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Deutscher Titel: Analyse des substratnahen Transports magnetischer Partikel für Lab-on-a-Chip Anwendungen: Modulationen des Streufeldes, Einfluss der Partikeleigenschaften und dreidimensionale Trajektorien

Zugleich: Dissertation, Universität Kassel, 2021

Die vorliegende Arbeit umfasst die Synthese und Charakterisierung 23 neuartiger, multifunktionaler Kompositmaterialien basierend auf lanthanidhaltigen Verbindungen sowie verschiedenen Nano- und Mikropartikeln. Die dargestellten Materialien konnten als Core/Shell-Systeme mit einem nano- bzw. mikropartikelhaltigen Kern und einer lanthanidhaltigen Hülle charakterisiert werden und vereinen aufgrund ihres Kompositcharakters die spezifischen Eigenschaften der Einzelkomponenten wie Lumineszenz, Superparamagnetismus oder Reflexionseigen-schaften miteinander. Zur Synthese multifunktionaler, lumineszierender Materialien wurden zirconylbasierte, lumineszierende Nanopartikel mit Lanthanidchloriden und lanthanidhaltigen MOFs funktionalisiert. Die Kompositsysteme LnCl3@ZrO(FMN) (FMN = Flavinmononukleotid, Ln = Y, Sc, La, Eu, Tb, Ho) ermöglichen eine Modifizierung der Lumineszenzeigenschaf-ten der Materialien abhängig von der Reaktionstemperatur sowie dem verwendeten Selten-Erd-Ion. Durch Variation der Nanopartikelkomponente konnte mittels der Kom-posite LnCl3@ZrO(MFP) (MFP = Methylfluoresceinphosphat) ein zusätzlicher sol-vatochromer Effekt der Systeme eingeführt werden, während das Kompositmaterial YCl3@ZrO(RP) (RP = Resorufinphosphat) eine andere Chromatizität zugänglich macht. Durch Modifizierung von ZrO(FMN)- und ZrO(MFP)-Nanopartikeln mit 3∞[Eu2(BDC)3]· 2DMF·2H2O (BDC2- = Benzol-1,4-dicarboxylat) wurden Kompositmaterialien dargestellt, die zwei Lumineszenzprozesse mit unterschiedlicher Chromatizität und unterschiedli-cher Anregbarkeit miteinander kombinieren und somit eine reversible Schaltbarkeit zwischen beiden Prozessen durch Variation der Anregungswellenlänge ermöglichen. Zur Synthese luminomagnetischer Materialien wurden superparamagnetische Fe3O4/SiO2-Mikropartikel mit einer Vielzahl lanthanidhaltiger MOFs, die sich hinsichtlich ihrer Lumineszenzeigenschaften und ihrer Stabilität gegenüber Luft und Wasser unterscheiden, modifiziert. Als MOFs wurden hierbei 2∞[Ln2Cl6(Bipy)3]·2Bipy (Bipy = 4,4‘-Bipyridin, Ln = Nd, Sm, Eu, Tb, Er), 3∞[Eu(Im)2], 3∞[Ba0.95Eu0.05(Im)2] (Im = Imidazolat) und 3∞[Eu2(BDC)3]·2DMF·2H2O eingesetzt. Die Variation der zur Funktionalisierung verwendeten Komponente oder eine Kombination mehrerer MOFs ermöglicht eine Anpassung der Lumineszenz der Kompositmaterialien innerhalb des kompletten sichtbaren Spektralbereichs sowie im NIR-Bereich. Die dargestellten luminomagnetische Kompositmaterialien mit wasserempfindlichen MOFs können zur Detektion von Wasser in verschiedenen organischen Lösungsmitteln verwendet werden und stellen somit eine mobile und einfach anwendbare Alternative zur Karl-Fischer-Titration mit einer vergleichbaren Sensitivität dar. So eignen sich die Kompositsysteme 2∞[Eu2Cl6(Bipy)3]·2Bipy@Fe3O4/SiO2 und 2∞[Eu2Cl6(Bipy)3]·2Bipy, 2∞[Tb2Cl6(Bipy)3]·2Bipy@Fe3O4/SiO2 als optische turn-off-Sensoren, während das Kom-posit 3∞[Eu2(BDC)3]·2DMF·2H2O,2∞[Tb2Cl6(Bipy)3]·2Bipy@Fe3O4/SiO2 als ratiometrischer Sensor verwendet werden kann. Als Alternative zu sphärischen Partikeln wurden auch anisotrope, stäbchenförmige Fe3O4/SiO2-Mikropartikel mittels 3∞[Eu2(BDC)3]·2DMF·2H2O modifiziert. Das resul-tierende Kompositmaterial vereint die isotropen Lumineszenzeigenschaften der MOF-Hülle mit der anisotropen Reflexion von sichtbarem Licht der. Durch die Wahl der Anregungswellenlänge und Richtung eines externen Magnetfelds wird eine stufenlose und reversible Schaltbarkeit zwischen isotropen und anisotropen Eigenschaften ermöglicht. Durch mechanochemische Umsetzung der MOF-Edukte [LnCl3(Py)4]·0.5Py (Ln = Eu, Ho) und 4,4‘-Bipyridin konnte eine Vielzahl von literaturbekannten lanthanidhaltigen Komplexen und Koordinationspolymeren mittels einer neuen und zeiteffizienten Syntheseroute dargestellt werden. Hierbei kann die Verknüpfungsdimension der resultierenden Produkte abhängig