No description available.

No description available.

Injection of low-salinity water showed high potentials in improving oil recovery when compared to high-salinity water. However, the optimum water salinity and conditions are uncertain, due to the lack of understanding the mechanisms of fluid-rock interactions. The main objective of this study is to examine the potential and efficiency of low-salinity water in secondary and tertiary oil recovery for sandstone reservoirs. Similarly, this study aims to help in understanding the dominant mechanisms that aid in improving oil recovery by low-salinity waterflooding. Furthermore, the impact of cation type in injected brines on oil recovery was investigated. Coreflood experiments were conducted to determine the effect of water salinity and chemistry on oil recovery in the secondary and tertiary modes. The contact angle technique was used to study the impact of water salinity and composition on rock wettability. Moreover, the zeta potential at oil/brine and brine/rock interfaces was measured to explain the mechanism causing rock wettability alteration and improving oil recovery. Deionized water and different brines (from 500 to 174,000 mg/l), as well as single cation solutions were tested. Two types of crude oil with different properties and composition were used. Berea sandstone cores were utilized in the coreflood experiments. Coreflood tests indicated that injection of deionized water in the secondary mode resulted in significant oil recovery, up to 22% improvement, compared to seawater flooding. However, no more oil was recovered in the tertiary mode. In addition, injection of NaCl solution increased the oil recovery compared to injection of CaCl2 or MgCl2 at the same concentration. Contact angle results demonstrated that low-salinity water has an impact on the rock wettability; the more reduction in water salinity, the more a water-wet rock surface is produced. In addition, NaCl solutions made the rock more water-wet compared to CaCl2 or MgCl2 at the same concentration. Low-salinity water and NaCl solutions showed a highly negative charge at rock/brine and oil/brine interfaces by zeta potential measurements, which results in greater repulsive forces between the oil and rock surface. This leads to double-layer expansion and water-wet systems. These results demonstrate that the double-layer expansion is a primary mechanism of improving oil recovery when water chemical composition is manipulated.

The molecular structure and charge on solid surfaces in aqueous environments is of fundamental importance to various scientific research and applications, yet remain not sufficiently understood. The research herein uses sum frequency generation spectroscopy to reveal the molecular structure of the mineral and polymer surfaces, and also probes the water molecules near the charged aqueous interfaces to get information about the surface charge. The application of visible-infrared sum-frequency generation spectroscopy to polymer thin-films requires a careful interpretation of the results, as the electric field magnitude and phase at each interface must be determined in a manner that takes thin film interference effects into account. A straightforward method that has a concise analytic solution in the case of a single thin film that exhibits interference effects was proposed. This method enabled selective probing of transparent thin-films using sum frequency generation spectroscopy, hence eliminated the ambiguity of the contribution of signal from two interfaces. The method was then extended to multiple polarization schemes, enabling easier and more comprehensive study of the molecular orientation on thin-films. Nonlinear vibrational spectroscopy has also been used to study the temperature-dependent surface structure of polydimethylsiloxane when exposed to water and a perfluorinated hydrophobic liquid. Quantitative analysis of the methyl plane orientation was performed using a combination of vibrational peak ratios and peak amplitudes that enable proposed structures to be identified. For both environments, the tilt and twist of the methyl plane was found to increase with temperature in a reversible manner. This has been attributed to be a consequence of the backbone reorganization due to temperature-dependent density changes. At charged aqueous interfaces, the structure of water adjacent to solid interface is sensitive to the surface potential. As a result, close inspection of signals originating from these water molecules can be used to reveal the surface charge density. Nonlinear vibrational spectroscopy was used to monitor the water O-H stretching band over a temperature range of 10-75°C to account for the increase in surface potential from deprotonation. It has been demonstrated that the behavior at the silica surface is a balance between increasing surface charge, and a decreasing contribution of water molecules aligned by the surface charge. Together with a model that accounts for two different types of silanol sites, the change in enthalpy and entropy for deprotonation at each site were reported. The surface charge density of untreated polydimethylsiloxane surface in water with various ionic strengths was also determined. It was found that the surface charge could be explained with an ion adsorption model. A relationship between the surface potential and measured nonlinear optics response that is valid at high potentials and low ionic strength was proposed. Finally, a universal method was demonstrated to derive the surface potential with nonlinear optics by modulating the coherence length. / Graduate / 2022-09-07

