@phdthesis{Federico2011,
  author    = {Federico, Stefania},
  title     = {Synthetic peptides derived from decorin as building blocks for biomaterials based on supramolecular interactions},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-59661},
  school      = {Universit{\"a}t Potsdam},
  year      = {2011},
  abstract  = {In this work, the development of a new molecular building block, based on synthetic peptides derived from decorin, is presented. These peptides represent a promising basis for the design of polymer-based biomaterials that mimic the ECM on a molecular level and exploit specific biological recognition for technical applications. Multiple sequence alignments of the internal repeats of decorin that formed the inner and outer surface of the arch-shaped protein were used to develop consensus sequences. These sequences contained conserved sequence motifs that are likely to be related to structural and functional features of the protein. Peptides representative for the consensus sequences were synthesized by microwave-assisted solid phase peptide synthesis and purified by RP-HPLC, with purities higher than 95 mol\%. After confirming the desired masses by MALDI-TOF-MS, the primary structure of each peptide was investigated by 1H and 2D NMR, from which a full assignment of the chemical shifts was obtained. The characterization of the peptides conformation in solution was performed by CD spectroscopy, which demonstrated that using TFE, the peptides from the outer surface of decorin show a high propensity to fold into helical structures as observed in the original protein. To the contrary, the peptides from the inner surface did not show propensity to form stable secondary structure. The investigation of the binding capability of the peptides to Collagen I was performed by surface plasmon resonance analyses, from which all but one of the peptides representing the inner surface of decorin showed binding affinity to collagen with values of dissociation constant between 2•10-7 M and 2.3•10-4 M. On the other hand, the peptides representative for the outer surface of decorin did not show any significant interaction to collagen. This information was then used to develop experimental demonstration for the binding capabilities of the peptides from the inner surface of decorin to collagen even when used in more complicated situations close to possible appications. With this purpose, the peptide (LRELHLNNN) which showed the highest binding affinity to collagen (2•10-7 M) was functionalized with an N-terminal triple bond in order to obtain a peptide dimer via copper(I)-catalyzed cycloaddition reaction with 4,4'-diazidostilbene-2,2'-disulfonic acid. Rheological measurements showed that the presence of the peptide dimer was able to enhance the elastic modulus (G') of a collagen gel from ~ 600 Pa (collagen alone) to ~ 2700 Pa (collagen and peptide dimer). Moreover, it was shown that the mechanical properties of a collagen gel can be tailored by using different molar ratios of peptide dimer respect to collagen. The same peptide, functionalized with the triple bond, was used to obtain a peptide-dye conjugate by coupling it with N-(5'-azidopentanoyl)-5-aminofluorescein. An aqueous solution (5 vol\% methanol) of the peptide dye conjugate was injected into a collagen and a hyaluronic acid (HA) gel and images of fluorescence detection showed that the diffusion of the peptide was slower in the collagen gel compared to the HA gel. The third experimental demonstration was gained using the peptide (LSELRLHNN) which showed the lower binding affinity (2.3•10-4 M) to collagen. This peptide was grafted to hyaluronic acid via EDC-chemistry, with a degree of functionalization of 7 ± 2 mol\% as calculated by 1H-NMR. The grafting was further confirmed by FTIR and TGA measurements, which showed that the onset of decomposition for the HA-g-peptide decreased by 10 °C compared to the native HA. Rheological measurements showed that the elastic modulus of a system based on collagen and HA-g-peptide increased by almost two order of magnitude (G' = 200 Pa) compared to a system based on collagen and HA (G' = 0.9 Pa). Overall, this study showed that the synthetic peptides, which were identified from decorin, can be applied as potential building blocks for biomimetic materials that function via biological recognition.},
  language  = {en}
}
@phdthesis{Fellinger2011,
  author    = {Fellinger, Tim-Patrick},
  title     = {Hydrothermal and ionothermal carbon structures},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-57825},
  school      = {Universit{\"a}t Potsdam},
  year      = {2011},
