Inkjet Printing and Characterization of Applied Electrodes for Dielectric Elastomer Transducer
Dielectric elastomer (DE) transducers consist of a dielectric elastomer layer coated with flexible electrodes on both surfaces. Apart from the dielectric film, the properties of the electrodes affect the electromechanical behavior of the DE transducers as well. Electrodes must be able to sustain conductivity at large deformations, must exhibit a low stiffness and provide sufficient adhesion to the DE-layer. Different processing technologies exist for application of electrodes suitable for DE-transducer. Among them, the inkjet printing technique gained attention in recent years as a very precise and purely non-contact deposition method to fabricate thin electrode layers. In contrast to other methods, e. g. using a shadow mask in case of spraying, the inkjet technique is very versatile and allows a fast adjustment of the processed electrode geometry. In order to describe the requirements of the inkjet printing process and ink adaptation itself, we present a theoretical description of those processes accompanied with the definition of parameters, which need to be considered during experimental processing. Furthermore, we present first results of our adaptation of an ink formulation and an inkjet printing procedure. For this purpose a commercial electrode paste, Elastosil® LR 3162, made of carbon black-silicone composite, was adapted to the inkjet printing process. In first experimental studies, the adapted ink was inkjet printed onto dielectric elastomer layers by varying the inkjet printing parameters. Different measurements were performed in order to characterize separate dots as well as continuous lines and areas of the inkjet printed electrodes. The electrode thicknesses and its shapes were recorded by surface-profile measurements. The electrical properties of the printed electrodes as well as their mechanical influence on the elastic properties of the elastomer layers were measured under continuous and cyclic mechanical stretching.