Confocal microscopy applied to the study of single entity fluorescence and light scattering

A sample scanning confocal optical microscope (SCOM) was designed and constructed in order to perform local measurements of fluorescence, light scattering and Raman scattering. This instrument allows to measure time resolved fluorescence, Raman scattering and light scattering from the same diffraction limited spot. Fluorescence from single molecules and light scattering from metallic nanoparticles can be studied. First, the electric field distribution in the focus of the SCOM was modelled. This enables the design of illumination modes for different purposes, such as the determination of the three-dimensional orientation of single chromophores. Second, a method for the calculation of the de-excitation rates of a chromophore was presented. This permits to compare different detection schemes and experimental geometries in order to optimize the collection of fluorescence photons. Both methods were combined to calculate the SCOM fluorescence signal of a chromophore in a general layered system. The fluorescence excitation and emission of single molecules through a thin gold film was investigated experimentally and modelled. It was demonstrated that, due to the mediation of surface plasmons, single molecule fluorescence near a thin gold film can be excited and detected with an epi-illumination scheme through the film. Single molecule fluorescence as close as 15nm to the gold film was studied in this manner. The fluorescence dynamics (fluorescence blinking and excited state lifetime) of single molecules was studied in the presence and in the absence of a nearby gold film in order to investigate the influence of the metal on the electronic transition rates. The trace-histogram and the autocorrelation methods for the analysis of single molecule fluorescence blinking were presented and compared via the analysis of Monte-Carlo simulated data. The nearby gold influences the total decay rate in agreement to theory. The gold presence produced no influence on the ISC rate from the excited state to the triplet but increased by a factor of 2 the transition rate from the triplet to the singlet ground state. The photoluminescence blinking of Zn0.42Cd0.58Se QDs on glass and ITO substrates was investigated experimentally as a function of the excitation power (P) and modelled via Monte-Carlo simulations. At low P, it was observed that the probability of a certain on- or off-time follows a negative power-law with exponent near to 1.6. As P increased, the on-time fraction reduced on both substrates whereas the off-times did not change. A weak residual memory effect between consecutive on-times and consecutive off-times was observed but not between an on-time and the adjacent off-time. All of this suggests the presence of two independent mechanisms governing the lifetimes of the on- and off-states. The simulated data showed Poisson-distributed off- and on-intensities, demonstrating that the observed non-Poissonian on-intensity distribution of the QDs is not a product of the underlying power-law probability and that the blinking of QDs occurs between a non-emitting off-state and a distribution of emitting on-states with different intensities. All the experimentally observed photo-induced effects could be accounted for by introducing a characteristic lifetime tPI of the on-state in the simulations. The QDs on glass presented a tPI proportional to P-1 suggesting the presence of a one-photon process. Light scattering images and spectra of colloidal and C-shaped gold nano-particles were acquired. The minimum size of a metallic scatterer detectable with the SCOM lies around 20 nm.

Core-shell macromolecules with dendritic polyphenylene core and polymer shells

Core-shell macromolecules with dendritic polyphenylene core and polymer shell Zusammenfassung / Abstract Core-shell macromolecular structures have become of great interest in materials science because they gave an opportunity to combine a large variety of chemical and physical properties in the single molecule, by combination of different (in terms of chemistry and physics) cores and shells. The interest in such complex structures was provoked by their potential applications in the coating and painting industry (latexes), as supports for catalysts in polymer industry, or as nano-containers and transporters for genes or drug delivery. The aim of this study was the synthesis, characterization and further application of core-shell macromolecules possessing a hydrophobic stiff core (polyphenylene dendrimers) surrounded with a hydrophilic, soft, covalently bonded polymer shell (poly(ethylene oxide) and its copolymers). The requirements for such complex substances were that they should be well-defined in terms of molecular weight (narrow molecular weight distribution) and in molecular structure. The preparation of core-shell molecules containing dendrimer as a core was possible via two synthetic routs: ���grafting-onto��� and ���grafting-from���. The resulting core-shell macromolecules possessed narrow polydispersity as guaranteed by the excellent structural and functional definition of the dendrimer and the narrow polydispersity of the PEO, PS-b-PEO and PI-b-PEO attached to the dendrimer surface. Additional investigation of the size of the particles indicated a relation between both the length and the number of the polymer chains and the hydrodynamic radius determined by Dynamic Light Scattering and Fluorescent Correlation Spectroscopy. Core-shell nano-particles were applied as metallocene supports in heterogeneous olefin polymerizations. Our results indicate that such catalyst systems, that have a size of at least one order of magnitude smaller than the used by now organic supports, could be very useful as model compounds for investigations on catalyst fragmentation and its influence on the product parameters.