  abstract  = {The needs for sustainable energy generation, but also a sustainable chemistry display the basic motivation of the current thesis. By different single investigated cases, which are all related to the element carbon, the work can be devided into two major topics. At first, the sustainable synthesis of "useful" carbon materials employing the process of hydrothermal carbonisation (HC) is described. In the second part, the synthesis of heteroatom - containing carbon materials for electrochemical and fuel cell applications employing ionic liquid precursors is presented. On base of a thorough review of the literature on hydrothermolysis and hydrothermal carbonisation of sugars in addition to the chemistry of hydroxymethylfurfural, mechanistic considerations of the formation of hydrothermal carbon are proposed. On the base of these reaction schemes, the mineral borax, is introduced as an additive for the hydrothermal carbonisation of glucose. It was found to be a highly active catalyst, resulting in decreased reaction times and increased carbon yields. The chemical impact of borax, in the following is exploited for the modification of the micro- and nanostructure of hydrothermal carbon. From the borax - mediated aggregation of those primary species, widely applicable, low density, pure hydrothermal carbon aerogels with high porosities and specific surface areas are produced. To conclude the first section of the thesis, a short series of experiments is carried out, for the purpose of demonstrating the applicability of the HC model to "real" biowaste i.e. watermelon waste as feedstock for the production of useful materials. In part two cyano - containing ionic liquids are employed as precursors for the synthesis of high - performance, heteroatom - containing carbon materials. By varying the ionic liquid precursor and the carbonisation conditions, it was possible to design highly active non - metal electrocatalyst for the reduction of oxygen. In the direct reduction of oxygen to water (like used in polymer electrolyte fuel cells), compared to commercial platinum catalysts, astonishing activities are observed. In another example the selective and very cost efficient electrochemical synthesis of hydrogen peroxide is presented. In a last example the synthesis of graphitic boron carbon nitrides from the ionic liquid 1 - Ethyl - 3 - methylimidazolium - tetracyanoborate is investigated in detail. Due to the employment of unreactive salts as a new tool to generate high surface area these materials were first time shown to be another class of non - precious metal oxygen reduction electrocatalyst.},
  language  = {en}
}
@phdthesis{Gessner2011,
  author    = {Geßner, Andr{\´e}},
  title     = {Neuartige Lanthanoid-dotierte mikro- und mesopor{\"o}se Feststoffe : Charakterisierung von Ion-Wirt-Wechselwirkungen, Speziesverteilung und Lumineszenzeigenschaften mittels zeitaufgel{\"o}ster Lumineszenzspektroskopie},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-52371},
  school      = {Universit{\"a}t Potsdam},
  year      = {2011},
  abstract  = {Por{\"o}se Sol-Gel-Materialien finden in vielen Bereichen Anwendung bzw. sind Gegenstand der aktuellen Forschung. Zu diesen Bereichen z{\"a}hlen sowohl klassische Anwendungen, wie z. B. die Verwendung als Katalysator, Molekularsieb oder Trockenmittel, als auch nichtklassische Anwendungen, wie z. B. der Einsatz als Kontrastmittel in der Magnet-Resonanz-Tomographie oder in Form von d{\"u}nnen Zeolithfilmen als Isolatoren in Mikrochips. Auch f{\"u}r den Einsatz in der Photonik werden por{\"o}se Materialien in Betracht gezogen, wie die Entwicklung des Zeolith-Farbstoff-Lasers zeigt. Mikropor{\"o}se Zeolithe k{\"o}nnen generell {\"u}ber einfache Ionenaustauschreaktionen mit Lanthanoidionen in lumineszente Materialien umgewandelt werden. Neben der Erzeugung eines lumineszenten Materials, dessen Lumineszenzeigenschaften charakterisiert werden m{\"u}ssen, bietet die Nutzung von Lanthanoidionen die M{\"o}glichkeit diese Ionen als Sonde zur Charakterisierung der Ion-Wirt-Wechselwirkungen zu funktionalisieren, was z. B. in Bezug auf die Anwendung als Katalysator von großer Bedeutung ist. Dabei werden die einzigartigen Lumineszenzeigenschaften der Lanthanoidionen, in diesem Fall von Europium(III) und Terbium(III), genutzt. In dieser Arbeit wurden Lanthanoid-dotierte mikropor{\"o}se Zeolithe, mikropor{\"o}s-mesopor{\"o}se Hybridmaterialien und mesopor{\"o}se Silikate hinsichtlich ihrer Lumineszenzeigenschaften und ihrer Wechselwirkung des Wirtsmaterials mit den Lanthanoidionen mittels zeitaufgel{\"o}ster Lumineszenzspektroskopie untersucht. Zeitaufgel{\"o}ste Emissionsspektren (TRES) liefern dabei sowohl Informationen in der Wellenl{\"a}ngen- als auch in der Zeitdom{\"a}ne. Erstmalig wurden die TRES mittels einer umfangreichen Auswertemethodik behandelt. Neben der Anpassung des Abklingverhaltens mit einer diskreten Zahl von Exponentialfunktionen, wurden unterst{\"u}tzend auch Abklingzeitverteilungsanalysen durchgef{\"u}hrt. Zeitaufgel{\"o}ste fl{\"a}chennormierte Emissionsspektren (TRANES), eine Erweiterung der normalen TRES, konnten erstmals zur Bestimmung der Zahl der emittierenden Lanthanoidspezies in por{\"o}sen Materialien genutzt werden. Durch die Berechnung der Decayassoziierten Spektren (DAS) konnten den Lanthanoidspezies die entsprechenden Lumineszenzspektren zugeordnet werden. Zus{\"a}tzlich konnte, speziell im Fall der Europium-Lumineszenz, durch Kombination