Dissertation Defence: Engineering Poly(3,4-Ethylenedioxythiophene):Poly(Styrene Sulfonate) (PEDOT:PSS) Structure: Pathway to Electromagnetic Interference Shields and Soft Actuators

Hatef Yousefian, supervised by [supervision name], will defend their [dissertation] titled “Engineering Poly(3,4-Ethylenedioxythiophene):Poly(Styrene Sulfonate) (PEDOT:PSS) Structure: Pathway to Electromagnetic Interference Shields and Soft Actuators” in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Mechanical Engineering.

An abstract for Hatef Yousefian’s dissertation is included below.

Examinations are open to all members of the campus community as well as the general public. Registration is not required for in-person exams.

---

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.