@article{MorgnerBennemannCywińskietal.2017, author = {Morgner, Frank and Bennemann, Mark and Cywiński, Piotr J. and Kollosche, Matthias and G{\´o}rski, Krzysztof and Pietraszkiewicz, Marek and Geßner, Andr{\´e} and L{\"o}hmannsr{\"o}ben, Hans-Gerd}, title = {Elastic FRET sensors for contactless pressure measurement}, series = {RSC Advances : an international journal to further the chemical sciences}, volume = {7}, journal = {RSC Advances : an international journal to further the chemical sciences}, publisher = {RSC Publishing}, address = {Cambridge}, issn = {2046-2069}, doi = {10.1039/c7ra06379b}, pages = {50578 -- 50583}, year = {2017}, abstract = {Contactless pressure monitoring based on Forster resonance energy transfer between donor/acceptor pairs immobilized within elastomers is demonstrated. The donor/acceptor energy transfer is employed by dispersing terbium(III) tris[(2-hydroxybenzoyl)-2-aminoethyl] amine complex (LLC, donor) and CdSe/ZnS quantum dots (QD655, acceptor) in styrene-ethylene/buthylene-styrene (SEBS) and poly(dimethylsiloxane) (PDMS). The continuous monitoring of QD luminescence showed a reversible intensity change as the pressure signal is alternated between two stable states indicating a pressure sensitivity of 6350 cps kPa(-1). Time-resolved measurements show the pressure impact on the FRET signal due to an increase of decay time (270 ms up to 420 ms) for the donor signal and parallel drop of decay time (170 mu s to 155 mu s) for the acceptor signal as the net pressure applied. The LLC/QD655 sensors enable a contactless readout as well as space resolved monitoring to enable miniaturization towards smaller integrated stretchable opto-electronics. Elastic FRET sensors can potentially lead to developing profitable analysis systems capable to outdo conventional wired electronic systems (inductive, capacitive, ultrasonic and photoelectric sensors) especially for point-of-care diagnostics, biological monitoring required for wearable electronics.}, language = {en} } @article{StoyanovKolloscheMcCarthyetal.2010, author = {Stoyanov, Hristiyan and Kollosche, Matthias and McCarthy, Denis N. and Kofod, Guggi}, title = {Molecular composites with enhanced energy density for electroactive polymers}, issn = {0959-9428}, doi = {10.1039/C0jm00519c}, year = {2010}, abstract = {Actuators based on soft dielectric elastomers deform due to electric field induced Maxwell's stress, interacting with the mechanical properties of the material. The relatively high operating voltages of such actuators can be reduced by increasing the permittivity of the active material, while maintaining the mechanical properties and high electrical breakdown strength. Approaches relying on the use of highly polarizable molecules or conjugated polymers have so far provided the best results, however it has been difficult to maintain high breakdown strengths. In this work, a new approach for increasing the electrostatic energy density of a soft polymer based on molecular composites is presented, relying on chemically grafting soft gel-state pi-conjugated conducting macromolecules (polyaniline (PANI)) to a flexible elastomer backbone SEBS-g-MA (poly-styrene-co-ethylene-co-butylene-co-styrene-g-maleic anhydride). The approach was found to result in composites of increased permittivity (470\% over the elastomer matrix) with hardly any reduction in breakdown strength (from 140 to 120 V mu m(-1)), resulting in a large increase in stored electrostatic energy. This led to an improvement in the measured electromechanical response as well as in the maximum actuation strain. A transition was observed when amounts of PANI exceeded 2 vol\%, which was ascribed to the exhaustion of the MA- functionality of the SEBS-g-MA. The transition led to drastic increases in permittivity and conductivity, and a sharp drop in electrical breakdown strength. Although the transition caused further improvement of the electromechanical response, the reduction in electrical breakdown strength caused a limitation of the maximum achievable actuation strain.}, language = {en} } @article{StoyanovKolloscheRisseetal.2013, author = {Stoyanov, Hristiyan and Kollosche, Matthias and Risse, Sebastian and Wache, Remi and Kofod, Guggi}, title = {Soft conductive elastomer materials for stretchable electronics and voltage controlled artificial muscles}, series = {Advanced materials}, volume = {25}, journal = {Advanced materials}, number = {4}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {0935-9648}, doi = {10.1002/adma.201202728}, pages = {578 -- 583}, year = {2013}, abstract = {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\%.}, language = {en} } @article{StoyanovMcCarthyKolloscheetal.2009, author = {Stoyanov, Hristiyan and Mc Carthy, Denis N. and Kollosche, Matthias and Kofod, Guggi}, title = {Dielectric properties and electric breakdown strength of a subpercolative composite of carbon black in thermoplastic copolymer}, issn = {0003-6951}, doi = {10.1063/1.3154553}, year = {2009}, abstract = {We investigate the dielectric properties and electric breakdown strength of subpercolative composites of conductive carbon black particles in a rubber insulating matrix. A significant increase in the permittivity in the vicinity of the insulator to conductor transition was observed, with relatively low increases in dielectric loss; however, a rapid decrease in electric breakdown strength was inevitable. A steplike feature was ascribed to agglomeration effects. The low ultimate values of the electric field strength of such composites appear to prohibit practical use.