TY  - JOUR
A1  - Risse, Sebastian
A1  - Kussmaul, Björn
A1  - Krüger, Hartmut
A1  - Kofod, Guggi
T1  - A versatile method for enhancement of electromechanical sensitivity of silicone elastomers
JF  - RSC Advances
N2  - Dielectric elastomer actuators (DEAs) draw their function from their dielectric and mechanical properties. The paper describes the fabrication and various properties of molecularly grafted silicone elastomer films. This was achieved by addition of high-dipole molecular co-substituents to off-the-shelf silicone elastomer kits, Elastosil RT 625 and Sylgard 184 by Wacker and Dow Corning, respectively. Strong push-pull dipoles were chemically grafted to both polymer networks during a one step film formation process. All manufactured films were characterized using (13) C-NMR and FT-IR spectroscopy, confirming a successful attachment of the dipoles to the silicone network. Differential scanning calorimetry (DSC) results showed that grafted dipoles were distributed homogeneously throughout the material avoiding the formation of nano-scale aggregates. The permittivity increased with the amount of dipole at all frequencies, while the Young's modulus and electrical breakdown strength were reduced. Actuation strain measurements in the pure shear configuration independently confirmed the increase in electromechanical sensitivity. The ability to enhance electromechanical properties of off-the-shelf materials could strongly expand the range of actuator properties available to researchers and end-users.
Y1  - 2012
U6  - https://doi.org/10.1039/c2ra21541a
SN  - 2046-2069
VL  - 2
IS  - 24
SP  - 9029
EP  - 9035
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  - 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  - Zhu, Jian
A1  - Suo, Zhigang
A1  - Kofod, Guggi
T1  - Complex interplay of nonlinear processes in dielectric elastomers
JF  - Physical review : E, Statistical, nonlinear and soft matter physics
N2  - 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.
Y1  - 2012
U6  - https://doi.org/10.1103/PhysRevE.85.051801
SN  - 1539-3755
VL  - 85
IS  - 5
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Stoyanov, Hristiyan
A1  - Mc Carthy, Denis N.
A1  - Kollosche, Matthias
A1  - Kofod, Guggi
T1  - Dielectric properties and electric breakdown strength of a subpercolative composite of carbon black in thermoplastic copolymer
N2  - 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.
Y1  - 2009
UR  - http://apl.aip.org/
U6  - https://doi.org/10.1063/1.3154553
SN  - 0003-6951
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  - Döring, Sebastian
A1  - Kollosche, Matthias
A1  - Rabe, Torsten
A1  - Stumpe, Joachim
A1  - Kofod, Guggi
T1  - Electrically tunable polymer DFB laser
JF  - Advanced materials
Y1  - 2011
U6  - https://doi.org/10.1002/adma.201102465
SN  - 0935-9648
VL  - 23
IS  - 37
SP  - 4265
EP  - 4269
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Kofod, Guggi
A1  - Mc Carthy, Denis N.
A1  - Krissler, Jan
A1  - Lang, Günter
A1  - Jordan, Grace
T1  - Electroelastic optical fiber positioning with submicrometer accuracy : model and experiment
N2  - We present accurate electromechanical measurements on a balanced push-pull dielectric elastomer actuator, demonstrating submicrometer accurate position control. An analytical model based on a simplified pure-shear dielectric elastomer film with prestretch is found to capture the voltage-displacement behavior, with reduced output due to the boundary conditions. Two complementary experiments show that actuation coefficients of 0.5-1 nm/V-2 are obtainable with the demonstrated device, enabling motion control with submicrometer accuracy in a voltage range below 200 V.
