Light sensitivity of conducting polymer based solid contacts

The results of a systematic study of the light sensitivity and long-term potential stability (30d) of poly(pyrrole) (PPy), poly(3-octylthiophene) (POT), poly(3,4-ethylenedioxythiophene) (PEDOT), poly(aniline) (PANI) and plasticized poly(vinyl chloride) (PVC) containing 20% (m/m) PANI are reported. Thin films were prepared either electrochemically or by the solution casting technique. These materials are commonly used as ion-to-electron transduction materials in all-solid-state solid contact ion-selective electrodes.

The potential stability test done in 0.1 M KCl (pH 7.5) simulates the extreme situation when the CP based SC becomes in direct contact with water. Films prepared of a nanodispersion of PANI showed both good potential stability and insensitivity to light even under illumination with very intensive light (>105 lx). In contrary, it was observed that POT is very light sensitive.

Upon illumination with intensive light, the potential responses of POT films prepared by solution casting and electropolymerization were 315 mV and 590 mV, respectively. A room light sensitivity of approximately -10 mV to -15 mV was observed for these films. The other CPs in this study were insensitive to room light (ca. 150 lx), but were light sensitive under illumination with intensive light. The potential drift of PPy(Cl) is below -10 uV/h (3-30d), whereas the other most stable CPs in this study had a slightly higher potential drift.