Vapor-Phase Deposition of Electroactive Polymers onto Electrospun Commodity Polyacrylonitrile Nanofibers

Electroactive polymers (EAPs) offer unique electrical and mechanical properties suitable for energy, environmental, and biomedical applications. Integrating EAPs with nanofibrous substrates can further enhance performance through the high surface area, interconnected porosity, mechanical flexibility, and tunable morphology of electrospun nanofibers. However, achieving uniform integration of EAPs on high-aspect-ratio nanofibers remains challenging due to poor coating homogeneity, limited penetration, and the reliance on toxic solvents in conventional deposition techniques. Here, a solvent-free vapor-phase deposition (VPD) process was developed to produce environmentally friendly and tunable EAP coatings on electrospun polyacrylonitrile (PAN) nanofibers. Electrospinning conditions were optimized to produce uniform PAN nanofibers with an average diameter of 350 nm. Poly-(3,4-ethylenedioxythiophene) (PEDOT), polypyrrole (PPy), poly-(3-hexylthiophene) (P3HT), and poly-(2,2'-bithiophene) (PBTH) were deposited via oxidative vapor-phase polymerization using iron-(III) chloride (FeCl₃) as the oxidant. Increasing FeCl₃ concentration enhanced polymer deposition, resulting in increased nanofiber diameter and weight. Energy dispersive spectroscopy (EDS) confirmed increased sulfur-to-nitrogen ratios for PEDOT, PBTH, and P3HT coatings prepared with higher oxidant concentrations. Fourier transform infrared spectroscopy (FTIR) verified complete EAP coverage by the appearance of characteristic EAPs CC and thiophene vibrations and the disappearance of PAN nitrile band. Four-point probe measurements showed that nanofiber conductivity was maximized at intermediate oxidant concentrations (2-3 M FeCl₃), with the highest values of 0.41 S cm^-1 for PPy-coated PAN nanofibers and 0.11 S cm^-1 for PEDOT-coated nanofibers. Cyclic voltammetry (CV) demonstrated reversible redox behavior and quasi rectangular voltammograms for PEDOT-coated nanofibers at scan rates of 1-8 mV s^-1, highlighting their potential as conductive platforms for charge storage and charge-transport applications.