Y1  - 2009
UR  - http://apl.aip.org/
U6  - https://doi.org/10.1063/1.3134002
SN  - 0003-6951
ER  - 
TY  - JOUR
A1  - Kofod, Guggi
A1  - Wirges, Werner
A1  - Paajanen, Mika
A1  - Bauer, Siegfried
T1  - Energy minimization for self-organized structure formation and actuation
N2  - An approach for creating complex structures with embedded actuation in planar manufacturing steps is presented. Self-organization and energy minimization are central to this approach, illustrated with a model based on minimization of the hyperelastic free energy strain function of a stretched elastomer and the bending elastic energy of a plastic frame. A tulip-shaped gripper structure illustrates the technological potential of the approach. Advantages are simplicity of manufacture, complexity of final structures, and the ease with which any electroactive material can be exploited as means of actuation. (c) 2007 American Institute of Physics.
Y1  - 2007
UR  - http://apl.aip.org/
U6  - https://doi.org/10.1063/1.2695785
SN  - 0003-6951
ER  - 
TY  - JOUR
A1  - Kussmaul, Bjoern
A1  - Risse, Sebastian
A1  - Kofod, Guggi
A1  - Wache, Remi
A1  - Wegener, Michael
A1  - McCarthy, Denis N.
A1  - Krüger, Hartmut
A1  - Gerhard, Reimund
T1  - Enhancement of dielectric permittivity and electromechanical response in silicone elastomers molecular grafting of organic dipoles to the macromolecular Network
JF  - Advanced functional materials
N2  - A novel method is established for permittivity enhancement of a silicone matrix for dielectric elastomer actuators (DEAs) by molecular level modifications of the elastomer matrix. A push-pull dipole is synthesized to be compatible with the silicone crosslinking chemistry, allowing for direct grafting to the crosslinker molecules in a one-step film formation process. This method prevents agglomeration and yields elastomer films that are homogeneous down to the molecular level. The dipole-to-silicone network grafting reaction is studied by FTIR. The chemical, thermal, mechanical and electrical properties of films with dipole contents ranging from 0 wt% to 13.4 wt% were thoroughly characterized. The grafting of dipoles modifies the relative permittivity and the stiffness, resulting in the actuation strain at a given electrical field being improved by a factor of six.
KW  - dipole grafting
KW  - silicone based dielectric elastomer actuators
KW  - permittivity enhancement
Y1  - 2011
U6  - https://doi.org/10.1002/adfm.201100884
SN  - 1616-301X
VL  - 21
IS  - 23
SP  - 4589
EP  - 4594
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - McCarthy, Denis N.
A1  - Stoyanov, Hristiyan
A1  - Rychkov, Dmitry
A1  - Ragusch, Huelya
A1  - Melzer, Michael
A1  - Kofod, Guggi
T1  - Increased permittivity nanocomposite dielectrics by controlled interfacial interactions
JF  - Composites science and technology
N2  - 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.
KW  - Ceramics
KW  - Nanocomposites
KW  - Actuator
KW  - Interface
KW  - Electrical properties
Y1  - 2012
U6  - https://doi.org/10.1016/j.compscitech.2012.01.026
SN  - 0266-3538
VL  - 72
IS  - 6
SP  - 731
EP  - 736
PB  - Elsevier
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Zhu, Jian
A1  - Stoyanov, Hristiyan
A1  - Kofod, Guggi
A1  - Suo, Zhigang
T1  - Large deformation and electromechanical instability of a dielectric elastomer tube actuator
N2  - This paper theoretically analyzes a dielectric elastomer tube actuator (DETA). Subject to a voltage difference between the inner and outer surfaces, the actuator reduces in thickness and expands in length, so that the same voltage will induce an even higher electric field. This positive feedback may cause the actuator to thin down drastically, resulting in electrical breakdown. We obtain an analytical solution of the actuator undergoing finite deformation when the elastomer obeys the neo-Hookean model. The critical strain of actuation is calculated in terms of various parameters of design. We also discuss the effect of the strain-stiffening on electromechanical behavior of DETAs by using the model of freely joined links. (C) 2010 American Institute of Physics. [doi:10.1063/1.3490186]
Y1  - 2010
UR  - http://jap.aip.org/
U6  - https://doi.org/10.1063/1.3490186
SN  - 0021-8979
ER  - 
TY  - JOUR
A1  - Kussmaul, Björn
A1  - Risse, Sebastian
A1  - Wegener, Michael
A1  - Kofod, Guggi
A1  - Krüger, Hartmut
T1  - Matrix stiffness dependent electro-mechanical response of dipole grafted silicones
JF  - Smart materials and structures
N2  - The properties of dielectric elastomer actuators can be optimized by modifying the dielectric or mechanical properties of the dielectric elastomer. This paper presents the simultaneous control of both dielectric and mechanical properties, in a silicone elastomer network comprising cross-linker, chains and grafted molecular dipoles. Chains with two different molecular weights were each combined with varying amounts of grafted dipole. Chemical and physical characterization showed that networks with stoichiometric control of cross-linking density and permittivity were obtained, and that longer chain lengths resulted in higher electrical field response due to the reduction in cross-linking density and correspondingly in mechanical stiffness. Both actuation sensitivities were enhanced by 6.3 and 4.6 times for the short and long chain matrix material, respectively.
