical processes. While there has been considerable effort invested in understanding the bulk properties of aqueous mixtures, very few studies have concentrated on their behavior in interfacial systems. Interfacial properties, which are important for applications like coatings and chemical separations, are defined by the molecular structuring of the fluid at the interface. The goal of this thesis is to understand and alter the wetting of solid surfaces by aqueous mixtures. In particular, we study the partitioning of aqueous mixtures of polar and non-polar molecules to different surfaces. What makes aqueous mixtures interesting is the hydrogen bonding nature of water that plays very different roles in the partitioning of polar and non-polar components of the aqueous mixtures. In this thesis, hydrogen bonding is modeled using a thermodynamic perturbation theory due to Wertheim. The theory, included in a classical Density Functional Theory framework, is used to study the molecular structure and interfacial properties of the system. We extend and apply the theory to study a number of aqueous mixtures. Key contributions of this thesis include 1. Predicting the interfacial properties of aqueous mixtures of short alcohols close to a hydrophobic surface 2. Extension of the first order perturbation theory to study the competition between intra and intermolecular hydrogen bonding of molecules in the presence of an explicit water-like solvent 3. Studying the effect of physical conditions and surface chemistry on the wetting of different surfaces by water-oil mixtures 4. Analyzing molecular simulation models for water-alkane interactions through a solubility study
Modeling of Asphaltene Precipitation and Deposition
(2016-06-06) Al Hammadi, Ali AbdulKareem; Chapman, Walter G
The tendency of Asphaltene to deposit and block tubing can potentially lead to production loss and significant cost of remediation. Unlike other deposits, the deposition behavior of Asphaltene is still not fully understood and is hindered by asphaltene complex nature. This thesis will provide insight into the mechanism of Asphaltene deposition through a better understanding of its thermodynamics and kinetics. Despite the contribution made by this thesis to better understand its behaviors, asphaltene still represents an ongoing challenge. Generally, a lengthy and time consuming characterization is required to obtain the optimum parameters before using EOS for crude oils. Therefore, an automatic characterization has been developed. In this thesis, a comparison between CPA and PC-SAFT EOSs is presented to illustrate their potential and limitations on the prediction of asphaltene phase behavior, and PVT properties over a range of pressure and temperature. With an optimized characterization, both EOSs give acceptable predictions of the asphaltene precipitation tendency. However, PC-SAFT is superior in the prediction of derivative properties especially at high pressures. As gas injection is crucial part of enhanced oil recovery, the effect of various gases on asphaltene phase behavior is presented. Nitrogen is shown to be the strongest precipitant while hydrogen sulfide stabilizes asphaltene. The addition of polystyrene to a mixture of asphaltene and toluene causes phase separation into two liquids due to depletion flocculation and is modeled using PC-SAFT EOS. The effects of temperature, pressure and polystyrene MW on the mixture phase behavior are investigated. The phase behavior was not sensitive to the range of pressures studied; however, increasing temperature or reducing polystyrene MW caused the one phase region to expand. The paper demonstrates that a solution model with rigorous physics can capture the depletion flocculation mechanism typically presented as colloidal behavior. This thesis also introduces Asphaltene Deposition Tool by incorporating both asphaltene kinetics and thermodynamics. The asphaltene phase behavior is described by PC-SAFT EOS while transport equations are coupled with kinetic rates of precipitation, aggregation and deposition. The transport model is simplified resulting in dramatic speed up of the simulator. Furthermore, this thesis presents a field case as well as the effects of different gases and GOR on asphaltene deposition.