von zeitlicher und spektraler Information das zeitabh{\"a}ngige Asymmetrieverh{\"a}ltnis R und die spektrale Evolution des 5D0-7F0-{\"U}bergangs mit der Zeit t untersucht und somit wesentliche Informationen {\"u}ber die Verteilung der Europiumionen im Wirtsmaterial erhalten werden. {\"U}ber die Abklingzeit und das Asymmetrieverh{\"a}ltnis R konnten R{\"u}ckschl{\"u}sse auf die Zahl der OH-Oszillatoren in der ersten Koordinationssph{\"a}re und die Symmetrie der Koordinationsumgebung gezogen werden. F{\"u}r die mikropor{\"o}sen und mikropor{\"o}s-mesopor{\"o}sen Materialien wurden verschiedene Lanthanoidspezies, im Regelfall zwei, gefunden, welche entsprechend der beschriebenen Methoden charakterisiert wurden. Diese Lanthanoidspezies konnten Positionen in den Materialien zugeordnet werden, die sich im tief Inneren des Porensystems oder auf bzw. nahe der {\"a}ußeren Oberfl{\"a}che oder in den Mesoporen befinden. Erstere Spezies ist aufgrund ihrer Position im Material gut vor Feuchtigkeitseinfl{\"u}ssen gesch{\"u}tzt, was sich deutlich in entsprechend langen Lumineszenzabklingzeiten {\"a}ußert. Zus{\"a}tzlich ist diese Europiumspezies durch unsymmetrische Koordinationsumgebung charakterisiert, was auf einen signifikanten Anteil an Koordination der Lanthanoidionen durch die Sauerstoffatome im Wirtsgitter zur{\"u}ckzuf{\"u}hren ist. Ionen, die sich nahe oder auf der {\"a}ußeren Oberfl{\"a}che befinden, sind dagegen f{\"u}r Feuchtigkeit zug{\"a}nglicher, was in k{\"u}rzeren Lumineszenzabklingzeiten und einer symmetrischeren Koordinationsumgebung resultiert. Der Anteil von Wassermolek{\"u}len in der ersten Koordinationssph{\"a}re ist hier deutlich gr{\"o}ßer, als bei den Ionen, die sich tiefer im Porensystem befinden und entspricht in vielen F{\"a}llen der Koordinationszahl eines vollst{\"a}ndig hydratisierten Lanthanoidions. Auch der Einfluss von Oberfl{\"a}chenmodifikationen auf die Speziesverteilung und das Verhalten der Materialien gegen{\"u}ber Feuchtigkeit wurde untersucht. Dabei gelang es den Einfluss der Feuchtigkeit auf die Lumineszenzeigenschaften und die Speziesverteilung durch die Oberfl{\"a}chenmodifikation zu verringern und die Lumineszenzeigenschaften teilweise zu konservieren. Im Fall der mesopor{\"o}sen Silikamonolithe wurde auch eine heterogene Verteilung der Lanthanoidionen im Porensystem gefunden. Hier wechselwirkt ein Teil der Ionen mit der Porenwand, w{\"a}hrend sich die restlichen Ionen in der w{\"a}ßrigen Phase innerhalb des Porensystems aufhalten. Das Aufbringen von Oberfl{\"a}chenmodifikationen f{\"u}hrte zu einer Wechselwirkung der Ionen mit diesen Oberfl{\"a}chenmodifikationen, was sich in Abh{\"a}ngigkeit von der Oberfl{\"a}chenbeladung in den enstprechenden Lumineszenzeigenschaften niederschlug.},
  language  = {de}
}
@phdthesis{Goebel2011,
  author    = {G{\"o}bel, Ronald},
  title     = {Hybridmaterialien aus mesopor{\"o}sen Silica und ionischen Fl{\"u}ssigkeiten},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-54022},
  school      = {Universit{\"a}t Potsdam},
  year      = {2011},
  abstract  = {Die vorliegende Arbeit besch{\"a}ftigt sich mit der Synthese und Charakterisierung mesopor{\"o}ser monolithischer Silica und deren Hybridmaterialien mit Ionischen Fl{\"u}ssigkeiten (ILs, ionic liquids). Zur Synthese der Silicaproben wurde ein Sol-Gel-Verfahren, ausgehend von einer Pr{\"a}kursorverbindung wie Tetramethylorthosilicat angewendet. Der Katalysator mit der geringsten Basizit{\"a}t f{\"u}hrte zum Material mit der kleinsten Porengr{\"o}ße und der gr{\"o}ßten spezifischen Oberfl{\"a}che. Eine Kombination von por{\"o}sen Silica mit ILs f{\"u}hrt zur Materialklasse der Silica-Ionogele. Diese Hybridmaterialien verbinden die Eigenschaften eines por{\"o}sen Festk{\"o}rpers mit denen einer IL (Leitf{\"a}higkeit, weites elektrochemisches Fenster, gute thermische Stabilit{\"a}t) und bieten vielf{\"a}ltige Einsatzm{\"o}glichkeiten z.B. in der Katalyse- Solar- und Sensortechnik. Um diese Materialien f{\"u}r ihren Verwendungszweck zu optimieren, bedarf es deren umfassenden Charakterisierung. Daher wurde in der vorliegenden Arbeit das thermische Verhalten von Silica-Ionogelen unter Verwendung verschiedener 1-Ethyl-3-methylimidazolium [Emim]-basierter ILs untersucht. Interessanterweise zeigen die untersuchten ILs deutliche {\"A}nderungen in ihrem thermischen Verhalten, wenn diese in por{\"o}sen Materialien eingeschlossen werden (Confinement). W{\"a}hrend sich die untersuchten reinen ILs durch klar unterscheidbare Phasen{\"u}berg{\"a}nge auszeichnen, konnten f{\"u}r die entsprechenden Hybridmaterialien deutlich schw{\"a}cher ausgepr{\"a}gte {\"U}berg{\"a}nge beobachtet werden. Einzelne Phasen{\"u}berg{\"a}nge wurden unterdr{\"u}ckt (Glas- und Kristallisations{\"u}berg{\"a}nge), w{\"a}hrend z.B. Schmelz{\"u}berg{\"a}nge in verbreiterten Temperaturbereichen, zum Teil als einzeln getrennte Schmelzpeaks beobachtet wurden. Diese Untersuchungen belegen deutliche Eigenschafts{\"a}nderungen der ILs in eingeschr{\"a}nkten Geometrien. {\"U}ber Festk{\"o}rper-NMR-Spektroskopie