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Suche nach „[D.] [Rychkov]“ hat 4 Publikationen gefunden
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    Zeitschriftenartikel

    Wang, J., D. Rychkov, Q. Nguyen, Gerhard, R.

    Unexpected bipolar space-charge polarization across transcrystalline interfaces in polypropylene electret films

    Journal of Applied Physics, vol. 128, no. 13

    2020

    DOI: 10.1063/5.0022071

    Abstract anzeigen

    A double-layer transcrystalline polypropylene (PP) film with a flat central interface layer between its two transcrystalline layers is obtained by recrystallization from the melt between two polytetrafluoroethylene (PTFE) surfaces on both sides of the PP film. Its electret properties are studied and compared with those of a single-layer transcrystalline PP film re-crystallized in contact with only one PTFE surface. Within experimental uncertainty, the two types of transcrystalline films exhibit the same thermal properties and crystallinities. After thermal poling, however, two hetero-charge layers of opposite polarity are found on the internal interfaces of the double-layer transcrystalline films and may together be considered as micrometer-sized dipoles. The unexpected phenomenon does not occur in single-layer transcrystalline samples without a central interface layer, suggesting that the interfaces between the transcrystalline layers and the micrometer-thick central interface layer may be the origin of deeper traps rather than the crystalline structures in the transcrystallites or the spherulites. The origin of the interfacial charges was also studied by means of an injection-blocking charging method, which revealed that intrinsic charge carriers introduced during recrystallization are most likely responsible for the interfacial charges. It is fascinating that a material as familiar as PP can exhibit such intriguing properties with a special bipolar space-charge polarization across the central interface layer after quasi-epitaxial surface moulding into a double-layer transcrystalline form. In addition to applications in electret (micro-)devices for electro-mechanical transduction, the highly ordered structures may also be employed as a new paradigm for studying charge storage and transport in polymer electrets and in dielectrics for DC electrical insulation.

    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, 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.