von verschiedenen Reaktionsparametern, die den Energieeintrags der Kugelmühle beeinflussen, gesteuert werden., The thesis at hand deals with the synthesis and characterization of 23 novel multi-functional composite materials that are based on lanthanide containing compounds as well as different nano- and microparticles. The synthesized compounds can be described as core/shell systems with a nanoparticle and microparticle containing core, respectively, and a lanthanide containing shell. Due to their composite character, the materials combine the specific properties of their single constituents such as luminescence, superparamagnetism or reflection properties. For the synthesis of multifunctional luminescent materials, zirconyl containing, lumines-cent nanoparticles were modified with lanthanide chlorides as well as lanthanide con-taining MOFs. The composite materials LnCl3@ZrO(FMN) (FMN = flavin mononucleo-tide, Ln = Y, Sc, La, Eu, Tb, Ho) enable a modification of the materials’ luminescence properties in dependence on the reaction temperature and the particular rare earth ion. Variation of the nanoparticle component leads on the one hand to formation of the sys-tem LnCl3@ZrO(MFP) (MFP = methylfluorescein phosphate), which exhibits a strong solvatochromic effect, and on the other hand to the composite YCl3@ZrO(RP) (RP = resorufin phosphate), which makes another chromaticity of the luminescence ac-cessible. The modification of ZrO(FMN) and ZrO(MFP) nanoparticles with 3∞[Eu2(BDC)3]· 2DMF·2H2O (BDC2- = benzene-1,4-dicarboxylate) results in composite materials that combine two luminescence processes with a different chromaticity and a diverse excita-tion range. Therefore, a continuous and reversible switching between both processes can be executed by variation of the excitation wavelength. For the synthesis of luminomagnetic materials, superparamagnetic Fe3O4/SiO2 micro-particles were modified with a variety of lanthanide containing MOFs that differ in terms of their luminescence properties and their water and air stability. For this purpose, the MOFs 2∞[Ln2Cl6(Bipy)3]·2Bipy (Bipy = 4,4’-Bipyridine, Ln = Nd, Sm, Eu, Tb, Er), 3∞[Eu(Im)2], 3∞[Ba0.95Eu0.05(Im)2] (Im- = imidazolate) and 3∞[Eu2(BDC)3]·2DMF·2H2O were employed for microparticle functionalization. By variation of the selected MOF or a combination of two different compounds, the luminescence properties of the composite materials could be adjusted in the whole visible spectral region as well as in the NIR region. The synthesized luminomagnetic composite materials with water sensitive MOFs can be applied for the detection of water in various organic solvents. Therefore, such compo-sites can be used as alternative to the Karl-Fischer titration that is easy applicable, mo-bile and exhibits similar detection limits. The composite materials 2∞[Eu2Cl6(Bipy)3]· 2Bipy@Fe3O4/SiO2 and 2∞[Eu2Cl6(Bipy)3]·2Bipy,2∞[Tb2Cl6(Bipy)3]·2Bipy@Fe3O4/SiO2 can be deployed as optical turn-off sensors, while the composite system 3∞[Eu2(BDC)3]· 2DMF·2H2O,2∞[Tb2Cl6(Bipy)3]·2Bipy@Fe3O4/SiO2 is suitable for a ratiometric determina-tion of the water content. As alternative to spherical particles, anisotropic rod-like Fe3O4/SiO2 microparticles were functionalized with 3∞[Eu2(BDC)3]·2DMF·2H2O. The resulting composite material com-bines the isotropic luminescence of the MOF shell with the anisotropic reflection of visible light of the microparticle component. A continuous and reversible switching between both optical properties is enabled by the variation of the excitation wavelength and the direction of an external magnetic field. The mechanochemical reaction of the MOF precursors [LnCl3(Py)4]·0.5Py (Ln = Eu, Ho) and 4,4’-bipyridine leads to a variety of lanthanide containing complexes and coordina-tion polymers that have already been reported in literature. Thus, a novel and time effi-cient synthesis route could be described for an alternative preparation of these com-pounds. The dimensionality of the resulting substances can be influenced in dependence on different reaction parameters that have an influence on the application of energy by the ball mill.

