Dopant induced specificity in sensor behaviour of conducting polyaniline materials with organic solvents

Polyaniline (Pani) emeraldine salt (Pani-SO42−) and a composite with an inorganic metal complex dopant, chromium(III) trioxalate (CTO) were synthesised by chemical oxidative polymerisation method and Pani with an organic dopant, naphthalene-1,5-disulphonic acid (NSA) by electrochemical method. Spectral (UV-Vis and IR) and structural characterisations show that the incorporation of polar CTO and relatively non-polar NSA dopants has modified the physico-chemical nature of Pani, leading to the following increasing order of conductivity, Pani-CTO<Pani-SO42−<Pani-NSA. Sensor behaviour of these three materials with the saturated vapours of two groups of organic solvents, viz. (i) CH2Cl2, CHCl3 and CCl4, less-polar weakly interacting type and (ii) CH3CN, MeOH, DMSO and NMP, polar coordinating type, has been investigated by change in conductivity. Each polymer material responds characteristically and reversibly to a particular solvent vapour by decline in conductivity and the magnitude depends on the type and strength of interaction that each solvent vapour exhibits on the material. Spectral and CV features are so favourable as to adduce the conductivity data and to bring out a plausible mechanism as well in solvent-sensing.