A Systematic Investigation of Microstructure, Thermal Stability, Conductivity, and Solubility in Polyaniline Doped with Oxalic Acid

Introduction

Conductive polymers, particularly polyaniline (PANI), are crucial in materials science, but their application is often limited by the use of corrosive mineral acids like HCl for doping. This study investigates the use of oxalic acid, a safer organic acid, as a functional dopant to create an environmentally benign and more processable form of PANI.

Methods

Polyaniline was synthesized and doped separately with hydrochloric acid (PANI-HCl) and oxalic acid (PANI-OA). The resulting materials were comprehensively characterized using FTIR and UV-Vis spectroscopy, Scanning Electron Microscopy (SEM), Thermogravimetric Analysis (TGA), four-point probe conductivity measurements, and qualitative solubility tests.

Results

FTIR analysis confirmed the successful doping of PANI with oxalic acid, evidenced by significant shifts in the benzenoid and quinoid ring stretching vibrations and an enhanced band at ~1158 cm⁻¹, indicating charge delocalization. Furthermore, SEM imaging revealed a significant morphological transformation from a classic "cauliflower-like" structure in PANI-HCl to an ordered "rod-like" microstructure in PANI-OA. This structural change was accompanied by a trade-off in performance where PANI-OA exhibited lower electrical conductivity (1.23 S/cm) and reduced thermal stability compared to PANI-HCl (329 S/cm). However, these drawbacks were offset by a critical gain in processability, as PANI-OA demonstrated excellent solubility in polar aprotic solvents, whereas PANI-HCl remained intractable.

Conclusion

Doping polyaniline with oxalic acid sacrifices conductivity and thermal stability for major gains in processability, safety, and morphological control. This work validates the use of functional organic dopants to engineer task-specific conductive polymers with tailored properties for solution-based fabrication.