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Version: publishedVersion × Subject: surfactant ×

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Now showing 1 - 5 of 5
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    Hybrid nanostructured particles via surfactant-free double miniemulsion polymerization
    ([London] : Nature Publishing Group UK, 2018) Zhao, Yongliang; Liu, Junli; Chen, Zhi; Zhu, Xiaomin; Möller, Martin
    Double emulsions are complex fluid systems, in which droplets of a dispersed liquid phase contain even smaller dispersed liquid droplets. Particularly, water-in-oil-in-water double emulsions provide significant advantages over simple oil-in-water emulsions for microencapsulation, such as carrier of both aqueous and oily payloads and sustained release profile. However, double emulsions are thermodynamically unstable systems consisting typically of relatively large droplets. Here we show that nanoscale water-in-oil-in-water double emulsions can be prepared by adding a silica precursor polymer, hyperbranched polyethoxysiloxane, to the oil phase without any additional surfactants. The resulting double miniemulsions are transformed to robust water@SiO2@polymer@SiO2 nanocapsules via conversion of the precursor to silica and polymerization of the oil phase. Other intriguing nanostructures like nanorattles and Janus-like nanomushrooms can also be obtained by changing preparation conditions. This simple surfactant-free double miniemulsion polymerization technique opens a promising avenue for mass production of various complex hybrid nanostructures that are amenable to numerous applications.
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    Unravelling New Processes at Interfaces: Photochemical Isoprene Production at the Sea Surface
    (Columbus, Ohio : American Chemical Society, 2015) Ciuraru, Raluca; Fine, Ludovic; van Pinxteren, Manuela; D’Anna, Barbara; Herrmann, Hartmut; George, Christian
    Isoprene is an important reactive gas that is produced mainly in terrestrial ecosystems but is also produced in marine ecosystems. In the marine environment, isoprene is produced in the seawater by various biological processes. Here, we show that photosensitized reactions involving the sea-surface microlayer lead to the production of significant amounts of isoprene. It is suggested that H-abstraction processes are initiated by photochemically excited dissolved organic matter which will the degrade fatty acids acting as surfactants. This chemical interfacial processing may represent a significant abiotic source of isoprene in the marine boundary layer.
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    Screening Libraries of Amphiphilic Janus Dendrimers Based on Natural Phenolic Acids to Discover Monodisperse Unilamellar Dendrimersomes
    (Columbus, Ohio : American Chemical Society, 2019) Buzzacchera, Irene; Xiao, Qi; Han, Hong; Rahimi, Khosrow; Li, Shangda; Kostina, Nina Yu; Toebes, B. Jelle; Wilner, Samantha E.; Möller, Martin; Rodriguez-Emmenegger, Cesar; Baumgart, Tobias; Wilson, Daniela A.; Wilson, Christopher J.; Klein, Michael L.; Percec, Virgil
    Natural, including plant, and synthetic phenolic acids are employed as building blocks for the synthesis of constitutional isomeric libraries of self-assembling dendrons and dendrimers that are the simplest examples of programmed synthetic macromolecules. Amphiphilic Janus dendrimers are synthesized from a diversity of building blocks including natural phenolic acids. They self-assemble in water or buffer into vesicular dendrimersomes employed as biological membrane mimics, hybrid and synthetic cells. These dendrimersomes are predominantly uni- or multilamellar vesicles with size and polydispersity that is predicted by their primary structure. However, in numerous cases, unilamellar dendrimersomes completely free of multilamellar assemblies are desirable. Here, we report the synthesis and structural analysis of a library containing 13 amphiphilic Janus dendrimers containing linear and branched alkyl chains on their hydrophobic part. They were prepared by an optimized iterative modular synthesis starting from natural phenolic acids. Monodisperse dendrimersomes were prepared by injection and giant polydisperse by hydration. Both were structurally characterized to select the molecular design principles that provide unilamellar dendrimersomes in higher yields and shorter reaction times than under previously used reaction conditions. These dendrimersomes are expected to provide important tools for synthetic cell biology, encapsulation, and delivery.
