Development of analytical methodologies for iodine species in gaseous and particulate phases of the coastal atmosphere

It has been demonstrated that iodine does have an important influence on atmospheric chemistry, especially the formation of new particles and the enrichment of iodine in marine aerosols. It was pointed out that the most probable chemical species involved in the production or growth of these particles are iodine oxides, produced photochemically from biogenic halocarbon emissions and/or iodine emission from the sea surface. However, the iodine chemistry from gaseous to particulate phase in the coastal atmosphere and the chemical nature of the condensing iodine species are still not understood. A Tenax / Carbotrap adsorption sampling technique and a thermo-desorption / cryo-trap / GC-MS system has been further developed and improved for the volatile organic iodine species in the gas phase. Several iodo-hydrocarbons such as CH3I, C2H5I, CH2ICl, CH2IBr and CH2I2 etc., have been measured in samples from a calibration test gas source (standards), real air samples and samples from seaweeds / macro-algae emission experiments. A denuder sampling technique has been developed to characterise potential precursor compounds of coastal particle formation processes, such as molecular iodine in the gas phase. Starch, TMAH (TetraMethylAmmonium Hydroxide) and TBAH (TetraButylAmmonium Hydroxide) coated denuders were tested for their efficiencies to collect I2 at the inner surface, followed by a TMAH extraction and ICP/MS determination, adding tellurium as an internal standard. The developed method has been proved to be an effective, accurate and suitable process for I2 measurement in the field, with the estimated detection limit of ~0.10 ng∙L-1 for a sampling volume of 15 L. An H2O/TMAH-Extraction-ICP/MS method has been developed for the accurate and sensitive determination of iodine species in tropospheric aerosol particles. The particle samples were collected on cellulose-nitrate filters using conventional filter holders or on cellulose nitrate/tedlar-foils using a 5-stage Berner impactor for size-segregated particle analysis. The water soluble species as IO3- and I- were separated by anion exchanging process after water extraction. Non-water soluble species including iodine oxide and organic iodine were digested and extracted by TMAH. Afterwards the triple samples were analysed by ICP/MS. The detection limit for particulate iodine was determined to be 0.10~0.20 ng•m-3 for sampling volumes of 40~100 m3. The developed methods have been used in two field measurements in May 2002 and September 2003, at and around the Mace Head Atmospheric Research Station (MHARS) located at the west coast of Ireland. Elemental iodine as a precursor of the iodine chemistry in the coastal atmosphere, was determined in the gas phase at a seaweed hot-spot around the MHARS, showing I2 concentrations were in the range of 0~1.6 ng∙L-1 and indicating a positive correlation with the ozone concentration. A seaweed-chamber experiment performed at the field measurement station showed that the I2 emission rate from macro-algae was in the range of 0.019~0.022 ng•min-1•kg-1. During these experiments, nanometer-particle concentrations were obtained from the Scanning Mobility Particle Sizer (SMPS) measurements. Particle number concentrations were found to have a linear correlation with elemental iodine in the gas phase of the seaweeds chamber, showing that gaseous I2 is one of the important precursors of the new particle formation in the coastal atmosphere. Iodine contents in the particle phase were measured in both field campaigns at and around the field measurement station. Total iodine concentrations were found to be in the range of 1.0 ~ 21.0 ng∙m-3 in the PM2.5 samples. A significant correlation between the total iodine concentrations and the nanometer-particle number concentrations was observed. The particulate iodine species analysis indicated that iodide contents are usually higher than those of iodate in all samples, with ratios in the range of 2~5:1. It is possible that those water soluble iodine species are transferred through the sea-air interface into the particle phase. The ratio of water soluble (iodate + iodide) and non-water soluble species (probably iodine oxide and organic iodine compounds) was observed to be in the range of 1:1 to 1:2. It appears that higher concentrated non-water soluble species, as the products of the photolysis from the gas phase into the particle phase, can be obtained in those samples while the nucleation events occur. That supports the idea that iodine chemistry in the coastal boundary layer is linked with new particle formation events. Furthermore, artificial aerosol particles were formed from gaseous iodine sources (e.g. CH2I2) using a laboratory reaction-chamber experiment, in which the reaction constant of the CH2I2 photolysis was calculated to be based upon the first order reaction kinetic. The end products of iodine chemistry in the particle phase were identified and quantified.

