Ink-jet printed conducting polyaniline based flexible humidity sensor

Ink-jet printed, intrinsically conducting polymer (ICP), polyaniline have been used for humidity sensing at room temperature. Polyaniline based, aqueous ink-jet printable ink has been synthesized by single step, chemical oxidative polymerization technique. Sulphonic acids were used as a dopant during the in situ polymerization process. This is a single step polymerization process for the direct synthesis of conducting emeraldine salt phase of the polymer as an ink formulation. The synthesized polyaniline ink was further characterized by spectroscopic (UV–visible and FT-IR) analysis which confirmed the presence of conducting emeraldine salt phase of the polymer. The viscosity of the ink was measured by using Brook-field viscometer. The successive trials were performed for the printing of IDT pattern on the flexible, untreated polymer substrate using HP ink-jet-printer. The printed sensor was subjected for the humidity sensing measurements. The change in the resistance with change in the %RH was observed. It is suggested that the increase in conductivity at high humidity may be related to a vapour-induced change in the transfer of charge carriers between the polymer chains. The synthesized polyaniline based ink can also be considered as a good candidate for variety of ink-jet printed low cost electronics devices.