Synthesis of nano-sized polyindole via emulsion polymerization and doping

• PIn synthesized with various oxidant and surfactant types was studied.
• Over-oxidation level of PIn/FeCl3 was lower than PIn/APS.
• PIn in emulsion of SDS provided higher electrical conductivity than CTAB and TW80.
• PIn doped with HClO4 at different doping mole ratios was reported.
• The highest electrical conductivity of PIn was 14.56 ± 2.39 S cm−1.

The nano-sized PIn were successfully synthesized via emulsion polymerization at room temperature. Effects of oxidizing agent type (APS and FeCl3) and various emulsion systems using different surfactants and concentrations were studied. Three surfactant types namely cationic cetyltrimethylammonium bromide (CTAB), anionic sodium dodecylsulfate (SDS), and non-ionic polysorbate 80 (TW80) were utilized. PIn with higher electrical conductivity was obtained by using FeCl3 because it was of a lower oxidizing capacity leading to lower over-oxidation. The emulsion system of SDS provided the smallest particle in nanometer size of 60.3 ± 10.8 nm in diameter and higher electrical conductivity than CTAB and TW80 because the anionic surfactant was an efficient dopant. Thermal stability of PIn in various conditions was also investigated, PIn/APS manifested the highest thermal stability as it produced a higher char yield than the PIn synthesized with the other conditions. Higher electrical conductivity of PIn was improved by doping with HClO4 at different doping mole ratios. At the doping mole ratio of 25:1, the electrical conductivity of PIn increased by 4–5 orders of magnitude comparing to PIn before doping. In this work, the highest electrical conductivity of PIn was 14.56 ± 2.39 S cm−1 which has never been reported previously.