Browsing by Subject "nanoparticle"

Now showing 1 - 7 of 7
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    Aerosol Ion Mobility based Techniques for the Improved Analysis of Chemical Mixtures
    (2022-04) Lee, Jihyeon
    Particle and ion separations in the gas phase are typically based upon ion mobility (K), also often called the electrical mobility, or simply, the mobility. The mobility is the proportionality coefficient between the steady velocity a particle (charged) moves with and the magnitude of an applied external electric field driving motion. At low electric field strengths, particles are in thermal equilibrium with ambient gas molecules, and the mobility is a constant value independent of field strength. Under these conditions, the mobility is largely a function of particle size, and can be linked to particle diameter. Meanwhile, at high electric field, the translational kinetic energy of charged particles and ions exceeds the thermal energy of gas molecules, and this leads to deviations from thermal equilibrium. Under these conditions the mobility is a function of the field strength, specifically the ratio of the field strength to the gas number density (E/N). The goal of the studies described here was to exploit ion mobility measurement principles in numerous new ways, at both low and high field strengths, to develop particle analysis techniques amenable not only to aerosol particles, but also to particles from liquid suspensions introduced into the gas phase via sprays. The first portion of my dissertation research focuses on an air-jet nebulizer-IMS system consisting of a nanoparticle nebulizer (NPN), a differential mobility analyzer (DMA), and a condensation particle counter (CPC) for the size analysis of chemical mechanical planarization (CMP) slurries. For silica slurries, an air-jet nebulizer-IMS system showed better repeatability and capability for multimodal size distributions. For non-silica slurries, the air-jet nebulizer-IMS system, DLS, and EM differed from each other with peak size shifts of 10 nm or less. The second portion of my dissertation focuses on an IMS-IMS system consisting of two nano DMAs to examine vapor binding to protein molecules in the gas phase. These experiments were performed to determine if vapor binding, leading to mobility shifts, was vapor and protein specific, which would lead to expanded separation capabilities with IMS. In the experiments, the first DMA determined the mobility of protein ions at atmospheric pressure conditions and the second DMA examined shifts in their mobility after the introduction of condensable vapor molecules. It is found that low charge state protein ions adsorb water, nonane, and 1-butanol vapor molecules and the affinity of protein ions to nonane is shown to be higher than to butanol or water when - Köhler theory is applied to experimental results. The third portion of my dissertation research focuses on an IMS-DMS system consisting of a DMA and a field asymmetric ion mobility spectrometer (FAIMS). This system allows a tandem mobility analysis by separating ions both at low field limit and at high field limit. Importantly DMA-FAIMS analysis also enables determination of the actual mobility versus E/N function in a single system. This study also results in the realization of a DMA-FAIMS system and demonstrates the capability of separating ions with the same mobility; benefitting analysis methods in atmospheric new particle formation events and detection of pesticide volatility. The last portion of my dissertation focuses on a Langevin dynamics simulation of particulate film deposition with polydisperse and agglomerated particles. While distinct from the other studies in that it is numerical, the simulations depend upon modeling particle equations of motion, which are also the fundamental equations governing IMS separation. Simulation-deposited films are characterized based their porosities and pore size distributions which are incorporated into calculation of thermal conductivities. The results suggest that the pore size distribution is highly dependent on porosity regardless of other parameters and particle deposited films can achieve comparable thermal conductivities to conventional aerogels.
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    Bacterial Response to Nanoparticles at the Molecular Level
    (2018-05) Qiu, Tian
    Nanotechnology has been an emerging field due to the promising properties of engineered nanomaterials, materials with at least one dimension less than 100 nanometers. With increasing application of NPs, the risk of these novel materials to environment requires thorough investigation to prevent negative impacts. NPs have enormous variety due to combinations of chemical compositions, sizes, shapes, structures and surface modifications. Building predictive models that link NP properties to biological outcomes is the key to proactive safer NP design. High-throughput toxicity screening and investigating toxicity mechanisms are the common two strategies building towards predictive models of nanotoxicity. These two strategies work together: high-throughput assays facilitate preliminary screening of potentially toxic materials for further mechanistic studies to discover biomarkers and molecular pathways of interest, which will in turn be validated on multiple materials and organisms with high-throughput screening. My thesis work combines both strategies to develop high-throughput screening assays and mechanistic understanding at different molecular levels of how an environmental bacterium, Shewanella oneidensis MR-1, responds to various NP exposures. In this work, Chapter 1 reviews recent advances in analytical nanotoxicology and identifies four key areas that would further bring the field to its maturity. Chapter 2 represents a comprehensive mechanistic study on bacteria responding to TiO2 NPs with UVA illumination. Chapter 3 uses gene expression to explore molecular response among two organisms at different trophic levels to positively and negatively charged gold NPs. Chapter 4 identifies that purification method can be one neglected source of apparent NP toxicity. A high-throughput bacterial viability assay that is free of NP interference is presented in Chapter 5. Finally, in Chapter 6, DNA damage is revealed as a toxicity mechanism for nanoscale complex metal oxide nanomaterials to bacteria.