Mechanical microcontacts of powder particles studied with the quartz crystal microbalance

Within this work, a particle-polymer surface system is studied with respect to the particle-surface interactions. The latter are governed by micromechanics and are an important aspect for a wide range of industrial applications. Here, a new methodology is developed for understanding the adhesion process and measure the relevant forces, based on the quartz crystal microbalance, QCM. rnThe potential of the QCM technique for studying particle-surface interactions and reflect the adhesion process is evaluated by carrying out experiments with a custom-made setup, consisting of the QCM with a 160 nm thick film of polystyrene (PS) spin-coated onto the quartz and of glass particles, of different diameters (5-20��m), deposited onto the polymer surface. Shifts in the QCM resonance frequency are monitored as a function of the oscillation amplitude. The induced frequency shifts of the 3rd overtone are found to decrease or increase, depending on the particle-surface coupling type and the applied oscillation (frequency and amplitude). For strong coupling the 3rd harmonic decreased, corresponding to an ���added mass��� on the quartz surface. However, positive frequency shifts are observed in some cases and are attributed to weak-coupling between particle and surface. Higher overtones, i.e. the 5th and 7th, were utilized in order to derive additional information about the interactions taking place. For small particles, the shift for specific overtones can increase after annealing, while for large particle diameters annealing causes a negative frequency shift. The lower overtones correspond to a generally strong-coupling regime with mainly negative frequency shifts observed, while the 7th appears to be sensitive to the contact break-down and the recorded shifts are positive.rnDuring oscillation, the motion of the particles and the induced frequency shift of the QCM are governed by a balance between inertial forces and contact forces. The adherence of the particles can be increased by annealing the PS film at 150��C, which led to the formation of a PS meniscus. For the interpretation, the Hertz, Johnson-Kendall-Roberts, Derjaguin-M��ller-Toporov and the Mindlin theory of partial slip are considered. The Mindlin approach is utilized to describe partial slip. When partial slip takes place induced by an oscillating load, a part of the contact ruptures. This results in a decrease of the effective contact stiffness. Additionally, there are long-term memory effects due to the consolidation which along with the QCM vibrations induce a coupling increase. However, the latter can also break the contact, lead to detachment and even surface damage and deformation due to inertia. For strong coupling the particles appear to move with the vibrations and simply act as added effective mass leading to a decrease of the resonance frequency, in agreement with the Sauerbrey equation that is commonly used to calculate the added mass on a QCM). When the system enters the weak-coupling regime the particles are not able to follow the fast movement of the QCM surface. Hence, they effectively act as adding a ���spring��� with an additional coupling constant and increase the resonance frequency. The frequency shift, however, is not a unique function of the coupling constant. Furthermore, the critical oscillation amplitude is determined, above which particle detach. No movement is detected at much lower amplitudes, while for intermediate values, lateral particle displacement is observed. rnIn order to validate the QCM results and study the particle effects on the surface, atomic force microscopy, AFM, is additionally utilized, to image surfaces and measure surface forces. By studying the surface of the polymer film after excitation and particle removal, AFM imaging helped in detecting three different meniscus types for the contact area: the ���full contact���, the ���asymmetrical��� and a third one including a ���homocentric smaller meniscus���. The different meniscus forms result in varying bond intensity between particles and polymer film, which could explain the deviation between number of particles per surface area measured by imaging and the values provided by the QCM - frequency shift analysis. The asymmetric and the homocentric contact types are suggested to be responsible for the positive frequency shifts observed for all three measured overtones, i.e. for the weak-coupling regime, while the ���full contact��� type resulted in a negative frequency shift, by effectively contributing to the mass increase of the quartz..rnThe interplay between inertia and contact forces for the particle-surface system leads to strong- or weak-coupling, with the particle affecting in three mentioned ways the polymer surface. This is manifested in the frequency shifts of the QCM system harmonics which are used to differentiate between the two interaction types and reflect the overall state of adhesion for particles of different size.rn

