TY - JOUR A1 - Kollosche, Matthias A1 - Kofod, Guggi A1 - Suo, Zhigang A1 - Zhu, Jian T1 - Temporal evolution and instability in a viscoelastic dielectric elastomer JF - Journal of the mechanics and physics of solids N2 - Dielectric elastomer transducers are being developed for applications in stretchable electronics, tunable optics, biomedical devices, and soft machines. These transducers exhibit highly nonlinear electromechanical behavior: a dielectric membrane under voltage can form wrinkles, undergo snap-through instability, and suffer electrical breakdown. We investigate temporal evolution and instability by conducting a large set of experiments under various prestretches and loading rates, and by developing a model that allows viscoelastic instability. We use the model to classify types of instability, and map the experimental observations according to prestretches and loading rates. The model describes the entire set of experimental observations. A new type of instability is discovered, which we call wrinkle-to-wrinkle transition. A flat membrane at a critical voltage forms wrinkles and then, at a second critical voltage, snaps into another state of winkles of a shorter wavelength. This study demonstrates that viscoelasticity is essential to the understanding of temporal evolution and instability of dielectric elastomers. (C) 2014 Elsevier Ltd. All rights reserved. KW - Dielectric elastomer KW - Viscoelasticity KW - Snap-through instability KW - Phase transition KW - Wrinkling Y1 - 2015 U6 - https://doi.org/10.1016/j.jmps.2014.11.013 SN - 0022-5096 SN - 1873-4782 VL - 76 SP - 47 EP - 64 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Wache, Remi A1 - McCarthy, Denis N. A1 - Risse, Sebastian A1 - Kofod, Guggi T1 - Rotary Motion Achieved by New Torsional Dielectric Elastomer Actuators Design JF - IEEE ASME transactions on mechatronics N2 - This paper reports a new way to produce a rotation motion actuated by dielectric elastomer actuators. Two specific electrode designs have been developed and the rotation of the actuator centers has been demonstrated and measured. At low strains, the rotation shows a nearly quadratic dependence with the voltage. This behavior was used to compare the performances between the two proposed designs. Among the tested configurations, a maximal rotation of 10 degrees was achieved. KW - Dielectric elastomer actuator (DEA) KW - electroactive polymer KW - rotation Y1 - 2015 U6 - https://doi.org/10.1109/TMECH.2014.2301633 SN - 1083-4435 SN - 1941-014X VL - 20 IS - 2 SP - 975 EP - 977 PB - Inst. of Electr. and Electronics Engineers CY - Piscataway ER - TY - JOUR A1 - Carpi, Federico A1 - Anderson, Iain A1 - Bauer, Siegfried A1 - Frediani, Gabriele A1 - Gallone, Giuseppe A1 - Gei, Massimiliano A1 - Graaf, Christian A1 - Jean-Mistral, Claire A1 - Kaal, William A1 - Kofod, Guggi A1 - Kollosche, Matthias A1 - Kornbluh, Roy A1 - Lassen, Benny A1 - Matysek, Marc A1 - Michel, Silvain A1 - Nowak, Stephan A1 - Pei, Qibing A1 - Pelrine, Ron A1 - Rechenbach, Bjorn A1 - Rosset, Samuel A1 - Shea, Herbert T1 - Standards for dielectric elastomer transducers JF - Smart materials and structures N2 - Dielectric elastomer transducers consist of thin electrically insulating elastomeric membranes coated on both sides with compliant electrodes. They are a promising electromechanically active polymer technology that may be used for actuators, strain sensors, and electrical generators that harvest mechanical energy. The rapid development of this field calls for the first standards, collecting guidelines on how to assess and compare the performance of materials and devices. This paper addresses this need, presenting standardized methods for material characterisation, device testing and performance measurement. These proposed standards are intended to have a general scope and a broad applicability to different material types and device configurations. Nevertheless, they also intentionally exclude some aspects where knowledge and/or consensus in the literature were deemed to be insufficient. This is a sign of a young and vital field, whose research development is expected to benefit from this effort towards standardisation. KW - standard KW - dielectric elastomer KW - actuator KW - electromechanically active polymer KW - EAP KW - electroactive polymer KW - transducer Y1 - 2015 U6 - https://doi.org/10.1088/0964-1726/24/10/105025 