87 search hits
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Crystalline-core micelles based on triblock terpolymers with polyethylene middle blocks
(2012)
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Joachim Schmelz
- This thesis is focused on the crystallization-induced structure formation of polyethylene containing triblock terpolymers in organic solvents to surface-compartmentalized worm-like crystalline-core micelles (wCCMs). Obtaining profound knowledge of the parameters controlling the self-assembly process allowed the production of a variety of complex one-dimensional micellar architectures with many potential applications, such as adaptive surfactants.
At first, the basic parameters that control the crystallization-induced self-assembly were explored using symmetric polystyrene-block-polyethylene-block-poly(methyl methacrylate) (PS-b-PE-b-PMMA) triblock terpolymers and a PS-b-PE-b-PS triblock copolymer. In good solvents for the PE block, e.g. THF and toluene, the selective formation of wCCMs was observed over a wide range of concentration, applied crystallization temperature and polymer composition. Whereas wCCMs produced by PS-b-PE-b-PS showed a homogeneous PS corona, a patch-like compartmentalization of the corona was observed if the micelles were formed by PS-b-PE-b-PMMA. As THF shows equal solvent quality for both corona blocks, wCCMs with almost alternating PS and PMMA compartments of about 15 nm were observed in this solvent. However, if structure formation was conducted in bad solvents for PE, such as dioxane or dimethylacetamide, spherical micelles with amorphous PE cores were formed already before crystallization. Hence, the subsequent crystallization of PE resulted in spherical CCMs with a patchy or a homogeneous corona depending on the used triblock. These findings allow the highly selective production of stable spherical or worm-like CCMs from the same polymer.
As the corona structure of the patchy micelles self-assembled from triblock terpolymers was mainly deduced from transmission electron microscopy (TEM) performed on dried samples, a small-angle neutron scattering (SANS) study was performed in order to elucidate the morphology in solution. Therefore a partly deuterated triblock terpolymer was synthesized and measured at different contrasts to allow the selective detection of the different corona compartments. The resulting SANS curves could be interpreted using a form factor model for core-shell cylinders with alternating PS and PMMA hemishells including interparticle interactions, thus validating the TEM observations. Notably, Janus-type and patchy cylinders can be clearly distinguished using the applied form factor model.
Moreover, the controlled formation of wCCMs with tunable corona composition and structure was achieved using the cocrystallization of different triblock copolymers. Via random cocrystallization of PS-b-PE-b-PMMA and PS-b-PE-b-PS the corona morphology could be tuned continuously from a mixed corona at low PMMA content over spherical PMMA patches of increasing number and size to alternating PS and PMMA patches. This approach allows to manufacture wCCMs with predefined corona structure omitting the need to synthesize a new tailor-made triblock terpolymer for every desired morphology.
By establishing the controlled crystallization-driven self-assembly of triblock terpolymers with PE middle blocks, it was further possible to prepare wCCMs with predefined average lengths up to 500 nm and length polydispersities as low as Lw/Ln = 1.1. Here, self-assembled spherical CCMs of PS-b-PE-b-PS were used as seeds for the controlled growth of PS-b-PE-b-PS unimers. Upon further addition of PS-b-PE-b-PMMA unimers these grew epitaxially onto the preexisting wCCMs, resulting in triblock co-micelles that consisted of middle blocks with a homogeneous PS corona and outer blocks with alternating PS/PMMA compartments. These structures represent not only the first block co-micelles including blocks with a patchy corona, but also the first ones produced from purely organic block copolymers.
In view of application, the ability of patchy wCCMs formed by PS-b-PE-b-PMMA to stabilize interfaces was investigated using pendant-drop tensiometry. The observed reduction of the interfacial tension at the toluene/water interface was significantly higher than that of comparable triblock terpolymer single chains and that of wCCMs with a homogeneous PS corona. Interestingly, the obtained equilibrium interfacial tension equaled that of Janus cylinders with similar dimensions. To explain this unexpected finding the corona chains were proposed to adapt to the interface via selective collapse and shielding of the incompatible part of the corona chains. Studying wCCMs formed by several triblock terpolymers with different compositions, the interfacial activity was found to increase with increasing overall length of the corona chains, and to a certain extent with the molar fraction of PS units in the corona.
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The Watermill Center. A Laboratory for Performance. Robert Wilson's Legacy, hrg. von José Enrique Macián, Sue Jane Stoker und Jörn Weisbrodt, Stuttgart: Daco 2012.
