Sensors and Actuators A 148 (2008) 105–110 Contents lists available at ScienceDirect Sensors and Actuators A: Physical journal homepage: www.elsevier.com/locate/sna Actuating abilities of electroactive carbon nanopowder/polyurethane composite films L. Petit ∗ , B. Guiffard, L. Seveyrat, D. Guyomar Laboratory of Electrical Engineering and Ferroelectricity, LGEF INSA Lyon, Bâtiment Gustave Ferrié, 8 rue de la Physique, 69621 Villeurbanne Cedex, France article info Article history: Received 19 March 2008 Received in revised form 10 July 2008 Accepted 4 August 2008 Available online 22 August 2008 Keywords: Electroactive polymers Carbon filling Strain Finite element modeling Hyperelasticity Actuation properties abstract This paper discusses the electromechanical potential improvement of polyurethane (PU) composite films by incorporation of carbon nanopowder in the polymer matrix. The beneficial influence on the electric field-induced is firstly measured and discussed. The observed non-linear mechanical behaviour of both pure PU elastomer and carbon/PU compos- ite is described using constitutive hyperelastic Ogden Model. Finite Element Modeling with hyperelastic elements confirm the validity of the chosen model, assuming that actuation pressure is only due to elec- trostatic (Coulomb) forces at the electrodes. It also allows to predict the strain and stress distributions in the polymer films and the influence of the electrode size. Finally, mechanical performances of pure PU and composite C/PU disk actuators are compared in terms of strain energy density and actuation pressure under quasistatic state (non-linear actuator behaviour). The C/PU actuator exhibits an output mechanical energy increased by 50% compared to pure PU. © 2008 Elsevier B.V. All rights reserved. 1. Introduction In the last decade, electroactive polymers have attracted much attention owing to their interesting electromechanical properties. In particular, some dielectric elastomers such as PU exhibit very high electric field-induced strains. Thus, they can be used as actu- ators in telerobotics or in medicine being directly integrated in the human body acting as micropumps or microvalves (bioma- terials), for instance. However, the experimentally observed large deformations (11%) are obtained under quite elevated electric fields (120MV/m), which can be a severe drawback for actuating appli- cations [1]. Recently [2], our group has shown that carbon black nanoparticles incorporation in a certain polyurethane (PU) matrix could lead to a strain value of -6.5% under a field of 12.5 kV/mm, a threefold reduction in the driving field level, compared with that applied to the pure PU to get the same strain. The ori- gin of strain enhancement by carbon black filling is not clearly determined but it is clearly not induced by a percolative effect raising the dielectric constant [3]. Previously [4], some researchers attributed the enhanced electromechanical response in thin film PU to the existence of space charges in the film thickness. It has been experimentally evidenced by our group [5] that space charges are present in both pure PU and C/PU films, so the higher strain ∗ Corresponding author. Tel.: +33 (0) 4 72 43 79 54; fax: +33 (0) 4 72 43 85 32. E-mail address: lionel.petit@insa-lyon.fr (L. Petit). response observed in C/PU composites would not be due to a higher non-uniform space charges distribution and hence non-uniform distribution of electric field across the film. Although the elec- tromechanical characteristics of PU and C/PU films are not well understood, the objectives of the present study are threefold: firstly describe the experimental electric field-induced strain through a hyperelastic model; secondly validate the model using Finite Ele- ment Analysis and give the strain and stress distributions in the films configuration and thirdly evaluate the mechanical character- istics (energy, pressure) when the film is subjected to a (quasi)static electric field. 2. Experimental procedure 2.1. Elaboration of composite films The chosen PU is the polyether-type thermoplastic TPU5888 from Estane Company. PU and C/PU films were prepared by the solution cast method. Commercially available granules of PU were dissolved in N,N-dimethylformamide at ∼70 ◦ C for 1 h. When nec- essary, 1 vol.% of amorphous carbon nanopowder (Aldrich, average particle size: 30 nm) were added to the solution under magnetic stirring. At constant temperature, the stirring time varies between 1.5 and 2.5 h, which allows obtaining different film thickness. Then, the mixed solution was poured onto a glass plate and dried at 70 ◦ C under air atmosphere during 15 h. The films thickness lies between 70 and 110 m. For electromechanical characterization, gold elec- 0924-4247/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.sna.2008.08.009