Matching Items (6)
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- All Subjects: Nanoparticles
- Creators: Lind, Mary Laura
Description
Gold-silver alloy nanoparticles (NPs) capped with adenosine 5'-triphosphate were synthesized by borohydride reduction of dilute aqueous metal precursors. High-resolution transmission electron microscopy showed the as-synthesized particles to be spherical with average diameters ~4 nm. Optical properties were measured by UV-Visible spectroscopy (UV-Vis), and the formation of alloy NPs was verified across all gold:silver ratios by a linear shift in the plasmon band maxima against alloy composition. The molar absorptivities of the NPs decreased non-linearly with increasing gold content from 2.0 x 108 M-1 cm-1 (fÉmax = 404 nm) for pure silver to 4.1 x 107 M-1 cm-1 (fÉmax = 511 nm) for pure gold. The NPs were immobilized onto transparent indium-tin oxide composite electrodes using layer-by-layer (LbL) deposition with poly(diallyldimethylammonium) acting as a cationic binder. The UV-Vis absorbance of the LbL film was used to calculate the surface coverage of alloy NPs on the electrode. Typical preparations had average NP surface coverages of 2.8 x 10-13 mol NPs/cm2 (~5% of cubic closest packing) with saturated films reaching ~20% of ccp for single-layer preparations (1.0 ~ 10-12 mol NPs/cm2). X-ray photoelectron spectroscopy confirmed the presence of alloy NPs in the LbL film and showed silver enrichment of the NP surfaces by ~9%. Irreversible oxidative dissolution (dealloying) of the less noble silver atoms from the NPs on LbL electrodes was performed by cyclic voltammetry (CV) in sulfuric acid. Alloy NPs with higher gold content required larger overpotentials for silver dealloying. Dealloying of the more-noble gold atoms from the alloy NPs was also achieved by CV in sodium chloride. The silver was oxidized first to cohesive silver chloride, and then gold dealloyed to soluble HAuCl4- at higher potentials. Silver oxidation was inhibited during the first oxidative scan, but subsequent cycles showed typical, reversible silver-to-silver chloride voltammetry. The potentials for both silver oxidation and gold dealloying also shifted to more oxidizing potentials with increasing gold content, and both processes converged for alloy NPs with >60% gold content. Charge-mediated electrochemistry of silver NPs immobilized in LbL films, using Fc(meOH) as the charge carrier, showed that 67% of the NPs were electrochemically inactive.
ContributorsStarr, Christopher A (Author) / Buttry, Daniel A (Thesis advisor) / Petuskey, William (Committee member) / Jones, Anne (Committee member) / Arizona State University (Publisher)
Created2014
Description
Environmentally responsive microgels have drawn significant attention due to their intrinsic ability to change volume in response to various external stimuli such as pH, temperature, osmotic pressure, or electric and magnetic fields. The extent of particle swelling is controlled by the nature of the polymer-solvent interaction. This thesis focuses on design and synthesis of environmentally responsive microgels and their composites, and encompasses methods of utilizing microgel systems in applications as vehicles for the adsorption, retention, and targeted delivery of chemical species. Furthermore, self-assembled microgel particles at ionic liquid (IL)-water interfaces demonstrate responsive colloidal lattice morphology. The thesis first reports on the fundamental aspects of synthesis, functionalization, and characteristic properties of multifunctional environmentally responsive microgels derived from poly(N-isopropylacrylamide) (PNIPAm) and other functional co-monomers. In particular, the uptake and release of active chemical species such as rheology modifiers into and from these ionic microgels is demonstrated. Moreover, a facile tunable method for the formation of organic-inorganic composites with Fe3O4 nanoparticles adsorbed and embedded within ionic microgel particles is explored. Additionally, the development of zwitterionic microgels (ZI-MG) is presented. These aqueous ZI-MG dispersions exhibit reversible parabolic swelling as a function of pH and display a minimum hydrodynamic diameter at a tunable isoelectric point (IEP). This study also elucidates the controlled uptake and release of surfactants from these particle systems. The extent of surfactant loading and the ensuing relative swelling/deswelling behaviors within the polymer networks are explained in terms of their binding interactions. The latter part of this thesis highlights the versatility of fluorescently labeled microgel particles as stabilizers for IL-water droplets. When the prepared particles form monolayers and equilibrate at the liquid-liquid interface, the colloidal lattice organization may re-order itself depending on the surface charge of these particles. Finally, it is shown that the spontaneously formed and densely packed layers of microgel particles can be employed for extraction applications, as the interface remains permeable to small active species.
ContributorsChen, Haobo (Author) / Dai, Lenore L (Committee member) / Chen, Kangping (Committee member) / Forzani, Erica (Committee member) / Lind, Mary Laura (Committee member) / Mu, Bin (Committee member) / Arizona State University (Publisher)
Created2015
Description
The overall goal of this project is to use metallic nanoparticles to develop a thin, ductile amorphous film at room temperature. Currently bulk metallic glasses are mainly formed via quenching, which requires very high cooling rates to achieve an amorphous molecular structure. These formations often fail in a brittle manner. The advantages of using a bottom-up approach with amorphous nanoparticles at ambient conditions is that the ductility of the metal can be improved, and the process will be less energy intensive. The nanoparticles used are iron precursors with ATMP and DTPMP ligand stabilizers and dispersed in methanol. Three forms of experimentation were applied over the course of this project. The first was a simple, preliminary data collection approach where the particles were dispersed onto a glass slide and left to dry under various conditions. The second method was hypersonic particle deposition, which accelerated the particles to high speeds and bombarded onto a glass or silicon substrate. The third method used Langmuir-Blodgett concepts and equipment to make a film. Qualitative analyses were used to determine the efficacy of each approach, including SEM imaging. In the end, none of the approaches proved successful. The first approach showed inconsistencies in the film formation and aggregation of the particles. The results from the hypersonic particle deposition technique showed that not enough particles were deposited to make a consistent film, and many of the particles that were able to be deposited were aggregated. The Langmuir-Blodgett method showed potential, but aggregation of the particles and uneven film formation were challenges here as well. Although there are ways the three discussed experimental approaches could be optimized, the next best step is to try completely new approaches, such as convective assembly and 3D printing to form the ideal nanoparticle film.
