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Polymer optical fibers (POFs) are a rather new tool for high-speed data transfer by modulated light. They allow the transport of high amounts of data over distances up to about 100 m without be influenced by external electromagnetic fields. Due to organic chemical nature of POFs, they are sensitive to the climate of their environment and therefore the optical fiber properties are as well. Hence, the optical stability is a key issue for long-term applications of POFs. The causes for a loss of optical transmission due to climatic exposures (aging/degradation) are researched by means of chemical analytical tools such as chemiluminescence (CL) and Fourier transform infrared (FTIR) spectroscopy for five different (with respect to manufacturers) step-index multimode PMMA based POFs and for seven different climatic conditions. Three of the five POF samples are studied more in detail to realize the effects of individual parameters and for forecasting longterm optical stability by short-term exposure tests. At first, the unexposed POF components (core, cladding, and bare POF as combination of core and cladding) are characterized with respect to important physical and chemical properties. The glass transition temperature Tg, and the melting temperature Tm are in the region of 120 °C to 140 °C, the molecular weight (Mw) of cores is in the order of 105 g mol-1. POFs are found to have different chemical compositions of their claddings as could be detected by FTIR, but identical compositions of their cores. Two of the POFs are exposed as cables (core, cladding and jacket) for about 3300 hours to the climate 92 °C / 95 % relative humidity (RH) resulting in a different transmission decrease. Investigating the related unexposed and exposed bare POFs for degradation using CL, FTIR, thermogravimetry (TG), UV/visible transmittance and gel permeation chromatography (GPC) suggest that claddings of POFs are more affected than cores. Probably the observed loss of transmission is mainly due to increased light absorption and imperfections at the core-cladding boundary caused by a large degradation of claddings. Hence, it is highly possible that the optical transmission stability of POFs is governed mainly by the thermo-oxidative stability of the cladding and minor of the core. Three bare POFs (core and cladding only) are exposed for different duration of exposure time (30 hours to 4500 hours) to 92 °C / 95 %RH, 92 °C / 50 %RH, 50 °C / 95 %RH, 90 °C / low humidity, 100 °C / low humidity, 110 °C / low humidity and 120 °C / low humidity. In these climates their transmission variations are found to be different from each other, too. The outcomes strongly inform that under high temperature and high humid climates physical changes such as volume expansion, are the main sources for the loss of optical transmission. Also, the optical transmission stability of POFs is found to be dependent on chemical compositions of claddings. Under high temperature and low humid conditions, a loss of transmission at the early stages of the exposure is mainly caused by physical changes, presumable by corecladding interface imperfections. For the later stages of exposures it is proposed to an additional increase of light absorption by core and cladding owes to degradation. Optical simulation results obtained parallel by Mr. L. Jankowski (a PhD student of BAM) are found to confirm these results. For bare POFs, too, the optical stability of POFs seems to depend on their thermo-oxidative stability. Some short-term exposure tests are conducted to realize influences of individual climatic parameters on the transmission property of POFs. It is found that at stationary high temperature and variable humidity conditions POFs display to a certain amount a reversible transmission loss due to physically absorbed water. But in the case of varying temperature and constant high humidity such reversibility is hardly noticeable. However, at room temperature and varying humidity, POFs display fully reversible transmission loss. The whole research described above has to be regarded as a starting point for further investigations. The restricted distribution of fundamental POF data by the manufacturers and the time consuming aging by climatic exposures restrict the results more or less to the samples, investigated here. Significant general statements require for example additional information concerning the variation of POF properties due to production. Nevertheless the tests, described here, have the capability for approximating and forecasting the long-term optical transmission stability of POFs. -------------- Auch im Druck erschienen: Appajaiah, Anilkumar: Climatic stability of polymer optical fibers (POF) / Anilkumar Appajaiah. - Bremerhaven : Wirtschaftsverl. NW, Verl. für neue Wiss., 2005. - Getr. Zählung [ca. 175 S.]. : Ill., graph. Darst. - (BAM-Dissertationsreihe ; 9) ISBN 3-86509-302-7