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    Interactions between Plasma and Liquid Micro-Droplets
    (2021-02) Nayak, Gaurav
    The interaction of plasmas with a liquid phase results into various complex multiphase phenomena that is beneficial for a wide range of applications, such as water treatment, nanoparticle synthesis, material processing, combustion, decontamination, food safety and human health care. These applications have been made possible due to the transferof highly reactive species from the gas phase plasma to the bulk liquid phase. Upon interaction with a liquid phase, atmospheric pressure non-equilibrium plasmas produce numerous chemically reactive species, including ions, radicals, electrons and (V)UV photons. The resulting short-lived highly reactive species can exhibit huge density gradients in the liquid phase as their finite lifetime does not allow them to penetrate into the bulk liquid. This makes the multiphase reactivity transfer highly transport limited. Additionally, the presence of electric field-induced effects, charging, evaporation and heat and mass transfer makes plasma-liquid interaction studies more challenging due to the lack of a detailed understanding of the inter-coupling of these phenomena and their direct impact on the plasma-produced reactive species fluxes to the liquid. To understand and overcome the challenge of transport limitations, a novel plasma-liquid configuration was developed, which involves plasma activation of small dispersed liquid droplets or aerosols. The key advantage of such a configuration is that the large surface-to-volume ratio of these micrometer-sized liquid droplets enhances the reactivity transfer from the gas phase plasma to the liquid phase. Since the droplets are immersed in the plasma, the short-lived reactive species (electrons, ions and radicals) produced in the gas phase plasma due to electron impact processes on average only need to cover smaller length scales to reach and subsequently penetrate the droplet. The foremost goal of the research reported in this thesis is the development of a controlled and well-defined plasma-microdroplet reactor, which is easy to model and experimentally accessible with different diagnostic techniques enabling to obtain quantitative measurements of reactive species densities. Due to the efficient generation of reactive species, a radiofrequency (RF)-driven capacitively coupled diffuse plasma generated in parallel-plate configuration at atmospheric pressure is used in this work. Complete characterization of the RF plasma is helpful for the assessment of the role of different gas-phase reactive species generated by the plasma and their respective fluxes to the liquid microdroplets in transit through the plasma. The reactive species potentially playing a key role in plasma-liquid interactions include electrons, OH radicals, H and O atoms, singlet oxygen, O3, He and Ar metastable atoms and molecules. The absolute densities of electrons and metastable atoms and molecules along with gas and electron temperatures that play a major role in plasma-induced chemistry in He and Ar plasmas were measured using optical emission and broadband absorption spectroscopy. We found that the densities of He and Ar metastables peaked near the sheath edges away from the droplet trajectory, while the densities in the bulk were below their respective detection limits. The Ar and He metastable fluxes to the droplet were found to be 2 orders of magnitude and 5 times smaller than the electron flux to droplet, respectively. Hence, the effect of Ar and He metastable atoms on the droplet chemistry can be considered negligible compared to charged species fluxes. However, these metastable species are an important source of ionization in such low electron density plasmas and play, nonetheless, a major role in the plasma dynamics including ionization processes and the generation of radicals in the gas phase. An understanding of the dynamics of liquid microdroplets in the plasma is important as it not only relays information about the residence time of the droplets in the plasma (i.e. treatment time of the solution by short-lived plasma-produced species) but also droplet charging and the presence of electric fields when entering and exiting the plasma. This residence time dictates the fate of the droplet chemistry and its interactions with the plasma. We characterized the droplet and its trajectory by fast frame imaging in diffuse He glow discharge. From the droplet velocity and acceleration data, the various forces acting on the droplet were evaluated. Using the equilibrium of forces and the droplet charge estimated from an analytical model, the electric field at the plasma edges was determined. We also report on the effect of the initial droplet acceleration