Browsing by Subject "Nanoparticle"
Now showing 1 - 20 of 41
Results Per Page
Sort Options
Item A Big Response to a ?Small? Problem: Identifying the Oxidative Potential of Nanomaterials and the Physicochemical Characteristics That Play a Role(2012-02-14) Berg, James MichaelNanotechnology as a science is emerging rapidly. As materials are synthesized and utilized at the nanometer size scale, concerns of potential health and safety effects are arising. In an effort to elucidate the physicochemical characteristics of nanoparticles influential in toxicological studies, surface properties of metal oxide and carbonaceous nanoparticles were measured. These properties include zeta potential, dissolution and surface-bound chemical components. Subsequently, the role of these properties in oxidative stress was examined in vitro. This work identifies the influence that pH has on the zeta potential of nanoparticles. The zeta potential has the ability to alter colloidal stability, as the largest nanoparticle agglomerate is seen at or near the isoelectric point for each of the particles tested. Furthermore, it was observed that metal oxide nanoparticles which exhibit a charged surface at physiological pH, lead to decreased in vitro cellular viability as compared to those that were neutral. Thus, nanoparticle zeta potential may be an important factor to consider when attempting to predict nanoparticle toxicity. Real world exposure to nanoparticles is a mixture of various particulates and organics. Therefore, to simulate this particle mixture, iron oxide (Fe2O3) and engineered carbon black (ECB) were utilized in combination to identify potential synergistic reactions. Following in vitro exposure, both nanoparticle types are internalized into endosomes, where liberated Fe3+ reacts with hydroquinone moieties on the ECB surface yielding Fe2+. This bioavailable iron may then generate oxidative stress through intracellular pathways including the Fenton reaction. As oxidative stress is common in particulate toxicology, a comparison between the antioxidant defenses of epithelial (A549) and mesothelial (MeT-5A) cell lines was made. The A549 cell line exhibits alterations in the NRF2-KEAP1 transcription factor system and therefore retains high basal levels of phase II antioxidants. Both cell types were exposed to 33 nm silica where intracellular oxidant generation coupled with markers of oxidative stress were observed. While the MeT-5A cells exhibited a decrease in cell viability, the A549 cell line did not. Therefore, proper characterization of both material and biological systems prior to toxicity testing will help to further define the risks associated with the use of nanotechnology.Item Application of enzymatic catalysis and galvanic processes for biosensor development(2011-08) Zaccheo, Brian Andrew; Crooks, Richard M. (Richard McConnell); Browning, Karen; Hoffman, David; Johnston, Keith P.; Stevenson, KeithMethods for integrating enzyme systems with electrochemical reactions having applications to diagnostic sensing are described. Diagnostic tests that include biological molecules can be classified as biosensors. Existing testing methods often require trained technicians to perform, and laboratory settings with complex infrastructure. The theme of this dissertation is the development of methods that are faster, easier to use, and more applicable for non-laboratory environments. These goals are accomplished in systems using enzymatic catalysis and galvanic processes. Two biosensors with specific model pathologies have been designed and demonstrated in this study. The first assay senses a DNA fragment representing the Epstein Barr virus and uses enzyme-mediated Ag deposition over a v microfabricated chip. The chip contains a specially designed pair of electrodes in an interdigitated array (IDA). Detection is signaled by a change in the resistance between the two electrodes. The second biosensor discussed in this study is targeted towards the digestive enzyme trypsin. It is selfpowered due to its construction within an open-circuit galvanic cell. In this system, a small volume of blood serum is introduced onto the device over barriers made of protein and Al that block the anode from solution. In the presence of trypsin, the protein gel is rendered more permeable to sodium hydroxide. Adding hydroxide initiates the dissolution of the Al layer, closing the cell circuit and illuminating a light-emitting diode (LED). A relationship was observed between LED illumination time and trypsin concentration. Biosensors that utilize enzymes to generate or amplify a detectable signal are widely used, and the final project of this study uses a nanoparticle based approach to protect the catalytic activity of alkaline phosphatase (AlkP) from hostile chemicals. By incubating Au colloid with AlkP overnight and adding Ag+, core@shell nanoparticles of Au@Ag2O can be isolated that show AlkP activity. The resulting enzyme-metal composite material was analytically characterized and demonstrated greater activity in the presence of organic inhibitors relative to either wild type vi or Au colloid-associated AlkP without the Ag2O shell. The stabilization procedure is complete in one day using a onepot synthesis. This method may provide opportunities to carry out biosensing chemistry in previously incompatible chemical environments.Item The application of light trapping structures and of InGaAs/GaAs quantum wells and quantum dots to improving the performance of single-junction GaAs solar cells(2012-05) McPheeters, Claiborne Ott; Yu, Edward T.; Alu, Andrea; Bank, Seth R.; Chen, Ray T.; Zhang, John X.High efficiency photovoltaic solar cells are expected to continue to be important for a variety of terrestrial and space power applications. Solar cells made of optically thick materials often cannot meet the cost, efficiency, or physical requirements for specialized applications and, increasingly, for traditional applications. This dissertation investigates improving the performance of single-junction GaAs solar cells by incorporating InGaAs/GaAs quantum wells and quantum dots to increase their spectral response bandwidth, and by incorporating structures that confine light in the devices to improve their absorption of it. InGaAs/GaAs quantum dots-in-wells extend the response of GaAs homojunction devices to wavelengths >1200 nm. Nanoparticles that are randomly deposited on the top of optically thick devices scatter light into waveguide modes of the device structures, increasing their absorption of electromagnetic energy and improving their short-circuit current by up to 16%. Multiply periodic diffractive structures have been optimized using rigorous software algorithms and fabricated on the back sides of thin film quantum dot-in-well solar cells, improving their spectral response at wavelengths 850 nm to 1200 nm, where only the