Die vorliegende Arbeit beschreibt das Verhalten von Polypeptid-Blockcopolymeren in der festen Phase und in selektiven Lösungsmitteln. Blockcopolymere auf Basis von Poly(L-glutaminsäure-5-benzylester) (PBLGlu) oder Poly(Nε-benzoyloxycarbonyl-L-lysin) (PZLLys), die in dieser Arbeit eingesetzt wurden, besitzen wegen ihrer helikalen Sekundärstruktur eine sog. Stäbchen-Knäuel-Geometrie, wobei die Knäuelkomponente Polystyrol oder Polybutadien ist. Die Phasenbildung dieser Blockcopolymere ist durch die Packungseigenschaften des rigiden Blocks beeinflusst. Es wurden bevorzugt lamellare Strukturen gebildet, in denen die Stäbchen parallel angeordnet sind. Das Vorhandensein eines permanenten Dipolmomentes führt zur Wechselwirkung zwischen den Helices und zur Erhöhung des Ordnungsgrades in der Phase. Ein zusätzlicher Parameter, der die Morphologie der Phase beeinflußt, ist die Chiralität der Peptidhelix, durch die chirale Überstrukturen induziert werden. In dünnen Filmen (40 nm), wo die Geometrie begrenzt ist, führt es zu Frustrationen in der Phase. Die dadurch entstandene Spannung wurde durch einen zick-zack-artigen Lamellenverlauf abgebaut. In selektiven Lösungsmitteln für die synthetische Komponente (PS) bilden die Polypeptid-Blockcopolymere vesikuläre Strukturen, deren kugel- oder wurmförmige Geometrie von der Elastizität der Membran abhängig ist. Durch Entfernung der Z-Schutzgruppe kann PZLLys in eine wasserlösliche Form überführt werden, so dass die PB-PLLys Blockcopolymere unter Bildung von Vesikeln in Wasser löslich sind. Dabei ist die Konformation des Peptids vom pH-Wert des Mediums abhängig und kann von einem Knäuel zu einer Helix reversibel geschaltet werden. Beim Modifizieren der Sekundärstruktur wurde eine Änderung der Aggregationszahl beobachtet. Somit können diese Blockcopolymere für die Herstellung von schaltbaren Aggregaten eingesetzt werden.
Ellipsometrische Lichtstreuung als neue Methode zur Charakterisierung der Grenzfläche von Kolloiden
(2004)
Die ellipsometrische Lichtstreuung wird als eine neue, leistungsfähige Methode zur Charakterisierung von Schichten um kolloidale Partikel vorgestellt. Theoretische Grundlage der Methode ist die Mie-Theorie der Lichtstreuung. Experimentell wurde die Polarisationsoptik eines Null-Ellipsometers in den Strahlengang eines Lichtstreuaufbaus eingebaut. Wie in der Reflexionsellipsometrie um den Brewsterwinkel herum erhält man in der ellipsometrischen Streuung einen Winkelbereich, in dem die Methode empfindlich auf Schichten an der Oberfläche der Partikel ist. An verschiedenen Systemen wurde die Tauglichkeit der ellipsometrischen Streuung zur Charakterisierung von Schichten auf Partikeln demonstriert. So wurden Dicke und Brechungsindex einer thermosensitiven Schicht von Poly(N-isopropylacrylamid) auf einem Poly(methylmethacrylat)-Kern bestimmt. Damit ist es möglich, experimentell den Schichtbrechungsindex und damit den Quellungsgrad zu bestimmen. Des Weiteren wurde der Einfluss der NaCl-Konzentration auf die Polyelektrolythülle von Poly(methylmethacrylat)-Poly(styrolsulfonat)-Blockcopolymer-Partikeln untersucht. Die Polyelektrolytketten liegen im hier untersuchten Beispiel nicht gestreckt vor. Als drittes wurde die Verteilung von niedermolekularen Ionen um elektrostatisch stabilisierte Poly(styrol)-Latexpartikel in Wasser untersucht. Hier wurde gezeigt, dass die beobachteten Schichtdicken und Schichtbrechungsindizes viel größer sind, als nach der klassischen Poisson-Boltzmann-Theorie zu erwarten ist. Des Weiteren wurde die Doppelbrechung von unilamellaren Lipidvesikeln bestimmt. Außerdem wurden Messungen der dynamische Lichtstreuung im Intensitätsminimum der Ellipsometrie durchgeführt. Dabei wird ein Prozess mit einer Korrelationszeit, die unabhängig vom Streuvektor, aber abhängig von der verwendeten Wellenlänge ist, sichtbar. Die Natur dieses Prozesses konnte hier nicht vollständig geklärt werden.