Multiscale and Multidimensional Thermodynamic Modeling of Block Copolymer Self-assembly in Solution
(2020-03-06) Xi, Shun; Chapman, Walter G
The study of block copolymer self-assembly in solution has been an active subject for years. As one of the most versatile molecules in nature, it is a chemical and biological building block for life. Lipids in aqueous solution self-organize to a bilayer structure that effectively compartmentalize cellular spaces for complex biochemical processes. Industrial products related to block copolymer self-assembly in solution have been created through intensive experimental and engineering efforts. Although models for block copolymer melts have been successful, a consistent theoretical understanding of block copolymers in solution has not kept with the applications. Challenges arise from its nature that block copolymer self-assembly in solution is a multiscale and multidimensional problem. Extremely diluted block copolymer solutions are homogeneous that can be well understood by an equation of state model. Inhomogeneity appears when the polymer concentration is above critical micelle concentration and the block copolymers form isolated micelles in dilute solution. Longrange ordered lyotropic liquid crystals of multidimensional mesophases are formed in concentrated solution when the block copolymers of individual micelles overlap. This thesis aims to develop a consistent thermodynamic model for block copolymer self-assembly in solution in multiscale and multidimension, based on a particular molecular density functional theory (DFT): interfacial statistical associating fluid theory (iSAFT). This DFT model ultimately predicts phase behaviors of self-assembly in solution, explains thermodynamic factors that influence the phase behaviors from a microscopic view at molecular level, and provides a guidance to design operating conditions and to select candidate materials for the related applications. Key contributions of this thesis include: 1. A quantitative approach to predict critical micelle concentrations and aggregation numbers of micelles of both diblock copolymers and triblock copolymers, and to explain inhomogeneous micellar solubilization in dilute aqueous solution; 2. Description of solvent regulated mesophase behaviors of block copolymers in solution having two-dimensional inhomogeneity, and how solvent selectivity and molecular packing parameter affect the phase behaviors in concentrated solution; 3. A new efficient numerical algorithm for molecular density functional theory with application to iSAFT to improve convergence, stability, and performance of DFT solution algorithm in cylindrical geometry.
Novel Dynamics and Structures Using Paramagnetic Colloids with Rotating Magnetic Fields
(2015-04-21) Du, Di; Biswal, Sibani Lisa; Chapman, Walter G; Pasquali, Matteo; Natelson, Douglas
Micron-sized colloids have long been used as model systems to study the dynamic and thermodynamic behavior of atomic systems. This is attributed to the fact that their dynamics are driven by thermal energy and they are large enough to be visualized using optical microscopy. Moreover, the interactions between particles can be tuned by surface functionalization or application of external fields. In this thesis, I will introduce the use of various rotating magnetic fields on a system of confined paramagnetic colloids to model different physical phenomena in two dimensions (2-D), whose dynamics are not easily observed at a single molecule length scale. The dynamics of a particle pair under a classic rotating magnetic field is first described with a modified Mason number, to describe the relationship between magnetic, viscous, and electrostatic interactions governing the rotational dyanmics. Next, I will describe a novel method to induce an isotropic attractive interaction between paramagnetic colloids when the frequency of the rotating field is sufficiently high. The pair interaction potential is comprised of a long-range attractive interaction induced by the external magnetic field and an electrostatic Yukawa-type repulsive interaction from the charged surfaces of the particles. This interaction potential is described by a theoretical model, which is verified by experimental measurement. Three-body effects are also measured using a three-particle system, which is the leading term of many-body effect. By solving the Laplace’s equation for magnetostatics, this three-body effect is proved to be negligible for particles far from the edges of a many-particle cluster. This validates the assumption of pair additivity in the interaction potential used in a Monte Carlo simulation. The tunable isotropic interaction provides an ideal platform to study the phase behavior of 2-D atomic systems. The melting thermodynamics and dynamics are studied in detail using simulation and experiment respectively. Thermodynamics properties, such as radial distribution function, translational order parameter, bond-orientational order parameter and Lindemann parameter of different phases are measured to show that melting transition for this system is first-order as opposed to the KTHNY theory, which states melting in 2-D should be a two-stage second-order transition. Phase coexistences are observed for the first time in 2-D system with long-range attraction, which further confirms the first-order nature of the transition. The simultaneous dislocation unbinding and disclination unbinding observed in experiment explains the inconsistency against the prediction given by the KTHNY theory. The phase diagram of this system is also constructed, which is shown to be very similar to that of atomic systems. Another novel aspect described in this thesis is the development of a novel method to achieve microscale swimming. A constant offset can be added to the rotating magnetic field if the temporal symmetry needs to be broken, and the resulting field is referred to as an eccentric rotating magnetic field. Under such a field, paramagnetic particles with mismatched sizes are shown to be able to swim in a directed manner. Swimmers consisting of multiple particles are able to fragment their arms. Stochastic forces can change the type of the fragmentation from the surrounding fluid, leading to decreased or increased swimming speed for different swimmers.