quantum dot-in-well structures absorb light, by factors of up to 10. The improvement results from coupling of diffracted light to waveguide modes of the thin film device structure, and from Fabry-Perot interference effects. Simulations of absorption in these device structures corroborate the measured results and indicate that quantum well solar cells of ~2 µm in thickness, and which are equipped with optimized backside gratings, can achieve 1 Sun Airmass 0 short-circuit current densities of up to ~5 mA/cm2 (15%) greater than GaAs homojunction devices, and of up to >2 mA/cm2 (7%) greater than quantum well devices, with planar back reflectors. A combination of Fabry-Perot interference and diffraction into waveguide modes of the thin devices is shown to dominate the simulated device response spectra. Simulations also demonstrate the importance of low-loss metals for realizing optimal light trapping structures. Such device geometries are promising for reducing the cost of high efficiency solar cells that may be suitable for a variety of traditional and emerging applications.Item Calculations of oxygen reduction reaction on nanoparticles(2010-05) Tang, Wenjie, 1982-; Henkelman, Graeme; Crooks, Richard M.; Rossky, Peter J.; Makarov, Dmitrii E.; Mullins, C. B.Proton exchange membrane fuel cells are attractive power sources because they are highly efficient and do not pollute the environment. However, the use of Pt-based catalysts in present fuel cell technologies is not optimal: Pt is rare and expensive, and even the best commercial Pt cathodes have high overpotentials due to slow oxygen reduction kinetics. As a result, much effort has gone toward developing cheaper, more effective catalysts. Nanoparticles are attractive because they have different catalytic properties than analogous bulk systems, require less material, and have tunable reactivities based on their composition and size. It is important to perform detailed studies of nanoparticle catalysts since composition and size effects are poorly understood. Computational simulations of such materials can provide useful insights and potentially aid in the design of new catalysts. Here, I examine composition and size effects in nanoparticle catalysts using computational methods. Two bimetallic systems are investigated to explore composition effects: Pd-shell particles with several different core metals, and Pd/Cu random alloy particles. Depending on how the two metals are mixed (core-shell or random alloy), charge transfer and strain due to alloying are found to have different contributions to the catalytic activity. Size effects are studied for pure Pt particles, where corner and edge sites are found to play an important role. The binding geometries of molecular oxygen to corner and edge sites lead to peroxide formation instead of water on small Pt particles. Results form these calculations can provide useful information for designing novel catalysts in the future. By changing the composition and/or size of nanoparticles in the proper way, the interaction between the adsorbate and catalyst can be optimized, and better catalysts can be obtained.Item Catalytic Nanoparticle Additives in the Combustion of AP/HTPB Composite Solid Propellant(2012-02-14) Kreitz, Kevin R.Presented in this thesis is a study of the effects of nano-sized particles used as a catalytic additive in composite solid propellant. This study was done with titanium oxide (titania)-based particles, but much of the findings and theory are applicable to any metal oxide produced by a similar method. The process required for efficiently producing larger batches of nanoparticle additives was seen to have a significant impact on the effectiveness of the additive to modify the burning rate of composite propellant consisting of ammonium perchlorate (AP) and hydroxyl terminated polybutadiene (HTPB). Specifically, titania was seen to be both an effective and ineffective burning rate modifier depending on how the nanoparticle additive was dried and subsequently heat treated. Nanoadditives were produced by various synthesis methods and tested in composite propellant consisting of 80 percent AP. Processability and scale-up effects are examined in selecting ideal synthesis methods of nanoscale titanium oxide for use as a burning rate modifier in composite propellant. Sintering of spray-dried additive agglomerates during the heat-treating process was shown to make the agglomerates difficult to break up during mixing and hinder the dispersion of the additive in the propellant. A link between additive processing, agglomerate dispersion mechanics and ultimately catalytic effect on the burning rate of AP/HTPB propellants has been developed by the theories presented in this thesis. This thesis studies the interaction between additive dispersion and the dispersion of reactions created by using fine AP in multimodal propellants. A limit in dispersion with powder additives was seen to cause the titania catalyst to be less effective in propellants containing fine AP. A new method for incorporating metal oxide nanoadditives into composite propellant with very high dispersion by suspending the additive material in the propellant binder is introduced. This new method has produced increases in burning rate of 50 to 60 percent over baseline propellants. This thesis reviews these studies with a particular focus on the application and scale-up of these nanoparticle additives to implement these additives in actual motor propellants and assesses many of the current problems and difficulties that hinder the nanoadditives? true potential in composite propellant.Item Characterization of dendrimer encapsulated nanoparticles by extended x-ray absorption fine structure and electrochemical methods(2011-12) Myers, Vera Sue; Crooks, Richard M. (Richard McConnell)The small size regime and bulky hydrocarbon exterior of dendrimer encapsulated nanoparticles (DENs) often make characterization of these materials a unique challenge. Here, I report on three studies utilizing the techniques of extended X-ray absorption fine structure (EXAFS) and electrochemistry to probe the properties and behavior of these materials. First, the synthesis and characterization of PdCu bimetallic nanoparticles, and Pd and Cu monometallic nanoparticles, consisting of an average of ~64 atoms is described. The bimetallic nanoparticles were prepared by co-complexation of Pd²⁺ and Cu²⁺ salts to interior functional groups of a dendrimer template followed by chemical reduction to yield DENs. EXAFS spectroscopy indicates that these particles have an alloy structure. This is a rare example of a stable nanoparticle in this size range that consists of one reactive metal and one substantially more noble metal. Second, in-situ electrochemical EXAFS is used to evaluate the structure of Pt DENs during the oxygen reduction reaction (ORR). The DENs