ContributorsKline, Katelyn Ann (Author) / Lind, Mary Laura (Thesis director) / Cay, Pinar (Committee member) / Chemical Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2016-12
Description
One of the grand challenges of engineering is to provide access to clean water because it is predicted that by 2025 more than two thirds of the world’s population will face severe water shortages. To combat this global issue, our lab focuses on creating a novel composite membrane to recover potable water from waste. For use as the water-selective component in this membrane design Linde Type A zeolites were synthesized for optimal size without the use of a template. Current template-free synthesis of zeolite LTA produces particles that are too large for our application therefore the particle size was reduced in this study to reduce fouling of the membrane while also investigating the nanoparticle synthesis mechanisms. The time and temperature of the reaction and the aging of the precursor gel were systematically modified and observed to determine the optimal conditions for producing the particles. Scanning electron microscopy, x-ray diffraction, and energy dispersive x-ray analysis were used for characterization. Sub-micron sized particles were synthesized at 2 weeks aging time at -8°C with an average size of 0.6 micrometers, a size suitable for our membrane. There is a limit to the posterity and uniformity of particles produced from modifying the reaction time and temperature. All results follow general crystallization theory. Longer aging produced smaller particles, consistent with nucleation theory. Spinodal decomposition is predicted to affect nucleation clustering during aging due to the temperature scheme. Efforts will be made to shorten the effective aging time and these particles will eventually be incorporated into our mixed matrix osmosis membrane.
ContributorsKing, Julia Ann (Author) / Lind, Mary Laura (Thesis director) / Durgun, Pinar Cay (Committee member) / Chemical Engineering Program (Contributor) / Materials Science and Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2016-05
Description
Neurological disorders are difficult to treat with current drug delivery methods due to their inefficiency and the lack of knowledge of the mechanisms behind drug delivery across the blood brain barrier (BBB). Nanoparticles (NPs) are a promising drug delivery method due to their biocompatibility and ability to be modified by cell penetrating peptides, such as transactivating transciptor (TAT) peptide, which has been shown to increase efficiency of delivery. There are multiple proposed mechanisms of TAT-mediated delivery that also have size restrictions on the molecules that can undergo each BBB crossing mechanism. The effect of nanoparticle size on TAT-mediated delivery in vivo is an important aspect to research in order to better understand the delivery mechanisms and to create more efficient NPs. NPs called FluoSpheres are used because they come in defined diameters unlike polymeric NPs that have a broad distribution of diameters. Both modified and unmodified 100nm and 200nm NPs were able to bypass the BBB and were seen in the brain, spinal cord, liver, and spleen using confocal microscopy and a biodistribution study. Statistically significant differences in delivery rate of the different sized NPs or between TAT-modified and unmodified NPs were not found. Therefore in future work a larger range of diameter size will be evaluated. Also the unmodified NPs will be conjugated with scrambled peptide to ensure that both unmodified and TAT-modified NPs are prepared in identical fashion to better understand the role of size on TAT targeting. Although all the NPs were able to bypass the BBB, future work will hopefully provide a better representation of how NP size effects the rate of TAT-mediated delivery to the CNS.
ContributorsCeton, Ricki Ronea (Author) / Stabenfeldt, Sarah (Thesis director) / Sirianni, Rachael (Committee member) / Harrington Bioengineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2016-05
Description
Water-soluble, adenosine triphosphate (ATP)-stabilized palladium nanoparticles have been synthesized by reduction of palladium salt in the presence of excess ATP. They have been characterized by electron microscopy, energy dispersive X-ray spectroscopy, ultraviolet-visible (UV-Vis) spectroscopy, and X-ray diffraction in order to determine particle size, shape, composition and crystal structure. The particles were then subsequently attached to a glassy carbon electrode (GCE) in order to explore their electrochemical properties with regard to hydrogen insertion in 1 M sodium hydroxide. The particles were found to be in the size range 2.5 to 4 nm with good size dispersion. The ATP capping ligand allowed the particles to be air-stable and re-dissolved without agglomeration. It was found that the NPs could be firmly attached to the working electrode via cycling the voltage repeatedly in a NP/phosphate solution. Further electrochemical experiments were conducted to investigate the adsorption and absorption of hydrogen in the NPs in 1 M sodium hydroxide. Results for cyclic voltammetry experiments were consistent with those for nanostructured and thin-film palladium in basic solution. Absorbed hydrogen content was analyzed as a function of potential. The maximum hydrogen:Pd ratio was found to be ~0.7, close the theoretical maximum value for β phase palladium hydride.
ContributorsLamb, Timothy (Author) / Buttry, Daniel A (Thesis advisor) / Yarger, Jeffery (Committee member) / Ros, Alexandra (Committee member) / Arizona State University (Publisher)
Created2013