A methodology towards geometry optimization of high performance polypyrrole (PPy) actuators

This paper focuses on a geometry optimization methodology based on a Jumped-parameter mathematical model, which accepts the voltage as the input, and bending angle and bending moment as the outputs, for a trilayer bending-type polymer actuator. An analogy is made between thermal strain and the real strain in the actuator to establish the mathematical model, which is solved using the finite element method in order to obtain theoretical results. The polypyrrole (PPy) actuator, which consists of five layers of three different materials, operates in a non-aquatic medium, i.e., air, as opposed to its predecessors. With reference to its operation principle, the movement or propagation of dopant ions and solvent molecules into the PPy layers is mimicked with a temperature distribution model to improve the accuracy of the model. Theoretical and experimental results presented suggest that the model is valid to predict the bending angle and bending moment outputs of the PPy actuators quite well for a range of input voltages and actuator thicknesses. The model has been employed to determine the actuator geometry, resulting in improved/higher bending angle and bending moment outputs. The geometry optimization results for an actuator with a constant length and width demonstrate that the thicker is the root of the actuator, where it is clamped, the higher is the bending moment, as compared to an actuator with a uniform thickness.