contained an average of just 225 atoms each. The results indicate that the Pt coordination number (CN) decreases when the electrode potential is moved to positive values. The results are interpreted in terms of an ordered core, disordered shell model. The structure of the DENs is not significantly impacted by the presence of dioxygen, but other electrogenerated species may have a significant impact on nanoparticle structure. Third, the electrochemical dissolution of Cu DENs is investigated using anodic stripping voltammetry (ASV). The effect of the scan rate and Cu loading on the electrode to the stripping wave is performed. The results indicate a large, positive shift of the stripping potential for the dendrimer-metal composites, but no size-dependent changes to peak position.Item Characterization of thin film properties of melamine based dendrimer nanoparticles(Texas A&M University, 2005-02-17) Boo, Woong JaeWith the given information that dendrimers have precisely controlled their sizes and spherical structures in the molecular level, the aim of this study is to show that dendrimer particles can become ordered into a self-assembled regular structure due to the nature of their regular sizes and shapes. For this project, melamine based generation 3 dendrimer was used for solution cast of thin films from the dendrimer-chloroform solutions with different casting conditions, i.e. various solution concentrations, casting temperatures, and substrates. As a result of these experiments, unique phenomena of highly ordered uniform 2-D contraction separations were observed during the solvent evaporation from the dendrimer films. The cast films from the concentration of 0.8 wt% and higher exhibit regular 2-D separation contraction patterns and make well-developed regularly arrayed structures due to the interaction between the contraction stresses and adhesion strength between films and substrates. From the DSC tests, both powder and cast film samples of a dendrimer show similar melting behaviors with different areas under the melting peaks. The results of these tests show that dendrimers, when they are in a descent environment that provides dendrimers with molecular mobility due to surface ionic bonding strength, can make a structural order and regularity in their macroscopic structures.Item Compressibility of nanoparticle stabilized foams for foamed cement applications(2014-12) Salas Porras, Ricardo Federico; Bryant, Steven L.; Bommer, Paul MichaelFoamed cement is widely used in the oil and gas industry to provide zonal isolation. Foamed cement provides various advantages vs. pure cement. The primary purpose of foamed cement is to reduce the density of the cement mixture. Consequently, foamed cement can be used in weak formations were reduced exerted hydrostatic pressure is needed to prevent/control cement circulation loss into the formation. However, Due to gas compressibility, foamed cement’s gas injection rate has to be constantly adjusted in order to create a constant density slurry through the height of the cement column. Furthermore, foamed cement’s properties include higher ductility, constant pressure exertion to the formation during cement transition time (gelling) and lower thermal conductivity. The ability of solid silica nanoparticles to generate stable gas/water foams was researched for foamed cement applications. Solid nanoparticles have been shown to permanently stabilize foams by assembling into layers at the gas/water interface. A potential decrease in compressibility of the gas phase by the presence of these armoring bubble layers was investigated. Enhancement of cement’s splitting tensile strength and compressive strength by silica nanoparticles was also investigated. The addition of uncoated silica nanoparticles at various concentrations did not appear to enhance neither cement’s splitting tensile or compressive strength. In most tests with varying silica nanoparticles concentrations, the samples with nanoparticles exhibited a slightly reduced splitting tensile and compressive strength. The exception being the compressive strength of the samples mixed with the highest nanoparticle concentration tested. However, the strength improvement was small vs. its pure cement counterpart. An apparatus to test the compressibility of nanoparticle stabilized foams was built for this research. The functionality of the apparatus was validated using various test fluids. The validation process allowed for the establishment of a compressibility benchmark to compare the compressibility of nanoparticle stabilized foams. A vital conclusion of this process was that generating the particle stabilized foams under pressure would allow for greater discernment between the existence of the armored bubble effect and gas dissolution into the water phase. A type of nanoparticle was identified as having the capacity to generate long term stable foams without the need of surfactant. Partially hydrophobic surface treated silica nanoparticles were utilized to generate gas/water foams under pressure and subsequently their compressibility was measured. The compressibility of these foams did not appear to show the armored bubble effect behaving as an equivalent ideal gas + water mixture. An additional surfactant and particle stabilized foam recipe was tested and displayed the same results. It was concluded that either the particle layers were not fully forming in the foam or in the case they were forming; either foam geometry was not conductive to the distribution of forces or they likely had limited rigidity and buckled when compressed. If the latter was true, the apparatus was not sensible enough to measure the limited rigidity.Item Design of nanocomposites for electrocatalysis and energy storage : metal/metal oxide nanoparticles on carbon supports(2012-08) Slanac, Daniel Adam; Johnston, Keith P., 1955-; Stevenson, Keith J.; Mullins, Charles C.; Korgel, Brian A.; Ferreira, Paulo J.Controlling catalyst morphology and composition are required to make meaningful structure-activity/stability relationships for the design of future catalysts. Herein, we have employed strategies of presynthesis and infusion or electroless deposition to achieve exquisite control over catalyst composite morphology. The oxygen reduction (ORR) and the oxygen evolution reactions (OER) were chosen as model systems, as their slow kinetics is a major limiting factor preventing the commercialization of fuel cells and rechargeable metal air batteries. In acid, bimetallic (Pt-Cu, Pd-Pt) and monometallic (Pt) catalysts were presynthesized in the presence of capping ligands. Well alloyed Pt-Cu nanoparticles (3-5 nm) adsorbed on graphitic mesoporous carbon (GMC) displayed an ORR activity >4x that of commercial Pt. For both presynthesized Pt and Pt-Cu nanocrystals on GMC, no activity loss was also observed during degradation cycling