EPR-Spektroskopie zur Untersuchung von Struktur und Dynamik in Polymer-Ton-Nanokompositen

Ziel der vorliegenden Arbeit war die Untersuchung von Struktur und Dynamik in Polymer-Ton-Nanokompositen mittels EPR-Spektroskopie; damit sollten ein Beitrag zur Analyse der Tensidschicht in solchen Systemen geleistet und die Ergebnisse anderer Messmethoden ergänzt werden. Die Tensidschicht in Polymer-Ton-Nanokompositen nimmt großen Einfluss auf das System, denn sie bestimmt die Wechselwirkung zwischen Ton und Polymer: Damit hydrophiler Ton gut mit hydrophobem Polymer (hier Polystyrol) mischbar ist, muss das Schichtsilikat zunächst mit Tensiden organisch-modifiziert werden; dies geschieht durch Kationenaustausch der Natriumionen im Ton gegen Tenside. Um mit Hilfe der EPR einen Einblick in die Tensidschicht zu gewinnen, muss etwa 1% der zur Tonmodifizierung eingesetzten Amphiphile spinmarkiert sein. So gelang es im Rahmen dieser Arbeit, Tenside mit verschiedenen Kopfgruppen, nämlich Trimethylammonium- bzw. Trimethylphosphoniumtenside, zu synthetisieren und sie an verschiedenen Positionen ihrer hydrophoben Alkylkette mit einem Nitroxidradikal zu markieren. Das Nitroxidradikal diente als Spinsonde für die EPR-Experimente. Neben der Synthese verschiedener, spinmarkierter Amphiphile, der anschließenden Darstellung organisch-modifizierten Tons (Kationenaustausch) und verschiedener Polymer-Ton-Nanokomposite (Schmelzinterkalation) wurden alle Proben mittels EPR-Spektroskopie untersucht; dabei wurden sowohl cw- als auch gepulste Messtechniken eingesetzt. Aus cw-Experimenten ging hervor, dass die Dynamik der gesamten Tensidschicht mit der Temperatur zunimmt und die Mobilität der hydrophoben Tensidalkylkette mit wachsendem Abstand zu ihrer Kopfgruppe wächst. Zugabe von Polymer behindert bei steigender Temperatur das Anschwellen des Tons bei Aufschmelzen der Tensidschicht; die Dynamik des Systems ist eingeschränkt. Mit Hilfe gepulster EPR-Messungen (ENDOR und ESEEM), die Informationen über Abstände bzw. Kontakt in den untersuchten Systemen lieferten, ließ sich ein Strukturmodell der Polymer-Ton-Nanokomposite skizzieren, das Vorstellungen anderer, älterer Methoden unterstützt: Hierbei richten sich die Tenside in Multischichten unterschiedlicher Mobilität parallel zur Tonoberfläche aus. -------------------------------------------------------------------------------- Inhaltszusammenfassung in einer weiteren Sprache (englisch) A variety of electron paramagnetic resonance (EPR) techniques were applied to spin-labeled surfactants to obtain a deeper understanding of the surfactant layer in polymer-clay-nanocomposites. This surfactant layer has a major influence on the system by mediating the interaction between clay and polymer: A good dispersion of the hydrophilic clay in the hydrophobic polymer (here polystyrene) can only be obtained by organically modifying the silicate, which in turn can be achieved by cation exchange of the sodium ions in the clay against surfactants. For investigation of the surfactant layer by EPR spectroscopy a small amount (1%) of the used surfactants has to be spin-labeled. In this thesis surfactants with different ionic headgroups, namely trimethylammonium- bzw. trimethylphosphonium surfactants, were successfully synthesized and labeled with a nitroxide radical at different positions along their hydrophobic alkyl chain. The nitroxide radical acts as the spin label for the EPR experiments. Following the synthesis of different, spin-labeled surfactants, the preparation of organically modified clay (cation exchange) and of several polymer-clay-nanocomposites (melt intercalation), all samples were characterized by EPR spectroscopy in continuous-wave (CW) and pulsed mode. CW experiments showed that the dynamics of the surfactant layer increases with temperature and that the mobility of the hydrophobic surfactant alkyl chains raises with increasing distance to their headgroups. Addition of polymer hinders the swelling of the clay when the surfactant layer is melting at elevated temperatures; the dynamics of the system is thus limited. Together with pulsed EPR measurements (ENDOR und ESEEM), which probe distances and surfactant-polymer contact in the investigated material, all experiments support and emphasize already existing models of the structure in organoclay and polymer-clay-nanocomposites: Here the surfactants lie flatly on the surface of the clay platelets with a mobility gradient along their alkyl chains and form multilayers with different mobility of directly attached and interlayered surfactants