(2012)
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Ulrike Hartung
- Robert Wilson ist ein Theaterkünstler, der etwas geschafft hat, was eine Seltenheit in der Welt des Theaters ist: Er ist – und das lässt sich ohne Übertreibung konstatieren – ein internationaler Superstar, der nicht nur weltweit bekannt ist, sondern der es darüber hinaus vermag, sowohl eine breite Masse an Theaterpublikum zu bedienen als auch ein ebenso weites Feld an wissenschaftlicher Diskussion anzuregen. Wer es sich als Intendant finanziell erlauben kann, Robert Wilson und sein Team – keine seiner Arbeiten wäre denkbar ohne die Unterstützung seiner ihm treu ergebenen Mitarbeiter – für eine Produktion oder auch nur ein Gastspiel zu engagieren, kann davon ausgehen, dass er, zumindest was diese Vorstellungsabende angeht, keine Probleme mit der Auslastung haben wird. [...]
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Daniela Schulz, Wenn die Musik spielt... Der deutsche Schlagerfilm der 1950er bis 1970er Jahre, Bielefeld: Transcript 2012
(2012)
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Hans J. Wulff
- In vielen Geschichten des deutschen Films steht der Schlagerfilm als lebendiger Beweis für das Zurücktreten jedweden ästhetischen Anspruchs, den Film erfüllen könnte. Stattdessen trete ein flaches Unterhaltungskonzept in den Vordergrund, durchsetzt mit restaurativen Elementen, ablenkend von den Realitäten der Zeit, eskapistischen Neigungen eines kleinbürgerlichen Publikums Vorschub leistend. Es besteht allerdings kein Zweifel daran, dass der Schlagerfilm eines der größten und erfolgreichsten Genres der deutschen Filmproduktion der 1950er bis Mitte der 1970er Jahre gewesen ist. Und doch ist eine Untersuchung des mehrere hundert Filme umfassenden Korpus bis heute ausgeblieben1. Schulz' Kölner Dissertation aus dem Jahre 2011 betritt also Neuland, allein der Mut, sich der so missachteten Gattung anzunehmen, verdient Respekt.
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Silent Sound Art: Performing the Unheard
(2012)
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Elen Flügge
- This article is a reflection on silent sound art, exemplified here by the works of Peter Ablinger and Akio Suzuki, in the context of a partially historical con-sideration of the participatory subject in Installation Art, with a primary focus on artistic movements and selected works from the late 1950s to the early 1970s by John Cage, George Brecht, and La Monte Young.
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Rapporti tra opera e fruitore nelle origini dell’installazione sonora (1900–1966)
(2012)
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Giacomo Albert
- One feature that defines sound installation as a genre is the participation of the user. Upon entering the space of a work, the user assumes an active role. Thereby the work takes on a theatrical and formative dimension: an art initially defined through space reveals its temporality. This essay analyzes the theatrical dimension, that is, the "modal structure," of works up to 1967, the first period of the sound installation genre. Both interactive and non-interactive works are considered. The analysis shows various models of theatricality for the first years of the genre, during which a diversity of origins and genealogy is reflected. What is common to these experiments is that they seek to involve the viewers, a strategy whose roots lie in the aesthetics and experiments of the first half of the twentieth century, but which since 1955 has become conspicuous.
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Gebiete und Karten der neuen Musik erfahren. Über das Klangkunstprojekt sounding D
(2012)
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Barbara Barthelmes
- sounding D ist ein Klangkunstprojekt, das 2010 vom Netzwerk Neue Musik realisiert wurde. Die Arbeit zeichnet sich durch ihren speziellen Charakter von Ortsbestimmtheit aus. Der Klangzug sounding D, angelehnt an John Cages Il treno (1978), fuhr zwei Wochen durch Deutschland und richtete an 15 Stationen Zwischenstopps ein. In jedem Ort, dem per se eine individuelle Klanglichkeit anhaftet, wurden zahlreiche Klangkunstarbeiten oder Musikperformances organisiert. Die im Inneren des Zuges befindliche Klanginstallation Outside In (Blue) von Robin Minard und der während der Fahrt topografisch erschlossene Raum Deutschlands riefen spannende Wechselbeziehungen hervor. Das Ergebnis ist eine Kartografie der zeitgenössischen Musikszene in Deutschland.
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Editorial 2012/4: Ars acustica – Audio Art – Klangkunst
(2012)
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Sarah Mauksch
Wolf-Dieter Ernst
- Während der Beschäftigung mit den Texten aus der aktuellen Ausgabe unserer Zeitschrift formulierten sich einige Fragen stetig neu: Wie beispielsweise lassen sich die Begriffe der Ars acustica, Audio Art und Klangkunst voneinander trennen? Worin liegen ihre Überschneidungen und welche Synergieeffekte werden durch die Kombination der wesentlichen Bestandteile – nämlich bildnerisch-künstlerischer und akustischer Elemente – in den entsprechen den Kunstwerken erzeugt? In welchem Verhältnis steht Werk und Aufführung, wenn die Entgrenzung der Künste Programm wird?
