The electromechanical performance of interpenetrating polymer networks (IPN) in which one elastomer network is
under high tension balanced by compression of the second network, were investigated. Uniaxial stress relaxation
analysis confirmed significant decrease in viscoelasticity in comparison with 3M VHB films, the primary component
network in the IPN films. In dynamic mechanical analysis, the IPN composite showed a higher mechanical efficiency,
suggesting delayed relaxation of the acrylic chains in the presence of IPN formation. This improvement was found to be
dependant on the contents of poly(TMPTMA). Actuation performance without mechanical prestrain showed that these
IPN electroelastomers had demonstrated high elastic strain energy density (3.5 MJ/m3) and a high electromechanical
coupling factor (93.7%). These enhanced electromechanical performances indicate that IPN electroelastomer should be
suitable for diverse applications.
Dielectric elastomer actuators in a cylindrical configuration, called "spring roll", have been used by the Empa team for
the first arm wrestling match between a human and a robotic arm driven by electroactive polymers (EAP) on the EAPAD
conference 2005 in San Diego. In this work, electromechanical coupling in EAP is investigated at the example of spring
rolls. The commonly used equation derived by Pelrine et al. (Sensors and Actuators A, 64, 1998) is analyzed and the
influence of the uncoated ("passive") parts is evaluated. Longer passive parts cause a force reduction in axial direction
which affects the performance of the actuator. Results have shown that (i) the equation of Pelrine represents a simplified
description of electromechanical coupling; (ii) the equation can be used for modeling electromechanical coupling in
spring rolls and (iii) the relative force reduction agrees to a great extent with the ratio between the uncoated area of a
spring roll and the total (coated and uncoated) area. These results are relevant for design and optimization of spring rolls.
KEYWORDS: Polymers, Actuators, Polymeric actuators, Glasses, Dielectrics, Polymerization, 3D modeling, Data modeling, System on a chip, Electroactive polymers
Interpenetrating polymer networks (IPN) in which one elastomer network is under high tension balanced by
compression of the second network have been shown to exhibit electrically-induced strain up to 300% and promise a
number of polymer actuators with substantially enhanced performance and stability. This paper describes the
mechanical and thermal properties of the IPN electroelastomer films. The quasi-linear viscoelastic model and Yeoh
strain energy potential are used to characterize the viscoelastic response and stress-strain behavior of the IPN films in
comparison with 3M VHB films, primary component network in the IPN films. Material parameters were determined
from uniaxial stress relaxation experiments. An analysis of the results confirms that the IPN composites have reduced
viscoelasticity and fast stress-strain response due to preserved prestrain. Differential scanning calorimetry showed two
glass transition temperatures that are slightly shifted from the two component networks, respectively. The two networks
in the IPN are considered to be independent of each other. The thermal property is also studied with termogravimetric
analysis (TG).
Reliable models are required for the design and optimization of dielectric elastomer actuators. Thereby knowledge of the constitutive behavior of the elastomer is of crucial importance. In this work a pre-strained circular actuator made of a dielectric elastomer is investigated: constitutive models based on uniaxial data are verified by comparing calculation results with experimental observations. An analytical model is derived for the instantaneous response to an activation voltage in the pre-strained circular actuator and a finite element (FE) model is used to simulate the time dependent behavior. Hyperelastic models are used and three strain energy formulations (Yeoh, Ogden and Mooney-Rivlin) are compared in their predictive capabilities. The results of the calculations with the three strain energy forms differ significantly, although all forms were successfully fitted to the same uniaxial data set. Predictions of the actuator behavior based on the Yeoh form agree to a great extent with measurements of the response at different pre-strain levels and activation voltages.
Silicone and acrylic elastomers have received increased attention as dielectric electroactive polymer (EAP) materials for actuator technology. The goal of this work was to develop and characterize a new class of silicones (DC3481) and to compare it with acrylic elastomers. The influence of various types of hardeners, hardener concentration, prestrain and high dielectric organic fillers was studied by mechanical, electrical and electromechanical experiments. Furthermore the temperature dependence and the viscoelastic properties were investigated. The results show that by changing type and concentration of hardener, the Young's modulus can be varied. In order to increase the dielectric constant, the silicone was blended with organic materials. Compared to acrylic elastomers, this new class of silicone elastomers has the advantage of a constant stiffness over a wide range of temperature and a lower viscosity that results in a higher response speed of the actuator.
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