Einfluss von Stickstoffmonoxid, Hydroxylradikalen und Peroxynitrit auf DNA-Sch��den, DNA-Reparatur und Mutationen

Im Rahmen dieser Arbeit wurde untersucht ��ber welche Mechanismen und unter welchen Bedingungen Stickstoffmonoxid (NO) und verwandte reaktive Spezies wie Peroxynitrit und Hydroxylradikale zur Krebsentstehung beitragen k��nnen. NO f��hrte an zellfreier DNA kaum zu oxidativen DNA-Sch��den. Peroxynitrit, generiert aus 3-Morpholinosydnonimin (SIN-1), induzierte neben Einzel-strangbr��chen und AP-L��sionen vor allem oxidierte Purinmodifikationen (50 % 8-Hydroxyguanin (8-oxoG)). Hydroxylradikale, freigesetzt aus 4-Hydroxypyridinthion, induzierten neben Einzelstrangbr��chen und AP-L��sionen oxidierte Pyrimidinmodifikationen in der DNA. Nach Transformation und Replikation der gesch��digten DNA in E. coli DT-2 wurden ��berwiegend GC nach AT Transitionen (Hydroxylradikalsch��digung), wahrscheinlich verursacht durch das in der DNA induzierte 5-Hydroxycytidin, bzw. GC nach TA Transversionen (Peroxynitrit), verursacht durch das induzierte 8-oxoG, detektiert. In Zellkulturexperimenten f��hrte endogenes NO, freigesetzt von B6-INOS-Zellen (8��M) nicht zu einem Anstieg der Gleichgewichtsspiegel oxidativer DNA-Sch��den, hatte keinen Einfluss auf deren Induzierbarkeit und Reparatur, die Zellpro-liferation und den Glutathionspiegel, sch��tzte jedoch vor der Induktion von Einzelstrangbr��chen und Mikrokernen durch Wasserstoffperoxid. Exogenes NO, freigesetzt durch den Zerfall von Dipropylentriamin-NONOat, hemmte in Konzentrationen ab 0,5 mM spezifisch die Reparatur oxidativer DNA-Sch��den, nicht jedoch die von Pyrimidindimeren, AP-L��sionen und Einzelstrangbr��chen,und f��hrte in Konzentrationen > 1 mM zu einer Induktion von DNA-Sch��den in den B6-Mausfibroblasten. Dabei ��hnelte das induzierte Schadensprofil sehr dem von SIN-1.

Ma��geschneiderte Kieselgeltr��ger f��r die metallocen-katalysierte Polyolefinsynthese

Die vorliegende Arbeit besch��ftigt sich mit der Synthese und Charakterisierung von por��sen Kieselgelen und ihrem Einsatz als Tr��ger in der heterogenen metallocen-katalysierten Polymerisation von Ethylen. Im Vordergrund stand die Optimierung dieses Prozesses durch das Ma��scheidern der Tr��gereigenschaften unter sonst identischen Polymerisationsbedingungen und das Erforschen des heterogenen Polymerisationsprozesses. Das verwendete Katalysatorsystem (Methylaluminoxan mit Dicyclopentadienylzirkoniumdichlorid) besitzt sehr hohe Aktivit��ten und verbleibt im Falle der heterogenen Reaktionsf��hrung im Produkt. Der Mechanismus verl��uft ��ber mehrere Phasen, wobei besonderes Augenmerk auf die Tr��gerpartikelfragmentierung gelenkt wurde. Es wurden zwei Synthesekonzepte f��r die Herstellung der Tr��ger verfolgt. Im ersten Teil der Arbeit wurden monodisperse unpor��se Kieselgel-Nanopartikel (Monosphere) zu Agglomerattr��gern ��ber einen Spr��htrocknungsprozess aufgebaut. Die Stabilit��t der Agglomerate wurde ��ber den Zusatz von monodispersen Kieselgel-Binderpartikeln w��hrend der Herstellung variiert. Es wurden sowohl die porenstrukturellen als auch morphologischen Eigenschaften der Agglomeratprodukte untersucht und mit den physiko-chemischen Eigenschaften der Nanopartikel korreliert. In einem zweiten Ansatz wurden sph��rische hochpor��se Kieselgele mit abgestufter Porosit��t bei konstanter spezifischer Oberfl��che hergestellt und als Tr��ger in der Polyethylensynthese getestet.