Phase Behavior Model of Complex Fluids: Associating Solvents to Polymers
(2022-11-08) Alajmi, Mohammed M; Chapman, Walter G; Vargas, Francisco M
The broad aim of this work is to propose different modifications to the Cubic-plus-chain (CPC) equation of state (Sisco et al., Industrial & Engineering Chemistry Research, 2019) to improve modeling predictions and to model short and long-chain associating mixtures. The CPC equation hybridizes the classical cubic EoS with the chain term from the Statistical Associating Fluid Theory (SAFT) to develop an equation capable of modeling short and long-chain components. The CPC EoS is not limited to one classical EoS form, and different cubic forms can be used in the model. CPC-RK (RK reference form) and CPC-SRK (SRK reference form) are applied to model different binary mixtures ranging from alkanes to homopolymers. Different factors such as elevated pressures, polydispersity, molecular weight, and solvent types were analyzed to test the model performance. In addition, an extension is proposed to the CPC model framework to account for copolymers such as poly(ethylene-co-propylene) and poly(ethylene-co-vinyl acetate). Both CPC versions show good homopolymer and copolymer phase equilibria predictions compared with experimental cloud points and PC-SAFT simulation results. CPC-RK and CPC-SRK versions require using temperature-dependent binary interaction parameters (k_ij ). Moreover, those two versions do not predict liquid density accurately. Hence, different modifications are studied to improve the model description. A modified CPC version is proposed by incorporating short-range soft repulsion in the CPC framework, which is called CPC-SRK-b(T). A temperature-dependent function is introduced to the co-volume parameter in the CPC-SRK-b(T) model. CPC-SRK-b(T) overcomes limitations in CPC-RK and CPC-SRK versions by improving liquid density predictions and modeling various binary systems using a constant k_ij value. Simulation parameters database of CPC-SRK-b(T) for more than 50 components is provided. Furthermore, the cubic-plus-chain and association (CPCA) equation of state is proposed to account for short and long-chain associating fluids ranging from water and alkanols to associating polymers. CPCA shows excellent saturation pressure and liquid density predictions of pure associating components. Moreover, different mixtures’ categories including alcohol/alkane, alcohol/alcohol, alcohol/aromatics, alcohol/water, amine/alkane, and associating polymer/solvents are analyzed with CPCA showing good agreement with experimental data.
Simulation Studies on Polyampholytes can Inform Models of Protein Solution Thermodynamics
(2024-01-02) Adhikari Sridhar, Rohan; Chapman, Walter G
Intrinsically Disordered Proteins (IDPs) have an intricate involvement in intracellular phenomena. Their deep imprint on biological processes frequently implicates them in a variety of debilitating pathologies. They also pose complex scientific challenges to researchers due to their inadherence to our traditional understanding of protein functionality. Complementary research efforts between experimentalists and computational scientists are necessary to unlock our understanding of their physics. This thesis primarily focuses on the current computational models that seek to shed light on the unique properties of IDPs. Models that generate an ensemble of IDP structures and those that codify the information in the ensembles to convenient forms are both necessary for a comparison with experimental data. Obtaining an agreement with the ensemble averaged properties from experiments is the first step towards unlocking the possibilities from computational models. The most attractive amongst them is an atomistic description of IDP ensembles. Computational methods frequently resort to an implicit solvent assumption both to predict the conformations of IDPs and to interpret the generated data. The relaxation of a molecular solvent in implicit solvent models allows for their implementation with fewer computational resources. In the first part of this thesis, implicit solvent models of hydration and scattering are critically evaluated by isolating their central approximations. Implicit solvent models of hydration are shown to lack the necessary ability to discriminate between disparate conformations. Implicit solvent models of scattering analysis are shown to distort the information present in the system and blur our ability to detect the true merit of an ensemble generating method. Explicit solvent models foundationally incorporate a molecular nature of the solvent and hence are logical counterparts to implicit solvent models. In the final part of this thesis, explicit water simulations are used to generate ensembles of polyampholytes that are then input into an explicit water scattering model. Models with differing philosophies are tested on their predictions for the same system in order to generate detailed insights that have the potential to benefit future studies. The recent updates in the atomistic modeling of both proteins and waters are shown to translate to a better agreement when comparing with experimental data. The use of idealized mimics of IDPs also known as polyampholytes have allowed for the detailed studies in this thesis to be carried out. The ease of handling polyampholytes in computational studies promises to provide more foundational insights in the near future.
