Inkjet-Printed Polymer Films for the Detection of Organic Vapors

Inkjet printing has been used to prepare polymeric thin films for gas sensing. The conductive polymer poly(3,4-ethylene dioxythiophene) doped with polystyrene sulfonated acid (PEDOT-PSS) was used as the organic ink. The electrical resistance of the printed films was monitored during exposure to atmospheres containing alcohol vapors. Thin films (one to two printed layers) exhibited a sharp, nonreversible increase in film resistance (a "chemical fuse") which was attributed to a change in morphology of the PEDOT-PSS layer. The response time of the thin films was 6-10 min, depending on the film thickness. A longer response time was observed for three inkjet-printed layers. In contrast, thick films (> four printed layers) showed a reversible response (except for the initial exposure) to the same vapor. This was thought to originate from a screening effect between the positively charged PEDOT and negatively charged PSS dopant. The response times of the thick films were 8 and 6 min for methanol and ethanol, respectively. For both types of response, the inkjet-printed layers were found be more sensitive to methanol (0.05% ppm^-1) than to ethanol (0.03% ppm^-1)