Influence of galvanostatic electrodeposition parameters on the structure-property relationships of polyaniline thin films and their use as potentiometric and optical pH sensors

Galvanostaticaly electrodeposited polyaniline thin films were used as both potentiometric and optical pH chemical sensor. The galvanostatic deposition parameters were: deposited charge from 150 to 600 mC cm(-2), current density from 0.5 to 1.0 mA cm(-2 )and deposition time from 150 to 1200 s. The electrodeposited polyaniline thin films in these conditions presented passivation charge 150 +/- 12 mC cm(-2). The variation of the deposition parameters led to the production of thin films with distinct properties and characteristics. Basically, they presented two distinct oxidation states. The set of films produced using a current density of 0.5 mA cm(-2) showed the best performances for both sensors, reaching a sensitivity of 81 +/- 1 mV pH(-1) and 30 +/- 3 pH(-1 )for the potentiometric and optical pH chemical sensor, respectively. This set of films presented the best performances because they had a partially oxidized structure, the emeraldine base, which has the largest protonation potential and reaches a high electrical conductivity. The understanding of the mechanisms involved in pH detection is discussed based on the structure-property relationship established by the characterization of the PANI thin films together with the polymer's electrochemical and optical mechanism of sensitivity to pH variation.