The value of the surface charge density of polypropylene reported in literature has a three order of magnitude discrepancy. Nauruzbayeva et al report a 0.7nCcm−2 as the surface charge density of polypropylene as measured using the charge of electrified droplets[1]. Meagher and Craig reported result 111nCcm−2 as estimated by electric double layer theory from colloidal probe Atomic force microscopy (AFM) force spectroscopy [2]. We show that oxidation of hydrophobic surfaces as a potential mechanism in origin of these surface charges. Using colloidal probe AFM We measured the surface charge densities of Teflon AF, perfluorodecanethiol, Perfluorodecyltrichlorosilane(FDTS), Octadecyltrichlorosilane, polystyrene, and polypropylene. Also, The pH dependence of the surface charge density for FDTS was studied and it shows the behavior expected of a weak acid in response to pH. We suspect that the origin of the surface charges is mostly likely impurities or surface oxidation. We conclude that the electrometer and dispensed droplets approach cannot detect these charges because of the process of de-wetting all the surface be neutralized to maintain charge neutrality. This explanation supports Nauruzbayeva et al claims about surface bound charges[1].

No description available.

No description available.

Rare earth mineral recovery from alternative resources such as coal and coal byproducts is increasingly important to provide an opportunity for economic recovery from U.S. sources. Currently, China produces the majority of the 149,000 tons of rare earth elements used annually worldwide of which the U.S. imports 11% or around 16,000 tons. There are no significant mining operations producing rare earth elements in the U.S. However, there are many U.S. sources containing rare earth minerals such as monazite including heavy mineral sand and phosphate operations. Monazite mineral particles of a few microns have also been detected in Fire Clay seam coal. Preliminary attempts to concentrate the rare earth mineral using flotation test results indicated that monazite was floated together with carbonate minerals. The flotation chemistry of a monazite-carbonate mineral system has received limited attention by researchers. As such, a systematic study of monazite flotation chemistry was conducted and the results reported in this dissertation. The surface charging mechanisms of monazite in aqueous systems were studied using electrokinetic tests, solution equilibrium calculation, crystal structure analysis, and electrostatic model prediction. The surface charge of monazite was found to be developed by protonation/deprotonation reactions. In other words, the hydrogen and hydroxyl ions were potential determining ions instead of the lattice ions of monazite. Electrokinetic tests of natural monazite mineral showed that the isoelectric point (IEP) occurred at pH 6.0. Solution equilibrium calculation and electrostatic model predictions of cerium monazite (CePO4) yielded an IEP of pH 7.2. The discrepancy between the two IEP values may be due to the different REE composition and/or the amount of carbon dioxide dissolved in solution. A common collector used to produce a hydrophobic monazite surface is octanohydroxamic acid. Adsorption studies found multilayer formation of octanohydroxamic acid on monazite surfaces at pH values of 3.0, 6.0, and 9.0. A kinetic study showed that the maximum adsorption density and rate for below monolayer coverage occurred at a solution pH value of 9.0, which was attributed to the chemical reaction between octanohydroxamate species and surface active sites (e.g., REE(OH)2+). For beyond multilayer adsorption, maximum adsorption occurred at pH 11.0 due to the abundance of hydroxyl ions in solution. The contributing effect of hydroxyl ions was proven by titration tests and FTIR analyses. When calcium ions existed in solution, specific adsorption of Ca(OH)+ on monazite surfaces occurred in both neutral and basic environments as indicated by the electrokinetic results. At low concentrations, Ca(OH)+ competed with octanohydroxamic acid for P-OH sites. However, higher dosages of Ca(OH)+ served as active sites for octanohydroxamic acid. The monazite floatability was negatively affected by the hydration of the adsorbed calcium species. The calcium ion dissolved from calcite mineral surfaces, which exist in the coal sources, provided an explanation for the depression of monazite in the combined systems. Single mineral flotation of monazite and calcite showed that sodium silicate and sodium hexametaphosphate efficiently depressed calcite while providing minimal effects on monazite recovery. However, in the monazite-calcite combined system, both monazite and calcite were depressed using the two regulators. Electrokinetic data and solution equilibrium calculations indicated that hydrolyzed species of calcium such as Ca(OH)+ interacted with silicates and formed a compact hydrophilic layer on monazite surfaces by hydrogen bonding and surface reaction. The compact layer decreased collector adsorption due to steric hindrance. Using 6×10-5 M EDTA together with 2.5×10-4 M octanohydroxamic acid and 0.05 g/L sodium silicate, monazite recovery of more than 90% was achieved while only recovering 20% of calcite. Based on the fundamental study, rare earth concentrates with 4700 ppm of REEs were produced from the Fire Clay fine coal refuse using column flotation.

