Thesis (Ph. D)--Montana State University--Bozeman, 2005. / Typescript. Chairperson, Graduate Committee: Amend, John R. Includes bibliographical references (leaves 180-188).

Global average power consumption is 17 terawatts (10[to the power of]12W) and the rate of solar energy received at the Earth's surface is more than 120 petawatts (10[to the power of]15W). Therefore, the earth receives as much solar energy in one day as is used by the entire world in 20 years. Solar thermal collectors use absorber coatings and layers to convert incident radiation, via photothermal conversion, into useful energy i.e. heat. Re-radiation of this heat is minimised using a solar selective surface. Patterning non-thermal curing epoxy resins, in the micron scale, using electrohydrodynamic instability (EHD) patterning, could mitigate some of the challenges presented by other materials and methods used to produce these surfaces such as cost. Therefore, this was the objective of this study. As a contribution to the field of electrohydrodynamic instability patterning, the method of using this process to shape a thin, non-thermal curing epoxy resin film, was developed and the materials and equipment used are presented. Epoxy pillared surfaces, with pillar spcings from 3-200 [micrometres], were manufactured on silicon substrates using 30, 61 or 162 V and electrode gaps ranging from 3- 40 [micrometres]. A way of replicating the fabricated surfaces using moulding was also developed and is also described here. The patterned surfaces were replicated onto various substrates and were tested for their interaction with infrared (IR) radiation. In order to explore the range of versatility of theis technique for fabricating functional surfaces the structures surfaces were also tested as sustrates for tissue culture. To gain a better understanding and hence control over the use of electrohydrodynamic instability patterning with an epoxy resin, theories and numerical models of the process of electrohydrodynamic instability patterning were examined. Comparisons between predictions of results given by theory and our practical results are discussed since it was found that there was more disagreement between our results and theory when lower electric fields were being used. The studies of the interaction of the surfaces with IR radiation, and for use as tissue culture substrates, is also assessed and commented on. Lastly improvements that could be made and future work that could be undertaken is suggested.

Thesis (Ph. D.)--Syracuse University, 2003. / "Publication number AAT 3099729."

This dissertation is about the molecular modeling of fluids adsorbed in disordered porous materials. The goal is to obtain the relationship between the adsorption thermodynamics and adsorbent microstructure. This was accomplished by using molecular models that exhibit realistic three dimensional descriptions of the structural and energetic heterogeneities of the adsorbent. In these models the adsorbent is treated as a matrix of particles with a predetermined spatial arrangement. An important focus of the present work is on how the adsorbent microstructure affects the isosteric heat of adsorption. In these molecular models, microstructural variations can be made in several ways. These include: (i) changing the translational order of the matrix; (ii) the matrix particle connectivity; (iii) the porosity; (iv) the surface roughness. Our studies for a model of methane in silica xerogel show that the translational order of the matrix particles has the most significant effect. Surface roughness is also important and we have investigated several ways of incorporating this into the models. The effects of adsorbate molecular shape was investigated using two molecular models of ethane: (i) a single site model; (ii) a two site model. The effect of the adsorbate molecular shape on the adsorption isotherms is more pronounced at low temperature compared to that at high temperature. The nonspherical model tends to have a higher heat of adsorption. The differences in the adsorbate microstructures are similar to those found in the bulk fluids (e.g. a 'shoulder' in the site-site distribution functions). We have investigated the adsorption of methane-ethane mixtures in silica gel. Adsorption isotherms, heats of adsorption, and selectivities from the molecular model were calculated. These were compared with the ideal adsorbed solution (IAS) theory. It was found that the IAS theory gives very good predictions from low to moderate bulk pressures. Our work includes the first theoretical calculation of the component isosteric heats of adsorption for a mixture in a heterogeneous solid.

This research involves in vitro crystallization and the characterization of crystal structure of silk I. This polymorph, silk I, was discovered in the contents of the air-dried silk gland half a century ago. However, the metastable nature and the lack of orientation in the silk I samples have thwarted the understanding of this structure. We have successfully reproduced a silk I structure in vitro by foaming and enzymatic hydrolysis of silk fibroin. The processing parameters, the solution concentration and the pH, as well as the amorphous portion and the amino acid composition in the crystalline sequence of silk fibroin, were examined via studies of crystallization, the crystal structure of silk I foams, the Cp fraction, and a silk-like sequential polypeptide, Poly (L-Ala-Gly). The characterization techniques employed include electron diffraction coupled with TEM imaging, X-ray diffraction, infrared spectroscopy, and molecular simulations and simulated diffraction. Re-examination of the ‘ crankshaft model’ indicated that the crankshaft conformation proposed for silk I is incorrect and the hydrophilic serine residues are not negligible for the packing of the silk I structure. We proposed a tentative silk I model based on an almost fully extended chain conformation with a slight twist. Six staggered protein chains make a crystallographic repeat for an orthorhombic unit cell of 22.66 Å × 5.7 Å × 20.82 Å with a rise per residue of 3.47 Å. The solid state analog of the liquid crystalline structure of monodisperse poly (γ-benzyl α,L-glutamate) (PBLG) was studied using atomic force microscopy and electron diffraction coupled with TEM imaging. These PBLG molecules were produced by recombinant DNA technology, and display a smectic ordering resultant from rigid α-helical rods of uniform length. TEM and AFM have revealed a banded morphology, which indicates a twist of the director field as in a cholesteric or twisted smectic. Detailed examination of the relative orientation of the banding and the diffraction pattern leads to the conclusion that the structure observed is a twist-grain-boundary (TGB)-like phase. This is consistent with the superposition of a smectic-A layering resulting from the uniform rod length on the supramolecular twist (the cholesteric) present in the cholesteric.

