Electrically Controllable Deformations in Ionic Polymer Metal Composite Actuators

Ionic polymer metal composites (IPMC’s) exhibit spectacular coupling between electrical and mechanical domains. Sensing and actuation properties of these materials and the force and displacement characteristics have been investigated as a means of determining the electromechanical coupling coefficients of the material. An electric field applied across the thickness of the polymer causes electrophoretic ionic migration within the material. Electro-osmotic drag induces solvent migration in addition to the ion motion, and a stress is generated within the material causing the material to deform. This phenomenon is also reversible, making it possible to use ionic polymer materials as sensors, transducers and power generators. The salient feature of ionic polymeric materials, as compared to other electromechanical transducers such as piezoelectrics, is the large deformations that are achievable with low electric fields. Cantilever samples of ionic polymer material exhibit tip displacements on the order of their length with applied electric fields of the order of 10 volts per mm. Recent measurements of the motion of cantilever samples of ionic polymers have demonstrated a controllable, repeatable deformation in which the zero force position of the ionic polymer changes depending on the amplitude of the applied electric field. This effect appears to be controllable in the sense that the change in the zero force position of the polymer is a function of the amplitude of the applied electric field. It is also reversible to a degree because a step change in the voltage with the opposite polarity will change the shape of the ionic polymer strip back to a position that is close to the original position before cycling of the material. Thus, there is a potential to use this effect as a deformation memory mechanism within the polymer material. These observations and subsequent interpretations are reported in this presentation.