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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
71

The electrogenerated chemiluminescence of highly fluorescent organic chromophores and nanoparticles

Omer, Khalid Mohammad 27 August 2010 (has links)
Electrogenerated chemiluminescence (ECL) of new, highly fluorescent molecules was studied. Six novel, highly fluorescent, green emitters were synthesized by incorporating an acceptor group like 2,1,3-Benzothiadiazole between different donor groups. The structural effects on the electrochemical, spectroscopic, and ECL behavior are shown in detail. Stable electrochemistry and high PL quantum yield were observed. Most of the ECL was visible by the naked eye. Well-known, fluorescent, polyaromatic hydrocarbons (PAH), like 9,10-diphenylanthracene derivatives, pyrene, and anthracene were incorporated between two bulky fluorene derivative groups. The fluorene substitutions block the active positions of the PAH cores, permitting the formation of stable radical ions upon electrochemical oxidation or reduction. Such a tailoring led to increase electrochemical reversibility and tuning of the ECL wavelength. Fluorene-based DPA (FDF) is characterized by a highly efficient and stable blue-cyan color. Another interesting type of molecules was star-shaped structures. The effects of structure on the electrochemistry and spectroscopy of a series of star-shaped, rigid molecules was examined. T1-T4 is composed of oligofluorene arms with truxene as a central core basically there were weak donor and weak acceptors. The ECL quantum efficiency was near 80% for the long-arm T4. One of the interesting goals in ECL is to find ECL emitters in aqueous media. Organic nanoparticles (ONPs) were chosen to achieve this goal. An organic nanoparticle (ONPs) is still challenging area in nanoscience. The key factor of such a challenge comes from the difficulty to control the size and shape of the prepared nanoparticles. ONPs of common hydrocarbon ECL emitters like rubrene and 9,10-diphenylanthracene (DPA) were prepared in aqueous solution using a reprecipitation method. ECL of rubrene NPs was observed when tripropylamine (TPrA) was used as a coreactant, and weaker ECL of DPA NPs was observed when the oxalate ion was used as a coreactant. The ECL of ONPs in aqueous media may open a new field in ECL, allowing the exploration of more phenomena in organic nanoscience. Organic nanoparticle ECL (especially if one able to make small size to be diffused easily) has potential application as a tag for the analysis of biologically interesting molecules. / text
72

Nanoparticle dispersion flow for enhanced oil recovery using micromodels

Van Bramer, William Christopher 10 October 2014 (has links)
The injection of nanoparticles is a promising and novel approach to enhancing oil recovery in depleted fields. Nanoparticles have one dimension that is smaller than 100 nm and have many unique properties that are useful when it comes to oil recovery. Their small size and the ability to manipulate particle properties are a couple of the advantageous properties. The small size of nanoparticle allows them to easily pass through porous media. Manipulating nanoparticle properties allows for wettability modifications or controlled release of chemicals at a precise location in the formation. Injection of nanoparticle dispersions for secondary or tertiary recovery in corefloods has yielded positive results. Field tests using nanoparticles have also yielded positive results with increased oil recovery. While there has been a sizable amount of work related to corefloods, limited investigation has been reported using micromodels. Micromodels are valuable because they allow for pore scale viewing of the oil recovery, which is not possible with corefloods. In this research both polydimethylsiloxane (PDMS) and glass microfluidic devices were fabricated to test the EOR potential of different types of nanoparticles. Much of the work described in this thesis involved the use of a dead-end pore geometry to trap oil. First the pore space was filled with oil and then waterflooded. This left some oil trapped in the dead-end pores. PDMS micromodels proved difficult to trap oil in the dead-end pores; because of this glass micromodels were tested. After trapping oil, a nanoparticle dispersion was injected into the pore space to test the potential of the dispersion to reduce the residual oil saturation in the dead-end pores. The nanoparticle dispersion was injected at different flow rates (1 [mu]l/hr to 50 [mu]l/hr) to test the effect of flow rate on residual oil recovery. / text
73

development, characterization and evaluation of crystalline nanoparticles for enhancing the solubility, the disolution rate and the oral bioavailability of poorly water-soluble drugs

