Dr Remi Wache

KTP Associate - Product Development Engineer

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Further information

Biography

R. Waché is graduated from the Ecole Nationale Supérieure des Mines de Nancy, France in 2001. He conducted researches on polymer clay nanocomposites at the Institut Francais du Pétrole (IFP), to obtain his PhD in 2004 from the University of Brest, France. The next two years he developed controlled release formulations at Flamel Technologies. 2008 he collaborated at the Commissariat à l’Energie Atomique (CEA) on a joined project with Nanobiotix about nanoparticles to enhance radiotherapy efficiency. He studied dielectric elastomer actuators at the University of Potsdam, Germany. Recently he joined the University of Surrey, UK.

Publications

Journal articles

  • Wache R, McCarthy DN, Risse S, Kofod G. (2015) 'Rotary motion achieved by new torsional dielectric elastomer actuators design'. IEEE/ASME Transactions on Mechatronics, 20 (2), pp. 975-977.

    Abstract

    © 2014 IEEE.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° was achieved.

  • Wache R, Klopffer M-H, Gonzalez S. (2014) 'Characterization of Polymer Layered Silicate Nanocomposites by Rheology and Permeability Methods: Impact of the Interface Quality'. Oil Gas Sci. Technol. – Rev. IFP Energies nouvelles,

    Abstract

    Polymer clay nanocomposites are mostly described as materials with improved properties. However, many studies are not concluding about the possible benefits. This work reports permeability measurements on different polyolefins nanocomposites. Clay exfoliation has been proved by various techniques. Unfortunately, the nanocomposite does not exhibit good barrier properties. Hence, permeability coefficients were found to increase. A poor quality of the interface between filler and medium is likely to be responsible for this degradation. Insufficient interactions between silicate layers and the surrounding polymer lead to preferential pathways for diffusion. Organoclay exfoliation does not necessarily lead to better barrier properties. A good quality of the interface between polymer and filler is required to reach a high performance level. The standard techniques used to characterize exfoliation degree do not permit to highlight this kind of phenomena.

  • Wache R, McCarthy DN, Risse S, Kofod G. (2014) 'Rotary Motion Achieved by New Torsional Dielectric Elastomer Actuators Design'. IEEE/ASME Transactions on Mechatronics,

    Abstract

    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° was achieved.

  • Stoyanov H, Kollosche M, Risse S, Waché R, Kofod G. (2012) 'Soft Conductive Elastomer Materials for Stretchable Electronics and Voltage Controlled Artificial Muscles.'. Adv Mater,

    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%.

  • Wache R, Risse S, Schulze M, Kofod G. (2012) 'Polychloroprene: A new material for dielectric elastomer actuators'. Materials Research Society Symposium Proceedings, 1325, pp. 123-128.

    Abstract

    Dielectric Elastomer Actuators (DEAs) consist of an elastomeric layer sandwiched between two compliant electrodes. An electric field applied between the two electrodes will lead to a compression of the elastomer due to the Maxwell's pressure. DEA can be used for many active applications such as pumps, muscles and so on, where the voltage drives the motion, but they can also operate inversely for energy harvesting or for sensor applications, when the displacement of charges due to a change in thickness is stored or detected. Energy harvesting systems like buoys using wave energy or shoe soles extracting energy from walking have been demonstrated. In this contribution we investigate polychloroprene (CR) as a new material for DEA and describe its potential for use in energy harvesting. To this end, a full characterization of the material properties was undertaken. We find that the very high permittivity combined with good mechanical properties makes this material a promising novel candidate for the energy harvesting application. © 2011 Materials Research Society.

  • Kussmaul B, Risse S, Kofod G, Waché R, Wegener M, McCarthy DN, Krüger H, Gerhard R. (2011) 'Enhancement of dielectric permittivity and electromechanical response in silicone elastomers: Molecular grafting of organic dipoles to the macromolecular network'. Advanced Functional Materials, 21 (23), pp. 4589-4594.

    Abstract

    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. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  • Risse S, Kussmaul B, Krüger H, Wache R, Kofod G. (2011) 'DEA material enhancement with dipole grafted PDMS networks'. Proceedings of SPIE - The International Society for Optical Engineering, 7976

    Abstract

    Silicone elastomers are highly suitable for application in the field of dielectric elastomer actuators (DEA) due to their unique material properties (e.g. low glass temperature, thermal stability, large capability of chemical tailoring). The elastomer forming Polydimethysiloxane (PDMS) employed for this study consists of chains with vinyl termination and is cross linked via hydrosilylation to a cross linking molecule in the presence of platinum catalyst. Here, dipole molecules (N-Allyl-N-methyl-4-nitroaniline) were specifically synthesized such that they could chemically graft to the silicone network. The most prominent advantage of this approach is the achievement of a homogeneous distribution of dipoles in the PDMS matrix and a suppression of phase separation due to the grafting to the junction points of the rubber network. Several films with dipole contents v ranging from 0 % wt up to 10.9 % wt were prepared. The films were investigated to determine their mechanical (tensile testing), dielectric (dielectric relaxation spectroscopy) and electrical (electrical breakdown) properties. This new approach for composites on the molecular level leads to homogeneous films with enhanced material properties for DEA applications. An increase in permittivity from 3.3 to 6.0, a decrease in electrical breakdown from 130 V/μm to 50 V/μm and a lowering of the mechanical stiffness from 1700 kPa to 300 kPa was observed. © 2011 SPIE.