konnte außerdem gezeigt werden, daß die ILs in den mesopor{\"o}sen Silicamaterialien eine unerwartet hohe Mobilit{\"a}t aufweisen. Die ILs k{\"o}nnen als quasi-fl{\"u}ssig bezeichnet werden und zeigen die nach bestem Wissen h{\"o}chste Mobilit{\"a}t, die bisher f{\"u}r vergleichbare Hybridmaterialien beobachtet wurde. Durch Verwendung von funktionalisierten Pr{\"a}kursoren, sowie der Wahl der Reaktionsbedingungen, kann die Oberfl{\"a}che der Silicamaterialien chemisch funktionalisiert werden und damit die Materialeigenschaften in der gew{\"u}nschten Weise beeinflußt werden. In der vorliegenden Arbeit wurde der Einfluß der Oberfl{\"a}chenfunktionalit{\"a}t auf das thermische Verhalten hin untersucht. Dazu wurden zwei verschiedene M{\"o}glichkeiten der Funktionalisierung angewendet und miteinander verglichen. Bei der in-situ-Funktionalisierung wird die chemische Funktionalit{\"a}t w{\"a}hrend der Sol-Gel-Synthese {\"u}ber ein entsprechend funktionalisiertes Silan mit in das Silicamaterial einkondensiert. Eine postsynthetische Funktionalisierung erfolgt durch Reaktion der Endgruppen eines Silicamaterials mit geeigneten Reaktionspartnern. Um den Einfluß der physikalischen Eigenschaften der Probe auf die Reaktion zu untersuchen, wurden pulverisierte und monolithische Silicamaterialien miteinander verglichen. Im letzten Teil der Arbeit wurde die Vielf{\"a}ltigkeit, mit der Silicamaterialien postsynthetisch funktionalisiert werden k{\"o}nnen demonstriert. Durch die Kenntnis von Struktur-Eigenschaftsbeziehungen k{\"o}nnen die Eigenschaften von Silica-Ionogelen durch die geeignete Kombination von fester und mobiler Phase in der gew{\"u}nschten Weise ver{\"a}ndert werden. Die vorliegende Arbeit soll einen Beitrag zur Untersuchung dieser Beziehungen leisten, um das Potential dieser interessanten Materialien f{\"u}r Anwendungen nutzen zu k{\"o}nnen.},
  language  = {de}
}
@phdthesis{Haase2011,
  author    = {Haase, Martin F.},
  title     = {Modification of nanoparticle surfaces for emulsion stabilization and encapsulation of active molecules for anti-corrosive coatings},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-55413},
  school      = {Universit{\"a}t Potsdam},
  year      = {2011},
  abstract  = {Within this work, three physicochemical methods for the hydrophobization of initially hydrophilic solid particles are investigated. The modified particles are then used for the stabilization of oil-in-water (o/w) emulsions. For all introduced methods electrostatic interactions between strongly or weakly charged groups in the system are es-sential. (i) Short chain alkylammonium bromides (C4 - C12) adsorb on oppositely charged solid particles. Macroscopic contact angle measurements of water droplets under air and hexane on flat silica surfaces in dependency of the surface charge density and alkylchain-length allow the calculation of the surface energy and give insights into the emulsification properties of solid particles modified with alkyltrimethylammonium bromides. The measure-ments show an increase of the contact angle with increasing surface charge density, due to the enhanced adsorp-tion of the oppositely charged alkylammonium bromides. Contact angles are higher for longer alkylchain lengths. The surface energy calculations show that in particular the surface-hexane or surface-air interfacial en-ergy is being lowered upon alkylammonium adsorption, while a significant increase of the surface-water interfa-cial energy occurs only at long alkyl chain lengths and high surface charge densities. (ii) The thickness and the charge density of an adsorbed weak polyelectrolyte layer (e.g. PMAA, PAH) influence the wettability of nanoparticles (e.g. alumina, silica, see Scheme 1(b)). Furthermore, the isoelectric point and the pH range of colloidal stability of particle-polyelectrolyte composites depend on the thickness of the weak polye-lectrolyte layer. Silica nanoparticles with adsorbed PAH and alumina nanoparticles with adsorbed PMAA be-come interfacially active and thus able to stabilize o/w emulsions when the degree of dissociation of the polye-lectrolyte layer is below 80 \%. The average droplet size after emulsification of dodecane in water depends on the thickness and the degree of dissociation of the adsorbed PE-layer. The visualization of the particle-stabilized o/w emulsions by cryogenic SEM shows that for colloidally stable alumina-PMAA composites the oil-water interface is covered with a closely packed monolayer of particles, while for the colloidally unstable case closely packed aggregated particles deposit on the interface. (iii) By emulsifying a mixture of the corrosion inhibitor 8-hydroxyquinoline (8-HQ) and styrene with silica nanoparticles a highly stable o/w emulsion can be obtained in a narrow pH window. The amphoteric character of 8-HQ enables a pH dependent electrostatic interaction with silica nanoparticles, which can render them interfa-cially active. Depending on the concentration and the degree of dissociation of 8-HQ the adsorption onto silica results from