Crystal phases and glassy dynamics in monodisperse hard ellipsoids

We have performed Monte Carlo and molecular dynamics simulations of suspensions of monodisperse, hard ellipsoids of revolution. Hard-particle models play a key role in statistical mechanics. They are conceptually and computationally simple, and they offer insight into systems in which particle shape is important, including atomic, molecular, colloidal, and granular systems. In the high density phase diagram of prolate hard ellipsoids we have found a new crystal, which is more stable than the stretched FCC structure proposed previously . The new phase, SM2, has a simple monoclinic unit cell containing a basis of two ellipsoids with unequal orientations. The angle of inclination is very soft for length-to-width (aspect) ratio l/w=3, while the other angles are not. A symmetric state of the unit cell exists, related to the densest-known packings of ellipsoids; it is not always the stable one. Our results remove the stretched FCC structure for aspect ratio l/w=3 from the phase diagram of hard, uni-axial ellipsoids. We provide evidence that this holds between aspect ratios 3 and 6, and possibly beyond. Finally, ellipsoids in SM2 at l/w=1.55 exhibit end-over-end flipping, warranting studies of the cross-over to where this dynamics is not possible. Secondly, we studied the dynamics of nearly spherical ellipsoids. In equilibrium, they show a first-order transition from an isotropic phase to a rotator phase, where positions are crystalline but orientations are free. When over-compressing the isotropic phase into the rotator regime, we observed super-Arrhenius slowing down of diffusion and relaxation, and signatures of the cage effect. These features of glassy dynamics are sufficiently strong that asymptotic scaling laws of the Mode-Coupling Theory of the glass transition (MCT) could be tested, and were found to apply. We found strong coupling of positional and orientational degrees of freedom, leading to a common value for the MCT glass-transition volume fraction. Flipping modes were not slowed down significantly. We demonstrated that the results are independent of simulation method, as predicted by MCT. Further, we determined that even intra-cage motion is cooperative. We confirmed the presence of dynamical heterogeneities associated with the cage effect. The transit between cages was seen to occur on short time scales, compared to the time spent in cages; but the transit was shown not to involve displacements distinguishable in character from intra-cage motion. The presence of glassy dynamics was predicted by molecular MCT (MMCT). However, as MMCT disregards crystallization, a test by simulation was required. Glassy dynamics is unusual in monodisperse systems. Crystallization typically intervenes unless polydispersity, network-forming bonds or other asymmetries are introduced. We argue that particle anisometry acts as a sufficient source of disorder to prevent crystallization. This sheds new light on the question of which ingredients are required for glass formation.

Liquid crystalline phases of anisotropic, polymer functionalized nanoparticles

Diese Arbeit beschäftigt sich mit der Polymerfunktionalisierung formanisotroperrnNanopartikel wie TiO2 Nanostäbchen oder Kohlenstoff Nanoröhren. Dies dient derrnSolubilisierung und sterischen Stabilisierung in organischen Medien, da diesernionenfrei hergestellt werden können, was eine Nutzung für nanoskopische,rnelektrische Schaltkreise ermöglicht. Die Polymere wurden mittels der RAFTrn(reversible addition-fragmentation chain transfer) Polymerisation mit engenrnMolekulargewichtsverteilungen hergestellt. Im Detail wurden Ankergruppen inrnBlockcopolymere und an der Alphaposition eingeführt, welche eine Anbindung an diernNanopartikeloberfläche ermöglichen. Die Polymere wurden durch Variation derrnverschiedenen Blocklängen für eine bestmögliche Adsorption optimiert. Die sorngewonnenen Polymer funktionalisierten Nanopartikel zeigten eine gute Löslichkeit inrnorganischen Medien und zeigten zudem eine lyotropes, flüssigkristallinesrnPhasenverhalten. Dies war aufgrund der Formanisotropie zu erwarten, zeigte jedochrnebenfalls ein unerwartetes thermotropes Verhalten, welches durch die Polymerhüllernerzeugt wurde. Die Flüssigkristalle wurden eingehend mittels polarisierterrnMikroskopie und Differential Scanning Calorimetry (DSC) untersucht. Diernflüssigkristallinen Phasen aus Nanostäbchen und –röhren wurde dann zurrnOrientierung der anisotropen Nanopartikel benutzt und es konnten makroskopischrngeordnete Proben hergestellt werden. Die Polymerhülle um die Nanopartikelrnermöglichte es ebenfalls diese in Polymerfilme einzuarbeiten und sornNanopartikelverstärkte Kunststoffe herzustellen.