Synthesis and characterization of metal-chalcogenide MQ 2-Nanoparticles (M = Mo, W, Zr; Q = S, O)

Here, we present the adaptation and optimization of (i) the solvothermal and (ii) the metal-organic chemical vapor deposition (MOCVD) approach as simple methods for the high-yield synthesis of MQ2 (M=Mo, W, Zr; Q = O, S) nanoparticles. Extensive characterization was carried out using X-ray diffraction (XRD), scanning and transmission electron micros��copy (SEM/TEM) combined with energy dispersive X-ray analysis (EDXA), Raman spectroscopy, thermal analyses (DTA/TG), small angle X-ray scattering (SAXS) and BET measurements. After a general introduction to the state of the art, a simple route to nanostructured MoS2 based on the decomposition of the cluster-based precursor (NH4)2Mo3S13���xH2O under solvothermal conditions (toluene, 653 K) is presented. Solvothermal decomposition results in nanostructured material that is distinct from the material obtained by decomposition of the same precursor in sealed quartz tubes at the same temperature. When carried out in the presence of the surfactant cetyltrimethyl��ammonium bromide (CTAB), the decomposition product exhibits highly disordered MoS2 lamellae with high surface areas. The synthesis of WS2 onion-like nanoparticles by means of a single-step MOCVD process is discussed. Furthermore, the results of the successful transfer of the two-step MO��CVD based synthesis of MoQ2 nanoparticles (Q = S, Se), comprising the formation of amorphous precursor particles and followed by the formation of fullerene-like particles in a subsequent annealing step to the W-S system, are presented. Based on a study of the temperature dependence of the reactions a set of conditions for the formation of onion-like structures in a one-step reaction could be derived. The MOCVD approach allows a selective synthesis of open and filled fullerene-like chalcogenide nanoparticles. An in situ heating stage transmission electron microscopy (TEM) study was employed to comparatively investigate the growth mechanism of MoS2 and WS2 nanoparticles obtained from MOCVD upon annealing. Round, mainly amorphous particles in the pristine sample trans��form to hollow onion-like particles upon annealing. A significant difference between both compounds could be demonstrated in their crystallization conduct. Finally, the results of the in situ hea��ting experiments are compared to those obtained from an ex situ annealing process under Ar. Eventually, a low temperature synthesis of monodisperse ZrO2 nanoparticles with diameters of ~ 8 nm is introduced. Whereas the solvent could be omitted, the synthesis in an autoclave is crucial for gaining nano-sized (n) ZrO2 by thermal decomposition of Zr(C2O4)2. The n-ZrO2 particles exhibits high specific surface areas (up to 385 m2/g) which make them promising candidates as catalysts and catalyst supports. Co-existence of m- and t-ZrO2 nano-particles of 6-9 nm in diameter, i.e. above the critical particle size of 6 nm, demonstrates that the particle size is not the only factor for stabilization of the t-ZrO2 modification at room temperature. In conclusion, synthesis within an autoclave (with and without solvent) and the MOCVD process could be successfully adapted to the synthesis of MoS2, WS2 and ZrO2 nanoparticles. A comparative in situ heating stage TEM study elucidated the growth mechanism of MoS2 and WS2 fullerene-like particles. As the general processes are similar, a transfer of this synthesis approach to other layered transition metal chalcogenide systems is to be expected. Application of the obtained nanomaterials as lubricants (MoS2, WS2) or as dental filling materials (ZrO2) is currently under investigation.