electrostatic or aromatic interactions between 8-HQ and the particle-surface. At intermediate amounts of adsorbed 8-HQ the oil wettability of the particles becomes sufficient for stabilizing o/w emulsions. Cryogenic SEM visualization shows that the particles arrange then in a closely packed shell consisting of partly of aggregated domains on the droplet interface. For further increasing amounts of adsorbed 8-HQ the oil wet-tability is reduced again and the particles ability to stabilize emulsions decreases. By the addition of hexadecane to the oil phase the size of the droplets can be reduced down to 200 nm by in-creasing the silica mass fraction. Subsequent polymerization produces corrosion inhibitor filled (20 wt-\%) poly-styrene-silica composite particles. The measurement of the release of 8-hydroxyquinoline shows a rapid increase of 8-hydroxyquinoline in a stirred aqueous solution indicating the release of the total content in less than 5 min-utes. The method is extended for the encapsulation of other organic corrosion inhibitors. The silica-polymer-inhibitor composite particles are then dispersed in a water based alkyd emulsion, and the dispersion is used to coat flat aluminium substrates. After drying and cross-linking the polmer-film Confocal Laser Scanning Micros-copy is employed revealing a homogeneous distribution of the particles in the film. Electrochemical Impedance Spectroscopy in aqueous electrolyte solutions shows that films with aggregated particle domains degrade with time and don't provide long-term corrosion protection of the substrate. However, films with highly dispersed particles have high barrier properties for corrosive species. The comparison of films containing silica-polystyrene composite particles with and without 8-hydroxyquinoline shows higher electrochemical impedances when the inhibitor is present in the film. By applying the Scanning Vibrating Electrode Technique the localized corrosion rate in the fractured area of scratched polymer films containing the silica-polymer-inhibitor composite particles is studied. Electrochemical corrosion cannot be suppressed but the rate is lowered when inhibitor filled composite particles are present in the film. By depositing six polyelectrolyte layers on particle stabilized emulsion droplets their surface morphology changes significantly as shown by SEM visualization. When the oil wettability of the outer polyelectrolyte layer increases, the polyelectrolyte coated droplets can act as emulsion stabilizers themselves by attaching onto bigger oil droplets in a closely packed arrangement. In the presence of 3 mM LaCl3 8-HQ hydrophobized silica particles aggregate strongly on the oil-water inter-face. The application of an ultrasonic field can remove two dimensional shell-compartments from the droplet surface, which are then found in the aqueous bulk phase. Their size ranges up to 1/4th of the spherical particle shell.},
  language  = {en}
}
@phdthesis{Jiang2011,
  author    = {Jiang, Yuan},
  title     = {Precursor phases in non-classical crystallization},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-52460},
  school      = {Universit{\"a}t Potsdam},
  year      = {2011},
  abstract  = {The main objective of this thesis is to understand molecular crystallization as a multistep process with or without polymeric additives, including transient liquid-liquid phase separation, nanocrystal nucleation within the dense phase, and subsequent nanocrystal self-assembly or self-organization in sequence. The thesis starts with a quaternary model system, containing DL-Glutamic acid (Glu), polyethyleneimine (PEI), water, and EtOH, for the understanding of multistep precipitation of Glu with PEI as an additive. The experiments were performed by mixing Glu-PEI aqueous solution with a non-solvent EtOH. First, the phase diagram of the quaternary system is determined, obtaining precipitate, coacervates, or homogeneous mixtures by varying Glu/PEI w/w and water/EtOH v/v. Coacervation is observed to occur over a wide range of Glu/PEI with various volumes. The composition of coacervates is conveniently characterized by nuclear magnetic resonance spectroscopy. The observed coacervates are thermodynamically stable phases rich in solute, which is different from metastable polymer-induced liquid precursors. The combination of atomic force microscopy, small angle scattering, and ξ-potential measurements confirms the coexistence of monomers and Glu/PEI complexes and the aggregation of complexes in Glu-PEI-water systems. This suggests that there might be a direct structural transformation between the Glu-PEI complexes in aqueous solution and the metastable liquid precursors in a water-EtOH mixture. The multistep mechanism of Glu precipitation with PEI as an additive is investigated thereafter. The combination of stopped flow and small angle scattering demonstrates that the initially formed liquid precursors pass through an alteration of growth and coalescence. Combined with results from optical microscopy and scanning electron microscopy, the