Superfluid and antiferromagnetic phases in ultracold fermionic quantum gases

In this thesis several models are treated, which are relevant for ultracold fermionic quantum gases loaded onto optical lattices. In particular, imbalanced superfluid Fermi mixtures, which are considered as the best way to realize Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) states experimentally, and antiferromagnetic states, whose experimental realization is one of the next major goals, are examined analytically and numerically with the use of appropriate versions of the Hubbard model.rnrnThe usual Bardeen-Cooper-Schrieffer (BCS) superconductor is known to break down in a magnetic field with a strength exceeding the size of the superfluid gap. A spatially inhomogeneous spin-imbalanced superconductor with a complex order parameter known as FFLO-state is predicted to occur in translationally invariant systems. Since in ultracold quantum gases the experimental setups have a limited size and a trapping potential, we analyze the realistic situation of a non-translationally invariant finite sized Hubbard model for this purpose. We first argue analytically, why the order parameter should be real in a system with continuous coordinates, and map our statements onto the Hubbard model with discrete coordinates defined on a lattice. The relevant Hubbard model is then treated numerically within mean field theory. We show that the numerical results agree with our analytically derived statements and we simulate various experimentally relevant systems in this thesis.rnrnAnalogous calculations are presented for the situation at repulsive interaction strength where the N'eel state is expected to be realized experimentally in the near future. We map our analytical results obtained for the attractive model onto corresponding results for the repulsive model. We obtain a spatially invariant unit vector defining the direction of the order parameter as a consequence of the trapping potential, which is affirmed by our mean field numerical results for the repulsive case. Furthermore, we observe domain wall formation, antiferromagnetically induced density shifts, and we show the relevant role of spin-imbalance for antiferromagnetic states.rnrnSince the first step for understanding the physics of the examined models was the application of a mean field approximation, we analyze the effect of including the second order terms of the weak coupling perturbation expansion for the repulsive model. We show that our results survive the influence of quantum fluctuations and show that the renormalization factors for order parameters and critical temperatures lead to a weaker influence of the fluctuations on the results in finite sized systems than on the results in the thermodynamical limit. Furthermore, in the context of second order theory we address the question whether results obtained in the dynamical mean field theory (DMFT), which is meanwhile a frequently used method for describing trapped systems, survive the effect of the non-local Feynman diagrams neglected in DMFT.

Structural characterization of intermediate and metastable phases by electron microscopy

Structure characterization of nanocrystalline intermediates and metastable phases is of primary importance for a deep understanding of synthetic processes undergoing solid-to-solid state phase transitions. Understanding the evolution from the first nucleation stage to the final synthetic product supports not only the optimization of existing processes, but might assist in tailoring new synthetic paths. A systematic investigation of intermediates and metastable phases is hampered because it is impossible to produce large crystals and only in few cases a pure synthetic product can be obtained. Structure investigation by X-ray powder diffraction methods is still challenging on nanoscale, especially when the sample is polyphasic. Electron diffraction has the advantage to collect data from single nanoscopic crystals, but is limited by data incompleteness, dynamical effects and fast deterioration of the sample under the electron beam. Automated diffraction tomography (ADT), a recently developed technique, making possible to collect more complete three-dimensional electron diffraction data and to reduce at the same time dynamical scattering and beam damage, thus allowing to investigate even beam sensitive materials (f.e. hydrated phases and organics). At present, ADT is the only technique able to deliver complete three-dimensional structural information from single nanoscopic grains, independently from other surrounding phases. Thus, ADT is an ideal technique for the study of on-going processes where different phases exist at the same time and undergo several structural transitions. In this study ADT was used as the main technique for structural characterization for three different systems and combined subsequently with other techniques, among which high-resolution transmission electron microscopy (HRTEM), cryo-TEM imaging, X-ray powder diffraction (XRPD) and energy disperse X-ray spectroscopy (EDX).rnAs possible laser host materials, i.e. materials with a broad band emission in the near-infrared region, two unknown phases were investigated in the ternary oxide system M2O-Al2O3-WO3 (M = K, Na). Both phases exhibit low purity as well as non-homogeneous size distribution and particle morphology. The structures solved by ADT are also affected by pseudo-symmetry. rnSodium titanate nanotubes and nanowires are both intermediate products in the synthesis of TiO2 nanorods which are used as additives to colloidal TiO2 film for improving efficiency of dye-sensitized solar cells (DSSC). The structural transition from nantubes to nanowires was investigated in a step by step time-resolved study. Nanowires were discovered to consist of a hitherto unknown phase of sodium titanate. This new phase, typically affected by pervasive defects like mutual layer shift, was structurally determined ab-initio on the basis of ADT data. rnThe third system is related with calcium carbonate nucleation and early crystallization. The first part of this study is dedicated to the extensive investigations of calcium carbonate formation in a step by step analysis, up to the appearance of crystalline individua. The second part is dedicated to the structure determination by ADT of the first-to-form anhydrated phase of CaCO3: vaterite. An exhaustive structure analysis of vaterite had previously been hampered by diffuse scattering, extra periodicities and fast deterioration of the material under electron irradiation. rn