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Suche nach „[H.] [Stoyanov]“ hat 5 Publikationen gefunden
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    NachhaltigAngewandte Naturwissenschaften und WirtschaftsingenieurwesenTC Weißenburg

    Zeitschriftenartikel

    McCarthy, D.N., H. Stoyanov, Dmitry Rychkov, H. Ragusch, M. Melzer, G. Kofod

    Increased permittivity nanocomposite dielectrics by controlled interfacial interactions

    Composites Science and Technology, vol. 72, no. 6, pp. 731-736

    2012

    DOI: 10.1016/j.compscitech.2012.01.026

    Abstract anzeigen

    The use of nanoparticles in polymer composite dielectrics has promised great improvements, but useful results have been elusive. Here, the importance of the interfacial interactions between the nanoparticles and the polymer matrix are investigated in TiO2 nanocomposites for dielectric materials using surface functionalisation. The interface is observed to dominate the nanocomposite properties and leads to a threefold increase in permittivity at volume fractions as low as 10%. Surface functionalisation of the filler nanoparticles with silanes allows control of this interface, avoiding significant degradation of the other important material properties, particularly electrical breakdown strength, and resulting in a material that is demonstrated successfully as an active material in a dielectric elastomer actuator application with increased work output compared to the pure polymer. Although further permittivity increases are observed when the interface regions have formed a percolation network, the other material properties deteriorate. The observation of percolation behaviour allows the interface thickness to be estimated.

    NachhaltigAngewandte Naturwissenschaften und WirtschaftsingenieurwesenTC Weißenburg

    Beitrag (Sammelband oder Tagungsband)

    G. Kofod, H. Stoyanov, M. Kollosche, S. Risse, H. Ragusch, D. McCarthy, R. Wache, Dmitry Rychkov, M. Dansachmüller

    Molecular level materials design for improvements of actuation properties of dielectric elastomer actuators

    Proceedings of SPIE 7976

    2011

    DOI: 10.1117/12.880981

    Abstract anzeigen

    Dielectric elastomer actuators are soft electro-mechanical transducers with possible uses in robotic, orthopaedic and automotive applications. The active material must be soft and have a high ability to store electrical energy. Hence, three properties of the elastic medium in a dielectric elastomer actuator affect the actuation properties directly: dielectric constant, electric breakdown strength, and mechanical stiffness. The dielectric constant of a given elastomer can be improved by mixing it with other components with a higher dielectric constant, which can be classified as insulating or conducting. In this paper, an overview of all approaches proposed so far for dielectric constant improvement in these soft materials will be provided. Insulating particles such as TiO2 nanoparticles can raise the dielectric constant, but may also lead to stiffening of the composite, such that the overall actuation is lowered. It is shown here how a chemical coating of the TiO2 nanoparticles leads to verifiable improvements. Conducting material can also lead to improvements, as has been shown in several cases. Simple percolation, relying on the random distribution of conducting nanoparticles, commonly leads to drastic lowering of the breakdown strength. On the other hand, conducting polymer can also be employed, as has been demonstrated. We show here how an approach based on a specific chemical reaction between the conducting polymer and the elastomer network molecules solves the problem of premature breakdown which is otherwise typically found.

    NachhaltigAngewandte Naturwissenschaften und WirtschaftsingenieurwesenTC Weißenburg

    Beitrag (Sammelband oder Tagungsband)

    G. Kofod, H. Stoyanov, S. Risse, M. Kollosche, McCarthy, D.N., R. Kraehnert, H. Ragusch, Dmitry Rychkov

    Improvement of Materials for Dielectric Elastomer Actuators Based on Conducting Particle Composites

    Actuator 10, Bremen

    2010

    ISBN: 9783933339126

    NachhaltigAngewandte Naturwissenschaften und WirtschaftsingenieurwesenTC Weißenburg

    Beitrag (Sammelband oder Tagungsband)

    G. Kofod, H. Stoyanov, M. Kollosche, S. Risse, H. Ragusch, Dmitry Rychkov, M. Dansachmüller, D. McCarthy

    Nano-scale Materials Science for Soft Dielectrics: Composites for Dielectric Elastomer Actuators

    Proceedings of the 2010 10th IEEE International Conference on Solid Dielectrics (ICSD)

    2010

    DOI: 10.1109/ICSD.2010.5568262

    Abstract anzeigen

    Electro-mechanical transducers based on soft elastomers can be improved by suitable manipulation of dielectric properties, mechanical stiffness and electric breakdown strength. The dielectric constant of an elastomer can be improved by mixing with other components with a higher dielectric constant, and both insulating or conducting filler materials may be employed. We present our results on insulating nanoparticulate TiO 2 with various chemical modifications, which may lead to devices with improved properties. Conducting nanoparticles such as carbon black may lead to percolation-related enhancement, though with strongly detrimental side effects. On the other hand, a “molecular composite” approach, in which the conducting nanoparticles are grafted chemically to the backbone, appears valuable.

    NachhaltigAngewandte Naturwissenschaften und WirtschaftsingenieurwesenTC Weißenburg

    Beitrag (Sammelband oder Tagungsband)

    G. Kofod, D. McCarthy, H. Stoyanov, M. Kollosche, S. Risse, H. Ragusch, Dmitry Rychkov, M. Dansachmüller, R. Wache

    Materials science on the nano-scale for improvements in actuation properties of dielectric elastomer actuators

    Proceedings of SPIE 7642

    2010

    DOI: 10.1117/12.847281

    Abstract anzeigen

    We discuss various approaches to increasing the dielectric constant of elastomer materials, for use in dielectric elastomer actuators. High permittivity metal-oxide nano-particles can show elevated impact compared to larger size particles, but suffer from water uptake. Composites with conducting particles lead to extremely high permittivity caused by percolation, but they often suffer early breakdown. We present experiments on approaches combining metal-oxides and metal particles, which compensate for the drawbacks, and may lead to useful DEA materials in which all relevant properties are technologically useful. The key seems to be to avoid percolation and achieve a constant nearest-neighbor separation.