<p> Attempts to prepare silicone oligonucleotide copolymers are complicated by the large difference in hydrophobicity in the two materials. Two approaches were followed to overcome this challenge. Initially, highly sterically hindered tetraisopropyldisiloxanes were used to bind 5'-0-(4,4'-dimethoxytrityl)-thyrnidine at the 5'-0H. These compounds proved to be hydrolytically more stable than the analogous dimethylsiloxane compounds, which were also prepared. Alternatively, Si-C bonds, which are hydrolytically stable, can be used to bind the two species together. Introduction of allyl ether by traditional Williamson conditions was followed by hydrosilylation with hydride terminated (Si-H) silicone, catalyzed by using platinum complexes, to give the nucleoside-functionalized silicone. We also introduced an epoxy group to one end of a silicone chain and found it to be stable to hydrolysis. Once the epoxy group binds nucleoside-functionalized silicone to solid phase, it is expected that the nucleoside-functionalized silicone via a trimethylene spacer linkage might be a starter for preparation of oligonucleotide-functionalized silicones in future work. </p> / Thesis / Master of Science (MSc)

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Presented in this paper are experiments to test the hypothesis that drag reduction is possible over hydrophobic surfaces in the Wenzel state during laminar and turbulent flows. Quantification of surface drag reduction in rectangular channel flow over walls with specific hydrophobic or hydrophilic properties was obtained with pressure drop measurements along the channel for a range of Reynolds numbers between 350 and 5900. Several commercially available materials and coatings were chosen in order to span a range of contact angles between 30° and 135°. The results are within the bounds of the theoretical values calculated with the Colebrook equation, and do not show any reduction in wall shear stress as a function of material properties or surface chemistry. The differences between this experiment and others measuring pressure drop over hydrophobic surfaces is the macro-scale conditions and the hydrophobic surfaces being fully wetted. These experiments are further proof of the importance of a liquid-vapor interface for increasing the shear free area to produce drag reduction. / Master of Science

Enhanced transport of microbes in subsurface is a focus in bioaugmentation applications for remediation of groundwater. In this study, the effect of low-concentration monorhamnolipid biosurfactant on transport of Pseudomonas aeruginosa ATCC 9027 in natural porous media (silica sand and a sandy soil) with or without hexadecane as the nonaqueous phase liquids (NAPLs) was studied with miscible-displacement experiments using artificial groundwater as the background solution. Transport of two types of cells was investigated, glucose-grown and hexadecane-grown cells with lower and higher cell surface hydrophobicity (CSH), respectively. A clean-bed colloid deposition model was used to calculate deposition rate coefficients (k) for quantitative assessment on the effect of the rhamnolipid on the transport. In the absence of NAPLs, significant cell retention was observed in the sand (81% and 82% for glucose-grown and hexadecane-grown cells, respectively). Addition of low-concentration rhamnolipid enhanced cell transport, with 40 mg/L of rhamnolipid reducing retention to 50% and 60% for glucose-grown and hexadecane-grown cells, respectively. The k values for both glucose-grown and hexadecane-grown cells correlated linearly with rhamnolipid-dependent CSH quantitatively measured using a bacterial-adhesion-to-hydrocarbon method. Retention of cells by the soil was nearly complete (>99%). Forty milligrams per liter of rhamnolipid reduced the retention to 95%. The presence of NAPLs in the sand enhanced the retention of hexadecane-grown cells with higher CSH. Transport of cells in the presence of NAPLs was enhanced by rhamnolipid at all concentrations tested, and the relative enhancement was greater than in the absence of NAPLs. This study shows the importance of hydrophobic interaction on bacterial transport in natural porous media and the potential of using low-concentration rhamnolipid for facilitating cell transport in subsurface for bioaugmentation efforts.

Isoladores poliméricos têm crescentemente competido com os isoladores cerâmicos nas aplicações em sistemas elétricos de potência e é esperado que dominem as aplicações externas em alta tensão em um futuro próximo. Entretanto, há ainda algumas questões pendentes acerca do envelhecimento dos polímeros sobre estresse elétrico e climático. Dessa forma, a estabilidade da hidrofobicidade deve ser medida para estender o tempo de vida do isolador. Por esta razão, o desenvolvimento de um sistema de medição da degradação tem se tornado um fator relevante. Este trabalho apresenta e discute o desenvolvimento de um sistema para avaliação da hidrofobicidade em materiais poliméricos. São também discutidos os testes realizados em novas resinas derivadas do óleo de mamona. / Polymeric isolators have been competing increasingly with ceramic isolators in electric power system applications and is expected to dominate in the near future high voltage outdoor applications. However, there are still some outstanding questions regarding aging of polymers under climatic and electrical stresses. In this way, hydrophobicity has to been measured for to extend the life time of these insulators. For these reasons, the development of a degradation measurement system has become a relevant factor. This work presents and discusses the development of a hydrophobicity estimation system to polymeric materials. Also discussed are the tests carried out on the new castor oil resin.

