Polyaniline and its substituted derivatives as sensor for aliphatic alcohols

Polyaniline (PAni) as well as its substituted derivatives such as poly(o-toluidine) (Po-Tol), poly(o-anisidine) (Po-Anis), poly(N-methyl aniline) (PNMA), poly(N-ethyl aniline) (PNEA), poly(2,3 dimethyl aniline) (P2,3-DMA), poly(2,5 dimethyl aniline) (P2,5-DMA) and poly(diphenyl amine) (PDPA) were found to be sensitive to different alcohols such as methanol, ethanol, propanol, butanol and heptanol vapours. A negative change in resistance was observed upon exposing the polymers to methanol, ethanol or propanol vapours, whereas, a reverse trend has been observed for butanol and heptanol vapours. Although, the magnitude of change in resistance was found to be very high in many cases: poor response time was observed for most of the polymers. Rapid responses were exhibited only by P2,3-DMA and PAni for methanol and ethanol, respectively. High sensitivity value (>80%) have been obtained for saturated methanol vapours compared to other alcohols in all polymers. Further, measurable response (sensitivity ∼60%) has been obtained at lowest alcohol concentration of ∼3000 ppm with extended switching time. The results are explained on the basis of vapour induced change in the crystallinity of the polymer. The extent of change was found to be governed by the chain length of the alcohol and its chemical nature.