  • Kofod G, Stoyanov H, Kollosche M, Risse S, Ragusch H, McCarthy DN, Waché R, Rychkov D, Dansachmüller M. (2011) 'Molecular level materials design for improvements of actuation properties of dielectric elastomer actuators'. Proceedings of SPIE - The International Society for Optical Engineering, 7976

    Abstract

    Dielectric elastomer actuators are soft electro-mechanical transducers with possible uses in robotic, orthopaedic and automotive applications. The active material must be soft and have a high ability to store electrical energy. Hence, three properties of the elastic medium in a dielectric elastomer actuator affect the actuation properties directly: dielectric constant, electric breakdown strength, and mechanical stiffness. The dielectric constant of a given elastomer can be improved by mixing it with other components with a higher dielectric constant, which can be classified as insulating or conducting. In this paper, an overview of all approaches proposed so far for dielectric constant improvement in these soft materials will be provided. Insulating particles such as TiO2 nanoparticles can raise the dielectric constant, but may also lead to stiffening of the composite, such that the overall actuation is lowered. It is shown here how a chemical coating of the TiO2 nanoparticles leads to verifiable improvements. Conducting material can also lead to improvements, as has been shown in several cases. Simple percolation, relying on the random distribution of conducting nanoparticles, commonly leads to drastic lowering of the breakdown strength. On the other hand, conducting polymer can also be employed, as has been demonstrated. We show here how an approach based on a specific chemical reaction between the conducting polymer and the elastomer network molecules solves the problem of premature breakdown which is otherwise typically found. © 2011 SPIE.

  • Kofod G, McCarthy DN, Stoyanov H, Kollosche M, Risse S, Ragusch H, Rychkov D, Dansachmüller M, Waché R. (2010) 'Materials science on the nano-scale for improvements in actuation properties of dielectric elastomer actuators'. Proceedings of SPIE - The International Society for Optical Engineering, 7642

    Abstract

    We discuss various approaches to increasing the dielectric constant of elastomer materials, for use in dielectric elastomer actuators. High permittivity metal-oxide nano-particles can show elevated impact compared to larger size particles, but suffer from water uptake. Composites with conducting particles lead to extremely high permittivity caused by percolation, but they often suffer early breakdown. We present experiments on approaches combining metal-oxides and metal particles, which compensate for the drawbacks, and may lead to useful DEA materials in which all relevant properties are technologically useful. The key seems to be to avoid percolation and achieve a constant nearest-neighbor separation. © 2010 Copyright SPIE - The International Society for Optical Engineering.

Conference papers

  • Wache R, Florescu M, Sweeney SJ, Clowes SK. (2015) 'Selectively reflective transparent sheets'. SPIE-INT SOC OPTICAL ENGINEERING ACTIVE PHOTONIC MATERIALS VII, San Diego, CA: Conference on Active Photonic Materials VII 9546
  • Wache R, Klopffer M-H, Cangémi L, Tigane S. (2004) 'Phénomène de porosité et instabilités ductiles dans les matériaux hybrides polyéthylène/argile'. Poitiers, France: DEPOS19

    Abstract

    De nombreuses études actuelles traitent des mélanges de polymère avec de l’argile. Elles sont fréquemment référencées sous le nom de nanocomposites car elles se focalisent sur la dispersion à l’échelle nanométrique des feuillets d’argile. Cette faible dimension fait que les taux de charge sont peu importants. Les nanocomposites présentent potentiellement beaucoup d’intérêt face aux composites conventionnels. Toutefois beaucoup d’études ne sont pas encore concluantes. Le présent travail s’attache à décrire l’existence de phénomènes indésirables dans les mélanges polymère/argile, et cherche à comprendre l’origine de tels mécanismes. Plusieurs mélanges à base de polyéthylène, d’argile organophile et d’agents compatibilisants ont été réalisés avec des conditions de mise en œuvre variées (mélangeur interne, extrusion bivis et monovis…). Dans quelques cas, l’allongement à la rupture chute de manière catastrophique. La diminution de la ductilité semble dépendre fortement de la mise en œuvre. Les faciès de rupture révèlent l’existence de porosité. La « pseudo-fragilité » de certains mélanges pourrait être reliée à la taille des pores. Dans certains cas, les pores atteindraient des tailles critiques, éventuellement par coalescence, qui empêchent l’éprouvette dans son ensemble de supporter l’étirement même si localement le polymère reste ductile, tandis que dans d’autres cas, les dimensions des cavités sont plus faibles, de sorte que localement les chaînes peuvent se réorganiser à tout instant, et donc la striction se propage sur toute la longueur de l’éprouvette. Cette porosité de la structure ainsi mise en évidence pourrait être l’explication des résultats de perméabilité médiocres de ces échantillons. Quelques résultats complémentaires viennent montrer comment les techniques communes qui permettent de caractériser le degré d’exfoliation de l’argile (DRX, MET, Rhéologie), sont insensibles à ce genre de phénomènes.

  • Wache R, Klopffer M-H, Gonzalez S, Mederic P, Moan M. (2003) 'MALEATED POLYETHYLENE NANOCOMPOSITES: INFLUENCE OF CLAY CONTENT ON BARRIER AND MELT RHEOLOGICAL PROPERTIES'. Alicante: Eurofillers
  • Wache R, Klopffer M-H, Vinciguerra E, Gonzalez S. (2002) 'Formulation et caracterisation de nanocomposites a matrice polyethylene'. Tours: Materiaux 2002
  • Klopffer M-H, Wache R, Flaconneche B, Vinciguerra E, Gonzalez S. (2001) 'POLYMER CLAY NANOCOMPOSITES FOR THE ENHANCEMENT OF BARRIER PROPERTIES TO ORGANIC FLUIDS'. ECM San Diego: Nanocomposites: Bringing new values to polymers

Theses and dissertations

  • Wache R. (2004) Formulation et caractérisation de polyéthylènes chargés avec des argiles: Propriétés barrière des nanocomposites obtenus.

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