}, language = {en} } @article{LaflammeKolloscheConnoretal.2013, author = {Laflamme, Simon and Kollosche, Matthias and Connor, Jerome J. and Kofod, Guggi}, title = {Robust flexible capacitive surface sensor for structural health monitoring applications}, series = {Journal of engineering mechanics}, volume = {139}, journal = {Journal of engineering mechanics}, number = {7}, publisher = {American Society of Civil Engineers}, address = {Reston}, issn = {0733-9399}, doi = {10.1061/(ASCE)EM.1943-7889.0000530}, pages = {879 -- 885}, year = {2013}, abstract = {Early detection of possible defects in civil infrastructure is vital to ensuring timely maintenance and extending structure life expectancy. The authors recently proposed a novel method for structural health monitoring based on soft capacitors. The sensor consisted of an off-the-shelf flexible capacitor that could be easily deployed over large surfaces, the main advantages being cost-effectiveness, easy installation, and allowing simple signal processing. In this paper, a capacitive sensor with tailored mechanical and electrical properties is presented, resulting in greatly improved robustness while retaining measurement sensitivity. The sensor is fabricated from a thermoplastic elastomer mixed with titanium dioxide and sandwiched between conductive composite electrodes. Experimental verifications conducted on wood and concrete specimens demonstrate the improved robustness, as well as the ability of the sensing method to diagnose and locate strain.}, language = {en} } @article{KolloscheZhuSuoetal.2012, author = {Kollosche, Matthias and Zhu, Jian and Suo, Zhigang and Kofod, Guggi}, title = {Complex interplay of nonlinear processes in dielectric elastomers}, series = {Physical review : E, Statistical, nonlinear and soft matter physics}, volume = {85}, journal = {Physical review : E, Statistical, nonlinear and soft matter physics}, number = {5}, publisher = {American Physical Society}, address = {College Park}, issn = {1539-3755}, doi = {10.1103/PhysRevE.85.051801}, pages = {4}, year = {2012}, abstract = {A combination of experiment and theory shows that dielectric elastomers exhibit complex interplay of nonlinear processes. Membranes of a dielectric elastomer are prepared in various states of prestretches by using rigid clamps and mechanical forces. Upon actuation by voltage, some membranes form wrinkles followed by snap-through instability, others form wrinkles without the snap-through instability, and still others fail by local instability without forming wrinkles. Membranes surviving these nonlinear processes are found to attain a constant dielectric strength, independent of the state of prestretches. Giant voltage-induced stretch of 3.6 is attained.}, language = {en} } @article{ZhuKolloscheLuetal.2012, author = {Zhu, Jian and Kollosche, Matthias and Lu, Tongqing and Kofod, Guggi and Suo, Zhigang}, title = {Two types of transitions to wrinkles in dielectric elastomers}, series = {Soft matter}, volume = {8}, journal = {Soft matter}, number = {34}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1744-683X}, doi = {10.1039/c2sm26034d}, pages = {8840 -- 8846}, year = {2012}, abstract = {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.}, language = {en} } @article{KolloscheDoeringStumpeetal.2011, author = {Kollosche, Matthias and D{\"o}ring, Sebastian and Stumpe, Joachim and Kofod, Guggi}, title = {Voltage-controlled compression for period tuning of optical surface relief gratings}, series = {OPTICS LETTERS}, volume = {36}, journal = {OPTICS LETTERS}, number = {8}, publisher = {OPTICAL SOC AMER}, address = {WASHINGTON}, issn = {0146-9592}, pages = {1389 -- 1391}, year = {2011}, abstract = {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}, language = {en} } @article{CarpiAndersonBaueretal.2015, author = {Carpi, Federico and Anderson, Iain and Bauer, Siegfried and Frediani, Gabriele and Gallone, Giuseppe and Gei, Massimiliano and Graaf, Christian and Jean-Mistral, Claire and Kaal, William and Kofod, Guggi and Kollosche, Matthias and Kornbluh, Roy and Lassen, Benny and Matysek, Marc and Michel, Silvain and Nowak, Stephan and Pei, Qibing and Pelrine, Ron and Rechenbach, Bjorn and Rosset, Samuel and Shea, Herbert}, title = {Standards for dielectric elastomer transducers}, series = {Smart materials and structures}, volume = {24}, journal = {Smart materials and structures}, number = {10}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {0964-1726}, doi = {10.1088/0964-1726/24/10/105025}, pages = {25}, year = {2015}, abstract = {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.}, language = {en} } @article{SaleemDowneyLaflammeetal.2015, author = {Saleem, Hussam and Downey, Austin and Laflamme, Simon and Kollosche, Matthias and Ubertini, Filippo}, title = {Investigation of Dynamic Properties of a Novel Capacitive-based Sensing Skin for Nondestructive Testing}, series = {Materials evaluation}, volume = {73}, journal = {Materials evaluation}, number = {10}, publisher = {American Society for Nondestructive Testing}, address = {Columbus}, issn = {0025-5327}, pages = {1390 -- 1397}, year = {2015}, abstract = {A capacitive-based soft elastomeric strain sensor was recently developed by the authors for structural health monitoring applications. Arranged in a network configuration, the sensor becomes a sensing skin, where local deformations can be monitored over a global area. The sensor transduces a change in geometry into a measurable change in capacitance, which can be converted into strain using a previously developed electromechanical model. Prior studies have demonstrated limitations of this electromechanical model for dynamic excitations beyond 15 Hz, because of a loss in linearity in the sensor's response. In this paper, the dynamic behavior beyond 15 Hz is further studied, and a new version of the electromechanical model is proposed to accommodate dynamic strain measurements up to 40 Hz. This behavior is characterized by subjecting the sensor to a frequency sweep and identifying possible sources of nonlinearities beyond 15 Hz. Results show possible frequency dependence of the materials' Poisson's ratios, which are successfully modeled and integrated into the electromechanical model. This demonstrates that the proposed sensor can be used for monitoring and evaluation of structural responses up to 40 Hz, a range covering the vast majority of the dominating frequency responses of civil infrastructures.}, language = {en} }