Titanium dioxide (TiO2) attracts extensive attention due to its widespread technological and environmental applications. This study seeks to investigate the surface charging behavior of the two TiO2 polymorphs, anatase and rutile, using Flow Adsorption Microcalorimetry (FAMC). FAMC allows direct quantitative measurement of the heat of a surface reaction; these calorimetric heats are directly proportional to the surface charge. Determining the magnitude of positive and negative charges at the surface over a range of pHs allows for the determination of the point of zero net charge (PZNC) via a unique calorimetric method that removes many of the shortcomings related to the other analytical techniques used for such measurements.

<p>Ferroelectric thin films (FETFs) offer a promising new platform for advancing liquid-phase interfacial sensing devices. FETFs are capable of expressing surface charge densities that are an order of magnitude higher than those of traditional charged surfaces in liquid environments (e.g., common oxides, self-assembled monolayers, or electrets). Furthermore, the switchable polarization state of FETFs enables patterning of charge-heterogeneous surfaces whose charge patterns persist over a range of environmental conditions. Integration of FETFs into liquid-phase interfacial sensing devices, however, requires the fabrication of films with nanometer-scale surface roughness, high remnant polarization values, and interfacial stability during prolonged exposure. The objectives of my research were to i) fabricate ferroelectric ultra-smooth lead zirconium titanate (US-PZT) thin films with nanometer-scale surface roughness, ii) establish the interfacial stability of these films after prolonged exposure to aqueous environments, iii) measure the interfacial forces as a function of film polarization and ionic strength, iv) calculate the surface potential of the US-PZT surface using electric double layer (EDL) theory, and v) demonstrate the guided deposition of charged colloidal particles onto locally polarized US-PZT thin films from solution. </p><p>I demonstrate the use of ferroelectric US-PZT thin films to manipulate EDL interaction forces in aqueous environments. My work conclusively shows that the polarization state of US-PZT controls EDL formation and can be used to induce the guided deposition of charged colloidal particles in solution. </p><p>I present a robust fabrication scheme for making ferroelectric US-PZT thin films from a sol-gel precursor. By optimizing critical thermal processing steps I am able to minimize the in-plane stress of the film and reliably produce US-PZT thin films on the wafer-scale with mean surface roughness values of only 2.4 nm over a 25 &#956;m2 area. I then establish US-PZT film stability in water by measuring changes in film topography, crystallinity, surface chemistry, and electrical properties as a function of exposure duration. My results show that fabrication of crack-free US-PZT thin film is critical for long-term film fidelity in aqueous environments. Furthermore, I found no change in film topography or bulk composition with increasing exposure duration. Prolonged exposure to aqueous environments, however, gradually oxidizes the surface of the US-PZT wich results in a decrease in film resistivity and polarization saturation. Next, I used colloidal probe force microscopy (CPFM) to measure the EDL interaction force as a function of separation distance between polarized US-PZT thin films and a clean borosilicate probe. CPFM measurements were performed on oppositely polarized US-PZT thin films, which expressed either a positive or negative surface charge, and over a range of ionic strengths. The inner-Helmholtz plane (IHP) potential of the US-PZT was determined by fitting the CPFM force-separation data to number of EDL models, including; an analytical EDL model using a constant potential boundary condition with a Stern layer, a charge regulation EDL model, and a numerical EDL model using the non-linear Poisson-Boltzmann equation. Each model provides good agreement with the experimentally measured and predict high IHP surface potential for the polarized US-PZT thin films in solution. Finally, I demonstrate the use of polarized US-PZT to induce the guided deposition of positively or negatively charged colloidal particles from aqueous environments. I explore the effects of ionic strength, particle size, surface roughness, and pH on particle deposition. </p><p>Overall, this work demonstrates, for the first time, that FETFs can be used as a platform to manipulate colloidal particles in aqueous environments. The experimental results demonstrate that the surface charge of the FETF is reduced by charge shielding and perform similarly to traditional, charged surfaces in aqueous environments.</p> / Dissertation