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Light Harvesting using Metal-Organic and Organic Sensitizers in Hybrid Solar Cells: Synthesis, Characterisation and Application
(2012)
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Katja Gräf
- This thesis addresses the question how to improve light harvesting with novel tailor-made metal-organic and organic sensitizers for solid-state hybrid solar cell applications. Two approaches are in the focus: 1) the design and synthesis of sensitizers featuring high extinction coefficients over a broad wavelength range and 2) modern device concepts to further enhance or extend the absorption by the combination of two sensitizers. In short: The primary goal was to broaden and boost the optical density of hybrid solar cells. To reach this, novel sensitizer with extended conjugated π-system providing excellent optical properties had to be designed and synthesised in complex multi-step reaction sequences. For ideal sensitizers, further aspects had to be taken into account such as structural demands, electronic properties, and the tendency towards aggregation.
The first part of this thesis deals with the synthesis, characterisation and application of a series of metal-organic ruthenium(II) donor-antenna complexes. In addition to the typically broad absorption of Ru(II)bis(bipyridyl)(NCS)2 complexes in the blue-green region arising from MLCT, these dyes feature much higher extinction coefficients in comparison to a commercially available reference dye lacking any donor-antenna groups. By the application of these Ru(II) complexes in solid-state dye-sensitized solar cells, we found a clear structure-property relationship. The performance - especially the photocurrent density - was significantly improved with increasing extension of the delocalized system of the donor-antenna groups.
To further boost the optical density in hybrid solar cells sensitized with a donor-antenna ruthenium dye (Ru-TPA-NCS), we developed an innovative and technically relevant concept for multichromophore sensitization involving a second sensitizer (TPD-dye). The latter absorbs in a region where Ru-TPA-NCS absorbs weakly. The solar cells were fabricated according to a novel method developed by us. However, the power conversion efficiencies of multichromophore hybrid blend solar cells were initially low due the weak interconnectivity of the TiO2 particles. This issue was addressed by an optimization of the TiO2:spiro-OMeTAD ratio and the addition of PCBM
A further concept dealing with the combination of two sensitizers in solid-state dye-sensitized solar cell was accomplished by co-sensitization of a triphenyldiamine-based dye (TPD-dye) absorbing in the blue region and squaraine dye (SQ-dye) mainly absorbing the red part of the visible spectrum. In this way, the optical response of the device was extended up to 700 nm. Under optimized conditions, a conversion efficiency of 2.41 % could be reached.
To accomplish the desired panchromaticity or even an extension of the absorption up to the NIR region with a single sensitizer, novel BODIPY dyes with excellent optical properties were designed and synthesised. We prepared BODIPYs with donor-groups to extend the delocalized system and integrated a meso-ethynyl bridge between the BODIPY core and the anchoring group to improve the electronic connection between them. For comparison, we synthesised the corresponding BODIPYs without donor-moieties and without ethynyl bridge. The multi-step synthetic routes were optimized, the mechanism of the donor-attachment was clarified and the introduction of the ethynylphenyl group in the meso-position was accomplished for the first time. The optical characterisation of the compounds disclosed an impressively broad and intensive spectral response, especially for a meso-ethynylphenyl BODIPY with donor-groups. This dye absorbs up to 1030 nm with high extinction coefficients. This makes suitable functionalised BODIPYs promising candidates for solar cell applications.
The next part took advantage of the excellent optical properties of BODIPYs and expanded the topic towards the concept of energy transfer. Here, an unattached energy donor dye provides additional adsorption and transfers the energy to a sensitizing acceptor dye. Indeed, for appropriate combinations an additional contribution to the external quantum efficiency was found in the absorption region of the energy donor dye.
Furthermore, a review chapter covering all aspects of dye-sensitized solar cells and the sensitizers is added as appendix.
In summary, this thesis presents the successful design, synthesis and characterisation of both metal-organic and organic sensitizers including ruthenium complexes, triphenyldiamine-based dyes, a squaraine sensitizer and BODIPY dyes. The sensitizers (either individually or in combination with complementary sensitizers) provide excellent optical properties for the application in solar cells. The applicability of these sensitizers was successfully demonstrated in standard solid-state dye-sensitized solar cells, in newly developed multichromophore hybrid blend solar cells, co-sensitized solar cells and in solid-state dye-sensitized solar cells taking advantage of energy transfer.
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Measurement of emotional reactions to television advertisements – A state of the art review
(2012)
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Christian Wolterink
- Human emotions and their measurement present a complex and intricate affair
which perpetuates an ongoing discourse in marketing research. Since emotions
play a pivotal role in the success of advertisements, the exploitation of tools for
their precise measurement is crucial to researchers and practitioners alike. Yet,
there is no single gold standard instrument existent that enables a comprehensive
detection of all emotion facets at once. This thesis therefore focuses on the theoretical
conceptualization of emotion, and afterwards presents a variety of measurement
methods that address different emotion components. Thereby, particular
emphasis is placed on their applicability as regards television commercials.