during droplet ejection from the piezoelectric nozzle, the plasma composition (He with admixtures of Ar, H2O, H2 and O2), gas flow rate, and the plasma power on the droplet dynamics. Plasmas in or in contact with water have been extensively investigated in the context of plasma-aided decomposition and mineralization of recalcitrant organic pollutants in water for environmental remediation. However, plasma, while being highly effective, sometimes lacks energy efficiency. The water treatment is often due to the transfer of long-lived species into the liquid bulk and secondary reactions. Using the approach of microdroplets treated by plasma, the efficiency of plasma treatment of organics in liquid water microdroplets can be improved by increasing the species fluxes to the droplets. Using detailed plasma diagnostics, droplet characterization and ex situ chemical analysis of the treated droplets, we assessed the relative importance of short-lived radicals, such as O and H atoms, singlet oxygen, solvated electrons and ions, besides OH radicals, responsible for the decomposition of formate, a model organic compound inwater treatment studies, dissolved in droplets. We ascertained the role of OH and O radicals in electronegative plasmas. We also showed for electropositive plasmas that solvated electrons and/or ions injected into the droplet were dominantly responsible for plasma-induced chemistry in the droplet. Results suggested that the charged species lead to the formation of H or OH radicals near the droplet interface via secondary reactions, enabling further decomposition of formate in the droplets. The obtained results allowed us to estimate minimum values of transport properties of O in solution and reaction rates of O radical with formate using a one-dimensional reaction-diffusion model. Gold and silver nanoparticles (AuNP and AgNP) exhibit unique optical, electrical, and thermal properties, and can be synthesized by plasmas in a green and environmentally friendly approach without the use of hazardous chemicals, and without producing harmful byproducts. Previously, researchers have established unprecedented gold ions reduction synthesis rates in liquid droplets treated by an RF plasma to synthesize AuNPs. The reported reduction rates are several orders of magnitude larger than for any other reported electron-initiated methods. The mechanism for the synthesis of nanoparticles using this approach is still largely unknown. Using the known gas-phase plasma properties, absorption spectroscopy, and transmission electron microscopy (TEM), we identified the role of hydrogen peroxide in the reduction of gold ions. On the other hand, the reported results for AgNP formation from Ag ions in the same reactor, suggested that the effect of solvated electrons and H radicals were dominant for the reduction of silver ions. We also demonstrate the possibility to use plasma-droplet interactions for the synthesis of surfactant-free, spherical and crystalline Au and AgNPs without the use of any stabilizer(s) within a few milliseconds. In view of the recent COVID-19 pandemic caused by the airborne transmission of SARS-CoV-2 virus aerosols, many excellent surveillance and control measures are being implemented in conned spaces, where the effect of the virus transmission is the highest. The application of plasma-aided virus disinfection is quite nascent, and the interaction of plasma with the virus aerosols in air streams has not been dealt with in detail. The actual mechanism for the virus inactivation is often ascribed to ozone, however, in short time scales of milliseconds, more reactive species might be needed to obtain an effective inactivation. We report on the use of a dielectric barrier discharge (DBD) for in-flight inactivation of airborne aerosolized porcine reproductive and respiratory syndrome (PRRS) virus. The measurements were performed in a laboratory-scale wind test tunnel. Using infectivity tests and reverse transcriptase quantitative polymerase chain reaction (RT-qPCR), we showed a 3.5 log10 reduction in the viable virus titer during in-flight treatment by the DBD within a few milliseconds. We identified both short-lived species such as OH radicals and singlet oxygen and peroxynitrous acid chemistry at low pH in the virus-laden droplets responsible for the observed inactivation of virus aerosols by plasma. The fundamental understanding of the interactions of plasma and liquid microdroplets, gained in this work, have the potential to increase significantly the efficacy of plasma processes. There is no doubt that improved reactor design and plasma generation informed by our findings will further advance the development of such unique interactions for the novel applications of water treatment, nanoparticle synthesis and virus aerosol inactivation.