due to strong metal-support interactions and the oxidation resistance of graphitic carbon. Similar strong metal-support interactions were achieved on non-graphitic carbon for Pd3Pt2 (<4 nm) nanoparticles due to disorder in the metal surface This led to enhanced mass activity 1.8x versus pure Pt, as well as improved stability. For basic electrolytes, we developed an electroless co-deposition scheme to deposit Ag (3 nm) next to MnOx nanodomains on carbon. We achieved a mass activity for Ag-MnOx/VC, 3x beyond the linear combination of pure component activities due to ensemble effects, where Ag and MnOx domains catalyze different ORR steps, and ligand effects from the unique electronic interaction at the Ag-MnOx interface. Activity synergy was also shown for Ag-Pd alloys (~5 nm), achieving up to 5x activity on a Pd basis, resulting from the unique alloy surface of single Pd atoms surrounded by Ag. Lastly, we combined arrested growth of amorphous nanoparticles with thin film freezing to create a high surface area, pure phase perovskite aggregate of nanoparticles after calcination. Sintering was mitigated during the high temperature calcination required to form the perovskite crystals. The high surface areas and phase purity led to OER mass activities ~2.5x higher than the benchmark IrO2 catalyst.Item Determining arrangements of optically bound nanoparticle clusters in three dimensions in a Gaussian beam standing wave optical trap(2015-08) Grimm, Philipp Martin; Florin, Ernst-Ludwig; Fink, ManfredThe invention of optical tweezers in 1986 has enabled controlled trapping and manipulating of dielectric particles in the microscopic and nanoscopic regime. More recently, using a specialized optical trap, a novel ultra-strong particle-particle interaction, based on scattered fields and induced dipoles was discovered, namely lateral optical binding. It can be used to achieve self-assembly of nanoparticles into contactless clusters with stable configurations. Experiments have shown that coupling of these clusters to the external electromagnetic field depends on the cluster geometry. The observation was attributed to asymmetries in cluster constituents, such as different particle radii, but a simultaneous experimental observation of cluster geometry and particle radii remained challenging. In this thesis a new method is introduced which measures simultaneously the configuration of a pair of optically bound nanoparticles in three dimensions as well as the ratio of particle radii. This ratio is approximated in two different ways, by analyzing the particle widths in darkfield microscopy images and by analyzing the power of the light scattered from the nanospheres. After validating the procedure and data evaluation for a single immobilized bead it was applied to optically bound particle pairs in a Gaussian beam standing wave optical trap. Both particle size estimations provide similar results. It can be concluded that the difference in brightness observed for distinct nanoparticles originates from a difference in their radii and not from their relative displacements along the optical axis. Nevertheless, two particles with significant difference in radius tend to assemble at slightly different axial positions. This deviation from ideal lateral optical binding may cause additional geometry dependency on the coupling of the cluster to the external optical field and should be included into simulations on optical binding dynamics. Finally, an astonishing symmetry break even for particle pairs with similar radii was observed. The center of mass of these clusters shows a shift a few times as large as the exciting wavelength and particle separation distance away from the trap center to a new, well-defined equilibrium position. This observation challenges the current theoretical explanation of the lateral shifts which requires an asymmetry in the cluster constituents.Item Evaluation of Alpha-Phased Zirconium Phosphate Nanoparticles as a Clay Stabilizer and an EOR Agent(2014-12-15) Zhou, YiFines migration, which is the detachment and movement of fines from sand surfaces, leads to the plugging of throats in porous media and becomes an important reason for formation damage. Enhanced Oil Recovery (EOR) is the technique to extract more oil after secondary recovery. Nanoparticles are used as clay stabilizers and EOR agent because of their very small size, large surface area, and surface electrical charge. In this paper, an ?-ZrP nanoparticle-based treatment is developed to prevent fines migration in sandstone formations and recovery more oil in carbonate. To test the ability of ?-ZrP nanofluids as a clay stabilizer, coreflood tests were conducted using alpha phased zirconium phosphate based nanofluids as a clay stabilizer with Berea sandstone cores (6 in. in length, 1.5 in. in diameter) under a pressure of 1000 psi and temperature of 300?F. In these experiments, ?-ZrP nanofluids were injected at concentrations of 0.1, 0.5, and 1.0 wt% at a flow rate of 2 cm^3/min. Both DI water and brine were used as diluting agents. After each treatment, a post-flush of fresh water was applied. The pressure drop across the core was measured, the core effluent samples were collected, and the permeability changes were calculated. Also, the surface tensions and viscosities of the treatment fluids were measured. Lab results indicated that ?-ZrP nanofluid mitigated fines migration in Berea sandstone up to 300?F. Because fresh water tends to cause formation damages, nanoparticles diluted with brine showed less permeability change than those diluted with DI water. The best treatment we had was the ?-ZrP nanofluid diluted with brine (5 wt% KCl) at a concentration of 0.5 wt%. To use ?-ZrP nanofluids as an EOR agent, Indiana limestone core was pre-flushed with brine, and then saturated with oil (dodecane). In addition, brine was injected again with different flow rates of 0.5, 1.0 and 2.0 cm^3/min for about 5 PV each. After that, 1 PV of EOR agent was injected at 0.5 cm3/min from bottom to top. A post-flush of brine was applied and the effluents were collected to find out the total oil recovered. The test result gave a 13.68% oil recovery in the EOR stage. The alpha-phased zirconium phosphate nanofluids had never been applied before for subsurface use. It was discussed as an clay stabilizer and EOR agent in this study. This work provides new insights into the application of nanoparticles in the oil and gas industry.Item Experimental measurement of sweep efficiency during multi-phase displacement in the presence of nanoparticles(2013-05) Aminzadeh Goharrizi, Behdad; DiCarlo, David Anthony, 1969-The efficiency of one fluid displacing another in permeable media depends greatly on the pore-scale dynamics at the main wetting front. Experiments have shown that the frontal dynamics can result in two different flow regimes: a stable and