NachhaltigAngewandte Naturwissenschaften und WirtschaftsingenieurwesenTSZ WeißenburgZeitschriftenartikel
Altafim, R.A.P., Dmitry Rychkov, Wirges, W., Gerhard, R., Basso, H.C., R.A.C. Altafim, M. Melzer
Laminated tubular-channel ferroelectret systems from low-density polyethylene films and from fluoroethylene-propylene copolymer films-A comparison
IEEE Transactions on Dielectrics and Electrical Insulation, vol. 19, no. 4, pp. 1116-1123
2012
DOI: 10.1109/TDEI.2012.6259978
NachhaltigAngewandte Naturwissenschaften und WirtschaftsingenieurwesenTSZ WeißenburgZeitschriftenartikel
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 WirtschaftsingenieurwesenTSZ WeißenburgZeitschriftenartikel
Dmitry Rychkov, Altafim, R.A.P., Qiu, X., Gerhard, R.
Treatment with orthophosphoric acid enhances the thermal stability of the piezoelectricity in low-density polyethylene ferroelectrets
Journal of Applied Physics, vol. 111, no. 12
2012
DOI: 10.1063/1.4729866
Abstract anzeigen
Ferroelectrets have been fabricated from low-density polyethylene (LDPE) films by means of a template-based lamination. The temperature dependence of the piezoelectric d33 coefficient has been investigated. It was found that low-density polyethylene ferroelectrets have rather low thermal stability with the piezoelectric coefficient decaying almost to zero already at 100 °C. This behavior is attributed to the poor electret properties of the polyethylene films used for the fabrication of the ferroelectrets. In order to improve the charge trapping and the thermal stability of electret charge and piezoelectricity, LDPE ferroelectrets were treated with orthophosphoric acid. The treatment resulted in considerable improvements of the charge stability in LDPE films and in ferroelectret systems made from them. For example, the charge and piezoelectric-coefficient decay curves shifted to higher temperatures by 60 K and 40 K, respectively. It is shown that the decay of the piezoelectric coefficient in LDPE ferroelectrets is governed by the relaxation of less stable positive charges. The treatment also leads to noticeable changes in the chemical composition of the LDPE surface. Infrared spectroscopy reveals absorption bands attributed to phosphorus-containing structures, while scanning electron microscopy shows new island-like structures, 50–200 nm in diameter, on the modified surface.
NachhaltigAngewandte Naturwissenschaften und WirtschaftsingenieurwesenTSZ WeißenburgZeitschriftenartikel
Dmitry Rychkov, Gerhard, R., Ivanov, V., Rychkov, A. A.
Enhanced electret charge stability on polyethylene films treated with titanium-tetrachloride vapor
IEEE Transactions on Dielectrics and Electrical Insulation, vol. 19, no. 4, pp. 1305-1311
2012
DOI: 10.1109/TDEI.2012.6260005
Abstract anzeigen
Low-density polyethylene (LDPE) films have been treated with titanium-tetrachloride vapor by means of the molecular-layer-deposition method. It is shown that such a treatment leads to a considerable improvement of the electret properties for both positively and negatively charged films. The temperature stability of the electret homo-charge has been increased by approximately 60°C. At the same time, the temporal stability of charge is also considerably improved. Modified low-density polyethylene films show no “cross-over phenomenon” when charged to higher voltages. Thus, it is now possible to produce electrets from polyethylene films with high initial charge densities, but without a strongly reduced charge stability. The influence of a chemical treatment with titanium-tetrachloride vapor on charge injection from aluminum electrodes into polyethylene films was also investigated. It is found that the interface between an aluminum electrode and a modified LDPE surface layer has different injection properties for positive and negative charges. Electrons can be injected across the modified interface, whereas injection of holes is either very limited or non-existent.
NachhaltigAngewandte Naturwissenschaften und WirtschaftsingenieurwesenTSZ WeißenburgZeitschriftenartikel
Dmitry Rychkov, Yablokov, M., Rychkov, A. A.
Chemical and physical surface modification of PTFE films—an approach to produce stable electrets
Applied Physics A - Materials Science and Processing, vol. 107, no. 3, pp. 589-596
2012
DOI: 10.1007/s00339-012-6834-5
Abstract anzeigen
The thermal stability of positive charge has been investigated in chemically and physically treated polytetrafluoroethylene (PTFE) films. It has been found that virgin films, oriented by the manufacturer, display an increase in thermal stability of positive charge with an increase of the initial value of surface potential. Such an anomalous behavior is explained by the influence of a negative tribocharge, trapped some small distance below the surface. In PTFE samples treated with orthophosphoric acid and with tetraethoxysilane, a considerable improvement of positive charge stability has been achieved, but no influence of the initial value of surface potential has been observed. However, this influence should be kept in mind when comparing charge stability in virgin and modified samples. In nonoriented PTFE films, no influence of the initial value of surface potential on charge stability has been observed. This could be due to the fact that these films did not possess a noticeable negative tribocharge. After the treatment in glow-discharge defluorination, oxidation and appearance of polar groups have been detected on the surface. These changes in chemical composition of a PTFE surface resulted in a noticeable improvement in thermal stability of positively charged electrets. This improvement is attributed to the formation of deeper traps on the modified surface.
