Patternable bi-ionic actuator: an example of new functionality of actuation, folding and unfolding of electrochemical spring

A new type of bending actuation, attained for folding and unfolding of a film, has been successfully demonstrated by patterning technique. The films exhibiting such behaviors were fabricated by the three steps of successive electrodeposition of PPy layers with masking technique. This has resulted into a film having the patchwork quilt form, constituted with two types of bi-ionic bending units [W. Takashima, S.S. Pandey, K. Kaneto, Sens. Actuators B 89 (2003) 48–52]. Cyclic electrochemical stimulation on the film, having a stripe shape pattern, successfully induced the reversible folding and unfolding deformations in the oxidized and the reduced states, respectively. Thus, such a film exhibiting its performance like a linear actuator can be visualized as an electrochemically active spring. The total length of the spring was found to change reversibly from 100% in maximum (unfolded) to 40% in minimum (folded) states, indicating to possess an extra-large strain of 60%. The stripe-pitch dependence on bending performance elucidates that the small pitch facilitates the bending performance because of high torque as well as effective bending. The results can be expressed as the enhancement of load-lifting performance by structural optimization for effective collection of the torque to a desired direction.