an unstable front. In stable displacements, any perturbation of the front will diminish with time and the effect of variation in permeability will be lessened. In contrast, in unstable displacements any perturbation of the front will grow with time and any variation in permeability will be magnified. In this dissertation, the stability of two different displacement processes are contemplated; a) vertical infiltration of dense liquid into dry sand from above and b) horizontal displacement of nanoparticle suspension with high pressure liquid CO₂. Significant insights are obtained by measuring the in-situ flow patterns in real time with a light transmission method and CT scanning. Vertical infiltration of dense fluid into dry sands from above is often observed to be unstable and produce gravity driven fingers. The formation of gravity fingers can have large consequences on the sweep efficiency of a displacement. Infiltration experiments showed that gravity driven fingers have a unique saturation profile known as saturation overshoot with a higher saturation at the finger tips than the saturation at the finger tail. Despite the vast number of theoretical and experimental investigations, conditions under which the front is unstable, remain unclear. To determine what controls the saturation overshoot and how it relates to the dynamics at the initial wetting front, saturation overshoot was measured as a function of flux for seven different liquids. These liquids gave a range of molecular weights, viscosities, and vapor pressures. It is found that for each fluid there is a flux (called overshoot flux) below which saturation overshoot ceases and the front is diffuse. The magnitude of the overshoot flux depends inversely on the invading fluid's viscosity and shows little or no dependence on the invading fluid's surface tension, vapor pressure, or miscibility with water. Since the saturation overshoot is not described by the continuum multi-phase flow models, the experimental results are used to develop a semi-continuum model that bridges the continuum-scale and pore-scale physics. The proposed model predicts the observed dependence of overshoot on media permeability and invading fluid properties. At the planned depth for CO₂ injection, either as an enhanced oil recovery technique or for CO₂ storage, CO₂ is typically less dense and less viscous than the in-situ fluid. Therefore, CO₂ injection is unstable and produces viscous fingers. This can greatly reduce the efficiency of a CO₂ flood or CO₂ storage capacity of an aquifer. To remedy this behavior, surface treated nanoparticles were used to reduce the mobility of injected CO₂. Displacement experiments were performed at low pressure with a CO₂ analogue (n-octane) fluid and at high pressure with liquid CO₂. Saturation distributions and pressure drops were measured in real time with the CT scanner when high pressure liquid CO₂ or n-octane was used to displace brine in different cores with and without suspended nanoparticles. In the presence of nanoparticles, the displacement front is more spatially uniform with a later breakthrough compared to the same experiment with no suspended nanoparticles. These observations suggest that nanoparticle stabilized foam, which forms during the displacement, acts to suppress the instability. It is argued that the generation of droplets occurs at the leading front of all drainage displacements. In the presence of nanoparticles, these droplets are preserved when nanoparticle adhere at the fluid-fluid interface. The new mechanism for foam generation described here, provides an interesting alternative for mobility control in CO₂ floods. Moreover, the same mechanism can potentially a) increase the CO₂ storage capacity of an aquifer, b) enhance the CO₂ capillary trapping, and c) provide an engineered barrier to CO₂ leakage from a storage sites, thereby alleviating the risk of contaminating the overlying fresh groundwater resources for CO₂ storage projects.Item Generation, stability, and transport of nanoparticle-stabilized oil-in-water emulsions in porous media(2014-05) Gabel, Scott Thomas; Bryant, Steven L.; Huh, ChunThe ability of nanoparticles to stabilize oil/water emulsions provides many interesting opportunities for the petroleum industry. Emulsions can be used as a displacing fluid for enhanced oil recovery to improve sweep efficiencies. Emulsions can be used to improve conformance control by effectively blocking thief zones in reservoirs with a high degree of heterogeneity. As shown in this thesis emulsions can be used to deliver fluids that contact and mobilize residual oil. It is imperative to understand emulsion behavior in porous media for design purposes in enhanced or improved oil recovery processes involving emulsions. Nanoparticle-stabilized oil-in-water emulsions were continuously generated by co-injecting aqueous nanoparticle dispersion and oil through a beadpack. There exists a critical shear rate below which a stable emulsion will not be generated. The critical shear rate increased with decreasing bead size. Above the critical shear rate, the droplet size of the generated emulsion was a function of shear rate and decreased with increasing shear rate. The stable emulsions were characterized by their droplet size and rheology. The emulsion viscosity was highly dependent upon droplet size and not the bulk oil viscosity in the emulsion. The emulsions were highly shear thinning and emulsions with smaller droplets were more viscous than emulsions with larger droplets. Highly stable emulsions that were generated by co-injection were collected, separated from excess phase(s) and injected into beadpacks. In most experiments the injected emulsion coalesced into the bulk fluids. Whether the bulk fluids generated a new emulsion in the bead pack depended on the shear rate, bead size, and initial saturation of the beadpack. Different beadpack experiments showed the transition from one flow regime to a second flow regime as the slow movement of a coalescence/regeneration front propagated through the beadpack. Coreflood experiments confirmed the mechanisms hypothesized for the beadpack emulsion injection experiments. When a stable emulsion was injected the effluent emulsion rheology and droplet size were altered solely as a result of being forced through sandstone cores, not because of fluids contacted within the core. The shear rate controlled whether the emulsion coalesced and produced no effluent emulsion, regenerated into an emulsion with larger droplets, or regenerated into an emulsion with smaller droplets. Oil recovery experiments showed that nanoparticle-stabilized oil-in-water emulsion increased the recovery of oil compared to a waterflood for cores with immobile and mobile oil. The mechanism is the coalesced oil droplets form a flowing phase that is miscible with oil present in the core and