Polychloroprene: a new material for Dielectric Elastomer Actuators
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Polychloroprene: a new material for Dielectric Elastomer Actuators. Rémi Waché1, Sebastian Risse1, Manuel Schulze1 and Guggi Kofod1 1 University of Potsdam, Institute of Physics and Astronomy, Applied Condensed Matter Physics, Karl-Liebknecht-Strasse 24-25, Raum 2.28.0.004, 14476 Potsdam, Germany 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. INTRODUCTION The development of Dielectric Elastomer Actuators (DEAs) is a growing research field since the beginning of the XXIth century [1]. They are made simply from an elastomer film coated with compliant electrodes on both faces. The energy state of such a device is determined by the electrical field as well as the strain. Application of a voltage leads to a strain which can be used to cause motion in the surroundings, a process known as actuation. Inversely, a change of strain can induce field modification useful for energy harvesting. The DEA device is essentially a capacitor, hence the energy E related to the charged state is given by E=½CU², where C is the capacitance and U the voltage. The capacitance is linked to the state of strain by the geometry of the device, C= r 0A/t with İr the dielectric constant, İ0 the vacuum permittivity, A the area of the device and t its thickness. Elastomers are considered incompressible in volume, therefore the strain in the thickness direction sz affects the geometry through A/t=A0/(t0(1+sz)²). Combining the previous equations, the energy level becomes related to the strain and the voltage: E=
1 A § U ε rε 0 0 ¨¨ 2 t0 © 1 + s z
· ¸ ¸ ¹
2
(1)
From this relation it appears clear that the permittivity directly affects the harvesting of energy. It should be also added that the level of strain which can be reached by an outside force, the “free external” energy source, is linked to the mechanical properties of the material. This can be quantified by the elastic modulus of the material. Indeed under mechanical solicitation
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(compression, tension, or shear) a soft material will undergo higher strains than a stiffer one. The simplest way is to co
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