Herein, the development of a novel composite particle system prepared from superparamagnetic Fe3O4@SiO2 microparticles as core and coated with a carbon shell is presented. The coating with carbon is done by pyrolyzing furan resin, which was previously deposited on the particle surface by polymerization of furfuryl alcohol. The novel composite material thus combines magnetic and sorptive properties. Upon pyrolysis the magnetic material is converted from magnetite to a‐iron and fayalite, changing its behavior from superparamagnetic to ferromagnetic with nearly zero remanence. The magnetic properties can be utilized to magnetically collect the particles dispersed in fluids, whereas the sorptive properties of the carbon shell can be used to remove organic contaminants from these fluids. The adsorption behavior of the composite particles and a potential electrochemical regeneration route are investigated, using the model dye methylene blue.

This work reports on a remotely controllable, all‐magnetic reflective diffraction grating‐like optical element for electromagnetic waves in the visible spectrum. The switchable grating is realized by the unique interplay between nanostructured superparamagnetic plate‐like microrods and a magnetic stray field landscape generated by an engineered magnetic stripe domain pattern superimposed by a small external magnetic field. It is shown that the purposeful design of local magnetic field sources in such a continuous thin‐film system enables a precise manipulation of the microrod alignment and, hence, dynamic control of the corresponding grating constant. It is demonstrated that the magnetic grating can be turned on and off due to disappearance of the engineered domain pattern when magnetically saturated. Moreover, the grating constant can be dynamically changed between two states when applying an AC external magnetic field. The experimental findings are corroborated by a theoretical model based on a quantitative description of the involved forces among the microrods and between microrods and substrate, respectively. These results therefore serve as a basis for smart surfaces with switchable diffraction properties on demand upon remote control.

A smart optical composite material with dynamic isotropic and anisotropic optical properties by combination of luminescence and high reflectivity was developed. This combination enables switching between luminescence and angle-dependent reflectivity by changing the applied wavelength of light. The composite is formed as anisotropic core/shell particles by coating superparamagnetic iron oxide-silica microrods with a layer of the luminescent metal-organic framework (MOF) 3IF[Eu2(BDC)3]·2DMF·2H2O (BDC2- = 1,4-benzenedicarboxylate). The composite particles can be rotated by an external magnet. Their anisotropic shape causes changes in the reflectivity and diffraction of light depending on the orientation of the composite particle. These rotation-dependent optical properties are complemented by an isotropic luminescence resulting from the MOF shell. If illuminated by UV light, the particles exhibit isotropic luminescence while the same sample shows anisotropic optical properties when illuminated with visible light. In addition to direct switching, the optical properties can be tailored continuously between isotropic red emission and anisotropic reflection of light if the illuminating light is tuned through fractions of both UV and visible light. The integration and control of light emission modes within a homogeneous particle dispersion marks a smart optical material, addressing fundamental directions for research on switchable multifunctional materials. The material can function as an optic compass or could be used as an optic shutter that can be switched by a magnetic field, e.g., for an intensity control for waveguides in the visible range.

Smart optical composite materials suitable for ratiometric sensing applications and harvesting options have been developed. The hybrid materials consist of core/shell particles with Fe3O4/SiO2 as the core and different luminescent lanthanide-containing metal-organic frameworks (MOFs) as the shell. The magnetic properties enable collection of microparticles via an external magnetic field and, thus, a strong signal augmentation of the luminescence signal. Thereby, MOF luminescence functions as a read-out signal of the sensing that can be influenced by different chemical compounds, e.g. by quenching with low concentrations of water. The combination of MOFs, which contain different luminescence centers combined with a different sensitivity towards water, results in a system that can be exploited as a ratiometric sensor. We have utilized the MOFs 3IF[Eu2(BDC)3]·2H2O·2DMF (BDC2− = benzene dicarboxylate) and 2IF[Ln2Cl6(bipy)3]·2bipy (Ln = Eu, Tb; bipy = 4,4'-bipyridine) for functionalization of the microparticles, resulting in a color-tuned yellow-emitting mixed-MOF composite system together with a Fe3O4/SiO2 core. Interaction with water decreases the luminescence unequally for both luminescence centers, which enables a quantitative determination of the water content by analysis of the ratio of the Tb3+ and Eu3+ luminescence bands. This process is supported by possible harvesting via superparamagnetism of the composite. Altogether, high sensitivity with a detection limit of 0.3% (20 mg) is achieved, equal to Karl-Fischer titration but also suitable for an ""on-the-fly"" analysis.

Herein, we present the generation of a novel complex particle system consisting of superparamagnetic Fe3O4/SiO2 composite microparticle cores, coated with luminescent metal-organic frameworks (MOFs) of the constitution IF2[Ln2Cl6(bipy)3]·2bipy (bipy = 4,4'-bipyridine) that was achieved by intriguing reaction conditions including mechanochemistry. The novel composites combine the properties of both constituents: superparamagnetism and luminescence. The magnetic properties can be exploited to magnetically collect the particles from dispersions in fluids and, by gathering them at one spot, to augment the luminescence originating from the MOF modification on the particles. The luminescence can be influenced by chemical compounds, e.g., by quenching observed for low concentrations of water. Thus, the new composite systems present an innovative concept of property combination that can be potentially used for the detection of water traces in organic solvents as a magnetically augmentable, luminescent water detector.