Solubility, Precipitation Kinetic, and Chemical Control of Iron Sulfide
(2024-04-18) Wang, Xin; Tomson, Mason B; Chapman, Walter G; Getachew, Bezawit
The iron sulfides (FeS) constitute a diverse group of solids and dissolved complexes, many of which play critical roles in the natural system, such as marine sedimentation and biochemical processes. It has also become a significant problem in various industrial processes, such as water and wastewater treatment, metal equipment corrosion by hydrogen sulfide, and oil and gas production. Extensive studies have been done in the past century to better understand, predict, and control the sulfide mineral precipitation, of which the importance can never be overstated. In this work, a systematic study of the solubility, precipitation kinetics, and the chemical dispersion control of iron sulfide is conducted to better understand iron sulfide scale prediction and control in industrial processes.
Systematic Extensions and Applications of Density Gradient Theory
(2018-06-12) Mu, Xiaoqun; Chapman, Walter G
Due to the importance of interfacial tension (IFT) in many industrial processes and daily activities, different methods have been developed to obtain IFT information for better process design and quality control in a variety of chemical systems. Compared with experimental measurements, model calculation is faster and lower-cost, allowing interpolation and extrapolation of data. Among many other models, density gradient theory (DGT) has gained popularity for simple functional form and accurate IFT predictions. Through more than a century of history, DGT has been developed and successfully implemented in IFT calculations of many pure and mixed systems. The strengths of the conventional DGT model have been well studied, while several major limitations are identified in our implementations, which restrict the model from being applied to a broader range of systems. These limitations include: • The established reference fluid algorithm for DGT equations needs the preselection of a component with a monotonic density profile, and there is no clear strategy for this selection. Furthermore, the algorithm does not allow any extensions to the current DGT functional form. • The conventional DGT model built for open systems fails to describe the IFT on spherical interfaces, since no stable droplets form when the system is allowed to have mass exchange with the ambient environment. A closed system with conserved mass would stabilize the droplet, but applications of DGT to closed systems are lacking in literature. • The conventional DGT model assumes that each molecule occupies a single position in space regardless of its molecular structure. This assumption prevents accurate application of DGT for surfactant molecules with amphiphilic chain structures. In addition to the model limitations, we also identify several potential applications of the DGT model that are highly needed in this field: • A quick and accurate surface energy model for DGT that defines the wetting boundary conditions for a 2D or 3D fluid model. • Software with different DGT models that can be easily used by engineers with relatively little background. In this thesis, we present a multistage work that addresses these challenges and needs. Firstly, we develop a novel and robust algorithm, which handles DGT equations smoothly and serves as a powerful tool to support the next-step model developments. Secondly, we construct a mass-conserved DGT model for closed systems, which can be used to study the IFT of droplets during the nucleation process. Thirdly, a modified DGT model for surfactant molecules is developed by introducing a chain formation term in the free energy expression. Fourthly, a surface free energy model is derived to define solid-fluid interactions. Finally, we develop a MATLAB based software, which integrates different DGT models and numerical algorithms into an user-friendly interface. With systematic extensions of the DGT model, we have shaped the model to meet IFT calculation requirements in different scenarios. These model development progresses also unveil the great potential of DGT as an interface model for broader academic and industrial applications in the future.