thus achieves a much more efficient displacement. The possible continuous generation and coalescence of droplets may have increased the apparent viscosity, improving the sweep efficiency of the emulsion injection. A novel oil recovery mechanism was shown in imbibition experiments where nanoparticle dispersion was used to displace oil. Large shear rates coupled with the affinity for nanoparticles at the oil water interface enabled residual oil to be mobilized, or for residual oil blobs to spawn smaller droplets that are stabilized by the nanoparticles and thus can be transported with the dispersion through the core.Item Heterogeneous or Competitive Self-Assembly at Liquid-Liquid Interfaces(Texas Tech University, 2009-08) Luo, Mingxiang; Dai, Lenore L.; Simon, Sindee L.; Hase, William L.; Vaughn, Mark W.; Khare, RajeshSelf-assembly of nano-sized objects at liquid-liquid interfaces is of tremendous interest for various natural and industrial applications. For example, surfactant interfacial self-assembly is critical in numerous processes such as lubrication, detergency, biological transferring, and polymer processing. On the other hand, self-assembled nanoparticles at liquid-liquid interfaces serve as building blocks for bottom-up assembly of new functional materials with unique physical properties. However, many industrial processes are performed in the presence of both surfactants and nanoparticles. In spite of the importance, interfacial adsorption when a system contains both surfactants and colloidal particles has not been extensively studied. In particular, there is a limited understanding when nanoparticles are involved. In this dissertation, I have performed molecular dynamics simulations and some experimental work to study the heterogeneous or competitive self-assembly of surfactants and nanoparticles at water-trichloroethylene (TCE) interfaces. Interfacial structures, morphology, dynamics properties, and the influences of surfactant and nanoparticle assembly on interfacial properties were studied. I also included some preliminary study on hybrid organic-inorganic solar cells, in which the self-assembly of polymers and nanoparticles in the bulk solution and at liquid-solid interfaces is considered to be critical in film morphology. Polymer-fullerene bulk heterojunctions (BHJs) are currently the most efficient combination for organic solar cells; however, the efficiency is not good. One of the promising approaches to improve device efficiency is to use semiconductor nanocrystals as electron acceptor or alkyl thiols as co-solvent. Hybrid polymer-inorganic nanocrystal composites offer an attractive means to combine the merits of polymer and inorganic nanocrystals to achieve higher power conversion efficiency. This study focuses on integrating ZnO and CdSe nanocrystals or 1-octadecanethiol (ODT) into P3HT: PCBM BHJs to improve photovoltaic performance under ambient conditions. The preliminary results reveal that both CdSe and ODT under optimum conditions provided significant enhancement on power conversion efficiency compared with pure organic composites; however, ZnO failed to improve the device performance.Item Localized surface plasmon resonance spectroscopy of gold and silver nanoparticles and plasmon enhanced fluorescence(2011-12) Vokac, Elizabeth Anne; Willets, Katherine A.; Brodbelt, Jennifer S.This thesis presents spectroscopic studies of metallic nanoparticle localized surface plasmons and plasmon enhanced fluorescence. We investigated the dielectric sensitivity of silver nanoprisms to an external electric field and gold nanorods to the formation of a self-assembled surface monolayer. Dark field microscopy was used to image plasmonic scattering from single nanoparticles, and a liquid crystal tunable filter was used to construct corresponding spectra. The plasmon resonances of silver nanoprisms displayed both reversible red shifts and irreversible blue shifts along with drastic intensity changes upon exposure to an applied bias. The plasmon resonances of gold nanorods showed sensitivity to the presence of alkanethiol molecules adhered to the particle surface by a moderate red shift. An increase in the effective external dielectric caused a shift toward longer wavelengths. We imaged plasmon enhanced fluorescence in order to optimize experimental parameters for a developing project that can characterize nanoparticle structure on sub-wavelength dimensions. Preliminary controls were performed to account for the effect of O₂ plasma treatment, solvent and alkanethiol monolayer formation on surface plasmon resonances. We found that O₂ plasma treatment for different time intervals did not result in a plasmon shift compared to untreated nanoparticles exposed to N₂; however when exposed to solvent the surface plasmons of the treated particles shifted five times as far toward the red. Interestingly, the solvent effect only resulted in a plasmon shift when the particles were N₂ dried after solvent incubation. Gold nanorods incubated in ethanol showed no wavelength maximum shift in pure solvent over time, but shifted moderately to the red after incubation in a solution of alkanethiol molecules. Conditions for the plasmon enhanced fluorescence study were optimized using a dye conjugate of the same alkanethiol molecule used previously by formation from solution in a monolayer on the gold nanorod surface. The appropriate synthesis for dye functionalization, molecular concentrations, solvents and optical settings were determined.Item Magnetic induction heating of superparamagnetic nanoparticles for applications in the energy industry(2012-12) Davidson, Andrew Marshall; Bryant, Steven L.; Huh, ChunA novel method of delivering thermal energy efficiently for flow assurance and for improved heavy oil production/transport is described. The method, an improved form of magnetic induction heating, uses superparamagnetic nanoparticles that generate heat locally when exposed to a high frequency magnetic field oscillation, via a process known as Neel relaxation. This concept is currently used in biomedicine to locally heat and ablate cancerous tissues. Dependence of the rate of heat generation by commercially available, single-domain Fe3O4 nanoparticles of ~10 nm size, on the magnetic field strength and frequency was quantified. Experiments were conducted for nanoparticles dispersed in water, in hydrocarbon liquid, and embedded in a thin, solid film dubbed “nanopaint”. For a stationary fluid heat generation increases linearly with loading of nanoparticles. The rate of heat transfer from the nanopaint to a flowing fluid was up to three times greater than the heat transfer rate to a static fluid. Dispersion models indicated that the thermal conductivity of the dispersing fluid did not greatly influence the heat transfer results, whereas differences in size between hydrophilic and hydrophobic