Herein, the formation of hollow microballoons derived from superparamagnetic iron oxide nanoparticles with silica patches is reported. Depending on the experimental conditions, single- or multishelled superparamagnetic microballoons as well as multivesicular structures were obtained. We show how such structural changes follow a lifelike process that is based on self-directing Pickering emulsions. We further demonstrate that the key toward the formation of such complex architectures is the patchy nature of the nanoparticles. Interestingly, no well-defined ordering of patches on the particles surface is required, unlike what theorists formerly predicted. The resultant hollow microballoons may be turned into hollow carbonaceous magnetic microspheres by simple pyrolysis. This opens the way to additional potential applications for such ultralightweight (density: 0.16 g·cm-3) materials.

An innovative mechanochemical method is reported for the in situ formation of crystalline metal-complexes on the surface of superparamagnetic nanocomposite microparticles. The process is demonstrated for coating Fe3O4 multicore-silica matrix particles with the 1,2,4-1H-triazole complex [ZnCl2(TzH)2]. The use of mechanochemistry demonstrates a flexible process to obtain functional shells on magnetic particle cores without the need for complicated surface-functionalisation reactions in solution. Simple mixing of the desired shell-precursors ZnCl2 and 1,2,4-1H-triazole (TzH) with the magnetic particles in a ball mill is sufficient to tailor the particle surfaces with novel functionalities while retaining the superparamagnetic behaviour.

A process is reported to obtain a nanoparticle sol from co-precipitated iron oxide particles without using any surfactant. The sol - a true ferrofluid - is not only stable over a wide range of pH but also in physiological solutions. This is a decisive step towards biomedical applications where nanoparticle agglomeration could so far only be prevented by using unwanted surfactants.

Hydrothermal method of nanoparticle preparation, involving oleic acid, has received certain attention in the last years. However, the published works lack systematic approach to the subject, and the mechanism was not thoroughly investigated, so as to achieve a predictable outcome of the synthesis. The present work investigated the influence of composition of organic and water phase on the synthesis of cobalt ferrite (cobalt(II)-iron(III) oxide) and magnetite nanoparticles, and the mechanism of nanoparticle formation was proposed. Organic phase was based on pentanol, octanol or toluene, containing the precursor - metal oleate. Besides hydrophobic particles, it was even possible to directly prepare hydrophilic oleate-coated particles by using water phase with sodium oleate. Synthetic procedure was then simplified by a separate preparation of cobalt-iron oleate, which led also to a product of narrower size distribution and better phase purity. Size control in the range of 6-11 nm and a batch yield of ca. 500 mg was achieved. Attention was given also to the surface modification of the particles, thus imparting them hydrophilicity. Small di- or tricarboxylic acids were utilized, as well as carboxylmethyl dextran and titanium dioxide. Titanium dioxide required additional protection with...

The aim of the work is characterization of structure and magnetic properties of various CoFe2O4/SiO2 nanocomposites. Emphasis was put on the corelation of the magnetic properties with particle size (samples with different annealing temperature) and with strenght of the interparticle interactions (samples with different Fe/Si ratio or without silica matrix). Structure properties of all samples were determinated by powder x-ray diffraction, scanning and transmission electron microscopy. Magnetic properties were determinated by standard (temperature dependence of magnetization, magnetization isotherms) and advanced (a.c. susceptibility, memory effects) magnetic measurements. A sharp increase of the values of blocking temperature and coercivity with increase of strenght of the interparticle interactions and with increase of particle size was observed. Particle size determines the maximum value of coercivity and blocking temperature and strengh of the interparticle interactions shift this values in the interval determined by particle size.

Superparamagnetic nanoparticles of magnetite were coprecipitated from iron salts, dispersed with nitric acid and stabilised either by lactic acid (LA) or by a polycarboxylate-ether polymer (MELPERS4343, MP). The differently stabilised nanoparticles were incorporated into a silica matrix to form nanocomposite microparticles. The silica matrix was prepared either from tetraethylorthosilicate (TEOS) or from an aqueous sodium silicate (water glass) solution. Stabilisation of nanoparticles had a crucial influence on microparticle texture and nanoparticle distribution in the silica matrix. Magnetic measurements in combination with transmission electron microscopy (TEM) investigations suggest a uniform magnetic interaction of nanoparticles in case of LA stabilisation and magnetically interacting nanoparticle clusters of different sizes in case of MP stabilisation. Splitting of blocking temperature (TB) and irreversible temperature (Tir) in zero field cooled (ZFC) and field cooled (FC) measurements is discussed in terms of nanoparticle clustering.

