@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{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{StoyanovKolloscheRisseetal.2011, author = {Stoyanov, Hristiyan and Kollosche, Matthias and Risse, Sebastian and McCarthy, Denis N. and Kofod, Guggi}, title = {Elastic block copolymer nanocomposites with controlled interfacial interactions for artificial muscles with direct voltage control}, series = {Soft matter}, volume = {7}, journal = {Soft matter}, number = {1}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1744-683X}, doi = {10.1039/c0sm00715c}, pages = {194 -- 202}, year = {2011}, abstract = {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.}, language = {en} } @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{DoeringKolloscheRabeetal.2011, author = {D{\"o}ring, Sebastian and Kollosche, Matthias and Rabe, Torsten and Stumpe, Joachim and Kofod, Guggi}, title = {Electrically tunable polymer DFB laser}, series = {Advanced materials}, volume = {23}, journal = {Advanced materials}, number = {37}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {0935-9648}, doi = {10.1002/adma.201102465}, pages = {4265 -- 4269}, year = {2011}, language = {en} } @article{RyabchunKolloscheWegeneretal.2016, author = {Ryabchun, Alexander and Kollosche, Matthias and Wegener, Michael and Sakhno, Oksana}, title = {Holographic Structuring of Elastomer Actuator: First True Monolithic Tunable Elastomer Optics}, series = {Advanced materials}, volume = {28}, journal = {Advanced materials}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {0935-9648}, doi = {10.1002/adma.201602881}, pages = {10217 -- 10223}, year = {2016}, abstract = {Volume diffraction gratings (VDGs) are inscribed selectively by diffusive introduction of benzophenone and subsequent UV-holographic structuring into an electroactive dielectric elastomer actuator (DEA), to afford a continuous voltage-controlled grating shift of 17\%. The internal stress coupling of DEA and optical domain allows for a new generation of true monolithic tunable elastomer optics with voltage controlled properties.}, language = {en} } @article{HollaenderKossackKolloscheetal.2016, author = {Holl{\"a}nder, Lars and Kossack, Wilhelm and Kollosche, Matthias and Wirges, Werner and Kremer, Friedrich and Gerhard, Reimund}, title = {Influence of the remanent polarisation on the liquid crystal alignment in composite films of ferroelectric poly(vinylidene fluoride-trifluoroethylene) and a cyanobiphenyl-based liquid crystal}, series = {Liquid crystals : an international journal of science and technology}, volume = {43}, journal = {Liquid crystals : an international journal of science and technology}, publisher = {Editions Rodopi BV}, address = {Abingdon}, issn = {0267-8292}, doi = {10.1080/02678292.2016.1185174}, pages = {1514 -- 1521}, year = {2016}, abstract = {Polymer-dispersed liquid crystals (PDLCs) of ferroelectric poly(vinylidene fluoride-trifluoroethylene) and nematic 4-cyano-4\&\#697;-n-hexylbiphenyl (6CB) or 4-cyano-4\&\#697;-n-pentylbiphenyl (5CB) were prepared to study the effect of the remanent polarisation of the polymer on the liquid crystal alignment. We measured the macroscopic alignment of the liquid crystal molecules in the thickness direction by means of Infrared Transition-Moment Orientational Analysis. Electrical poling at 100 V/µm caused an increased order parameter up to 0.15. After subsequent annealing above the nematic-to-isotropic phase-transition temperature, the order parameter was reduced to 0.02. Nevertheless, the order parameter was still higher than for non-poled film indicating a slight orientation in thickness direction. Both values are lower than those expected from model calculations. In agreement with dielectric measurements, we attribute this result to the shielding effect of mobile charge carriers within the liquid crystal inclusions.}, language = {en} } @article{SaleemThungaKolloscheetal.2014, author = {Saleem, H. and Thunga, M. and Kollosche, Matthias and Kessler, M. R. and Laflamme, S.