nanoparticles did. The model of static fluid in a nanopainted tube verified that the nanoparticle loading in the paint was ~30wt% and the nanopaint thickness was 600 µm. The model of flowing fluid in a nanopainted tube showed that internal mixing in the system, even at laminar flow rates, improved heat transfer to the center of the flowing fluid. A waveguide model verified the feasibility of using steel hydrocarbon transport pipelines as a means to guide electromagnetic energy to target heating locations along the pipeline if the energy is transmitted at frequencies above the cutoff frequency. Heating of nanopaint with external magnetic field application has immediate potential impact on oil and gas sector, because such coating could be applied to inner surfaces of pipelines and production facilities. A nanoparticle dispersion could also be injected into the reservoir zone or gravel pack near the production well, so that a thin, adsorbed layer of nanoparticles is created on pore walls. With localized inductive heating of those surfaces, hydrate formation or wax deposition could be prevented; and heavy oil production/transport could be improved by creating a ‘slippage layer’ on rock pore walls and inner surfaces of transport pipes.Item Magneto-plasmonic nanoparticle platform for detection of rare cells and cell therapy(2014-08) Wu, Chun-Hsien, active 21st century; Sokolov, Konstantin V. (Associate professor); Dunn, Andrew; Emelianov, Stanislav; Yeh, Hsin-Chih; Zal, TomaszMagnetic and plasmonic properties combined in a single nanostructure provide a synergy that is advantageous in a number of biomedical applications, such as contrast enhancement in multimodal imaging, simultaneous capture and detection of circulating tumor cells, and photothermal therapy of cancer. These applications have stimulated significant interest in development of magneto-plasmonic nanoparticles with optical absorbance in the near-infrared region and a strong magnetic moment. In this dissertation, we addressed this need to create a novel immunotargeted magneto-plasmonic nanoparticle platform. The nanostructures were synthetized by self-assembly of primary 6 nm iron oxide core-gold shell particles, resulting in densely packed spherical nanoclusters. The close proximity of the primary particles in the nanoclusters generates a greatly improved response to an external magnetic field and strong near-infrared plasmon resonances. A procedure for antibody conjugation and PEGylation to the hybrid nanoparticles was developed for biomedical applications which require molecular and biocompatible targeting. Furthermore, we presented two biomedical applications based on the immunotargeted hybrid nanoparticle platform, including circulating tumor cell (CTC) detection and cell-based immunotherapy of cancer. In the CTC detection assays, rare cancer cells were specifically targeted by antibody-conjugated nanoparticles and efficiently separated from normal blood cells by a magnetic force in a microfluidic chamber. The experiments in whole blood showed capture efficiency greater than 90% for a variety of cancers. We also explored photoacoustic imaging to detect nanoparticle-labeled CTCs in whole blood. The results showed excellent sensitivity to delineate the distribution of hybrid nanoparticles on the cancer cells. Thus, these works paves the way for a novel CTC detection approach which utilizes immunotargeted magneto-plasmonic nanoclusters for a simultaneous magnetic capture and photoacoustic detection of CTCs. In another application, we introduced a novel approach to label cytotoxic T cells using the magnetic nanoparticles with an expectation to enhance T cell recruitment in tumor under external magnetic stimulus. A series of in vitro experiments demonstrated highly controllable manipulation of labeled T cells. Thus, these results highlight the promise of using our nanoparticle platform as a multifunctional probe to manipulate and track immune cells in vivo and further improve the efficacy of cell-based cancer immunotherapy.Item Metal-polymer nanoparticulate systems for externally-controlled delivery(2010-12) Gran, Martin Luke; Peppas, Nicholas A., 1948-; Paul, Donald R.; Freeman, Benny D.; Johnston, Keith P.; Emelianov, StanislavMetal-polymer nanocomposites consisting of gold nanorods and temperature-responsive hydrogel nanoparticulates were investigated for use in externally-controlled drug delivery systems. Several different thermo-responsive hydrogels including poly(N-isopropyl acrylamide) (PNIPAAm) and poly(N-isopropryl acrylamide-co-acrylic acid) (P(NIPAAm-co-AA)) nanoparticles were synthesized for these nanocomposites using an aqueous dispersion polymerization method. In addition, nanoparticles of interpenetrating polymer networks (IPN) composed of poly(acrylamide) (PAAm) and poly(acrylic acid) (PAA) were synthesized using a water-in-oil emulsion polymerization. Temperature-responsive equilibrium swelling behavior of nanoparticles with varying crosslinking densities was characterized using dynamic light scattering. IPN systems exhibited a positive swelling response upon heating while PNIPAAm and copolymer systems collapsed upon increase in temperature above the transition point. Nanoparticles were characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) which demonstrated shape and morphology of polymer particles. Gold-polymer nanocomposites were formed by grafting gold nanorods to the surface of the polymer nanoparticles. Amine-functionalized gold nanorods were coupled to polymers using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) and N-hydroxysulfosuccinimide (Sulfo-NHS) to activate carboxyl groups on the surface of the polymer nanoparticles. TEM confirmed successful formation of the metal-polymer nanocomposites. Loading and release of a model therapeutic were done to assess the potential use of the polymer component of the nanocomposite for drug delivery. Fluorescein, a model for chemotherapeutics, was loaded into P(NIPAAm-co-AA) polymer nanoparticulates. Loading of the compound was shown to be a function of crosslinking density in the polymer network. Maximum loading was achieved using nanoparticles synthesized with a 10 mol% crosslinker feed ratio with entrapment efficiencies of 80.0 % and loading capacities of 12.0 %. Cytotoxicity studies were performed using a NIH/3T3 mouse fibroblast cell model. Cell viabilities in presence of P(NIPAAm-co-AA) nanoparticles were comparable to (not statistically different than) controls at concentrations up to 4 mg/ml. Similarly, gold-polymer composite concentrations up to 0.5 mg/ml caused limited cell death.Item Modeling of nanoparticle transport in porous media(2012-08) Zhang, Tiantian; Bryant, Steven L.; Huh, Chun; Delshad, Mojdeh; Prodanovic, Masa; Johnston, Keith P.The unique properties of engineered nanoparticles have many potential applications in