Superparamagnetic nanocomposite microparticles, compromised of magnetite nanoparticles in a silica matrix, have been synthesised and surface-modified to act as adsorbers for substances (e.g. toxic heavy metals or valuable resources) dissolved in fluids like water. The particles can be used for a magnetic-extraction-assisted separation process of these target substances which thereby can be recovered from the fluid., In der vorliegenden Arbeit wurden superparamagnetische Nanokomposit-Mikropartikel, bestehend aus Magnetitnanopartikeln in einer Silica-Matrix, hergestellt. Die Oberfläche der Partikel wurde modifiziert, so dass die Partikel als Adsorber für gelöste Substanzen (z.B. giftige Schwermetalle oder Wertstoffe) in Fluiden wie z.B. Wasser eingesetzt werden können. Mit Hilfe der Partikel kann eine Abtrennung und damit Rückgewinnung der Zielstoffe auf Basis eines Magnetseparationsprozesses durchgeführt werden.

Agglomerated superparamagnetic iron oxide nanoparticles can easily and in large scale be precipitated from iron salt solutions. Although the process is well known, it is ambiguously either assumed that magnetite or maghemite is obtained. The first part of our study clarifies this question using X-ray absorption spectroscopy. For further processing of the nanoparticles, i.e., for giving them a surface functionality or incorporating them into composites, it is important to break the agglomerates and individualize the particles at first. This can effectively be done with nitric acid treatment. The influence of this process on the particles chemistry and structure was analyzed in great detail using X-ray diffraction, X-ray absorption, and small-angle X-ray scattering. In contrast to our expectation, no oxidation from magnetite (Fe3O4) to maghemite (y-Fe2O3) was found; the formal valence of the particles in any case is magnetite (Fe3O4). Instead, an increase in the particles' surface disorder was discovered from X-ray absorption analyses and high-resolution transmission electron microscopy. The acid treatment roughens and distorts the surface of the nanoparticles which is connected with an increased spin disorder.

Im Rahmen dieser Dissertation wurden mithilfe der Mizelltechnik 12 nm bzw. 9 nm große Kobaltoxidteilchen in hexagonaler Ordnung hergestellt. In einem eigens entwickelten Wasserstoffplasmaprozessschritt wurden diese unter Beibehaltung der Ordnung zu elementarem Kobalt reduziert. Mittels des Röntgenzirkulardichosimus (XMCD) wurden die Teilchen magnetisch vermessen. Es konnte durch Auswertung der superparamagnetischen Magnetierungskurven gezeigt werden, dass sich die Teilchen magnetisch wie 2-4 nm große Teilchen verhalten. Es wurde nachgewiesen, dass in diesem Plasmaprozess Kobalthydrid (CoHx) hergestellt werden kann, das bei Zimmertemperatur stabil ist und sich erst bei 650 °C vollständig zersetzt. In dieser Dissertation wurde somit gezeigt, dass mittels Röntgenabsorptionsspektroskopie (XAS) CoHx experimentell nachweisbar ist. Es zeigen sich im Spektrum zusätzliche Schultern, die gegen die L3- bzw. L2-Kante um 2,2 bzw. 1,3 eV verschoben sind.

The present thesis provides an extensive and original contribution to the investigation of magnetic nanoparticles regarding synthesis and structural characterization using advanced scattering methods in all length scales between the atomic and mesoscopic size range. Particular emphasis is on determination of the magnetic structure of single nanoparticles as well as preparation and characterization of higher dimensional assemblies thereof. The unique physical properties arising from the finite size of magnetic nanoparticles are pronounced for very small particle sizes. With the aim of preparing magnetic nanoparticles suitable for investigation of such properties, a micellar synthesis route for very small cobalt nanoparticles is explored. Cobalt nanoparticles with diameters of less than 3 nm are prepared and characterized, and routes for variation of the particle size are developed. The needs and limitations of primary characterization and handling of such small and oxidation-sensitive nanoparticles are highlighted and discussed in detail. Comprehensive structural and magnetic characterization is performed on iron oxide nanoparticles of 10 nm in diameter. Particle size and narrow size distribution are determined with high precision. Investigation of the long range and local atomic structure reveals a particle size dependent magnetite - maghemite structure type with lattice distortions induced at the particle surface. The spatial magnetization distribution within these nanoparticles is determined to be constant in the particle core with a decrease towards the particle surface, thus indicating a magnetic dead layer or spin canting close to the surface. Magnetically induced arrangements of such nanoparticles into higher dimensional assemblies are investigated in solution and by deposition of long range ordered mesocrystals. Both cases reveal a strong dependence of the found structures on the nanoparticle shape (spheres, cubes, and heavily truncated cubes). Nanospheres and nanocubes form closed packed mesocrystals and a short range ordered hard spheres interaction potential in dispersion. In addition, the arrangements of the cuboidal nanoparticles exhibit a strong tendency of face to face oriented attachment, which may result from van der Waals interaction of the cubic facets. Mesocrystals of aged nanocubes with higher degree of truncation reveal a structural transition between the structures of nanocubes and nanospheres.