NachhaltigAngewandte Naturwissenschaften und WirtschaftsingenieurwesenTSZ WeißenburgBeitrag (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 WirtschaftsingenieurwesenTSZ WeißenburgBeitrag (Sammelband oder Tagungsband)
Dmitry Rychkov, A. Kuznetsov, Rychkov, A. A., V. Goldade
Electret Properties of Polyethylene Films Modified with Titanium Tetrachloride Vapor
Proceedings of the 14th International Symposium on Electrets (ISE11), Piscataway, NJ, USA
2011
DOI: 10.1109/ISE.2011.6085007
Abstract anzeigen
Low density polyethylene films have been treated with titanium tetrachloride vapor by means of the molecular layer deposition method. It has been shown that such a treatment leads to a considerable improvement of the electret properties. The thermal stability of the electret homocharge has been increased by 60°C. At the same time, the temporal stability of charge is also improved. The modified low density polyethylene films show no “crossover phenomenon” when charged to higher voltages. Thus it is now possible to produce electrets from polyethylene films with high values of the initial charge density without a detrimental influence on the charge stability.
NachhaltigAngewandte Naturwissenschaften und WirtschaftsingenieurwesenTSZ WeißenburgZeitschriftenartikel
Dmitry Rychkov, Gerhard, R.
Stabilization of positive charge on polytetrafluoroethylene electret films treated with titanium-tetrachloride vapor
Applied Physics Letters, vol. 98, no. 12
2011
DOI: 10.1063/1.3565166
Abstract anzeigen
The surface of polytetrafluoroethylene films was treated with titanium-tetrachloride vapor. The treatment was carried out in a flow reactor by means of molecular-layer deposition, a method from the arsenal of chemical nanotechnology. X-ray photoelectron spectroscopy reveals that such a treatment results in considerable changes in the chemical composition at and near the surface of the fluoropolymer film. Both, defluorination and oxidation of the surface were observed. At the same time, samples treated with titanium tetrachloride show a significant enhancement in the thermal stability of the positive homocharge. The thermally stimulated surface-potential-decay curves were observed to shift to higher temperatures by more than 100 °C
The authors are indebted to Dr. Andreas Holländer (Fraunhofer Institute for Applied Polymer Research, Potsdam-Golm, Germany) for making the XPS measurements possible and to Dr. Sergey Trifonov of St. Petersburg State Institute of Technology (St. Petetrsburg, Russia) for the treatment of PTFE films with titanium-tetrachloride vapor.
NachhaltigAngewandte Naturwissenschaften und WirtschaftsingenieurwesenTSZ WeißenburgZeitschriftenartikel
Dmitry Rychkov, Kuznetsov, A., Rychkov, A. A.
Electret Properties of Polyethylene and Polytetrafluoroethylene Films with Chemically Modified Surface
IEEE Transactions on Dielectrics and Electrical Insulation, vol. 18, no. 1, pp. 8-14
2011
DOI: 10.1109/TDEI.2011.5704487
Abstract anzeigen
This paper investigates the effect of chemical surface modification of polytetrafluoroethylene (PTFE) and low density polyethylene (LDPE) films on their electret properties. PTFE films were subjected to wet treatment with three different chemicals: orthophosphoric acid, tetrabutyl titanate and tetraethoxysilane. The technique based on the principles of molecular layer deposition (MLD) method was used to modify the surface of LDPE films with phosphorus trichloride vapors. The surfaces of the films were then corona charged, and the electret charge stability was studied by means of isothermal and thermally stimulated surface potential decay. Both PTFE and LDPE films, after the surface treatment, displayed a considerable enhancement in the charge stability compared to the virgin samples. It is important to note that the enhancement of the charge stability was achieved in the positively charged PTFE films, a result important to practical applications. We attribute this effect of charge stabilization to the formation of new energetically deep traps on the modified surface. Decrease in molecular mobility, due to attachment of new chemical structures to the surface macro molecules, may also contribute to the overall growth of the charge stability.
NachhaltigAngewandte Naturwissenschaften und WirtschaftsingenieurwesenTSZ WeißenburgBeitrag (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 WirtschaftsingenieurwesenTSZ WeißenburgBeitrag (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.
NachhaltigAngewandte Naturwissenschaften und WirtschaftsingenieurwesenTSZ WeißenburgBeitrag (Sammelband oder Tagungsband)
Dmitry Rychkov, M. Dansachmüller, H. Ragusch, A. Becker, G. Kofod
Force Relaxation in Charged Dielectric Elastomer Actuators
Proceedings of the 2010 10th IEEE International Conference on Solid Dielectrics (ICSD)
2010
DOI: 10.1109/ICSD.2010.5568252
Abstract anzeigen
A new method for the investigation of dielectric elastomer actuators is developed, in which the relaxation of actuation force is observed under constant strain condition in an open-circuit regime. Independent isothermal surface potential decay measurements were employed to study the charge storage properties of the same elastomer materials. The following materials were used for dielectric elastomer actuators fabrication: VHB (adhesive films by 3M) and Poly-styrene-ethylene-butadiene-styrene (SEBS-Dryflex). It is found that actuation force relaxation kinetics is largely dependent on charge storage and transport properties of the actuator's dielectric elastomer material.
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