nucleation of nanoplatelets happens within each liquid precursor droplet, and nanoplatelets reorient themselves and self-organize into a radial orientation in the crystalline microspheres. The recipe was then extended to the precipitation of organics in other oppositely charged amino acid-polyelectrolyte systems. After the success in preparing hierarchical microspheres in solution, the similar recipe can be extended to the preparation of patterned thin films on substrate. By dipping a quaternary DL-Lys·HCl (Lys)-polyacrylic acid (PAA)-water-EtOH dispersion on a hydrophilic slide, the fast evaporation process of the volatile solvent EtOH is responsible for the homogeneous nucleation of NPs. Then, the following complete evaporation causes the mesocrystallization of a continuous spherulitic thin film along the receding line of the liquid, which again transforms into a mesocrystalline thin film. Furthermore, annealing is used to optimize the property of mesocrystalline thin films. As evaporation is a non-equilibrium process, it can be used to tune the kinetics of crystallization. Therefore, hierarchical or periodical thin films are obtainable by starting the evaporation from microspheres recrystallization, obtaining mesocrystalline thin films with 4 hierarchy levels. The results reveal that evaporation provides an easy but effective way for the formation of patterned structures via the positioning of NPs after their fast nucleation, resulting in different kinds of patterns by controlling the concentration of NPs, solvent evaporation rate, and other physical forces. Non-classical crystallization is not limited to crystallizations with polymeric additives. We also observed the nucleation and growth of a new molecular layer on the growing DL-Glu·H2O crystals from a supersaturated mother liquor by using an in-situ atomic force microscopy (AFM), where the nucleation and growth of a molecular layer proceed via amorphous nanoparticle (NP) attachment and relaxation process before the observation of the growth of a newly formed molecular layer. NP attachment to the crystal surface is too fast to observe by using in-situ AFM. The height shrinkage of NPs, combined to the structural transformation from 3D amorphous NPs to 2D crystalline layer, is observed during the relaxation process. The nucleation and growth of a newly formed molecular layer from NP relaxation is contradictory to the classical nucleation theory, which hypothesizes that nuclei show the same crystallographic properties as a bulk crystal. The formation of a molecular layer by NP attachment and relaxation rather than attachment of single molecules provides a different picture from the currently held classical nucleation and growth theory regarding the growth of single crystals from solution.},
  language  = {de}
}
@phdthesis{Klinkusch2011,
  author    = {Klinkusch, Stefan},
  title     = {Simulations of laser-induced correlated many-electron dynamics in molecular systems},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-55445},
  school      = {Universit{\"a}t Potsdam},
  year      = {2011},
  abstract  = {In this thesis, simulations of laser-driven many-electron dynamics in molecules are presented, i.e., the interaction between molecules and an electromagnetic field is demonstrated. When a laser field is applied to a molecular system, a population of higher electronic states takes place as well as other processes, e.g. photoionization, which is described by an appropriate model. Also, a finite lifetime of an excited state can be described by such a model. In the second part, a method is postulated that is capable of describing electron correlation in a time-dependent scheme. This is done by introducing a single-electron entropy that is at least temporarily minimized in a further step.},
  language  = {en}
}
@phdthesis{Kopetzki2011,
  author    = {Kopetzki, Daniel},
  title     = {Exploring hydrothermal reactions : from prebiotic synthesis to green chemistry},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-52581},
  school      = {Universit{\"a}t Potsdam},
  year      = {2011},
  abstract  = {In this thesis chemical reactions under hydrothermal conditions were explored, whereby emphasis was put on green chemistry. Water at high temperature and pressure acts as a benign solvent. Motivation to work under hydrothermal conditions was well-founded in the tunability of physicochemical properties with temperature, e.g. of dielectric constant, density or ion product, which often resulted in surprising reactivity. Another cornerstone was the implementation of the principles of green chemistry. Besides the use of water as solvent, this included the employment of a sustainable feedstock and the sensible use of resources by minimizing waste and harmful intermediates and additives. To evaluate the feasibility of hydrothermal conditions for chemical synthesis, exemplary reactions were performed. These were carried out in a continuous flow reactor, allowing for precise control of reaction conditions and kinetics measurements. In most