Hecq, Jerome J 17 November 2006 (has links)
When considering oral administration, drug release from its pharmaceutical form and its dissolution into gastrointestinal fluids generally precedes absorption and systemic availability. The solubility-dissolution behaviour of a drug is frequently the rate-limiting step to absorption of drugs from the gastrointestinal tract (BCS class II drugs). Poor aqueous solubility has always been a very challenging obstacle as it is, together with membrane permeability, an essential factor in the limitation of a drug’s bioavailability following oral administration. Since an increasing number of newly developed drug candidates in pre-clinical development phases present poor water-solubility characteristics, there is a great need for formulation approaches to overcome this factor. Out of the many ways to increase a product’s solubility/dissolution rate characteristics with the aim of enhancing its oral bioavailability, drug formulation as nanoparticles has received much-increased interest over the last decade. The hypothesis behind dissolution rate enhancement, considering drug particle size reduction to nanometer range, lies primarily in a much-increased effective surface area (Noyes-Whitney) presented by the resulting drug nanoparticles. Out of the various technologies available for drug particle size reduction to nanometer range, milling using high pressure homogenization is regarded as one of the simplest and most effective techniques. High pressure homogenization is a solvent-free process and is relatively rapid (time-saving). Furthermore, and most importantly, the scaling up of this technique is already established; processing capacities ranging from 3 l/h (e.g. EmulsiFlex C3®: minimum sample volume - 10 ml) to 1000 l/h (e.g. EmulsiFlex C1000®: minimum sample volume - 2 l). Four model drugs were studied in this work. Nifedipine (NIF), an extensively studied poorly water-soluble drug in the literature, was used as the main model on which most of the development was done. In parallel to the work carried out on NIF, three UCB S.A. molecules currently under development were also studied as poorly water-soluble drugs: these being ucb-35440-3, UCB-A and UCB-B (salt of UCB-A). These three UCB S.A. model drugs are, contrarily to NIF, predicted highly dosed drugs and are weak bases, and thus present pH-dependent solubility profiles, which allowed us to investigate model drugs with different profiles. Firstly, investigations regarding appropriate formulation development (stabilizer (surfactant) selection) and appropriate high pressure homogenization operating conditions (pre-milling cycles, influence of the number of high pressure homogenizing cycles, influence of homogenizing pressure, influence of sample temperature) were made. It has been shown, through this development, for the four studied model drugs, that high pressure homogenization is an appropriate technique for reducing drug particle size to nanometer range (NIF  290 nm, ucb-35440-3  180 nm, UCB-A  350 nm and UCB-B  250 nm). Investigations regarding water-removal from the nanosuspensions obtained and most importantly regarding the redispersion characteristics of the retrieved powders (i.e. nanoparticles) were then carried out. In that regard, it has been shown that the presence of carriers in the formulation is essential for limiting nanoparticles agglomeration during the water-removal operation. Drug crystalline state characterizations before and following particle size reduction were then carried out on the three studied model drugs, mainly through DSC and PXRD studies. In fact, one of the advantages of this particle size reduction approach (using high pressure homogenization), versus other frequently studied solubility/dissolution rate enhancement technologies (e.g. such as solid dispersions), is that original crystalline state shall not be altered in such a way that the achieved increased solubility and dissolution rate characteristics do not rely on the presence of the amorphous form of the drug; this furthermore implying a greater time-stability of the developed formulations. Through the data obtained, it has been shown that original drug crystalline state seems to be unaltered following particle size reduction. In vitro solubility and dissolution characteristics were then evaluated on the formulations developed in order to verify the posed hypothesis regarding effective surface area increase. It has been shown through these studies that drug solubility and most importantly drug dissolution rate can be significantly enhanced for nanoparticulate systems (verified for NIF, ucb-35440-3, UCB-A and UCB-B). For example, solubility was enhanced from 26 µg/ml vs. 19.5 µg/ml for NIF nanoparticles and the dissolution characteristics showed that 100% of the tested dose (equivalent to 10 mg NIF) was already dissolved following 10 min vs. less than 5% for un-milled NIF. Following these very interesting and promising results, and preliminary to the in vivo pharmacokinetic studies carried out, in vitro permeation studies (apical to basolateral transfer studies) across intestinal cell models (Caco-2 and HT29-5M21 cultures and co-cultures) were carried out. This evaluation was only carried out using NIF as a model drug and showed a 6-fold increase in the permeation rate for NIF nanoparticles. The influence of chitosan (permeability enhancer/bioadhesive polymer) in the NIF nanoparticle formulation with regard to in vitro NIF permeation rate was also evaluated. In vivo pharmacokinetic studies in rats were conducted using NIF and ucb-35440-3 as model drugs. The very different profiles of these two model drugs allowed us to retrieve interesting information regarding the in vivo behaviour of the developed formulations. As expected from the in vitro (i.e. solubility/dissolution/permeation) studies and results obtained for NIF, an increased extent of exposure could be observed for NIF nanoparticles versus un-milled NIF; the difference being more pronounced when the formulations were orally administered into capsules (2.5-fold increase in extent of exposure and 6-fold increase in Cmax). For ucb-35440-3, a poorly water-soluble weak base with a reported significant food effect considering oral bioavailability, an increased extent of exposure for nanoparticles, versus the un-milled drug, could only be observed in fasted state (4-fold increase in extent of exposure and 2.7-fold increase in Cmax). These different, diet-relative observations allowed us to put forward some limitations and precautions (considering poorly water-soluble weak bases) relative to the possibility of drug reprecipitation following stomach’s exiting, particularly if dissolution in the stomach is quite fast (e.g. nanoparticulate systems). In parallel to the in vivo pharmacokinetic evaluation of NIF nanoparticles, evaluation of the antihypertensive effect of the systems developed following oral administration, using spontaneously hypertensive rats, was also carried out and compared to un-millled NIF. The results obtained showed a significant drop in systolic blood pressure for NIF nanoparticles (32% reduction of initial SBP following 30 min vs. 1% for un-milled NIF) and nicely complemented the in vitro and in vivo results obtained for NIF nanoparticles. Finally, a stability study of the optimized NIF nanoparticle formulation was carried out with respect to reported ICH conditions (25°C/60% RH; 30°C/65% RH; 40°C/75% RH). The results showed that the studied NIF nanoparticle formulation retains all its original characteristics (dissolution, crystalline state, redispersion characteristics); this being verified over time (12 months) and for each of the three storage conditions studied.
74

