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 vapourinduced 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.