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The origins of olivine fabric transitions and their effects on seismic anisotropy in the upper mantle
(2012)
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Sushant Shekhar
- Convecting mantle plays a central role in the thermal and geochemical evolution of the Earth. It provides the principal force responsible for major geological features such as mountains and ocean basins. Plate tectonics and its violent consequences such as earthquakes and volcanoes are all manifestations of the dynamics of the convective mantle. Shearing forces generated by mantle convection leads to lattice preferred orientation (LPO) of the major upper mantle mineral phases. LPO that develops in this way is thought to be the principal cause behind seismic anisotropy in the upper mantle, which can consequently be used to chart convective flow of the mantle.
Strong changes in seismic anisotropy occur in the top 300 km of the upper mantle where olivine is the principal mineral. In this study a solid media high pressure deformation apparatus, called the deformation-DIA or D-DIA, has been used to deform aggregates of San Carlos olivine in simple shear geometry at pressures between 3 and 8.5 GPa and temperatures from 1300-1500°C. As part of this project a high pressure and temperature solid-media cubic assembly was developed to facilitate these experiment that employed alumina pistons cut at 45° to shear the sample but minimized cold deformation of the sample by employing initially porous alumina in the sample column. Once stable high pressures and temperature were reached the cubic assembly was deformed by compressing two vertically oriented anvils of the D-DIA, while the four horizontally oriented anvils were maintained at a constant loading force. This assembly shortening led to shearing of the olivine sample. Recovered samples were analyzed for fabric development employing electron backscattered diffraction (EBSD) and microstructure was observed using transmission electron microscopy (TEM).
Experiments were performed at each pressure and temperature as a function of strain rate and H2O content. In dry olivine deformation experiments performed at slower strain rates an A-type fabric dominated at all pressures and temperatures, implying deformation by dislocation glide through the (010)[100] slip system. At higher strain rates evidence for the B-type fabric was observed, suggesting increased activity of the (010)[001] slip system at higher stresses. Recrystallization grains size and dislocation densities were used to estimate stresses in the samples and a good correlation was observed between strain rate and estimated flow stresses. Dry experiments from 8.5 GPa and 1500°C exhibited no LPO, which may be an indication for deformation through diffusion accommodated grain boundary sliding at these conditions. No indication was found that pressure influences the dominant slip system in olivine, in contrast to previous studies. It is considered that previously reported incidences of pressure effects can in fact be attributed to the development of higher stresses in experiments performed at higher pressures.
Fabrics in H2O bearing olivine deformed at similar conditions revealed the overriding dominance of the C-type fabric, developed through action of the (100)[001] slip system. Variations in pressure, temperature and strain rate had little influence on this fabric development. TEM observations confirmed the presence of dislocations with slip systems consistent with the development of the macroscopic fabrics. Viscoplastic self consistent modeling was employed to understand the development of fabric in the samples and to estimate the relative contributions of variations slip systems to the developed fabrics.
These results are used to construct an olivine fabric map which is found to be consistent with some previous studies at lower pressures. It is argued that the decrease in seismic anisotropy observed in the top 300 km of the upper mantle cannot originate from a pressure induced change in the dominant olivine deformation fabric. Instead it is argued that changes in the H2O content of olivine with depth cause a shift in the dominant fabric from A-type to C-type, with a possible excursion through the E-type fabric, dominant slip system (001)[100], which was, however, not observed in this study. Modeling is used to show that this variation in fabric with depth can cause the observed weakening the seismic anisotropy in the upper mantle if the olivine H2O content increases from below 100 ppm at 50 km to 250 ppm at 300 km. Rather than implying an increased in the H2O content of the mantle with depth, however, it is argued that this change in olivine H2O content can be caused by changes in the H2O olivine-pyroxene partition coefficients with depth, for a fixed bulk mantle H2O content of 200 ppm.
Similar deformation experiments performed on a peridotite assemblage at 8.5 GPa and 1300°C indicate identical olivine fabrics to those observed in monomineralic experiments at the same conditions. Fabrics for diopside and enstatite were found to be similar to those found in previously performed lower pressure experiments.
Experiments on a piezoelectric single crystal of GaPO4 were performed in the D-DIA and 6-ram MAVO press at high pressures in order to measure charge on the crystal developed through the application of deviatoric stresses. Electrical charges were measured through the use of an operational amplifier. Experiments performed at room temperature using a developed cubic assembly were successful in measuring quantifiable electrical charges resulting from the advancement of the deformation anvils by as little as 0.5 µm. Although the piezoelectric constant for this material is not yet calibrated at high pressures, stresses were estimated from the measured charges and measureable values were in the range 4-350 MPa.