The Hole Dynamic in PEDOT:PSS/Bacterial Cellulose Actuators

Actuators are one among numerous applications that have emerged from the utilization of conducting polymers. This class of material has attracted wide interest in the field of electronics, because they conduct both electronic and ionic charges through the bulk of their volume. This makes possible the application of electronic devices as electrochemical devices, which are termed as organic electrochemical transistor (OECT).<br/>Despite the extensive use as OECTs, there are still numerous discrepancies in the descriptions of the fundamental physics underlying the performance of these devices. Therefore, there is a growing emphasis on modeling the ion-electron interaction within conducting polymers. Recent publications have contributed fresh insights into the conduction mechanisms. However, the actuator community has yet to fully integrate these newfound understandings into their efforts to comprehend and model the mechanical response of conducting polymer actuators. Existing models for these actuators have primarily focused on ionic diffusion, which falls short of explaining all the existing experimental observations.<br/><br/>This study draws from three distinct bodies of literature, comprising the most pertinent existing model for conducting polymer actuators, advancements in the comprehension of ionic-electronic conduction in conducting polymers, and empirical observations that defy current models for conducting polymer actuators. Also, Electrochemical Impedance Spectroscopy (EIS) is used extensively to understand the actuation mechanism under dynamic conditions, considering the progress made in comprehending the physics of conducting polymers as previously mentioned.<br/><br/>The conducting polymer actuator is prepared using PEDOT:PSS and bacterial cellulose (BC) (as a substrate), which is operated in both depletion mode and enhancement mode, for different time scales. The doping (compensation) and dedoping (displacing) in PEDOT:PSS (using an electrolyte) results in displacement of the PEDOT:PSS/BC bi-layer. Notably, the actuator displacement is found to be asymmetric, contingent on the polarity, magnitude, and frequency/time period of the applied potential. The observed asymmetry in displacement as a function of these parameters remains unaccounted for by existing models for conducting polymer actuators.<br/><br/><b>Experimental Process</b><br/>Electrochemical Impedance Spectroscopy (EIS) is performed on a PEDOT:PSS/Bacterial cellulose bi-layer actuator, while the actuator is subjected to various electrostatic potential. The displacements of the actuator under these potentials are also recorded for different time periods. The EIS data is used to model electrical circuit for actuators under given potentials. Mott-Schottky analysis is performed to understand the energy band structure of the actuator-electrolyte system. Density Functional Theory simulations are performed to aid the conclusions derived from experimental data.<br/><br/><b>Significance</b><br/>The results and discussion which follows in this paper is significant in deriving an updated model for conducting polymer actuators, delving into quantum capacitance effects given the low charge density in conducting polymer, which is essential for reliable device performance and in defining the operating ranges for such actuators. This study becomes significantly important in the background of the development happening in the field of OECT, as it brings in the mechanical deformation corresponding to those findings.