Filtern
Dokumenttyp
Schlagworte
- Gold nanoparticles (2)
- Citrate reduction (1)
- Click chemistry (1)
- Continuous-wave plasma (1)
- Cotton effect (1)
- Crystal violet (1)
- Defects (1)
- Dendrimers (1)
- Electromagnetic enhancement factor (1)
- Growth mechanism (1)
Introduction of irregularities into plasma polymers by radiative and auto-oxidative processes
(2005)
Dünne, mit einem gepulsten Plasma hergestellte Polymerschichten wurden untersucht. Diese Plasmapolymere sollten eine chemisch besser definierte Struktur haben, weil der Anteil an rein chemisch polymerisiertem Produkt während der Plasma-aus-Zeit steigen sollte, während der Anteil an Schichtbildung, der innerhalb der kurzen Plasmapulse durch Monomerfragmentierung und statistische Polyrekombination erzeugt wird, zurückgedrängt wird. Der Monomerfragmentierungsprozeß ist im kontinuierlich brennenden Plasma (cw-Mode) demgegenüber der Hauptprozeß. Neben der Anwendung der klassischen Element- und Bindungsanalysentechnik XPS (X-ray Photoelectron Spectroscopy) wurden hier die Schichten auch mittels Thermolumineszenz untersucht. Defekte und Strukturanomalitäten in Polymeren sollten mit dieser Methode charakterisiert werden können. Untersuchungsobjekte waren funktionalgruppentragende Plasmapolymerschichten, die biosensorische oder biokompatible Funktionen besitzen oder als Haftvermittler in Metall-Polymercompositen eingesetzt werden.
Translated Abstract
Characterization of Plasmapolymers by Thermoluminescence
Thin plasma polymer films were deposited using the pulsed plasma (pp) mode. These plasma polymers should possess a more chemically regular structure because of the lower monomer fragmentation during the short plasma pulses and the chemical chain propagation during the plasma-less periods than those produced by the conventional continuous-wave (cw) mode. In addition to the use of the classic thin film characterization method XPS the method of thermoluminescence was applied to characterize defects and structural specifics in the polymer films produced by pp or cw-plasma mode. The thermoluminescence method was applied to functional groups-carrying plasma polymer layers, which are used in medical technology for forming biocompatible and bioactive coatings or in metal-polymer composites as adhesion-promoting interlayers.
Monodisperse, citrate-stabilized gold nanoparticles of sizes ranging from 15 to 40 nm were synthesized and characterized by small angle X-ray scattering and UV-vis experiments. Identical surface properties of nanoparticles of different sizes to avoid variation in the chemical surface-enhanced Raman scattering (SERS) enhancement, as well as selection of experimental conditions so that no aggregation took place, enabled the investigation of enhancement of individual nanospheres. Enhancement factors (EFs) for SERS were determined using the dye crystal violet (CV). EFs for individual gold nanospheres ranged from 102 to 103, in agreement with theoretical predictions. An increase of the EFs of individual spheres with size can be correlated to changes in the extinction spectra of nanoparticle solutions. This confirms that the increase in enhancement with increasing size results from an increase in electromagnetic enhancement. Beyond this dependence of EFs of isolated gold spheres on their size, EFs were shown to vary with analyte concentration as a result of analyte-induced aggregation. This has implications for the application of nanoparticle solutions as SERS substrates in quantitative analytical tasks.
Thin plasma polymer films were deposited using the pulsed plasma mode. These plasma polymers should possess a more regular structure than those produced by the conventional continuous-wave (cw) mode, because of lower monomer fragmentation caused by the plasma pulses and the chemical chain propagation during the plasmaless (free!) periods. The thermoluminescence method was applied to functional groups carrying plasma polymer layers which are used in medical technology. Examples are formation of biocompatible, biosensoric and bioactive coatings or in metal polymer composites such as adhesion-promoting interlayers.
In addition to the use of the conventional X-ray Photoelectron Spectroscopy for thin film characterization, the new method of thermoluminescence was applied to characterize undesired defects and structural specifics produced in the polymer films by pp or cw plasma mode. The main areas of focus were oxygen-containing groups produced by post-plasma oxygen introduction via auto-oxidation, oxidation of implemented unsaturations and trapped radical sites known as typical irregular structures in plasma polymers.
The dispersed iron oxide nanoparticles of ferrofluids in aqueous solution are difficult to characterize due to their protective polymer coatings. We report on the bimodal size distribution of superparamagnetic iron oxide nanoparticles found in the MRI contrast agent Resovist, which is a representative example of commercial nanoparticle-based pharmaceutical formulations. The radii of the majority of the nanoparticles (>99%) range from 4 to 13 nm (less than 1% of the particles display radii up to 21 nm). The maxima of the size distributions are at 5.0 and 9.9 nm. The analysis was performed with in situ characterization of Resovist via online coupling of asymmetrical flow field-flow fractionation (A4F) with small-angle X-ray scattering (SAXS) using a standard copper X-ray tube as a radiation source. The outlet of the A4F was directly coupled to a flow capillary on the SAXS instrument. SAXS curves of nanoparticle fractions were recorded at 1-min time intervals. We recommend using the A4F-SAXS coupling as a routine method for analysis of dispersed nanoparticles with sizes in the range of 1-100 nm. It allows a fast and quantitative comparison of different batches without the need for sample preparation.
A facile approach for the synthesis of monodisperse gold nanoparticles with radii in the range of 7 to 20 nm is presented. Starting from monodisperse seeds with radii of 7 nm, produced in the first step, the addition of a defined amount of additional precursor material permits distinct size regulation and the realization of predicted nanoparticle sizes. These information were derived from ex- and in situ investigations by comprehensive small angle X-ray scattering (SAXS), X-ray absorption near edge structure (XANES) and UV-Vis data to obtain information on the physicochemical mechanisms. The obtained mechanisms can be transferred to other seeded growth processes. Compared to similar approaches, the presented synthesis route circumvents the use of different reducing or stabilizing agents. The size of resulting nanoparticles can be varied over a large size range presented for the first time without a measurable change in the shape, polydispersity or surface chemistry. Thus, the resulting nanoparticles are ideal candidates for size dependence investigations.