Analyzing the structural behavior of conducting polymer actuators and its interdependence with the electrochemical phenomenon

This work reports the deformation behavior of a conducting polymer, poly(3,4-ethylene dioxythiophene):polystyrene sulfonate (PEDOT:PSS)/bacterial cellulose (BC) bi-layered cantilever type actuator. Herein, it was found that the type (i.e. bending and torsion) of deformation of (PEDOT:PSS)/BC actuator was non-trivially dependent on its dimensions (width and length). Increasing the actuator's width resulted in larger torsional deformation along the longitudinal axis against the increased area moment of inertia. The actuator with a width of 7.75 mm rotates similar to 90 degrees (i.e. the bottom cross-section) with respect to its top end. It was noticed that torsional motion dominated the deformation when the bending in the lateral direction was restricted. Further, the maximum tip displacement trivially increased with the length from 5.40 mm for an actuator of length 10 mm-12.40 mm for a length of 59.00 mm. However, the curvature of bending, which was proportional to the induced strain, was higher for smaller lengths. The change in the dimension of the actuator involves change in the stress field distribution (i.e. induced through electrochemical process) and simultaneously the resistance to deformation, resulting in a non-trivial relationship between the deformation and the dimensions. This can be advantageous from the design perspective in realizing different types of motions without incorporating additional materials. Structural theory and electrochemical impedance Spectroscopy were used to understand the mechanism of deformation dependence on the dimensions. The electrochemical impedance spectroscopy results indicated that electrolytic ions penetrate deeper into the PEDOT:PSS layer for actuators of smaller lengths. The increase in the curvature of the actuator could be explained based on the constancy of the strain produced due to the volume change per ion. The torsional motion increased because the stresses were being induced further away from the center in wider actuators. These observations and analyses reveal the interdependence of the structural behavior (i.e. dimensions) and the electrochemical phenomenon (i.e. deformation) in a conducting polymer actuator.