Combining the magnetic properties of a given material with the tremendous advantages of colloids can exponentially increase the advantages of both systems. This thesis deals with the field of magnetic nanotechnology. Thus, the design and characterization of new magnetic colloids with fascinating properties compared with the bulk materials is presented. Ferrofluids are referred to either as water or organic stable dispersions of superparamagnetic nanoparticles which respond to the application of an external magnetic field but lose their magnetization in the absence of a magnetic field. In the first part of this thesis, a three-step synthesis for the fabrication of a novel water-based ferrofluid is presented. The encapsulation of high amounts of magnetite into polystyrene particles can efficiently be achieved by a new process including two miniemulsion processes. The ferrofluids consist of novel magnetite polystyrene nanoparticles dispersed in water which are obtained by three-step process including coprecipitation of magnetite, its hydrophobization and further surfactant coating to enable the redispersion in water and the posterior encapsulation into polystyrene by miniemulsion polymerization. It is a desire to take advantage of a potential thermodynamic control for the design of nanoparticles, and the concept of "nanoreactors" where the essential ingredients for the formation of the nanoparticles are already in the beginning. The formulation and application of polymer particles and hybrid particles composed of polymeric and magnetic material is of high interest for biomedical applications. Ferrofluids can for instance be used in medicine for cancer therapy and magnetic resonance imaging. Superparamagnetic or paramagnetic colloids containing iron or gadolinium are also used as magnetic resonance imaging contrast agent, for example as a important tool in the diagnosis of cancer, since they enhance the relaxation of the water of the neighbouring zones. New nanostructured composites by the thermal decomposition of iron pentacarbonyl in the monomer phase and thereafter the formation of paramagnetic nanocomposites by miniemulsion polymerization are discussed in the second part of this thesis. In order to obtain the confined paramagnetic nanocomposites a two-step process was used. In the first step, the thermal decomposition of the iron pentacarbonyl was obtained in the monomer phase using oleic acid as stabilizer. In the second step, this iron-containing monomer dispersion was used for making a miniemulsion polymerization thereof. The addition of lanthanide complexes to ester-containing monomers such as butyl acrylate and subsequent polymerization leading to the spontaneous formation of highly organized layered nanocomposites is presented in the final part of this thesis. By an one-step miniemulsion process, the formation of a lamellar structure within the polymer nanoparticles is achieved. The magnetization and the NMR relaxation measurements have shown these new layered nanocomposites to be very apt for application as contrast agent in magnetic resonance imaging.
Nanostructured materials are the materials having structural features on the scale of nanometers i.e. 10-9 m. the structural features can enhance the natural properties of the materials or induce additional properties, which are useful for day to technology as well as the future technologies One way to synthesize nanostructured materials is using templating techniques. The templating process involves use of a certain “mould” or “scaffold” to generate the structure. The mould is called as the template, can be a single molecule or assembly of molecule or a larger object, which has its own structure. The product material can be obtained by filling the space around the template with a “precursor”, transformation of precursor into the desired material and then removal of template to get product. The precursor can be any chemical moiety that can be easily transformed in to the desired material. Alternatively the desired material is processed into very tiny bricks or “nano building blocks (NBB)” and the product is obtained by arrangement of the NBB by using a scaffold. We synthesized porous metal oxide spheres of namely TiO2-M2O3: titanium dioxide- M-oxide (M = aluminum, gallium and indium) TiO2-M2O3 and cerium oxide-zirconium oxide solid solution. We used porous polymeric beads as templates. These beads used for chromatographic purposes. For the synthesis of TiO2-M2O3 we used metal- alkoxides as precursor. The pore of beads were filled with precursor and then reacted with water to give transformation of the precursor to amorphous oxide network. The network is crystallized and template is removed by heat treatment at high temperatures. In a similar way we obtained porous spheres of CexZr1-xO2. For this we synthesized nanoparticle of CexZr1-xO2 and used then for the templating process to obtain porous CexZr1-xO2 spheres. Additionally, using the same nanoparticles we synthesized nano-porous powder using self-assembly process between a block-copolymers scaffold and nanoparticles. Morphological and physico-chemical properties of these materials were studies systematically by using various analytical techniques TiO2-M2O3 material were tested for photocatalytic degradation of 2-Chlorophenol a poisonous pollutant. While CexZr1-xO2 spheres were tested for methanol steam reforming reaction to generate hydrogen, which is a fuel for future generation power sources like fuel cells. All the materials showed good catalytic performance.