Processing and formulation of inkjet printable conducting polyaniline based ink for low cost, flexible humidity sensors using untreated polymeric substrate

Abstract

Conducting polymer, polyaniline based aqueous inkjet printable ink has been synthesized by a single-step chemical polymerization technique. Sulfonic 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. Ammonium persulfate was used as an oxidizing agent to initiate the polymerization. The synthesized polyaniline ink formulation was characterized by UV–vis and FT-IR spectroscopic analysis. The presence of a very sharp peak at 800 nm represents the presence of the conducting emeraldine salt phase of the polymer. This is further supported by FT-IR spectroscopic characterization. The viscosity of the ink was measured by using a Brookfield viscometer. Successive trials were performed for the printing of interdigitated patterns on the flexible untreated polymer substrate using an HP inkjet printer. The printed sensor was subjected to humidity sensing measurements. The change in the resistance with change in the % relative humidity (RH) was observed. The synthesized polyaniline based ink can be considered as a good candidate for a variety of inkjet printed low cost electronics devices.