Hydrophobic iron oxide nanoparticles with 25 or 10 nm in diameter and the fluorescent dye PMI were successfully loaded into poly(L-lactide) using the combination of miniemulsion and solvent evaporation techniques. The obtained particles have an average diameter of 120 nm (with 25 nm iron oxide) or 130 to 180 nm (with 10 nm magnetite) and show high stability in the aqueous phase. The iron oxide particles show superparamagnetic behaviour. Cell experiments with mesenchymal stem cells show very good particle uptake and excellent cell viability. The ability of the MSCs to differentiate as well as the phenotype are not changed by the particle uptake. Labeled MSCs can be distinguished from the negative control and can be detected in vivo in MRI as well. The magnetic properties of the PLLA particles and the possibility to encapsulate hydrophobic molecules (e.g. dyes, drugs) into the polymer matrix predestine these particles for magnetically targeted drug delivery and as contrast agent for magnetic resonance imaging. Functionalized PLLA/P(MAA-co-St), PLLA/P(AEMH-co-St) or PLLA/P(PEG-co-St) composite particles can be synthesized using a combination of miniemulsion, free radical copolymerization and solvent evaporation techniques. Depending on the synthesis route of the copolymer, nanoparticles between 120 and 180 nm in diameter are received. The morphology of the obtained nanoparticles can be altered by the synthesis route or the monomer ratio between homogeneous, hemispherical or Janus-like. The amount of functional groups on the surface can be varied by the monomer ratio or the preparation technique. Magnetic and functionalized PLLA based composite particles can be analog synthesized. Iron oxide particles with 25 as well as 10 nm in diameter were encapsulated into the composite particles.

The diversity of applications in the Internet and the heterogeneity of today's networked platforms make the development of communication protocols complex and time-consuming. This work introduces mechanisms, models, and tools to reduce the complexity and engineering effort required for protocol development and evaluation. It makes the following three key contributions:1. Similarities in protocol mechanisms are extracted into modular building blocks to reduce the complexity of communication system development.2. We introduce a platform abstraction layer to gradually evolve protocol implementations across platforms avoiding frequent reimplementation.3. Automated instrumentation of models with system properties allows to accurately analyzing the time dependent behavior and power consumption of networked devices.

Ill., graph. Darst.

Bislang war eine Signalverstärkung nötig für die Detektion einzelner magnetischer Marker mittels magnetoresistiver Sensoren. Die Detektion ohne Signalverstärkung mit Hilfe von magnetischen Tunnelelementen (englisch: "magnetic tunnel junction", MTJ) wäre ein Fortschritt im Bereich der Miniaturisierung und in der Anwendbarkeit als Biosensoren. Versuche mit konventionellen AlOx-Tunnelelementen wurden durchgeführt in Verbindung mit superparamagnetischen Teilchen, sog. Beads, die senkrecht zur Sensorebene gesättigt wurden. TMR-Messungen von Sensoren mit und ohne Bead, gesättigt und ungesättigt, wurden miteinander verglichen. Mit Helmholtz-Spulen ist eine verschobene Hysterese möglich, die auch schmaler ist, dagegen scheinen die Aufbauten mit Permanentmagneten nicht einsetzbar zu sein, da das magnetische Feld nicht homogen genug war. Von Elementen mit senkrechtem "pinning" wird erwartet, dass sie keine Hysterese zeigen. Für MgO-Tunnelelemente wurde senkrechtes pinning durch Formanisotropie verwirklicht. Mittels Elektronenstrahllithografie und Ionenätzen wurden Felder mit tausenden (Sub-)Mikrometerelementen hergestellt. Messungen auf Grundlage des magnetooptischen Kerr-Effekts zeigen Hysterese-freie Signale, wenn mit kleinen Feldern gemessen wird., Signal enhancement was so far necessary for detection of single magnetic markers using magnetoresistive sensors. Detection without signal enhancement on basis of a magnetic tunnel junction (MTJ) would be an important feature for miniaturization and for applications such as biosensors. Based on conventional MTJs with AlOx barrier several setups with out-of-plane saturation of superparamagnetic beads were analyzed. TMR measurements with and without beads on top of a sensor, alternatively saturated or not were compared. With Helmholtz coils a shifted and narrow hysteresis is possible, whereas permanent magnets seem to be not applicable due to a very inhomogeneous field in this setup. Elements are expected to have a hysteresis-free magnetic switching due to a perpendicular pinning. For MgO based sensors perpendicular pinning has been established via shape anisotropy. Arrays containing thousands of (sub-)micron elements were structured by electron beam lithography and ion beam etching. Measurements using the magneto-optical Kerr effect show a hysteresis-free signal for low magnetic fields.

In dieser Arbeit werden die strukturellen und magnetischen Eigenschaften von CoPt3-Partikeln untersucht. Insbesondere die Bestimmung des g-Faktors, der mit dem Spin- und Bahnmoment verknüpft ist, ist hierbei von Interesse sowie das Dämpfungsverhalten des unter Einfluss von Mikrowellenstrahlung stehenden Magnetisierungsvektors. Desweiteren ist die magnetische Anisotropieenergiedichte einzelner Partikel Gegenstand der Untersuchungen. In this work the structural and magnetic characteristics of CoPt3-particles are examined. In particular the determination of the g-factor, that is connected with the spin and orbital moment is of interest as well as the damping behavior of the magnetization vector under influence of a microwave radiation. Moreover the magnetic anisotropy energy density of individual particles is covered by the presented thesis.

