Effect of Crack Formation on Stretchable Silver Electrode for Dielectric Elastomer Actuators

Thin metal films are not commonly used electrodes for dielectric elastomer actuators as it is a common presumption that they are too stiff to allow large actuated strains. However, using thin metal film electrodes can improve reliability due to their ability to self heal, as shown from their use in metalized plastic film capacitors. Typically, from literature, actuated area strains do not exceed 10% when using thin, un-patterned, metal films formed by sputtering. However, in this present work, large actuated area strains of up to 50% have been demonstrated. This was accomplished by using thin silver film electrodes formed by electroless deposition, and it has been noticed that micro-cracks were present in such electrodes. In this paper, micro-cracks in thin silver electrodes are studied and compared against sputtered silver electrodes. This includes the study of the manner in which they affect the magnitude of actuated strain and the repeatability of the actuator. It has been found that the cracks have helped to improve actuated strain, yet did not affect repeatability, as the cracks did not propagate in subsequent activations. Instead, the cracked electrodes had reached a sort of "steady-state".