Y1  - 2012
U6  - https://doi.org/10.1088/0964-1726/21/6/064005
SN  - 0964-1726
VL  - 21
IS  - 6
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Stoyanov, Hristiyan
A1  - Kollosche, Matthias
A1  - McCarthy, Denis N.
A1  - Kofod, Guggi
T1  - Molecular composites with enhanced energy density for electroactive polymers
N2  - 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.
Y1  - 2010
UR  - http://www.rsc.org/Publishing/Journals/jm/index.asp
U6  - https://doi.org/10.1039/C0jm00519c
SN  - 0959-9428
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  - Vukicevic, Radovan
A1  - Vukovic, Ivana
A1  - Stoyanov, Hristiyan
A1  - Korwitz, Andreas
A1  - Pospiech, Doris
A1  - Kofod, Guggi
A1  - Loos, Katja
A1  - ten Brinke, Gerrit
A1  - Beuermann, Sabine
T1  - Poly(vinylidene fluoride)-functionalized single-walled carbon nanotubes for the preparation of composites with improved conductivity
JF  - Polymer Chemistry
N2  - The surface of single-walled carbon nanotubes (SWCNTs) was functionalized with azide-terminated poly(vinylidene fluoride) (PVDF). Functionalization was confirmed by dispersibility, Raman spectroscopy, and thermogravimetric analyses. Raman spectra show disordering of the SWCNTs, thus, strongly suggesting that PVDF was covalently attached to SWCNTs. Functionalized SWCNTs were mixed with commercially available PVDF in a twin-screw extruder and thin films were obtained by melt-pressing. Films containing 0.5 and 1 wt% PVDF-functionalized SWCNTs exhibited significantly improved electrical conductivity compared to PVDF films containing pristine SWCNTs.
Y1  - 2012
U6  - https://doi.org/10.1039/c2py20166f
SN  - 1759-9954
VL  - 3
IS  - 8
SP  - 2261
EP  - 2265
PB  - Royal Society of Chemistry
CY  - Cambridge
ER  - 
TY  - JOUR
A1  - Laflamme, Simon
A1  - Kollosche, Matthias
A1  - Connor, Jerome J.
A1  - Kofod, Guggi
T1  - Robust flexible capacitive surface sensor for structural health monitoring applications
JF  - Journal of engineering mechanics
N2  - 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.
KW  - Strain gages
KW  - Structural health monitoring
KW  - Monitoring
KW  - Probe instruments
KW  - Strain gauge
KW  - Structural health monitoring
KW  - Strain monitoring
KW  - Capacitive sensor
KW  - Dielectric polymer
KW  - Stretchable sensor
KW  - Flexible membrane
KW  - Sensing skin
Y1  - 2013
U6  - https://doi.org/10.1061/(ASCE)EM.1943-7889.0000530
SN  - 0733-9399
SN  - 1943-7889
VL  - 139
IS  - 7
SP  - 879
EP  - 885
PB  - American Society of Civil Engineers
CY  - Reston
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  - 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  - 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  - 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  - 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  - 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  - 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  - 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  - 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  - 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  - 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  - 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  -