Entwicklung und Charakterisierung von Gassterilisationsprozessen am Beispiel der Oberfl��chensterilisation mittels Wasserstoffperoxid und Ethylenoxid

Bei der Auswahl einer Sterilisationsmethode stehen, gem���� den Vorgaben des Europ��ischen Arzneibuches, die Sterilisation mittels Hitze (Dampf bzw. Hei��luft) oder ionisierender Strahlung im Vordergrund. Diese so genannten Referenzverfahren verf��gen neben einem breiten Wirkungsspektrum ��ber eine hohe Effektivit��t und zeichnen sich durch eine gute Reproduzierbarkeit aus. H��ufig jedoch verbieten die physikalisch ��� chemischen Eigenschaften des zu sterilisierenden Gutes eine Anwendung der Referenzverfahren. In derartigen F��llen muss nach geeigneten Alternativverfahren gesucht werden, will man eine aseptische Herstellung vermeiden. Besonders bei thermolabilen G��tern hat sich der Einsatz von gasf��rmigen Agenzien mit keimt��tender Wirkung bew��hrt. Bei entsprechenden Rahmenbedingungen ist hier eine Sterilisation unterhalb der Raumtemperatur m��glich. Die vorliegende Arbeit untersucht die Anwendbarkeit der Ethylenoxidsterilisation bzw. der Sterilisation mittels gasf��rmigen Wasserstoffperoxids (Vapour Phase Hydrogen Peroxide) auf verschiedene Materialoberfl��chen am Beispiel zweier aktueller Anwendungen aus der pharmazeutischen Industrie. Dabei werden die Vor- und Nachteile der beiden Verfahren aufgezeigt und in Relation zu den Referenzverfahren gestellt. Im Rahmen der abschlie��enden mikrobiologischen Leistungsbeurteilung beider Verfahren werden verschiedene methodische Ans��tze, wie Halbzyklus und Fraction Negative Analysis zur Anwendung gebracht und bewertet.

Hypersonic elastic excitations in soft mesoscopic structures

This dissertation is devoted to the experimental exploration of the propagation of elastic waves in soft mesoscopic structures with submicrometer dimensions. A strong motivation of this work is the large technological relevance and the fundamental importance of the subject. Elastic waves are accompanied by time-dependent fluctuations of local stress and strain fields in the medium. As such, the propagation phase velocities are intimately related to the elastic moduli. Knowledge of the elastic wave propagation directly provides information about the mechanical properties of the probed mesoscopic structures, which are not readily accessible experimentally. On the other hand, elastic waves, when propagating in an inhomogeneous medium with spatial inhomogeneities comparable to their wavelength, exhibit rather rich behavior, including the appearance of novel physical phenomena, such as phononic bandgap formation. So far, the experimental work has been restricted to macroscopic structures, which limit wave propagation below the KHz range. It was anticipated that an experimental approach capable of probing the interplay of the wave propagation with the controlled mesoscopic structures would contribute to deeper insights into the fundamental problem of elastic wave propagation in inhomogeneous systems. The mesoscopic nature of the structures to be studied precludes the use of traditional methods, such as sound transmission, for the study of elastic wave propagation. In this work, an optical method utilizing the inelastic scattering of photons by GHz frequency thermally excited elastic waves, known as Brillouin light scattering spectroscopy (BLS), was employed. Two important classes of soft structures were investigated: thin films and colloidal crystals. For the former, the main interest was the effect of the one-dimensional (1D) confinement on the wave propagation due to the presence of the free-surface or interface of the layer and the utilization of these waves to extract relevant material parameters. For the second system, the primary interest was the interaction of the elastic wave and the strong scattering medium with local resonance units in a three-dimensional (3D) periodic arrangement.