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    Manganese doped silica nanoparticles for acidic pH responsive TLR7 agonist delivery
    (2021-01) Dong, Fangyi
    Imiquimod is a Toll-like receptor 7 (TLR7) agonist approved for treating genital warts and actinic keratoses and has demonstrated promise as an anticancer vaccine adjuvant. However, as a small molecule, imiquimod suffers from poor pharmacokinetic properties that result in sub-optimal therapeutic activity and raise the risk of systemic side effects. Delivery systems such as nanoparticles could help improve the delivery of imiquimod to the target site and avoid undesirable side effects. Mesoporous silica nanoparticles (MSN) possess excellent chemical stability, high drug loading capacity, and a size range appropriate for imiquimod delivery. However, the inert nature of -Si-O – bonds in MSN limits its biodegradability. Previous studies have reported that doping manganese (Mn) ions endow acidic pH responsive degradation and drug release from MSN. Since TLR7 is located in the acidic endosomes of dendritic cells, pH responsiveness could significantly improve immune response and mitigate side effects of imiquimod. In the current study, PEGylated manganese doped silica nanoparticles (PEG-MnMSN) demonstrated good biocompatibility and excellent (41.96%) imiquimod encapsulation efficiency. The PEG-MnMSN also showed pH-responsive drug release, with a greater fraction of the encapsulated drug released in acidic pH (5.5) than at physiologic pH (7.4). Overall, our studies suggest PEG-MnMSN’s have exciting potential as a carrier for imiquimod-based cancer immunotherapy.
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    Measurement and Control of Occupational Exposure to Engineered Nanoparticles
    (2017-12) Thompson, Drew
    This dissertation consists of three studies concerning the measurement and control of inhalation exposure to engineered nanoparticles in the workplace. A key component in evaluating the potential health risks posed by nanomaterials is understanding how a worker may be exposed to airborne engineered nanoparticles. This information is not only needed for establishing safer nanomaterial work practices, toxicology studies also require doses which are relevant to actual workplace exposure. Emission monitoring and exposure assessments were conducted in nanotechnology workplaces in an effort to answer these questions. In Chapter 2, the synthesis of silicon carbide (SiC) nanoparticles in a prototype inductively coupled thermal plasma reactor and other supporting processes, such as the handling of precursor material, the collection of nanoparticles, and the cleaning of equipment, were monitored for particle emissions and potential worker exposure. The purpose of this study was to evaluate the effectiveness of engineering controls and best practice guidelines developed for the production and handling of nanoparticles, identify processes which result in a nanoparticle release, characterize these releases, and suggest possible administrative or engineering controls which may eliminate or control the exposure source. No particle release was detected during the synthesis and collection of SiC nanoparticles and the cleaning of the reactor. This was attributed to most of these processes occurring in closed systems operated at slight negative pressure. Other tasks occurring in more open spaces, such as the disconnection of a filter assembly from the reactor system and the use of compressed air for the cleaning of filters which collected synthesized SiC nanoparticles, resulted in releases of submicrometer particles with a mode size of ~ 170 – 180 nm. Observation of filter samples under scanning electron microscope confirmed that the particles were agglomerates of SiC nanoparticles. In Chapter 3, results are presented from an assessment of potential exposure to multi-walled carbon nanotubes (MWCNTs) conducted at an industrial facility where polymer nanocomposites were manufactured by an extrusion process. Recent animal studies have shown that carbon nanotubes (CNTs) may pose a significant health risk to those exposed in the workplace. To further understand this potential risk, effort must be taken to measure the occupational exposure to CNTs. Exposure to MWCNTs was quantified by the thermal-optical analysis for elemental carbon (EC) of respirable dust collected by personal sampling. All personal respirable samples collected (n = 8) had estimated 8-hour time weighted average (TWA) EC concentrations below the limit of detection for the analysis, and about one half the recommended exposure limit for CNTs of 1 µg EC/m3 as an 8-hour TWA respirable mass concentration. Potential exposure sources were identified and characterized by direct-reading instruments and area sampling. Area samples analyzed for EC yielded quantifiable mass concentrations inside an enclosure where unbound MWCNTs were handled and near a pelletizer where nanocomposite was cut, while those analyzed by electron microscopy detected the presence of MWCNTs at six locations throughout the facility. Through size selective area sampling, it was found that the airborne MWCNTs present in the workplace were in the form of large agglomerates. This was confirmed by electron microscopy, where most of the MWCNT structures observed were in the form of micrometer-sized, ropey agglomerates. However, a small fraction of single, free MWCNTs was also observed. It was found that the high number concentrations of nanoparticles, approximately 200,000 particles/cm3, present in the manufacturing facility were likely attributable to polymer fumes produced in the extrusion process. Chapter 4 details the development of a theoretical model to predict the filtration efficiency of electret filter media. Electret filters are filters whose fibers are semi-permanently charged. This charge results in electrostatic interactions between particles and fibers which can increase filtration efficiency without increasing the pressure drop across the filter, thus making electret media well-suited for use in local exhaust ventilation and respiratory protection. The numerical results were used to develop surrogate models which considered a random fiber orientation, filter solidity, particle interception, and dielectrophoretic, image, and Coulomb forces. The mean error of predicted single fiber efficiencies for the surrogate models of charged and uncharged particles were 6% and 0.8%, respectively. Aerosol penetration estimated by the surrogate models for a best fit effective surface charge density were compared to experimentally evaluated electret filters. Coefficients of determination for the fitted effective surface charge densities ranged from 0.82 to 0.98 and the effective surface charge densities were comparable to values reported in the literature.
