Effect of humidity on NH3 gas sensitivity of polyaniline blend films

The effect of humidity on the NH3 detection capability of polyaniline (PANI)-insulating matrix polymer blend films was investigated. Poly(methyl methacrylate) (PMMA) and polystyrene (PSt) were used as the matrix polymers. The presence of water vapor, functioning as the interference gas, led to the lowering of the NH3 response of the sensor in a humid atmosphere. Although PMMA had more hydrophilic character than PSt (PMMA sorbed more than eight times as much water as PSt), the influence of humidity on the sensor response was not as large as expected. This unexpected finding was due to the characteristic morphology of the “PANI–PMMA blend film”, that is, the blend film consisted of porous structures which resulted in a composition of the coexistence of the PANI–PMMA blend with the PANI and/or PMMA single species. In such cases, water molecules were able to interact with doped PANI directly, and the water sorbing characteristic of PMMA exerted less influence on the conductivity.