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    Density-Dependence of Surface Transport in Tellurium-Enriched Nanograined Bulk Bi2Te3
    (Weinheim : Wiley-VCH, 2023) Izadi, Sepideh; Bhattacharya, Ahana; Salloum, Sarah; Han, Jeong Woo; Schnatmann, Lauritz; Wolff, Ulrike; Perez, Nicolas; Bendt, Georg; Ennen, Inga; Hütten, Andreas; Nielsch, Kornelius; Schulz, Stephan; Mittendorff, Martin; Schierning, Gabi
    Three-dimensional topological insulators (3D TI) exhibit conventional parabolic bulk bands and protected Dirac surface states. A thorough investigation of the different transport channels provided by the bulk and surface carriers using macroscopic samples may provide a path toward accessing superior surface transport properties. Bi2Te3 materials make promising 3D TI models; however, due to their complicated defect chemistry, these materials have a high number of charge carriers in the bulk that dominate the transport, even as nanograined structures. To partially control the bulk charge carrier density, herein the synthesis of Te-enriched Bi2Te3 nanoparticles is reported. The resulting nanoparticles are compacted into nanograined pellets of varying porosity to tailor the surface-to-volume ratio, thereby emphasizing the surface transport channels. The nanograined pellets are characterized by a combination of resistivity, Hall- and magneto-conductance measurements together with (THz) time-domain reflectivity measurements. Using the Hikami-Larkin-Nagaoka (HLN) model, a characteristic coherence length of ≈200 nm is reported that is considerably larger than the diameter of the nanograins. The different contributions from the bulk and surface carriers are disentangled by THz spectroscopy, thus emphasizing the dominant role of the surface carriers. The results strongly suggest that the surface transport carriers have overcome the hindrance imposed by nanoparticle boundaries.
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    Growth kinetics, thermodynamics, and phase formation of group-III and IV oxides during molecular beam epitaxy
    (Berlin : Humboldt-Universität zu Berlin, 2017) Vogt, Patrick
    Die vorliegende Arbeit präsentiert eine erste umfassende Wachstumsstudie, und erste quantitative Wachstumsmodelle, von Gruppe-III und IV Oxiden synthetisiert mit sauerstoffplasmaunterstützter Molekularstrahlepitaxie (MBE). Diese entwickelten Modelle beinhalten kinetische und thermodynamische Effekte. Die erworbenen Erkenntnisse sind auf fundamentale Wachstumsprozesse in anderen Syntheseverfahren übertragbar, wie zum Beispiel der Laserdeposition oder metallorganische Gasphasenepitaxie. Die Wachstumsraten und Desorptionsraten werden in-situ mit Laser-Reflektometrie bzw. Quadrupol-Massenspektrometrie (QMS) bestimmt. Es werden die transparenten halbleitenden Oxide Ga2O3, In2O3 und SnO2 untersucht. Es ist bekannt, dass sich das Wachstum von Gruppe-III und IV Oxiden, aufgrund der Existenz von Suboxiden, fundamental von anderen halbleitenden Materialien unterscheidet. Es stellt sich heraus, dass die Wachstumsrate der untersuchten binären Oxide durch die Formierung und Desorption von Suboxiden flussstöchiometrisch und thermisch limitiert ist. Es werden die Suboxide Ga2O für Ga2O3, In2O für In2O3 und SnO für SnO2 identifiziert. Ein Suboxid ist ein untergeordneter Oxidationszustand, und es wird gezeigt, dass die untersuchten Oxide über einen Zwei-Stufen-Prozess gebildet werden: vom Metall zum Suboxid, und weiterer Oxidation vom Suboxid zum thermodynamisch stabilen festen Metalloxid. Dieser Zwei-Stufen-Prozess ist die Basis für die Entwicklung eines ersten quantitativen, semiempirschen MBE-Wachstumsmodells für binare Oxide die Suboxide besitzen. Dieses Model beschreibt und erklärt die gemessenen Wachstumsraten und Desorptionsraten. Es wird die Kinetik und Thermodynamik des ternären Oxidsystems (InxGa1−x)2O3 untersucht. Die gemittelten Einbauraten von In und Ga in ein makroskopisches Volumen von (InxGa1−x)2O3 Dünnschichten werden ex-situ mit energiedispersiver Röntgenspektroskopie gemessen. Diese Einbauraten werden systematisch analysiert und im Rahmen kinetischer und thermodynamischer Grenzen beschrieben. Es wird gezeigt, dass Ga den In-Einbau in (InxGa1−x)2O3 aufgrund seiner stabileren Ga–O Bindungen thermodynamisch verhindert. In diesen Zusammenhang wird ein neuer katalytisch-tensidischer Effekt des In auf den Einbau von Ga gefunden. Eine Folge dieses katalytisch-tensidischen Effektes ist die Formierung der thermodynamisch, metastabilen hexagonalen Ga2O3 phase mit sehr hoher Kristallqualität. Ein thermodynamisch induziertes, kinetisches Wachstumsmodel für (InxGa1−x)2O3 wird entwickelt, mit dem sich alle makroskopischen Metall-Einbauraten und Desorptionsraten vorhersagen lassen. Mögliche (InxGa1−x)2O3 Strukturen gewachsen mit MBE werden mittels Röntgenkristallographie bestimmt. Mit Hilfe der Röntgenstrukturanalyse wird ein erster makroskopischer Ansatz zur Bestimmung der mikroskopischen In Konzentration X in möglichen (InXGa1−X)2O3 Phasen hergeleitet. Es werden Löslichkeitsgrenzen von In bzw. Ga in monoklinem und kubischem (InXGa1−X)2O3 bestimmt.