| Abstract: | Polypyrrole–poly(vinyl alcohol) (PPy–PVA) composite films were prepared electrochemically by means of codeposition at a constant potential. Their sensing behaviors to various ethanol-vapor concentrations were investigated. Increasing the molar fraction of PVA up to PPy0.964PVA0.036 showed an increase of the sensitivity of the composite sensors. However, the sensitivity decreased if further PVA was incorporated. The ethanol-sensing behaviors were also largely dependent upon the electropolymerization charge, ranging from 50 to 200 mC in this investigation. Higher sensitivity was measured from the composite film prepared with a lower electrical charge. For example, a sensitivity of 7.70 mΩ mg−1 L, about 3.3 times the sensitivity of the pristine PPy sensor, was measured by the PPy0.964PVA0.036 composite film prepared at 50 mC. However, incorporating PVA into the conducting polymer was at the sacrifice of the response speed as well as the stability of the composite as it was under continuous exposure to ethanol vapor. An adsorption model based on the Langmuir isotherm was used to interpret the sensing behaviors and the equation derived from this model correlated well with the measured sensitivities. The sensing parameters including the adsorption equilibrium constant, Km, and the resistance change caused by a pseudomonolayer, m(r1 − r2)]/n, were determined and found to decrease with increasing polymerization charge. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2079–2087, 1999 |