experiments a temperature of 200 °C in combination with a pressure of 100 bar was chosen. In some cases the temperature was even raised to 300 °C. Water in this subcritical range can also be found in nature at hydrothermal vents on the ocean floor. On the primitive earth, environments with such conditions were however present in larger numbers. Therefore we tested whether biologically important carbohydrates could be formed at high temperature from the simple, probably prebiotic precursor formaldehyde. Indeed, this formose reaction could be carried out successfully, although the yield was lower compared to the counterpart reaction under ambient conditions. However, striking differences regarding selectivity and necessary catalysts were observed. At moderate temperatures bases and catalytically active cations like Ca2+ are necessary and the main products are hexoses and pentoses, which accumulate due to their higher stability. In contrast, in high-temperature water no catalyst was necessary but a slightly alkaline solution was sufficient. Hexoses were only formed in negligible amounts, whereas pentoses and the shorter carbohydrates accounted for the major fraction. Amongst the pentoses there was some preference for the formation of ribose. Even deoxy sugars could be detected in traces. The observation that catalysts can be avoided was successfully transferred to another reaction. In a green chemistry approach platform chemicals must be produced from sustainable resources. Carbohydrates can for instance be employed as a basis. They can be transformed to levulinic acid and formic acid, which can both react via a transfer hydrogenation to the green solvent and biofuel gamma-valerolactone. This second reaction usually requires catalysis by Ru or Pd, which are neither sustainable nor low-priced. Under hydrothermal conditions these heavy metals could be avoided and replaced by cheap salts, taking advantage of the temperature dependence of the acid dissociation constant. Simple sulfate was recognized as a temperature switchable base. With this additive high yield could be achieved by simultaneous prevention of waste. In contrast to conventional bases, which create salt upon neutralization, a temperature switchable base becomes neutral again when cooled down and thus can be reused. This adds another sustainable feature to the high atom economy of the presented hydrothermal synthesis. In a last study complex decomposition pathways of biomass were investigated. Gas chromatography in conjunction with mass spectroscopy has proven to be a powerful tool for the identification of unknowns. It was observed that several acids were formed when carbohydrates were treated with bases at high temperature. This procedure was also applied to digest wood. Afterwards it was possible to fermentate the solution and a good yield of methane was obtained. This has to be regarded in the light of the fact that wood practically cannot be used as a feedstock in a biogas factory. Thus the hydrothermal pretreatment is an efficient means to employ such materials as well. Also the reaction network of the hydrothermal decomposition of glycine was investigated using isotope-labeled compounds as comparison for the unambiguous identification of unknowns. This refined analysis allowed the identification of several new molecules and pathways, not yet described in literature. In summary several advantages could be taken from synthesis in high-temperature water. Many catalysts, absolutely necessary under ambient conditions, could either be completely avoided or replaced by cheap, sustainable alternatives. In this respect water is not only a green solvent, but helps to prevent waste and preserves resources.},
  language  = {en}
}
@phdthesis{Kraupner2011,
  author    = {Kraupner, Alexander},
  title     = {Neuartige Synthese magnetischer Nanostrukturen: Metallcarbide und Metallnitride der {\"U}bergangsmetalle Fe/Co/Ni},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-52314},
  school      = {Universit{\"a}t Potsdam},
  year      = {2011},
  abstract  = {Magnetische Nanopartikel bieten ein großes Potential, da sie einerseits die Eigenschaften ihrer Bulk-Materialien besitzen und anderseits, auf Grund ihrer Gr{\"o}ße, {\"u}ber komplett unterschiedliche magnetische Eigenschaften verf{\"u}gen k{\"o}nnen; Superparamagnetismus ist eine dieser Eigenschaften. Die meisten etablierten Anwendungen magnetischer Nanopartikel basieren heutzutage auf Eisenoxiden. Diese bieten gute magnetische Eigenschaften, sind chemisch relativ stabil, ungiftig und lassen sich auf vielen Synthesewegen relativ einfach herstellen. Die magnetischen Eigenschaften der Eisenoxide sind materialabh{\"a}ngig aber begrenzt, weshalb nach anderen Verbindungen mit besseren Eigenschaften gesucht werden muss. Eisencarbid (Fe3C) kann eine dieser Verbindungen sein. Dieses besitzt vergleichbare positive Eigenschaften wie Eisenoxid, jedoch viel bessere magnetische Eigenschaften, speziell eine h{\"o}here S{\"a}ttigungsmagnetisierung. Bis jetzt wurde Fe3C haupts{\"a}chlich