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    Polymer Reservoirs to Solubilize Hydrophobic Drugs
    (2018-08) Li, Ziang
    Research and development of new drug delivery formulations for hydrophobic drugs hold great promise for patients worldwide in the ever-growing pharmaceutical industry. A large portion of the drugs, both in the current market and the development pipeline, suffer from low aqueous solubility, therefore limiting their efficacy for oral administration. One effective way to resolve this problem is the use of an amorphous solid dispersion (ASD), a blend of drug and polymer. An ideal polymer candidate can kinetically stabilize the dispersed drug in its amorphous form in the solid state, while enhancing drug solubility and dissolution in the solution state. Despite recent advances in polymer development for oral drug delivery, the structure-property relationships and the underlying solubility enhancement mechanisms are not fully understood for ASDs. The goals of this dissertation are to develop effective polymers for oral drug delivery, and more importantly, to elucidate the mechanism(s) of drug solubility and dissolution enhancement by using well-defined polymer platforms. Specifically, three model systems were designed and synthesized, including blends of a commercially available polymer and self-assembled micelles in Chapter 3, micelle-forming statistical copolymers and diblock polymers in Chapter 4, and chemically crosslinked polymer nanogels in Chapter 5. It was observed universally in all these three systems that hydrophobic drugs can be sequestered in the slightly hydrophobic polymer reservoirs, and that the drug-polymer partitioning is stronger when the polymer chains are more crowded. The partitioning inhibits drug nucleation and crystal growth in aqueous solution, resulting in enhanced drug solubility. This mechanism is supported by a battery of state-of-the-art characterization experiments, including light scattering, nuclear Overhauser effect and diffusion ordered spectroscopy, cryogenic transmission electron microscopy, small-angle X-ray scattering, and in vitro dissolution tests. Potential applications of the discovered mechanism and the characterization experiments to other drug/polymer systems are discussed as future directions.
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    Structure-Property Relationships Of Nanostructured Materials For Electrochemical And Thermal Energy Storage Applications
    (2020-05) Tran, Nam
    Advance materials with nanostructure provide unique features to design a safe and efficient energy conversion and storage systems. In this thesis, the synthesis, characterization, and optimization of novel materials for electrical energy storage and thermal energy storage are explored. The first part of the thesis focuses on novel cathode materials, Li8ZrO6, for lithium-ion batteries. A synthesis method using pyrolysis of inorganic and organic precursors was utilized to prepare a nanostructured Li8ZrO6/C composite. The composite contained micron-sized particles of active material Li8ZrO6 in intimate contact of conductive carbon phase. The grain size of Li8ZrO6 was further reduced to below 50 nm using ball-milling approach. The composite can be used to make an electrode directly without any additional conductive phase. A new battery- testing program was developed to electrochemically and reversibly remove/re-insert up to 3 Li per formula unit of Li8ZrO6. A specific capacity of 221 mAh/g (corresponding to removal of 2 Li/f.u.) and 331 mAh/g (3 Li/f.u.) with 100% Coulombic efficiency were maintained for 140 cycles and 15 cycles, respectively. The structural change at different states of charge was predicted using quantum mechanical calculations and experimentally supported by XRD, XPS, and PDF data. Lithium intercalation (up to 2.5 Li/f.u.) of Li8ZrO6 followed a reversible path and lattice oxygen atoms were involved in the redox reaction during the charge/discharge processes. The effects of transition metals doping on bulk Li8ZrO6 were also investigated. The second part of the thesis describes the one-pot synthesis and properties of phase change material composites consisting of metal nanoparticles embedded in a mesoporous carbon network. The melting temperature, particle size, and the amount of energy stored/released was controlled by varying the loading of metals in the composite. The melting temperature of Bi metal nanoparticles in the composite can be tuned to 33 °C below the melting point of bulk metal. The specific enthalpies and the associated phase change temperatures of the metal nanoparticles were maintained over multiple melting/recrystallization cycles. The mesoporous carbon network prevented nanoparticles aggregation during and after the phase change and acted as a container to offset volume expansion of the metal during the melting process. The composites are stable in a sealed container for at least 11 months.