Development of large-strain and low-powered electro-active polymers (EAPs) using conductive fillers

During the last decade, Electro Active Polymers (EAPs) have attracted much attention especially because of their high level of generated strain. Mainly ferroelectric materials are used as fillers with elevated volume percentages in order to create a reasonable strain level. Aggregation problems should also be considered. With silicone or acrylic elastomers as the matrix, very high strains, even more than 300%, can today be obtained, however this requires a very high electric induction, e.g., 120 MV/m. Such a high electric requirement prevents these materials from being utilized with other electric components. There exist intermediate materials between traditional actuator materials, such as PZTs, and EAPs. These materials can generate higher strain levels than traditional PZT materials, and are expected to be driven with a low electric level. The present paper shows the easy fabrication method of such intermediate materials. Conductive fillers were incorporated into the polymeric material. As opposed to for ferroelectric filler materials which have many dipoles, there was no electric field inside the conductive fillers. As a consequence, electric charges were distributed over the surface of the filler particle surfaces. This mechanism increased the electric coefficient so that a high strain level could be obtained more efficiently than in the case of ferroelectric fillers. The improvement of electrostriction by adding very small volume percentages of fillers, 0.1-2 Vol.%, was thus confirmed. The composite films, fabricated by a very easy method, could generate more than 20% of strain at 15 MV/m.