Nonlocal density-functional theory has been applied to two chemical reaction systems of engineering interest, the HO2 system and the CH 2O2 system, in order to better understand the relative roles of different levels of density-functional theory in exploring complete reactive pathways, to explore the potential energy surfaces in greater detail than that obtained in previous work, and to validate the computational implementation. The HO2 system undergoes one of the most important elementary reactions in combustion, H + O2 → O + OH. The CH2O2 system undergoes the water-gas shift reaction, CO + H2O → CO2 + H2. Nonlocal capabilities as well as additional local methods were incorporated into the computational implementation. The application of nonlocal methods resulted in substantial improvements in accuracy over that from the use of local methods alone. A novel method for visualizing energy profiles of reaction systems has also been invented. This method is general in its application in the sense that it treats energy profiles involving arbitrary points in configuration space, including the important case of multiple reaction paths.

The objective of this dissertation is to employ molecular modeling concepts to investigate benzene transport in NaX type zeolite. Experimentally observed separation performance of NaX faujasite (FAU) membranes can be attributed to the intra-crystalline processes of sorption and diffusion. Membrane permeation occurs by sorption of the guest or sorbate (e.g. benzene) on surface-active host sites of zeolite (e.g. FAU) and simultaneous site-site molecular movement or intra-crystalline diffusion of sorbate. Such processes are controlled by host-guest and guest-guest interactions on the length scales of the pores. In this study, Molecular Dynamics (MD) simulations are performed to evaluate the Self—Ds(T, Θ) and Cooperative (or Maxwell-Stefan)—DMS(T, Θ) diffusivities and the respective energies of activation: [special characters omitted](Θ) and [special characters omitted](Θ) for benzene motion in NaX. The MD simulated Ds and [special characters omitted] favorably compare with predictions from experimental measurements (PFG-NMR, QENS). Consequently, the predicted DMS is applied in a transport model to predict benzene fluxes through ideal NaX membranes so as to ultimately evaluate and comprehend the experimentally observed fluxes in NaX FAU membranes. This contribution is aimed to be the first step towards understanding the experimentally observed permeation selectivity of benzene over cyclohexane in NaX membranes. Our efforts to understand how molecular interaction phenomena in the pores of the NaX FAU give rise to experimentally observed sorption-diffusion behavior, we believe would have an impact on the approach towards improving zeolite membrane performance and permselectivity in industrially important separations. In addition, this dissertation discusses two other challenging problems related to the field of microporous and mesoporous materials, namely—(a) Application of techniques such as Transmission electron microscopy (TEM), Electron diffraction (ED) and Energy dispersive X-ray (EDX) analysis in the characterization of the fine structures of porous materials, and (b) Formation of periodic Liesegang patterns of titania by chemical vapor deposition (CVD) in mesoporous glass.

We have modeled the thermodynamics and polymerization of silica, in order to understand the formation of complex materials such as zeolites. We have developed a simple molecular model of silica that is both physically realistic and computation ally efficient. We performed isobaric-isothermal Monte Carlo simulations to study the mechanical and phase behavior of this model, finding that it can be used as a qualitative representation of silica. Ratios of zero pressure bulk moduli and thermal expansion coefficients are shown to be in good agreement with experimental values for alpha-quartz, alpha-cristobalite, and coesite. A pressure-temperature phase diagram was constructed that shows three phases corresponding to cristobalite, quartz and coesite, and a fluid or glass phase, in good agreement with experiment. This phase diagram was extended to include the zeolitic polymorph silicalite-1. We found that silicalite-1 is a thermodynamically stable polymorph at high temperatures (>1000 K) and low pressures. This is surprising considering that zeolites were previously thought to be at most metastable. We then examined whether templated zeolites are thermodynamically stable under synthesis conditions (≈425 K). We found that an unphysically high template-zeolite attraction is needed to make this so, suggesting that zeolite formation is kinetically controlled. We have extended this model to simulate the early stages of silica polymerization in order to determine atomistic structures of silica nanoparticles. The chemistry was simulated with the reaction ensemble Monte Carlo method. We introduce a new sampling method based on altering topological graphs to move between different networked states. We find that this method overcomes the sampling difficulties present in networked systems. Using an experimentally derived thermochemistry, we studied the effect of pH on the growing networks. We found that at high pH, the networks are dissolved in the basic solution leaving highly ionized monomers. We also found that the nanoparticles exhibit radial structure: a core of bridging oxygens (Si-O-Si) surrounded by a shell of silanol groups (Si-OH), surrounded further by an outer shell of charged Si-O- groups.