}, title = {Interfacial treatment effects on behavior of soft nano-composites for highly stretchable dielectrics}, series = {Polymer : the international journal for the science and technology of polymers}, volume = {55}, journal = {Polymer : the international journal for the science and technology of polymers}, number = {17}, publisher = {Elsevier}, address = {Oxford}, issn = {0032-3861}, doi = {10.1016/j.polymer.2014.06.054}, pages = {4531 -- 4537}, year = {2014}, abstract = {We investigate the influence of interfacial treatment on the matrix filler interaction using a melt mixing process to fabricate robust and highly stretchable dielectrics. Silicone oil and silane coupling agent are studied as possible solutions to enhance the compatibility between the inorganic fillers and polymer matrix. Morphology, thermomechanical and dielectric behavior of the prepared specimens are studied. Results show that specimens filled with silicone oil coated particles have promising dielectric and thermal properties. The mechanical properties reveal a stiffness enhancement by 67\% with a high strain at break of 900\%. The relative permittivity of the specimens prepared with silicone oil increased by 45\% as observed from the dielectric analysis. (C) 2014 Elsevier Ltd. All rights reserved.}, 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} } @article{ZehbeKolloscheLardongetal.2016, author = {Zehbe, Kerstin and Kollosche, Matthias and Lardong, Sebastian and Kelling, Alexandra and Schilde, Uwe and Taubert, Andreas}, title = {Ionogels Based on Poly(methyl methacrylate) and Metal-Containing Ionic Liquids: Correlation between Structure and Mechanical and Electrical Properties}, series = {International journal of molecular sciences}, volume = {17}, journal = {International journal of molecular sciences}, publisher = {MDPI}, address = {Basel}, issn = {1422-0067}, doi = {10.3390/ijms17030391}, pages = {16}, year = {2016}, abstract = {Ionogels (IGs) based on poly(methyl methacrylate) (PMMA) and the metal-containing ionic liquids (ILs) bis-1-butyl-3-methlimidazolium tetrachloridocuprate(II), tetrachloride cobaltate(II), and tetrachlorido manganate(II) have been synthesized and their mechanical and electrical properties have been correlated with their microstructure. Unlike many previous examples, the current IGs show a decreasing stability in stress-strain experiments on increasing IL fractions. The conductivities of the current IGs are lower than those observed in similar examples in the literature. Both effects are caused by a two-phase structure with micrometer-sized IL-rich domains homogeneously dispersed an IL-deficient continuous PMMA phase. This study demonstrates that the IL-polymer miscibility and the morphology of the IGs are key parameters to control the (macroscopic) properties of IGs.}, 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{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{LaflammeKolloscheConnoretal.2012, author = {Laflamme, S. and Kollosche, Matthias and Connor, Jerome J. and Kofod, Guggi}, title = {Soft capacitive sensor for structural health monitoring of large-scale systems}, series = {Structural control \& health monitorin}, volume = {19}, journal = {Structural control \& health monitorin}, number = {1}, publisher = {Wiley-Blackwell}, address = {Hoboken}, issn = {1545-2263}, doi = {10.1002/stc.426}, pages = {70 -- 81}, year = {2012}, abstract = {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.}, 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{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{KolloscheStoyanovLaflammeetal.2011, author = {Kollosche, Matthias and Stoyanov, Hristiyan and Laflamme, Simon and Kofod, Guggi}, title = {Strongly enhanced sensitivity in elastic capacitive strain sensors}, series = {Journal of materials chemistry}, volume = {21}, journal = {Journal of materials chemistry}, number = {23}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {0959-9428}, doi = {10.1039/c0jm03786a}, pages = {8292 -- 8294}, year = {2011}, abstract = {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.}, language = {en} } @article{KolloscheKofodSuoetal.2015, author = {Kollosche, Matthias and Kofod, Guggi and Suo, Zhigang and Zhu, Jian}, title = {Temporal evolution and instability in a viscoelastic dielectric elastomer}, series = {Journal of the mechanics and physics of solids}, volume = {76}, journal = {Journal of the mechanics and physics of solids}, publisher = {Elsevier}, address = {Oxford}, issn = {0022-5096}, doi = {10.1016/j.jmps.2014.11.013}, pages = {47 -- 64}, year = {2015}, abstract = {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.}, 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} }