Dogs in society can prevent society going to the dogs

An editorial comment on the importance of dogs to society, to counter the emphasis given to the risks they pose

Psychology of Fragrance Use: Perception of Individual Odor and Perfume Blends Reveals a Mechanism for Idiosyncratic Effects on Fragrance Choice

Cross-culturally, fragrances are used to modulate body odor, but the psychology of fragrance choice has been largely overlooked. The prevalent view is that fragrances mask an individual's body odor and improve its pleasantness. In two experiments, we found positive effects of perfume on body odor perception. Importantly, however, this was modulated by significant interactions with individual odor donors. Fragrances thus appear to interact with body odor, creating an individually-specific odor mixture. In a third experiment, the odor mixture of an individual's body odor and their preferred perfume was perceived as more pleasant than a blend of the same body odor with a randomly-allocated perfume, even when there was no difference in pleasantness between the perfumes. This indicates that fragrance use extends beyond simple masking effects and that people choose perfumes that interact well with their own odor. Our results provide an explanation for the highly individual nature of perfume choice

Vocal Learning and Auditory-Vocal Feedback

Vocal learning is usually studied in songbirds and humans, species that can form auditory templates by listening to acoustic models and then learn to vocalize to match the template. Most other species are thought to develop vocalizations without auditory feedback. However, auditory input influences the acoustic structure of vocalizations in a broad distribution of birds and mammals. Vocalizations are dened here as sounds generated by forcing air past vibrating membranes. A vocal motor program may generate vocalizations such as crying or laughter, but auditory feedback may be required for matching precise acoustic features of vocalizations. This chapter discriminates limited vocal learning, which uses auditory input to fine-tune acoustic features of an inherited auditory template, from complex vocal learning, in which novel sounds are learned by matching a learned auditory template. Two or three songbird taxa and four or ve mammalian taxa are known for complex vocal learning. A broader range of mammals converge in the acoustic structure of vocalizations when in socially interacting groups, which qualifies as limited vocal learning. All birds and mammals tested use auditory-vocal feedback to adjust their vocalizations to compensate for the effects of noise, and many species modulate their signals as the costs and benefits of communicating vary. This chapter asks whether some auditory-vocal feedback may have provided neural substrates for the evolution of vocal learning. Progress will require more precise definitions of different forms of vocal learning, broad comparative review of their presence and absence, and behavioral and neurobiological investigations into the mechanisms underlying the skills.PostprintPeer reviewe

Evolution of Environmental Information Models

Part 6: Information SystemsInternational audienceReusability of environmental data is essential for environmental research and control; standardized data models are being created by various organizations to facilitate this process. Due to the evolving nature of environmental science, these data models must be continuously extended for the support of new concepts, thus rapidly breaking the level of standardization achieved. The definition of reusable properties would allow for standardization of this extension process. In this paper, we first analyze the requirements to reusable properties, and explain the rational for the decision that reusable properties tightly bound to a URI would be the most apt solution; the following list of requirements was defined in order to compare the viability of the options proposed: URI Coupling, DataType Coupling, Semantics Coupling and Persistence. We then go on to explore possible avenues for implementation of reusable URI-Properties, whereby the following approaches where analysed for applicability: Data Types, Interfaces, MOF level adjustment of UML and a solution utilizing stereotypes for the definition and use of reusable URI-Properties. Of these approaches, all were deemed feasible except for the MOF level adjustment of UML; MOF level adjustment is not possible due to cardinality constraints within the MOF definition. Examples were created for the other 3 possibilities, including serialization options towards XML Schema. These examples were then compared with the requirements defined for URI-Properties; based on this analysis, the UML Stereotype based solution for the specification and use of reusable URI-Properties was deemed as most viable and is described in further detail

A site-directed spin-labeling study of surfactants in polymer-clay nanocomposites

Polymer–clay nanocomposites exhibit much improved mechanical, physical, and chemical properties compared to the pure polymer. The interaction of polymer and organically modified silicates is mainly influenced by the surfactant layer in the system. To investigate the structure and dynamics of this surfactant layer, various electron paramagnetic spectroscopy (EPR) techniques were applied. Continuous wave EPR experiments showed a temperature-dependent heterogeneous mobility of the surfactant layer in organoclay as well as a difference in dynamics along the alkyl chain. Intercalation of polystyrene causes a significant slowdown in surfactant dynamics. Electron spin echo envelope modulation indicates a closer contact of the polymer with the mid of the surfactant tail than with the end of the tail. From the obtained data the picture of flatly lying surfactants on clay platelets with a mobility gradient along their alkyl chains can be drawn