Within the last decade, reactive distillation has become increasingly attractive as a potential process alternative for simultaneously conducting liquid-phase reaction and vapor-liquid separation, with the potential to overcome chemical equilibrium limitations and to simplify flowsheets. This dissertation develops a systematic steady-state design methodology for kinetically controlled, stagewise reactive distillation columns, taking into account a single isomolar or non-isomolar liquid phase reaction, heat effects, nonideal vapor-liquid equilibrium, and a distribution of liquid holdups on the reactive stages. “Kinetically controlled” means that chemical reaction equilibrium is not obtained on every tray, although vapor-liquid equilibrium is assumed. “Stagewise” implies a column consisting of discrete trays. The method is useful for developing a spectrum of feasible designs over a range of design conditions, which provides insight into the effect of such variables as reboil ratio, heat of reaction and Damkohler number on the total number of stages. The method is demonstrated by developing feasible column designs for the dehydration of methanol, the metathesis of 2-pentene, and the production of ethylene glycol. The influence of azeotropes on the design of ordinary distillation columns has been widely studied for many years. Azeotropes alter product distributions and attainable regions; cause distillation boundaries to occur; and have led to the creation of extractive and azeotropic distillation technology. It can be expected that reactive azeotropes have a similar impact on reactive distillation design. However, the influence that key physical property parameters (such as the reaction equilibrium constant) exert on reactive azeotropes is relatively unknown. New tools are needed to determine when reactive systems will exhibit reactive azeotropes and how these azeotropes will influence designs. Such a tool is described in this dissertation: an arc-length continuation technique used to determine the existence and location of both homogeneous and heterogeneous reactive azeotropes in an equilibrium reactive system. Using the techniques and methods developed, the use of reactive distillation in nontraditional applications are explored, such as in a system possessing a small reaction equilibrium constant (Keq [special characters omitted] 1) or kinetically resolving enantiomers from a racemic mixture.

In the last decade, there has been growing success at developing commercial processes which combine reaction and separation. This technology offers the potential of significantly improved economics, reduced emissions and direct energy integration between the reaction and separation processes in the system. In this dissertation, we develop tools to analyze and design reactive distillation systems with multiple kinetically controlled chemical reactions. Residue curve maps are a useful tool in the conceptual design of distillation systems. They are the trajectories on a phase plane of the composition in a still during a simple distillation or open evaporation experiment. We derive a system of equations to model kinetically controlled reactive simple distillation. From these equations we define a dimensionless parameter, the Damkohler number, which is a measure of the amount of reaction in the system. A Damkohler number of zero implies a non-reactive system while a Damkohler number approaching infinity implies a system in which there is simultaneous reaction and phase equilibrium. The structure of the residue curve map determines whether a reactive distillation is feasible, and the structure changes with the Damkohler number. A good knowledge of the reaction kinetics is important for the analysis and design of kinetically controlled reactive distillation systems. Closed batch isothermal kinetic experiments and binary non-reactive adsorption experiments were performed for the esterification of acetic acid with methanol on the heterogeneous Amberlyst 15W catalyst. The kinetic data were then fitted with a Langmuir-Hinshelwood/Hougen-Watson model and the model was used to predict the course of simple distillation experiments. The structure of a residue curve map is determined by the composition and temperature of the solutions of the simple distillation equations. We developed a systematic way of studying the effect of kinetics on the structure of the residue curve maps by performing a bifurcation analysis of the simple distillation equations as a function of the Damkohler number starting with the non-reactive case where the singular points are the pure components and the non-reactive azeotropes. Batch reactive distillation combines the advantages of reactive distillation and batch processes. We have developed a simplified model that can be used to quickly screen through design alternatives and operating strategies to develop estimates for the number of stages, distillate policies, the initial feed ratios in the still, etc. Once promising designs and policies have been identified, a more detailed simulation at a finite reflux and with a finite holdup in the column can be performed for the conditions of interest. This model was applied to the study of the esterification of acetic acid and butanol to produce butyl acetate. For this process, we have suggested a new operating policy which will increase the purity of the main product without introducing additional purification steps. The results were also compared to those from a more detailed model.