Development of polyamide 6/polypyrrole conductive nanofibrous structure: the contribution of dopant type

Abstract

Conductive polymers, which exhibit properties of both metals and polymers, have garnered significant attention. Among the various methods considered for developing conductive polymers, chemical synthesis has gained enormous interest due to its remarkable advantages, including lightweight, cost-effectiveness, and resistance to chemical substances. Polypyrrole (PPy), a well-known conductive polymer, has found extensive use in various fields such as biosensors, supercapacitors, and solar cells. In this study, we developed a conductive nanofibrous structure through the chemical synthesis of PPy on polyamide 6 (PA6) nanofibers. We used sodium p-toluenesulfonate (NaPTS) and lithium perchlorate (LiClO₄) as dopants. The structural and functional properties of the resulting conductive PA6 nanofibrous structure, including morphology, crystallinity, electrical conductivity, wettability, and electrochemical properties, were significantly influenced by the type of dopant. The average diameter of conductive PA6/PPy nanofibers increased with polymerization duration. Regardless of the dopant type, the crystallinity index (CI) of the conductive nanofibers PA6 + PPy + NaPTS (CI = 21.72%) and PA6 + PPy + LiClO₄ (CI = 31.97%) was smaller compared to that of PA6 nanofibers (CI = 40.52%). This difference was attributed to the amorphous nature of PPy. When polymerization was conducted for 1 h, the electrical conductivity values were 1.76 ± 0.12 S/cm for PA6/PPy nanofibers doped with NaPTS and 4.47 ± 0.31 S/cm for those doped with LiClO₄. By increasing the polymerization duration to 24 h, the electrical conductivity of PA6/PPy nanofibers improved by 99% and 92%, respectively. Coating PA6 nanofibers with PPy reduced their hydrophilicity degree, as indicated by water contact angles of 46.53 ± 2.53°. Regardless of the dopant type, water contact angles of 73.01 ± 5.92° and 72.13 ± 5.81° were obtained for NaPTS and LiClO₄ dopants, respectively. Additionally, a direct linear correlation was established between the charge transfer resistance (Rct) and electrical conductivity. Overall, the developed conductive nanofibrous structure holds immense potential for high-performance sensors.