Synthesis, characterization, and morphology of p‐toluene sulfonic acid‐doped polyaniline: A material for humidity sensing application

Polyaniline (PANI) doped with p‐toluene sulfonic acid was synthesized by chemical polymerization method using (NH4)2S2O8 as an oxidizing agent. This is a single step polymerization process for the direct synthesis of the conducting emeraldine salt (ES) phase, without the need of doping, dedoping, and redoping of the polymer. Presence of a free carrier tail at higher wavelength, characteristic of extended coil conformation along with a sharp polaronic peak is observed in the UV–vis spectrum of doped PANI in m‐cresol solvent. FT‐IR studies show the characteristic peaks of ES phase along with a sharp peak at 1120 cm−1 representing vibration band of the dopant ion. Clumps of small fibers resulting in a sponge‐like structure was observed under scanning electron microscope. Thermal studies revealed a three‐step decomposition pattern. Conductivity is found to increase with an increase in the temperature showing “thermal activation behavior.” Decrease in resistance with increasing humidity is observed in a broad range of humidity.