With the dramatic expansion of pinyon-juniper woodlands over the last century, improved understanding of how these woodlands modify infiltration properties is needed, in order for land managers to make informed decisions on how to best manage their specific resources. However, current methods for measuring soil infiltration are often limited by low sample sizes and high experimental error, due to constraints associated with remote, non agricultural settings. This thesis first presents a scheme for automating and calibrating two commercially available infiltrometers, which allows collection of a large number of precise unsaturated infiltration measurements in a relatively short period of time. Secondly, a new method to precisely determine saturated hydraulic conductivity from small intact soil cores collected in the field is demonstrated. This method removes bias due to measurement error using a multiple head linear regression approach. Finally, hundreds of fine spatial scale measurements of soil sorptivity, unsaturated hydraulic conductivity, saturated hydraulic conductivity, soil water content, and other soil descriptive measurements along radial line transects extending out from the trunk of juniper (Juniperus osteosperma) and pinyon pine (Pinus edulis) trees. Within the subcanopy of these trees, interactions among litter material, root distributions, and hydrophobic soil significantly influence ecohydrologic properties by limiting and redirecting infiltration below the soil surface. Consequently, hydrophobicity appears to be a mechanism that promotes survival of woody vegetation in arid environments, through decreasing evaporation rates from the soil surface. We further demonstrate how differences in unsaturated infiltration and soil water content between the subcanopy and intercanopy zones are not discrete. Unsaturated infiltration was significantly lower within the subcanopy than in the intercanopy, and increased by eight-fold across a gradient extending outward from near the edge of the canopy to approximately two times the canopy radius. This gradient was not strongly related to soil moisture. In the intercanopy, increasing structural development of biological soil crust cover beyond this gradient was positivity correlated with infiltration capacity. Consequently, these results indicate that the spatial location of the trees should be considered in the assessment and modeling of woody plant and biological soil crust influence on infiltration capacity in a pinyon-juniper ecosystem.

Immiscible dispersions of oil and water are encountered in many industries such as food, pharmaceuticals, and petroleum. Phase inversion is a key phenomenon that takes place in such systems whereby the dispersed phase and the continuous phase invert spontaneously. Stabilizers such as surfactants or solid nanoparticles have been used in the past to improve the stability of emulsions. However, the combined effects of surfactants and nanoparticles on phase inversion and stability of oil and water emulsions have not been studied. This study investigates the synergistic effects of silica nanoparticles (of varying hydrophobicities) and non-ionic surfactant on phase inversion of water-in-oil emulsion to oil-in-water emulsion. The effect of oil viscosity on phase inversion phenomenon is also studied. Stabilizers were initially dispersed in the oil phase with the help of a homogenizer. The water concentration of the system was gradually increased while maintaining the mixing. Online conductivity measurements were carried out to obtain the phase inversion point. Experimental results on the effects of pure stabilizers (either silica nanoparticles or surfactant) and mixed stabilizers (combined silica nanoparticles and surfactant) on phase inversion of emulsions are presented. The stability of these emulsions is also investigated. From the results obtained in this study it is clear that catastrophic phase inversion phenomenon and stability of water-in-oil emulsions can be controlled with the help of different stabilizers. In order to extend the critical dispersed phase volume fraction at which phase inversion occurs surfactant type stabilizer was found to be more effective than solid nanoparticles. On the other hand, emulsion stability was mainly dominated by solid nanoparticles. The hybrid of the two stabilizers and its effect on phase inversion and stability are discussed in the thesis.