Waveguide and optical studies of insulators using ion implantation

Oklur, Ibrahim January 1998 (has links)
No description available.
75

Electrostatic self assembly of multilayer films incorporating metallic nanoparticles

Cant, Nicola Elizabeth January 2003 (has links)
No description available.
76

The effects of manufactured nanoparticles on fish physiology, reproduction and behaviour

Ramsden, Christopher January 2012 (has links)
Over the last decade the development and use of nanomaterials (NMs) and nanoparticles (NPs) has increased at a great rate. As a result there is an ever increasing risk of exposing humans and wildlife to these potentially harmful materials. Titanium dioxide nanoparticles (TiO2 NPs) and carbon nanotubes (CNTs) are two of the most widely used NMs at present. Their potentially harmful effects on organisms and physicochemical properties have been investigated in a growing number of scientific studies. However understanding the level of risk they may pose is far from satisfactory. The present body of work has addressed various aspects of this field. In order to better quantify the fate of TiO2 NPs in the environment the methodology of measuring Ti from TiO2 NPs was improved using ICP-OES and single particle ICP-MS was demonstrated to provide the first steps towards characterising the nature of TiO2 NPs in liquid-phase media. The potential harm of TiO2 NPs and single walled carbon nanotubes (SWCNTs) to zebrafish was investigated in two separate studies. Little evidence of physiological toxicity was found and the only nano-scale effect of note was an increase in total glutathione of zebrafish exposed to TiO2 NPs. More subtle effects in reproductive studies were further investigated using the three-spined stickleback in a longer term investigation. Similarly to the zebrafish there was little evidence of any physiological disturbances and the well documented reproductive behaviour of the stickleback was not significantly altered as a result of TiO2 NP exposure. This body of work has added to the understanding of the potential toxic effects caused by exposure to both TiO2 NPs and SWCNTs. Improved methods for the detection and characterisation of TiO2 NPs have been demonstrated and the most sensitive tools for ecotoxicological assessments of NP toxicity have been elucidated.
77

