THE EFFECT OF INITIAL CONDUCTIVITY AND DOPING ANIONS ON GAS SENSITIVITY OF CONDUCTING POLYPYRROLE FILMS TO NH3

The action of ammonia on free-standing polypyrrole films doped with Cl O4- and TsO(-) having a high conductivity in the range 10-65 S cm(-1) has been investigated. The gas sensitivity of conducting polypyrrole f ilms to NH3, at room temperature, is dependent on the initial conducti vity of the polypyrrole films and doping anions. A low conductivity ca uses an increase in sensitivity of polypyrrole films to NH3. The films containing ClO4- counterions display a high sensitivity, in the range 88 to 155% at 10 ppm NH3, whereas those including TsO(-) have a low s ensitivity of around 20%. It is found that the sensitivity values of C lO4- - and TsO(-)-doped polypyrrole films remain constant for a period of 60 days in an ambient environment. The polypyrrole films formed by electrochemical oxidative polymerization are found to possess detecta ble sensitivity in the form of an increase in resistivity for NH3 gas.