Immiscible dispersions of oil and water are encountered in many industries such as food, pharmaceuticals, and petroleum. Phase inversion is a key phenomenon that takes place in such systems whereby the dispersed phase and the continuous phase invert spontaneously. Stabilizers such as surfactants or solid nanoparticles have been used in the past to improve the stability of emulsions. However, the combined effects of surfactants and nanoparticles on phase inversion and stability of oil and water emulsions have not been studied. This study investigates the synergistic effects of silica nanoparticles (of varying hydrophobicities) and non-ionic surfactant on phase inversion of water-in-oil emulsion to oil-in-water emulsion. The effect of oil viscosity on phase inversion phenomenon is also studied. Stabilizers were initially dispersed in the oil phase with the help of a homogenizer. The water concentration of the system was gradually increased while maintaining the mixing. Online conductivity measurements were carried out to obtain the phase inversion point. Experimental results on the effects of pure stabilizers (either silica nanoparticles or surfactant) and mixed stabilizers (combined silica nanoparticles and surfactant) on phase inversion of emulsions are presented. The stability of these emulsions is also investigated. From the results obtained in this study it is clear that catastrophic phase inversion phenomenon and stability of water-in-oil emulsions can be controlled with the help of different stabilizers. In order to extend the critical dispersed phase volume fraction at which phase inversion occurs surfactant type stabilizer was found to be more effective than solid nanoparticles. On the other hand, emulsion stability was mainly dominated by solid nanoparticles. The hybrid of the two stabilizers and its effect on phase inversion and stability are discussed in the thesis.

Temperature, pressure, and length scale dependence of the solvation of simple solvophobic solutes is investigated in the Jagla liquid, a simple liquid consisting of particles that interact via a spherically symmetric potential combining hard and soft core interactions. The results are compared with identical calculations for a model of a typical atomic liquid, the Lennard-Jones (LJ) potential, and with predictions for hydrophobic solvation in water using the recently developed cavity equation of state and the extended simple point charge model. We find that the Jagla liquid captures the qualitative thermodynamic behavior of hydrophobic hydration as a function of temperature and pressure for both small and large length scale solutes. In particular, for both the Jagla liquid and water, we observe temperature-dependent enthalpy and entropy of solvation for all solute sizes as well as a negative solvation entropy for sufficiently small solutes at low temperature. This feature of water-like solvation is distinct from the strictly positive and temperature independent enthalpy and entropy of cavity solvation observed in the Lennard-Jones fluid. The results suggest that a competition between two energy scales that favors low-density, open structures as temperature is decreased is an essential interaction of a liquid that models hydrophobic hydration. In addition the Jagla liquid dewets surfaces of large radii of curvature less readily than the Lennard-Jones liquid, and the so-called ``length scale crossover'' in solvation, whereby solvation free energies change from scaling with the solute volume to scaling with the solute surface area, occurs at length scales that are larger relative to the solvent size. Both features reflect a greater flexibility or elasticity in the Jagla liquid structure than that of a typical liquid, similar to water's ability to maintain its hydrogen bond network. The implications of the differences in crossover behavior between water-like and typical liquids are examined in the context of a simple thought experiment on the aggregation of solvophobic solutes that builds on ideas from Chandler and Rajamani et al. We find that water-like crossover behavior exposes a size range of solvophobic aggregates to destabilization upon cooling and pressurizing, which may thereby precipitate phenomena such as cold and pressure denaturation of proteins. Statistics of density fluctuations, void space, and pair distributions are analyzed for molecular-scale volumes. The pair distribution functions are used to provide an estimate of the size of the Jagla particle with a physical basis. The void distributions are observed to be distinct in the three liquids, with low temperature distributions in the LJ and Jagla liquids demonstrating a high degree of skewness. The void distributions observed in LJ liquid are hard sphere-like, while those of water and the Jagla liquid exhibit a higher degree of density inhomogeneity relative to a hard sphere system. The well-known Gaussian behavior of density fluctuations in molecular volumes in water is not generally observed in other liquids, as evidenced by the fact that this behavior is not consistently observed in either the LJ or the Jagla liquids. An exploratory study of the effects of explicit solvent on the sequence energy landscape of model heteropolymers has been performed. For a fixed set of configurations, the energy landscape of all possible sequences taken from a two letter alphabet consisting of only solvophilic and solvophobic monomers is characterized at different solvent temperatures. Non-trivial solvent and temperature effects are manifest in the distribution of sequences, confirming that the negation of these effects may have profound consequences on designability. / text

Thesis (Ph.D. in Bioinformatics) -- University of Colorado, 2005. / Typescript. Includes bibliographical references (leaves 116-124). Free to UCDHSC affiliates. Online version available via ProQuest Digital Dissertations;