In two thematically different parts, this work presents results of theinvestigation of novel nanoparticle matter composed of titanium nitride (TiN),zirconium nitride (ZrN), and nickel (Ni), respectively. All samples wereproduced with the nanoparticle beam apparatus LUCAS.In the first part, the focus mainly lies on the analysis of the optical andcolorimetric properties of TiN and ZrN nanoparticles and the discussion oftheir potential application as color pigments. The foundation for this purposeis laid by the illustration of the main features of the Mie and Generalized Mietheory, which describe the optical spectra of single and aggregated particles,respectively, as well as of the colorimetry, that is based upon therecommendations of the International Commission on Illumination (CIE) and isused to determine chromaticity coordinates from physical spectra. The chemicaland structural characterization shows, that with both nitrides crystalline and(almost) stoichiometric particles are formed under the used conditions andresonably small size distributions are achieved. Under the influence of oxygen,however, the particles are partly oxidized. On the basis of the opticalspectra of on quartz glass deposited particles the optical properties of bothnitrides are discussed. The experimental findings are compared with calculations(Mie theory and GMT). The colorimetric properties are determined from opticaltransmission measurements of embedded TiN and ZrN nanoparticles. The resultsare given in the CIELAB color system. The analysis indicates, that both speciesare principally suitable for the application as color pigments: depending on thesample parameters, TiN particles exhibit colors in the blue and blue-green partof the color plane, whereas ZrN particles yield red and violett colors. Theexperimental data can be understood with Mie theory based colorimetriccalculations. On the basis of TiN nanoparticles the important question isdiscussed, how the color of a sample can be modified.The second part of this work deals with the determination of the magneticproperties of in situ oxidized Ni/NiO core-shell nanoparticles, which are ofspecial interest because of their possible use in highly pure ferrofluids. Theinvestigations mainly concentrate on the question if the size-dependentsuperparamagnetism emerges and if the antiferromagnetic nickel oxide shellsinduce the so-called exchange bias in the Ni cores due to exchange anisotropy.Besides the theoretical fundamentals of both phenomena, experimental data ispresented that were obtained by zero field cooling, field cooling, andhysteresis measurements. They reveal that superparamagnetism cannot be verified.Exchange bias, however, is clearly visible. Optical spectra taken during theoxidation process of the nickel particles are also analysed. They show thegrowing influence of the oxide shells on the optical properties.