oil reservoirs, e.g., as emulsion stabilizers for enhanced oil recovery, or as nano-sensors for reservoir characterization. Long-distance propagation (>100 m) is a prerequisite for many of these applications. With diameters between 10 to 100 nanometers, nanoparticles can easily pass through typical pore throats in reservoirs, but physicochemical interaction between nanoparticles and pore walls may still lead to significant retention. A model that accounts for the key mechanisms of nanoparticle transport and retention is essential for design purposes. In this dissertation, interactions are analyzed between nanoparticles and solid surface for their effects on nanoparticle deposition during transport with single-phase flow. The analysis suggests that the DLVO theory cannot explain the low retention concentration of nanoparticles during transport in saturated porous media. Moreover, the hydrodynamic forces are not strong enough for nanoparticle removal from rough surface. Based on different filtration mechanisms, various continuum transport models are formulated and used to simulate our nanoparticle transport experiments through water-saturated sandpacks and consolidated cores. Every model is tested on an extensive set of experimental data collected by Yu (2012) and Murphy (2012). The data enable a rigorous validation of a model. For a set of experiments injecting the same kind of nanoparticle, the deposition rate coefficients in the model are obtained by history matching of one effluent concentration history. With simple assumptions, the same coefficients are used by the model to predict the effluent histories of other experiments when experimental conditions are varied. Compared to experimental results, colloid filtration model fails to predict normalized effluent concentrations that approach unity, and the kinetic Langmuir model is inconsistent with non-zero nanoparticle retention after postflush. The two-step model, two-rate model and two-site model all have both reversible and irreversible adsorptions and can generate effluent histories similar to experimental data. However, the two-step model built based on interaction energy curve fails to fit the experimental effluent histories with delay in the leading edge but no delay in the trailing edge. The two-rate model with constant retardation factor shows a big failure in capturing the dependence of nanoparticle breakthrough delay on flow velocity and injection concentration. With independent reversible and irreversible adsorption sites the two-site model has capability to capture most features of nanoparticle transport in water-saturated porous media. For a given kind of nanoparticles, it can fit one experimental effluent history and predict others successfully with varied experimental conditions. Some deviations exist between model prediction and experimental data with pump stop and very low injection concentration (0.1 wt%). More detailed analysis of nanoparticle adsorption capacity in water-saturated sandpacks reveals that the measured irreversible adsorption capacity is always less than 35% of monolayer packing density. Generally, its value increases with higher injection concentration and lower flow velocities. Reinjection experiments suggest that the irreversible adsorption capacity has fixed value with constant injection rate and dispersion concentration, but it becomes larger if reinjection occurs with larger concentration or smaller flow rate.Item Modeling of recovery process characterization using magnetic nanoparticles(2013-12) Rahmani, Amir Reza; Bryant, Steven L.; Huh, ChunStable dispersions of magnetic nanoparticles that are already in use in biomedicine as image-enhancing agents, also have potential use in subsurface applications. Surface-coated nanoparticles are capable of flowing through micron-size pores across long distances in a reservoir with modest retention in rock. Tracing these contrast agents using the current electromagnetic tomography technology could potentially help track the flood-front in waterflood and EOR processes and characterize the reservoir. The electromagnetic (EM) tomography used in the petroleum industry today is based on the difference between the electrical conductivity of reservoir fluids as well as other subsurface entities. The magnetic nanoparticles that are considered in this study, however, change the magnetic permeability of the flooded region, which is a novel application of the existing EM tomography technology. As the first fundamental step, the magnetic permeability change in rock due to injecting magnetic nanoparticles is quantified as a function of particle and reservoir properties. Subsequently, a new formulation is devised to compute the sensitivity of magnetic measurements to magnetic permeability perturbations. The results are then compared with the sensitivity to conductivity perturbations to identify the application space of magnetic contrast agents. Using numerical simulations, the progress of magnetic nanoparticle bank is monitored in the reservoir through time-lapse magnetic tomography measurements that are expected. Initially, simple models for displacement of injection banks are assumed and the level of complexity is gradually increased to incorporate the realities of fluid flow in the reservoir. The fluid-flow behavior of the nanoparticles is dynamically integrated with time-lapse magnetic response. Since the nanoparticles could help illuminate the flow paths, they could be used to indirectly measure reservoir heterogeneities. Therefore, numerous case studies are demonstrated where reservoir heterogeneity could potentially be inferred. Finally, fundamental pore-scale models are developed as a first step towards the multiple fluid phases extension of the EM tomography application. Using magnetic nanoparticles to improve electromagnetic tomography provides several strategic advantages. One key advantage is that the magnetic nanoparticles provide high resolution measurements at very low frequencies where the conductivity contrast is hardly detectable and casing effect is manageable. In addition, the sensitivity of magnetic measurements at the early stages of the flood is significantly improved with magnetic nanoparticles. Moreover, the vertical resolution of magnetic measurements is significantly enhanced with magnetic nanoparticles present in the vicinity of source or receiver. The fact that the progress of the magnetic slug can be detected at very early stages of the flood, that the traveling slug’s vertical boundaries can be identified at low frequencies, that the reservoir heterogeneities could potentially be characterized, and that the magnetic nanoparticles can be sensed much before the actual arrival of the slug at the observer well, provides significant value of using magnetic contrast agents for reservoir illumination.
- «
- 1 (current)
- 2
- 3
- »