NMR studies on supramolecular aggregates in solution and the solid state

The aim of this work presented here is the characterization of structure and dynamics of different types of supramolecular systems by advanced NMR spectroscopy. One of the characteristic features of NMR spectroscopy is based on its high selectivity. Thus, it is desirable to exploit this technique for studying structure and dynamics of large supramolecular systems without isotopic enrichment. The observed resonance frequencies are not only isotope specific but also influenced by local fields, in particular by the distribution of electron density around the investigated nucleus. Barbituric acid are well known for forming strongly hydrogen-bonded complexes with variety of adenine derivatives. The prototropic tautomerism of this material facilitates an adjustment to complementary bases containing a DDA(A = hydrogen bond acceptor site, D = hydrogen bond donor site) or ADA sequences, thereby yielding strongly hydrogen-bonded complexes. In this contribution solid-state structures of the enolizable chromophor "1-n-butyl-5-(4-nitrophenyl)-barbituric acid" that features adjustable hydrogen-bonding properties and the molecular assemblies with three different strength of bases (Proton sponge, adenine mimetic 2,6-diaminopyridine (DAP) and 2,6-diacetamidopyridine (DAC)) are studied. Diffusion NMR spectroscopy gives information over such interactions and has become the method of choice for measuring the diffusion coefficient, thereby reflecting the effective size and shape of a molecular species. In this work the investigation of supramolecular aggregates in solution state by means of DOSY NMR techniques are performed. The underlying principles of DOSY NMR experiment are discussed briefly and more importantly two applications demonstrating the potential of this method are focused on. Calix[n]arenes have gained a rather prominent position, both as host materials and as platforms to design specific receptors. In this respect, several different capsular contents of tetra urea calix[4]arenes (benzene, benzene-d6, 1-fluorobenzene, 1-fluorobenzene-d5, 1,4-difluorobenzene, and cobaltocenium) are studied by solid state NMR spectroscopy. In the solid state, the study of the interaction between tetra urea calix[4]arenes and guest is simplified by the fact that the guests molecule remains complexed and positioned within the cavity, thus allowing a more direct investigation of the host-guest interactions.

Design und Synthese ma��geschneiderter funktioneller Rylenfarbstoffe

Die vorgelegte Dissertation besch��ftigt sich mit der Darstellung und Untersuchung von funktionellen Farbstoffen auf der Basis von Rylendiimiden. Diese Substanzklasse zeichnet sich durch gute Funktionalisierbarkeit, hohe chemische und photochemische Stabilit��t sowie durch hohe Fluoreszenzquantenausbeuten und Extinktionskoeffizienten aus. Rylendiimide spielen eine bedeutsame Rolle in den modernen Materialwissenschaften. Ein Schwerpunkt der Arbeit liegt auf der Synthese und Untersuchung von neuen Perylendiimiden (PDI) im Hinblick auf eine Anwendung in der organischen Elektronik. Das Substitutionsmuster der PDI hat einen signifikanten Einflussrnauf deren supramolekulares Verhalten und die Leistungsf��higkeit in elektronischen Bauteilen. Durch das Einf��hren neuer Substituenten konnten weitergehende Erkenntnisse ��ber das supramolekulare Verhalten der PDI gewonnenrnwerden. Multichromophore sind wichtige Modellsysteme zur Untersuchung vonrnEnergietransportprozessen und Einzelphotonenquellen. Daher liegt ein weiterer Schwerpunkt auf der Synthese multichromophorer PDI-Systeme. Neben der Darstellung definierter dendritischer Nanoteilchen auf Basis von Poly(phenylenethinylen)-Dendrimeren besch��ftigt sich dieser Teil auch mit der Synthese hochverzweigter ethinylverkn��pfter Polymere auf Basis von PDI-Monomeren. Aufgrund ihrer au��ergew��hnlichen photochemischen Eigenschaften spielen Perylen- und Terrylendiimide eine wichtige Rolle als Fluoreszenzmarker.rnDaher besch��ftigt sich ein weiterer Aspekt dieser Arbeit mit der Synthese vonrnFluoreszenzmarkern, die sowohl in Polymerisationsreaktionen als auch inrnbiologischen Systemen Anwendung finden k��nnen.