Phototoxic Effects of Titanium Dioxide Nanoparticles on Daphnia Magna

Mansfield, Charles M. 12 1900 (has links)
Titanium dioxide nanoparticles (TiO2-NP) are one of the most abundantly utilized nanomaterials in the world. Studies have demonstrated the mechanism of acute toxicity in TiO2-NP to be the production of reactive oxygen species (ROS) leading to oxidative stress and mortality in exposed organisms. It has also been demonstrated that the anatase crystalline conformation is capable of catalyzing the cleavage of water molecules to further increase the concentration of ROS in the presence of ultraviolet radiation. This photoenhanced toxicity significantly lowers the toxicity threshold of TiO2-NP to environmentally relevant concentrations (ppb). The goal of this study was to determine whether dietary uptake and accumulation of TiO2-NP in the aquatic filter feeder Daphnia magna resulted in photoenhanced toxicity. D. magna and S. caprincornatum were exposed to aqueous solutions of 20ppm and 200ppm TiO2-NP for 24hrs and then transferred to clean moderately hard water. Samples were taken at various time points, dried, and TiO2 quantified using ICP-MS. Toxicity assays were run on D. magna using three TiO2-NP (20ppm, 200ppm) exposure protocols and two ultraviolet radiation treatments. The first exposure group was exposed to aqueous solutions of TiO2-NP for the duration of the test. The second exposure group was exposed to TiO2-NP for an hour and then transferred to clean water. The third exposure group was fed S. capricornatum that had been allowed to adsorb TiO2-NP. All samples were then placed in an outdoor UV exposure system and exposed to either full spectrum sunlight (with UV) or filtered sunlight (no UV). Here we show that TiO2 uptake peaked at one hour of exposure likely due to sedimentation of the particles out of suspension, thus decreasing bioavailability for the duration of the test. Interetsingly, when D. magna were moved to clean water, aqueous concentrations of TiO2 increase as a result of depuration from the gut tract. Data also suggests these excreted particles were bioavailable and re-consumed by D. magna. These data will contribute to the understanding of TiO2-NP environmental fate and toxicity.
78

Design and characterization of nanoparticles and their assemblies : Transmission electron microscopy investigations from atomic to mesoscopic length scales

Mayence, Arnaud January 2016 (has links)
Transmission electron microscopy (TEM) is a powerful and versatile tool for investigating nanomaterials. In this thesis, various transmission electron microscopy techniques are used to study the chemical and structural features of different types of inorganic nanoparticles of well-defined morphologies as well as their assemblies. The synthesis of spherical and anisotropic nanoparticles (iron oxide nanocubes and other morphologies, gadolinium orthophosphate nanorods, tungsten oxide nanowires and nanorods, palladium nanospheres, and facetted iron-manganese oxides hybrid nanoparticles) using thermal decomposition of metal complex precursors in high-boiling point organic solvents and hydrothermal process are described in details. Electron diffraction tomography (3D EDT) is a recently developed technique that is used to investigate the 3D structure of crystalline materials. Reciprocal space volume reconstruction of 3D EDT data of thin WO3 nanowires assembled into nanorods revealed single crystal domains of hexagonal symmetry. Moreover, the use of 3D EDT enabled to identify and solve the structures of individual GdPO4 nanorods in a mixed phase powder. The use of 3D EDT was extended using small-angle diffraction mode to investigate the packing arrangements and defects in nanoparticle assemblies. A high concentration of planar defects found in different nanoparticle assemblies highlights the competition between the fcc and hcp arrangements during the assembly process. Iron-manganese oxides hybrid nanoparticles with different three-dimensional configurations, i.e. core|shell and asymmetric facetted dimers, were investigated using a combination of several electron microscopy techniques (HRTEM, SAED, STEM-HAADF, EFTEM, EELS). The growth of the facetted cubic MnO phase onto preformed Fe3O4 seed particles occurs preferentially along the Fe3O4 nanocube edges forming a well-oriented crystalline interface despite the lattice mismatch and defects. Atomic resolution monitoring of the structural changes in Mn3O4|Fe3O4 and Fe3O4|Mn3O4 core|shell nanoparticles induced by the electron beam revealed a strain relief mechanism at the interface involving inhomogeneous diffusion of cations and defects creation. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4: Manuscript. Paper 5: Manuscript.</p>
79