Seit der ersten Herstellung von Ferrofluiden Mitte der Sechziger Jahre wird auf experimenteller und theoretischer Ebene intensiv am Verständnis des Verhaltens der Ferrofluide gearbeitet. Der Untersuchung des wechselseitigen Einflusses der magnetischen und rheologischen Eigenschaften (Magnetoviskoser Effekt) der Ferrofluide gilt hierbei besonderes Interesse, stellt dieser Effekt doch die Grundlage für das einzigartige Verhalten der Ferrofluide dar. Über diesen Zusammenhang wurde 1969 erstmals von R. E. Rosensweig berichtet: Wird ein Ferrofluid von einem konstanten Magnetfeld durchsetzt, so steigt dessen Viskosität mit zunehmender Feldstärke. Schert man ein feldfreies Ferrofluid, so ist die Bewegung der Partikel mit der Vortizität der Strömung verknüpft, diese führt zu einer Rotation der Partikel. Wird nun ein konstantes Magnetfeld überlagert, so findet abhängig vom Winkel zwischen Feld und der Vortizität der Strömung eine Konkurrenz der auf die Partikel wirkenden magnetischen und viskosen Drehmomente statt. Das Drehmoment, welches versucht die Partikel in Feldrichtung zu orientieren, verlangsamt die Rotation im Fluid und stellt makroskopisch eine Viskositätserhöhung dar. Eine erste theoretische Beschreibung wurde 1972 von Shliomis formuliert und berücksichtigt neben den magnetischen und mechanischen Drehmomenten auch die Brownschen Bewegung der magnetischen Partikel im Fluid. Beschreiben die ersten Arbeiten Ferrofluide als Ensemble nicht wechselwirkender, monodisperser Partikel so zeigten Messungen an konzentrierten Fluiden die Notwendigkeit des Einbezugs von Polydispersität und der Wechselwirkungen zwischen den magnetischen Partikeln. Aufgrund der Polydispersität der Partikelgrößen finden sich in den Fluiden Partikel mit mehr als dem zweifachen des Durchschnittsvolumens. Trotz ihrer geringen Konzentration hat diese Fraktion entscheidenden Einfluss auf das magnetoviskose Verhalten des Fluides. Aufgrund der langen Reichweite und der starken Größenabhängigkeit der magnetisch dipolaren Wechselwirkung bilden diese Partikel dynamische, kettenförmige Agglomerate, welche auch ohne Anwesenheit eines externen Magnetfeldes vorliegen. Diese dynamischen Ketten mit großem Aspektverhältnis (Verhältnis Länge:Durchmesser) dominieren das magnetoviskose Verhalten der Fluide. Vergleichbar einem Paddel findet bei Rotation in einem angelegten Feld ein, gegenüber einer Kugel, stark erhöhter Kraftübertrag auf das Fluid statt. Der damit verbundene Magnetoviskose Effekt übertrifft denjenigen vergleichbarer sphärischer Partikel um 2-3 Größenordnungen. Diese enorme Steigerung ist jedoch beschränkt auf den Bereich sehr kleiner Scherraten, denn die Scherung der Flüssigkeit führt zu einem Zerbrechen der kettenförmigen Agglomerate. Ziel der vorliegenden Arbeit ist die Synthese stabiler magnetische Partikelketten mit feld- und scherratenunabhängigem Aspektverhältnis. Damit kann mittels kleiner Magnetfelder (ca. 10mT) eine variable Viskositätsänderung von mehreren Größenordnungen induziert werden. Dieser Effekt ist dann auch im technologisch interessanten Bereich großer Scherraten erreichbar. Erreicht wurde diese festen, stangenförmigen Partikel mittels einer Aerosolsynthese im Verlaufe derer elementares Eisen verdampft, und zu Nanopartikeln kondensiert wurde. Diese Partikel wurden im Aerosol zu stabilen Ketten versintert (Nanostäbe) und mit Hilfe einer Ölsäurehülle vor weiterer Agglomeration geschützt. Ziel dieser Arbeit ist es, neben der Etablierung der Präparation, insbesondere die magnetischen und magnetoviskosen Eigenschaften solcher Nanostab-Ferrofluide zu erforschen. Since the first preparation of ferrofluids in the mids of the 60s the understanding of their behavior is a matter of both theoretical and experimental research. Especially the interaction of rheological and magnetic properties (known as the magnetoviscous effect) is a main concern for being the source of the unique behavior of ferrofluids. First published in 1969 by R. E. Rosensweig this effect describes the rise of the viscosity of an ferrofluid situated in a homogeneous magnetic field. Shearing of an ferrofluid leads to the rotation of the magnetic particles because of the coupling between their movements and the vorticity of the fluid. Superposition of a magnetic field causes a rivalry between the magnetic and the viscous torques. The magnetic torque tries to align the particles magnetic momentum in the direction of the field thus hindering their free rotation with the field therefore causing a rise of the viscosity of the fluid. Shliomis found a first theoretical description by taking account of both torques as well as the Brownian movement of the magnetic particles amongst the molecules of the fluid. Starting by considering ferrofluids as ensembles of non-interacting, identical particles later works included the influence of interactions between the now polydisperse particles being distributed over a range of different sizes.Despite their small volume fraction particles more than twice as large as the mean particle size dominate the magnetoviscous behavior due to the formation of dynamical chainlike structures. Long-range dipolar forces create linear dynamic aggregates of these hardmagnetic particles even in zero field. Like a paddle their rotation in the direction of the outer field can transfer much bigger forces than equally sized spherical particles therefore causing a strongly enhanced magnetoviscous effect. Changes in the viscosity 2-3 decades larger than expected for spherical particles. But tragically, this effect is limited to the range of very small shear rates because by rising the shear rate the fragile chains vanish and also the strong magnetoviscous effect. The goal of this work is therefore the creation of stable rodlike magnetic particles their size being independent of field strength and shear rate. With them it would be possible to achieve this huge effect with small magnetic fields (some 10mT) and for technological relevant shear rates. We succeeded in creating this particles by an aerosol process during which iron is evaporated and condensed to small nanometer sized particles. Insitu sintering of chainlike aggregates led to stable rodlike particles (nanorods) which withstand further agglomeration after covering them with a layer of oleic acid. Beside the establishment of the preparation we focused on the on the magnetic and the magnetoviscous properties of these nanorod-ferrofluids.

In dieser Arbeit wurden CoMn-Einkristalle temperatur- und druckabhängig mit Ultraschall untersucht. Die Proben zeigten verschiedene magnetische Ordnungen, wie ferro-, antiferro-, para-, superpara- und superantiferromagnetisch. Aus der Temperaturabhängigkeit der elastischen Konstanten konnten die Übergangstemperaturen der magnetischen und strukturellen Phasenübergänge bestimmt werden. Damit war es möglich, ein Phasendiagramm zu erstellen. Die beobachteten Anomalien konnten mit Hilfe der Landau-Theorie für Phasenübergänge 2.Ordnung und dem Vergleich der Daten mit einer paramagnetischen Referenzprobe erklärt werden. Im Zusammenhang mit den Invar-Eigenschaften der Proben wurde eine Abhängigkeit der Anomalie des Kompressionsmoduls von der Elektronenkonzentration gefunden. Um die magnetischen Eigenschaften der Legierungen zu untersuchen, wurden zusätzlich Messungen der Suszeptibilität und der Magnetisierung vorgenommen.