Characterization and modeling of PPy bilayer microactuators: Part 1. Curvature

Bilayer actuators of gold and polypyrrole doped with dodecylbenzenesulfonate, PPy(DBS), were microfabricated with lengths and thicknesses that varied over two orders of magnitude. The actuators were connected to rigid plates. The curvature of the bilayers was examined as a function of PPy and Au layer thicknesses to enable a determination of the actuation strain and Young's modulus of the PPy(DBS). Four different Au thicknesses were tested, and maximum curvature was obtained in all cases at a PPy:Au thickness ratio of 5:1. The data could not be fit with a constant value for the actuation strain; in addition, the PPy film bent even in the absence of an Au layer. Therefore, a model was developed that included strain and modulus variations along the direction of film thickness. The experimental data were fit with an exponential variation in actuation strain, starting at 20% at the surface of the PPy and decreasing to 3% at the gold interface in thicker films. The Young's modulus was found to be constant between 0.08 and 0.20 GPa in the oxidized state. These values differ significantly from thick-film values. With this information, micro-actuators can now be designed to achieve a specified radius of curvature.