Kvantově-mechanický popis plasmonických nanočástic / Quantum-mechanical description of plasmonic nanoparticles

Nečada, Marek January 2015 (has links)
Coupling of light to charges in a metallic nanoparticle leads to hybrid light-matter states, localised surface plasmon polaritons. They are characterised by very strong field intensities in vicinity of the nanoparticle. This field enhancement can be exploited by coupling the nanoparticles to quantum emitters, e.g. molecules or quantum dots. Many new applications are based on fabrication of arrays of metallic nanoparticles. Significant spatial coherence in such systems is caused by electromagnetic interaction between the nanoparticles. In this work, we study the possibilities of quantum-mechanical description of metallic nanoparticles and the interactions between them. Using the principles of molecular quantum electrodynamics and quantisation of quasistatic normal modes of charge oscillations, we propose a quantum model of interaction between dipole quasistatic oscillation modes and the electromagnetic field. This model is then applied to estimate how presence of another nanoparticle influences the spontaneous radiative decay rate of dipole charge oscillation mode using the third-order perturbation theory. Powered by TCPDF (www.tcpdf.org)
80

Synthesis and characterization of Ag, Au and Cu dendrimer-encapsulated nanoparticles as well as their application in catalysis

05 November 2012 (has links)
M.Sc. (Chemistry) / In this dissertation the synthesis, characterization and the application of Ag, Au and Cu dendrimer encapsulated nanoparticles (DENs) in catalysis are described. Ag, Au and Cu-DENs were synthesized using G4-G6 PAMAM-OH and G4-G6 PAMAM-NH2 dendrimers as templates as well as stabilizers. NaBH4 was used as a reducing agent for the synthesis of DENs. Binding studies were carried out in order to determine the maximum capacity of the dendrimer to which the metal ions can be added. These binding studies were performed using UV-vis spectroscopy. The synthesis of these nanoparticles (NPs) was carried out at room temperature. For the synthesis of Ag and Au-DENs with PAMAM-NH2 dendrimers, the pH of the aqueous dendrimer solution was first adjusted to acidic condition (~pH 2) using HCl before the addition of the respective metal ion precursor to the dendrimer. This is done to avoid coordination of the metal ions to the primary amine groups on the periphery of the dendrimer, which might lead to particle agglomeration. These prepared DENs were characterized by UV-vis spectroscopy and high resolution transmission (HRTEM) microscopy. The synthesized DENs were evaluated as catalysts in the reduction of 4-nitrophenol to 4-aminophenol by NaBH4. This reaction was monitored by UV-vis spectroscopy by following the absorbance at 400 nm These DENs were all found to be active catalysts for the afore-mentioned process. The rate constant for the reduction process was observed to decrease as the concentration of 4-nitrophenol increased. As the concentration of NaBH4 is increased, the rate constant was also found to increase, however this increase was only observed to a maximum concentration of NaBH4. The Au-DENs prepared using G4 PAMAM-NH2 dendrimers were subsequently immobilized onto a titania support via the sol-gel (Ti-Au-s) and wetness impregnation (Ti-Au-w) methods. The titania supported Au NPs were characterized using HRTEM, powder X-ray diffraction (PXRD), thermal gravimetric analysis (TGA), inductive coupled plasma-optical emission spectroscopy (ICP-OES) and Brunauer Emmett Teller (BET) surface area analysis. The dendrimer template was removed by calcining at 500 oC. The catalytic activity of these supported Au NPs was investigated in the oxidation of styrene using tert-butyl hydroperoxide (TBHP) as an oxidant. Benzaldehyde and styrene oxide were observed as the major products. The catalyst prepared by wetness impregnation method was found to give the highest styrene conversion as compared to the one prepared via sol-gel method. At 60 oC, the catalyst prepared by sol-gel method was found to selectively produce benzaldehyde while on the other hand, the catalyst prepared by wetness impregnation selectively produce styrene oxide. The highest conversion of styrene was observed at 70 oC for both catalysts. Ti-Au-w catalyst was generally found to give the highest styrene conversion.

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