SN - 0964-1726 SN - 1361-665X VL - 24 IS - 10 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Stoyanov, Hristiyan A1 - Kollosche, Matthias A1 - Risse, Sebastian A1 - McCarthy, Denis N. A1 - Kofod, Guggi T1 - Elastic block copolymer nanocomposites with controlled interfacial interactions for artificial muscles with direct voltage control JF - Soft matter N2 - Soft, physically crosslinking, block copolymer elastomers were filled with surface-treated nanoparticles, in order to evaluate the possibility for improvement of their properties when used as soft dielectric actuators. The nanoparticles led to improvements in dielectric properties, however they also reinforced the elastomer matrix. Comparing dielectric spectra of composites with untreated and surface-treated particles showed a measurable influence of the surface on the dielectric loss behaviour for high filler amounts, strongly indicating an improved host-guest interaction for the surface-treated particles. Breakdown strength was measured using a test bench and was found to be in good agreement with the results from the actuation measurements. Actuation responses predicted by a model for prestrained actuators agreed well with measurements up to a filler amount of 20%(vol). Strong improvements in actuation behaviour were observed, with an optimum near 15%(vol) nanoparticles, corresponding to a reduction in electrical field of 27% for identical actuation strains. The use of physically crosslinking elastomer ensured the mechanical properties of the matrix elastomer were unchanged by nanoparticles effecting the crosslinking reaction, contrary to similar experiments performed with chemically crosslinking elastomers. This allows for a firm conclusion about the positive effects of surface-treated nanoparticles on actuation behavior. Y1 - 2011 U6 - https://doi.org/10.1039/c0sm00715c SN - 1744-683X SN - 1744-6848 VL - 7 IS - 1 SP - 194 EP - 202 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Kollosche, Matthias A1 - Stoyanov, Hristiyan A1 - Laflamme, Simon A1 - Kofod, Guggi T1 - Strongly enhanced sensitivity in elastic capacitive strain sensors JF - Journal of materials chemistry N2 - Strain sensors based on dielectric elastomer capacitors function by the direct coupling of mechanical deformations with the capacitance. The coupling can be improved by enhancing the relative permittivity of the dielectric elastomer. Here, this is carried out through the grafting of conducting polymer (poly-aniline) to the elastomer backbone, leading to molecular composites. An enhancement in capacitance response of 46 times is observed. This could help to extend the possible range of miniaturization towards even smaller device features. Y1 - 2011 U6 - https://doi.org/10.1039/c0jm03786a SN - 0959-9428 VL - 21 IS - 23 SP - 8292 EP - 8294 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Ahnert, Karsten A1 - Abel, Markus A1 - Kollosche, Matthias A1 - Jorgensen, Per Jorgen A1 - Kofod, Guggi T1 - Soft capacitors for wave energy harvesting JF - Journal of materials chemistry N2 - Wave energy harvesting could be a substantial renewable energy source without impact on the global climate and ecology, yet practical attempts have struggled with the problems of wear and catastrophic failure. An innovative technology for ocean wave energy harvesting was recently proposed, based on the use of soft capacitors. This study presents a realistic theoretical and numerical model for the quantitative characterization of this harvesting method. Parameter regions with optimal behavior are found, and novel material descriptors are determined, which dramatically simplify analysis. The characteristics of currently available materials are evaluated, and found to merit a very conservative estimate of 10 years for raw material cost recovery. Y1 - 2011 U6 - https://doi.org/10.1039/c1jm12454d SN - 0959-9428 SN - 1364-5501 VL - 21 IS - 38 SP - 14492 EP - 14497 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Jordan, Grace A1 - McCarthy, Denis N. A1 - Schlepple, N. A1 - Krissler, Jan A1 - Schroeder, H. A1 - Kofod, Guggi T1 - Actuated micro-optical submount using a dielectric elastomer actuator JF - IEEE ASME transactions on mechatronics N2 - Analysis of the operating characteristics of a dielectric elastomer actuator (DEA) submount for the high-precision positioning of optical components in one dimension is