Windkanalstudien zum Graupelwachstum und Bestimmung von Retentionskoeffizienten verschiedener Spurengase w��hrend der Bereifung

Am vertikalen Windkanal der Johannes Gutenberg-Universit��t Mainz wurden physikalische und chemische Bereifungsexperimente durchgef��hrt. Dabei lagen die Umgebungstemperaturen bei allen Experimenten zwischen etwa -15 und -5��C und der Fl��ssigwassergehalt erstreckte sich von 0,9 bis etwa 1,6g/m��, typische Bedingungen f��r Mischphasenwolken in denen Bereifung stattfindet. Oberfl��chentemperaturmessungen an wachsenden h��ngenden Graupelpartikeln zeigten, dass w��hrend der Experimente trockene Wachstumsbedingungen herrschten.rnZun��chst wurde das Graupelwachstum an in einer laminaren Str��mung frei schwebenden Eispartikeln mit Anfangsradien zwischen 290 und 380��m, die mit fl��ssigen unterk��hlten Wolkentr��pfchen bereift wurden, studiert. Ziel war es, den Kollektionskern aus der Massenzunahme des bereiften Eispartikels und dem mittleren Fl��ssigwassergehalt w��hrend des Wachstumsexperimentes zu bestimmen. Die ermittelten Werte f��r die Kollektionskerne der bereiften Eispartikel erstreckten sich von 0,9 bis 2,3cm��/s in Abh��ngigkeit ihres Kollektorimpulses (Masse * Fallgeschwindigkeit des bereifenden Graupels), der zwischen 0,04 und 0,10gcm/s lag. Bei den Experimenten zeigte sich, dass die hier gemessenen Kollektionskerne h��her waren im Vergleich mit Kollektionskernen fl��ssiger Tropfen untereinander. Aus den aktuellen Ergebnissen dieser Arbeit und der vorhandenen Literaturwerte wurde ein empirischer Faktor entwickelt, der von dem Wolkentr��pfchenradius abh��ngig ist und diesen Unterschied beschreibt. F��r die untersuchten Gr����enbereiche von Kollektorpartikel und fl��ssigen Tr��pfchen k��nnen die korrigierten Kollektionskernwerte in Wolkenmodelle f��r die entsprechenden Gr����en eingebunden werden.rnBei den chemischen Experimenten zu dieser Arbeit wurde die Spurenstoffaufnahme verschiedener atmosph��rischer Spurengase (HNO3, HCl, H2O2, NH3 und SO2) w��hrend der Bereifung untersucht. Diese Experimente mussten aus technischen Gr��nden mit h��ngenden Eispartikeln, dendritischen Eiskristallen und Schneeflocken, bereift mit fl��ssigen Wolkenl��sungstr��pfchen, durchgef��hrt werden.rnDie Konzentrationen der L��sung, aus der die Wolkentr��pfchen mit Hilfe von Zweistoffd��sen erzeugt wurden, lagen zwischen 1 und 120mg/l. F��r die Experimente mit Ammoniak und Schwefeldioxid wurden Konzentrationen zwischen 1 und 22mg/l verwendet. Das Schmelzwasser der bereiften h��ngenden Graupel und Schneeflocken wurden ionenchromatographisch analysiert und zusammen mit der bekannten Konzentration der bereifenden Wolkentr��pfchen konnte der Retentionskoeffizient f��r jeden Spurenstoff bestimmt werden. Er gibt die Menge an Spurenstoff an, die bei der Phasenumwandlung von fl��ssig zu fest in die Eisphase ��bergeht. Salpeters��ure und Salzs��ure waren nahezu vollst��ndig retiniert (Mittelwerte der gesamten Experimente entsprechend 99��8% und 100��9%). F��r Wasserstoffperoxid wurde ein mittlerer Retentionskoeffizient von 65��17% bestimmt. rnDer mittlere Retentionskoeffizient von Ammoniak ergab sich unabh��ngig vom Fl��ssigwassergehalt zu 92��21%, w��hrend sich f��r Schwefeldioxid 53��10% f��r niedrige und 29��7% f��r hohe Fl��ssigphasenkonzentrationen ergaben. Bei einigen der untersuchten Spurenstoffe wurde eine Temperaturabh��ngigkeit beobachtet und wenn m��glich durch Parametrisierungen beschrieben.rn