Functionalized polyanilines made by nucleophilic addition reaction, applied in gas sensors field

Abstract

Resistive sensors for organic volatile compounds are built using functionalized polyanilines. The functionalization of polyaniline (PANI) is achieved by nucleophilic addition with thiols and is confirmed by X-ray Photoelectron Spectroscopy. The modified polymers tested as resistive sensors change the polymer sensitivity to volatile compounds. PANI shows a signal that increases when the chain length increases, however, functionalized polyanilines show a completely different behaviour. The sensitivity to long chain alcohols increases when PANI is modified with long alkyl chains, the opposite behaviour occurs when more hydrophilic groups are bonding to the polymer. We conclude that the different sensitivity of the functionalized polyanilines to the same volatile molecule allows identifying the analyte. In that way, multisensor arrays based on these materials could be used as an electronic nose. To explain this behaviour measurements of contact angle were performed. The data reveal that all modified polyanilines are more hydrophobic than PANI, this is likely to be due to the presence of the sulphur atoms. Therefore, we conclude that the hydrophobic/hydrophilic nature of the surface plays an important role but is not decisive in the sensor response. Also, Van der Waals interactions between the alkyl chains bound to de PANI and present in the sensed alcohols play an important role. Accordingly, the sensitivity for a plain alkane (heptane) increases strongly when PANI is modified with long alkyl chains.