The effect of folds in thin metal film electrodes used in dielectric elastomer actuators

Due to high electrical conductivity, metals have been the traditional material for electrodes. However, as metal films have low fracture strains, they are not commonly used as compliant electrodes in the field of dielectric elastomer actuators and generators. We have recently demonstrated that the use of metal films as electrodes can in fact allow dielectric elastomer actuators to have large actuated area strains of more than 100%. The metal film electrodes used have a network of crumples that unfolds as it is subjected to in-plane strains. This mechanism enables the metal electrodes to have a relatively low stiffening effect on the soft dielectric elastomer and to be able to retain its low resistance despite being highly strained; the latter characteristic would facilitate in the reduction of parasitic losses in dielectric elastomer generator applications. By metalizing a highly bi-axially pre-stretched dielectric elastomer that was subsequently partially relaxed, a bi-axial compressive force was introduced into the metal films, thereby causing a network of folds to form. In this paper, we study the change in the topography of the crumpled metal electrodes as the metal films are subjected to varying extents of bi-axial compression. It was also found that the way in which the metal films fold does in fact alter the electrodes' stretchability, as manifested in the performance of the dielectric elastomer actuators using these crumpled metal films as electrodes.