Thermodynamic Modeling of Associating Fluids: Theory and Application
(2018-08-02) Haghmoradi, Amin; Chapman, Walter G
The association interaction plays a significant role in self-assembly and determining the properties of associating fluids. The patch-patch attraction in patchy colloids, and hydrogen bonding are two examples of association. Due to the strength, range, and directionality of association, an accurate theory including information at the level of the structure of self-assembling species is required for a precise prediction of the behavior of these fluids. Wertheim\textquoteright s thermodynamic perturbation theory, which uses density expansion method, has presented a promising performance in capturing the thermo-physical properties of both hydrogen bonding and patchy colloidal fluids through prediction of all possible states of the bonding of associating species. While most of the previous studies were focused on utilizing the first order limit of Wertheim\textquoteright s theory, recent simulation and theoretical studies have shown that the simplifying assumptions included in the first order make it not capable of modeling complex self-assembling species. In this thesis, we develop Wertheim\textquoteright s theory beyond its first order to include accurate information about the structure of associating species like the size of association sites and their relative positions (in case of fluids with multiple sites), and possible self-assembled clusters of associated species. The theory developments are applied for both hydrogen bonding in molecular fluids and patchy colloids and verified with Monte Carlo simulations and previous experimental measurements results, where the agreements were excellent. Beyond the introduction and conclusion chapters, the scope of this thesis can be summarized into the followings: Chapter 2: the prediction of the self-assembly of a binary mixture of patchy colloids with two similar patches and small bond angle. Chapter 3: modeling the effect of hydrogen bond cooperativity and bond angle dependent ring formation for associating hard spheres and Lennard Jones spheres. Applying the final equations to predict the thermodynamic properties of hydrogen fluoride. Chapter 4: developing an asymmetric model for water including the effect of hydrogen bond cooperativity and multiple bonding at an association site. Chapter 5: the extension of Wertheim\textquoteright s theory for fluids of patchy colloids with two divalent patches confined between two planar hard walls in a classical density functional theory formalism. Chapter 6: investigating the effect steric hindrance for association between an associating fluid and a planar hard wall with discrete divalent active sites.
Thermodynamic Modeling of Fluid Distribution and Phase Behavior in Nanoporous Shale
(2019-04-19) Liu, Jinlu; Chapman, Walter G
Understanding fluid partitioning and phase behavior in unconventional shale is essential for reservoir characterization and production prediction. Unlike in conventional reservoirs where hydrocarbons are stored in pores of micrometers, a large fraction of the hydrocarbons in shale is trapped in nanosized pores and absorbed in organic matter kerogen, which makes the fluid distribution and phase behavior a complex problem. Despite the active research being done using experiments and molecular simulation to understand fluids in shale nanopore systems, a theoretical model that accurately predicts the thermodynamics of complex mixtures is of fundamental and practical value. This thesis aims to improve our understanding of thermodynamics of unconventional reservoir fluids using a theoretical modeling approach that is both verified versus molecular simulations of model systems and provide accurate predictions for real complex mixture systems. The goal is to develop a theory to describe the competitive adsorption of hydrocarbon mixtures in shale nanopores, phase transitions of fluids under nanopore confinement, characterization of different maturity kerogens, equilibrium partitioning of original fluid-in-place between different storage environments, and CO2 sorption selectivity with hydrocarbon mixtures under various conditions. In this work, a molecular density functional theory for associating chain molecules,i.e. interfacial Statistical Associating Fluid Theory, which accounts for molecular size and shape, van der Waals attraction, and hydrogen bonding interactions is used to study the microstructure, equilibrium partitioning, adsorption versus absorption, and phase behavior of fluid mixtures under nanopore confinement. Molecular dynamics and Monte Carlo simulation are used to validate the theoretical model. Key contributions of this thesis include: 1. Screening of methods to describe dispersion interactions in a DFT framework and systematically studying the vapor-liquid and fluid-solid interfaces of a model fluid with comparisons to molecular dynamics simulation; 2. Description of how the phase behavior for pure and mixed fluids changes due to nanopore confinement and the competitive adsorption of mixtures of alkanes molecules of different size and shape; 3. A new molecular modeling approach for nanoporous kerogen by creating a cross-linked network of asphaltene-like molecules, characterizing the solvent swelling response of kerogen and accounting for the dissolution of fluid molecules in kerogen pore walls; 4. Exploring the CO2 selective sorption behavior in a large parameter space including the effect of temperature, pressure, pore size, bulk fluid composition and pore wall properties, i.e. organic matter maturity, moisture level.

Browsing by Author "Chapman, Walter G"

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