presented. Precise alignment of a single-mode fiber is demonstrated and variation of the sensitivity of the submount motion by changing the bias voltage is confirmed. A comparison of the performance of the DEA submount with a piezoelectric alignment stage is made, which demonstrates that DEAs could present a very attractive, low-cost alternative to currently used manual technologies in overcoming the hurdle of expensive packaging of single-mode optical components. KW - Actuators KW - manufacturing automation KW - optical interconnections KW - packaging KW - position control Y1 - 2011 U6 - https://doi.org/10.1109/TMECH.2010.2089991 SN - 1083-4435 VL - 16 IS - 1 SP - 98 EP - 102 PB - Inst. of Electr. and Electronics Engineers CY - Piscataway ER - TY - JOUR A1 - Kofod, Guggi A1 - Stoyanov, Hristiyan A1 - Gerhard, Reimund T1 - Multilayer coaxial fiber dielectric elastomers for actuation and sensing JF - Applied physics : A, Materials science & processing N2 - A simple dip-coating technique was employed to manufacture coaxial actuators with multiple layers of alternating dielectric and conducting layers. A thin rubber string was coated with an electrode-insulator-electrode structure, giving rise to a thin, fiber-like actuator with coaxial geometry. The process was repeated to achieve a compact multilayer actuator with up to three coaxial dielectric layers. Mechanical and electromechanical characterization of the actuators is presented, showing actuation strains up to 8% and proper voltage-thickness scaling behavior. Also presented is a capacitance vs. extension plot, demonstrating that these structures can be used for compact and accurate capacitive strain sensing. Y1 - 2011 U6 - https://doi.org/10.1007/s00339-010-6066-5 SN - 0947-8396 SN - 1432-0630 VL - 102 IS - 3 SP - 577 EP - 581 PB - Springer CY - New York ER - TY - JOUR A1 - Kofod, Guggi A1 - Risse, Sebastian A1 - Stoyanov, Hristiyan A1 - McCarthy, Denis N. A1 - Sokolov, Sergey A1 - Krähnert, Ralph T1 - Broad-spectrum enhancement of polymer composite dielectric constant at ultra low volume fractions of silica-supported copper nanoparticles JF - ACS nano N2 - A new strategy for the synthesis of high permittivity polymer composites is demonstrated based on well-defined spatial distribution of ultralow amounts of conductive nanoparticles. The spatial distribution Was realized by immobilizing Cu nanoparticles within the pore system of Alia microspheres, preventing direct contact between individual Cu particles. Both Cu-loaded and unloaded silica microspheres were-then used as fillers in polymer composites prepared with thermoplastic SEBS rubber is the matrix. With a metallic Cu content of about 0.26 vol % In the compoilte, a relative increase of 94% In real permittivity was obtained. No Cu-induced relaxations were observed in the dielectric spectrum within the studied frequency range of 0.1 Hz to 1 MHz. When related to the amount of conductive nanoparticles, the obtained composites achieve the highest broad spectrum enhancement of permittivity ever reported for a polymer based composite. KW - nanocomposite KW - broad-spectrum permittivity enhancement KW - metal nanoparticles KW - uniform spatial arrangement Y1 - 2011 U6 - https://doi.org/10.1021/nn103097q SN - 1936-0851 VL - 5 IS - 3 SP - 1623 EP - 1629 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Kollosche, Matthias A1 - Döring, Sebastian A1 - Stumpe, Joachim A1 - Kofod, Guggi T1 - Voltage-controlled compression for period tuning of optical surface relief gratings JF - OPTICS LETTERS N2 - This Letter reports on new methods and a consistent model for voltage tunable optical transmission gratings. Elastomeric gratings were molded from holographically written surface relief gratings in an azobenzene sol-gel material. These were placed on top of a transparent electroactive elastomeric substrate. Two different electro-active substrate elastomers were employed, with a large range of prestretches. A novel finite-deformation theory was found to match the device response excellently, without fitting parameters. The results clearly show that the grating underwent pure-shear deformation, and more surprisingly, that the mechanical properties of the electro-active substrate did not affect device actuation. (C) 2011 Optical Society of America Y1 - 2011 SN - 0146-9592 VL - 36 IS - 8 SP - 1389 EP - 1391 PB - OPTICAL SOC AMER CY - WASHINGTON ER -