Engineering poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) structure : pathway to electromagnetic interference shields and soft actuators

Abstract

This thesis investigates the structural properties and functional performance of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), a frontrunner intrinsically conductive polymer (ICP), with the goal of engineering its electrical conductivity, stability, and multifunctionality for advanced applications, including electromagnetic interference (EMI) shields and soft actuators. Although PEDOT:PSS is well-known for its excellent processability, stability, and tunability, its conductivity remains limited due to the incomplete understanding of intra-grain and inter-grain charge transport mechanisms. To address this challenge, this work systematically explores solvent doping, acid post-treatment, and a novel sequential dual-treatment strategy, linking molecular conformation, crystalline ordering, and lamellar organization to macroscopic functionality. A systematic study of solvent doping and acid post-treatment is conducted on free-standing, micrometre-thick PEDOT:PSS films to elucidate their effects on phase separation, chain ordering, and conductivity. The free-standing films are selected because they provide the flexibility and stability required for practical devices, while also filling the gap left by earlier studies that focused mainly on ultrathin films (< 100 nm). In thicker films (> 5 µm), structural rearrangements are more constrained, providing new insights into how morphology influences charge transport. Thereupon, high- and low-boiling-point solvents, as well as a range of acids, are evaluated to establish correlations between intra- and inter-grain charge transport and macroscopic conductivity. Building on these insights, a dual-treatment process is developed, combining solvent and acid strategies to enhance crystallinity, conductivity, and durability simultaneously. This approach yields free-standing PEDOT:PSS films with conductivities exceeding those of conventionally treated films, while maintaining flexibility and environmental robustness. These engineered PEDOT:PSS structures are then translated into practical devices. Free-standing and transferable thin films (~ 5 µm) demonstrate lightweight, flexible, EMI shielding with repeatable transferability, making them suitable for integration onto complex geometries. Additionally, a Janus actuator is fabricated from dual-treated PEDOT:PSS, exhibiting multi-stimuli responsiveness (electricity, heat, and organic vapor) with low-voltage operation (~ 2-6 V). The actuator’s anisotropic structure, inspired by natural hygromorphic systems, enables reversible bending behavior relevant for soft robots and smart sensors. Overall, this thesis advances the fundamental understanding of structure-property relationships in PEDOT:PSS and introduces a novel dual-treatment route to unlock its multifunctional potential. The findings highlight sustainable, low-cost, and scalable pathways for next-generation EMI shields and soft actuators, bridging the gap between materials science and flexible electronic applications.