TY - JOUR A1 - Zhu, Jian A1 - Kollosche, Matthias A1 - Lu, Tongqing A1 - Kofod, Guggi A1 - Suo, Zhigang T1 - Two types of transitions to wrinkles in dielectric elastomers JF - Soft matter N2 - A membrane of a dielectric elastomer coated with compliant electrodes may form wrinkles as the applied voltage is ramped up. We present a combination of experiment and theory to investigate the transition to wrinkles using a clamped membrane subject to a constant force and a voltage ramp. Two types of transitions are identified. In type-I transition, the voltage-stretch curve is N-shaped, and flat and wrinkled regions coexist in separate areas of the membrane. The type-I transition progresses by nucleation of small wrinkled regions, followed by the growth of the wrinkled regions at the expense of the flat regions, until the entire membrane is wrinkled. By contrast, in type-II transition, the voltage-stretch curve is monotonic, and the entire flat membrane becomes wrinkled with no nucleation barrier. The two types of transitions are analogous to the first and the second order phase transitions. While the type-I transition is accompanied by a jump in the vertical displacement, type-II transition is accompanied by a continuous change in the vertical displacement. Such transitions may enable applications in muscle-like actuation and energy harvesting, where large deformation and large energy of conversion are desired. Y1 - 2012 U6 - https://doi.org/10.1039/c2sm26034d SN - 1744-683X VL - 8 IS - 34 SP - 8840 EP - 8846 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Mc Carthy, Denis N. A1 - Risse, Stefan A1 - Katekomol, Phisan A1 - Kofod, Guggi T1 - The effect of dispersion on the increased relative permittivity of TiO2/SEBS composites N2 - Polymer composites are currently suggested for use as improved dielectric materials in many applications. Here, the effect of particle size and dispersion on the electrical properties of composites of rutile TiO2 and poly(styrene- ethylene-butadiene-styrene) (SEBS) are investigated. Both 15 and 300 nm particles are mixed with SEBS, with amounts of sorbitan monopalmitate surfactant from 0 to 3.3 vol%, and their dielectric and mechanical properties are measured. Composites with the 300 nm TiO2 particles result in increases of 170% in relative permittivity over the pure polymer, far above those predicted by standard theories, such as Bruggeman (140%) and Yamada (114%), and improving dispersion with surfactant has little effect. The composites with 15 nm particles showed surprisingly large relative permittivity increases (350%), but improving the dispersion by the addition of any surfactant causes the relative permittivity to decrease to 240% of the pure polymer value. We suggest that the increase is due to the formation of a highly conductive layer in the polymer around the TiO2 particles. Y1 - 2009 UR - http://iopscience.iop.org/0022-3727/ U6 - https://doi.org/10.1088/0022-3727/42/14/145406 SN - 0022-3727 ER - 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 - Risse, Sebastian A1 - Kussmaul, Bjoern A1 - Krüger, Hartmut A1 - Kofod, Guggi T1 - Synergistic improvement of actuation properties with compatibilized high permittivity filler JF - Advanced functional materials N2 - Electroactive polymers can be used for actuators with many desirable features, including high electromechanical energy density, low weight, compactness, direct voltage control, and complete silence during actuation. These features may enable personalized robotics with much higher ability to delicately manipulate their surroundings than can be achieved with currently available actuators; however, much work is still necessary to enhance the electroactive materials. Electric field-driven actuator materials are improved by an increase in permittivity and by a reduction in stiffness. Here, a synergistic enhancement method based on a macromolecular plasticizing filler molecule with a combination of both high dipole moment and compatibilizer moieties, synthesized to simultaneously ensure improvement of electromechanical properties and compatibility with the host matrix is presented. Measurements show an 85% increase in permittivity combined with 290% reduction in mechanical stiffness. NMR measurements confirm the structure of the filler while DSC measurements confirm that it is compatible with the host matrix at all the mixture ratios investigated. Actuation strain measurements in the pure shear configuration display an increase in sensitivity to the electrical field of more than 450%, confirming that the filler molecule does not only improve dielectric and mechanical properties, it also leads to a synergistic enhancement of actuation properties by simple means. KW - allycyanide KW - silicone-based dielectric elastomer actuators KW - permittivity enhancement KW - compatibilized filler molecules Y1 - 2012 U6 - https://doi.org/10.1002/adfm.201200320 SN - 1616-301X VL - 22 IS - 18 SP - 3958 EP - 3962 PB - Wiley-VCH CY - Weinheim 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 - 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 - Wache, Remi A1 - Kofod, Guggi T1 - Soft conductive elastomer materials for stretchable electronics and voltage controlled artificial muscles JF - Advanced materials N2 - Block copolymer elastomer conductors (BEC) are mixtures of block copolymers grafted with conducting polymers, which are found to support very large strains, while retaining a high level of conductivity. These novel materials may find use in stretchable electronics. The use of BEC is demonstrated in a capacitive strain sensor and in an artificial muscle of the dielectric elastomer actuator type, supporting more than 100% actuation strain and capacity strain sensitivity up to 300%. KW - soft electrical connections KW - stretchable electronics KW - elastic conductor KW - compliant electrodes Y1 - 2013 U6 - https://doi.org/10.1002/adma.201202728 SN - 0935-9648 VL - 25 IS - 4 SP - 578 EP - 583 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Laflamme, S. A1 - Kollosche, Matthias A1 - Connor, Jerome J. A1 - Kofod, Guggi T1 - Soft capacitive sensor for structural health monitoring of large-scale systems JF - Structural control & health monitorin N2 - Structural integrity of infrastructures can be preserved if damage is diagnosed, localized, and repaired in time. During the past decade, there has been a considerable effort to automate the process of structural health monitoring, which is complicated by the inherent large size of civil structures. Hence, a need has arisen to develop new approaches that enable more effective health monitoring. In this paper, a new sensing technique for damage localization on large civil structures is proposed. Specifically, changes in strain are detected using a capacitance sensor built with a soft, stretchable dielectric polymer with attached stretchable metal film electrodes. A change in strain causes a measurable change in the capacitance of the sensor, which can be directly monitored when the sensor is fixed to a structure. The proposed method is shown here to permit an accurate detection of cracks. The proposed system deploys a layer of dielectric polymer on the surface of a structural element, and regularly monitors any change in capacitance, giving in turn information about the structural state. The smart material is composed of inexpensive silicone elastomers, which make the monitoring system a promising application for large surfaces. Results from tests conducted on small- scale specimens showed that the technology is capable of detecting cracks, and tests conducted on large- size specimens demonstrated that several sensor patches organized on a sensor sheet are capable of localizing a crack. The sensor strain also exhibits a high correlation with the loss of stiffness. KW - large-scale system KW - structural health monitoring KW - strain monitoring KW - capacitive sensor KW - dielectric polymer KW - stretchable sensor Y1 - 2012 U6 - https://doi.org/10.1002/stc.426 SN - 1545-2263 VL - 19 IS - 1 SP - 70 EP - 81 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Kofod, Guggi A1 - Paajanen, Mika A1 - Bauer, Siegfried T1 - Self-organized minimum-energy structures for dielectric elastomer actuators Y1 - 2006 UR - http://www.springerlink.com/content/100501 U6 - https://doi.org/10.1007/s00339-006-3680-3 SN - 0947-8396 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 -