in Gasphasenabscheidungsprozessen synthetisiert oder als Nebenprodukt bei der Synthese von Kohlenstoffstrukturen gefunden. Eine Methode, mit der gezielt Fe3C-Nanopartikel und andere Metallcarbide synthetisiert werden k{\"o}nnen, ist die „Harnstoff-Glas-Route". Neben den Metallcarbiden k{\"o}nnen mit dieser Methode auch die entsprechenden Metallnitride synthetisiert werden, was die breite Anwendbarkeit der Methode unterstreicht. Die „Harnstoff-Glas-Route" ist eine Kombination eines Sol-Gel-Prozesses mit einer anschließenden carbothermalen Reduktion/Nitridierung bei h{\"o}heren Temperaturen. Sie bietet den Vorteil einer einfachen und schnellen Synthese verschiedener Metallcarbide/nitride. Der Schwerpunkt in dieser Arbeit lag auf der Synthese von Eisencarbiden/nitriden, aber auch Nickel und Kobalt wurden betrachtet. Durch die Variation der Syntheseparameter konnten verschiedene Eisencarbid/nitrid Nanostrukturen synthetisiert werden. Fe3C-Nanopartikel im Gr{\"o}ßenbereich von d = 5 - 10 nm konnten, durch die Verwendung von Eisenchlorid, hergestellt werden. Die Nanopartikel weisen durch ihre geringe Gr{\"o}ße superparamagnetische Eigenschaften auf und besitzen, im Vergleich zu Eisenoxid Nanopartikeln im gleichen Gr{\"o}ßenbereich, eine h{\"o}here S{\"a}ttigungsmagnetisierung. Diese konnten in fortf{\"u}hrenden Experimenten erfolgreich in ionischen Fl{\"u}ssigkeiten und durch ein Polymer-Coating, im w{\"a}ssrigen Medium, dispergiert werden. Desweiteren wurde durch ein Templatieren mit kolloidalem Silika eine mesopor{\"o}se Fe3C-Nanostruktur hergestellt. Diese konnte erfolgreich in der katalytischen Spaltung von Ammoniak getestet werden. Mit der Verwendung von Eisenacetylacetonat konnten neben Fe3C-Nanopartikeln, nur durch Variation der Reaktionsparameter, auch Fe7C3- und Fe3N-Nanopartikel synthetisiert werden. Speziell f{\"u}r die Fe3C-Nanopartikel konnte die S{\"a}ttigungsmagnetisierung, im Vergleich zu den mit Eisenchlorid synthetisierten Nanopartikeln, nochmals erh{\"o}ht werden. Versuche mit Nickelacetat f{\"u}hrten zu Nickelnitrid (Ni3N) Nanokristallen. Eine zus{\"a}tzliche metallische Nickelphase f{\"u}hrte zu einer Selbstorganisation der Partikel in Scheiben-{\"a}hnliche {\"U}berstrukturen. Mittels Kobaltacetat konnten, in Sph{\"a}ren aggregierte, metallische Kobalt Nanopartikel synthetisiert werden. Kobaltcarbid/nitrid war mit den gegebenen Syntheseparametern nicht zug{\"a}nglich.},
  language  = {de}
}
@phdthesis{Kristen2011,
  author    = {Kristen, Juliane Ute},
  title     = {Amphiphilic BAB-triblock copolymers bearing fluorocarbon groups : synthesis and self-organization in aqueous media},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-61782},
  school      = {Universit{\"a}t Potsdam},
  year      = {2011},
  abstract  = {In this work new fluorinated and non-fluorinated mono- and bifunctional trithiocarbonates of the structure Z-C(=S)-S-R and Z-C(=S)-S-R-S-C(=S)-Z were synthesized for the use as chain transfer agents (CTAs) in the RAFT-process. All newly synthesized CTAs were tested for their efficiency to moderate the free radical polymerization process by polymerizing styrene (M3). Besides characterization of the homopolymers by GPC measurements, end- group analysis of the synthesized block copolymers via 1H-, 19F-NMR, and in some cases also UV-vis spectroscopy, were performed attaching suitable fluorinated moieties to the Z- and/or R-groups of the CTAs. Symmetric triblock copolymers of type BAB and non-symmetric fluorine end- capped polymers were accessible using the RAFT process in just two or one polymerization step. In particular, the RAFT-process enabled the controlled polymerization of hydrophilic monomers such as N-isopropylacrylamide (NIPAM) (M1) as well as N-acryloylpyrrolidine (NAP) (M2) for the A-blocks and of the hydrophobic monomers styrene (M3), 2-fluorostyrene (M4), 3-fluorostyrene (M5), 4-fluorostyrene (M6) and 2,3,4,5,6-pentafluorostyrene (M7) for the B-blocks. The properties of the BAB-triblock copolymers were investigated in dilute, concentrated and highly concentrated aqueous solutions using DLS, turbidimetry, 1H- and 19F-NMR, rheology, determination of the CMC, foam height- and surface tension measurements and microscopy. Furthermore, their ability to stabilize emulsions and microemulsions and the wetting behaviour of their aqueous solutions on different substrates was investigated. The behaviour of the fluorine end-functionalized polymers to form micelles was studied applying DLS measurements in diluted organic solution. All investigated BAB-triblock copolymers were able to form micelles and show surface activity at room temperature in dilute aqueous solution. The aqueous solutions displayed moderate foam formation. With different types and concentrations of oils, the formation of emulsions could be detected using a light microscope. A boosting effect in microemulsions could not be found adding BAB-triblock copolymers. At elevated polymer concentrations, the formation of hydrogels was proved applying rheology measurements.},
  language  = {en}
}