Recognition and exposition of intermolecular interaction between CH2H2Cl2 and CHCl3 by conducting polyaniline materials

A detailed study has been performed on the sensing of weakly interacting chlorinated hydrocarbon solvent vapours of CH2Cl2, and CHCl3 separately or combinedly from their solvent mixture (1:1 by volume) by three polyaniline materials, polyaniline sulphate (PANI), PANI doped with naphthalenesulphonic acid (PANI-NSA) and PANI-poly(vinyl alcohol) blend (PANI-PVA) of 2:1 molar ratio. Each sensor material responded through a decrease in conductivity reversibly and their activities were monitored by normalized conductivity change (NCC). The NCC values for the two solvents are in the decreasing order, PANI-NSA > PANI > PANI-PVA which is also the order of conductivity. However, the NCC values of the vapour mixture are abnormally far higher than the sum of NCC values of individual solvent vapours in all the three materials. Originally CH2Cl2 has a weaker interaction than CHCl3 with polyaniline materials. Nevertheless, it gets 'activated' in the molecular pair with CHCl3 through electronic effects and the pair exhibits concerted interaction with polyaniline materials causing abnormal conductivity changes. Conductivity studies performed in different solvent sequence vapour exposures, spectral (IR, UV-vis and EPR) and structural (XRD) studies have not only confirmed this concerted type of interaction but also demonstrated the dominance of CH2Cl2 vapour in molecular pair interaction with polyaniline. In the two solvent cases, the vaporized molecules neutralize the polarons by acting as reducers and bring about a decline in conductivity. On the contrary, with mixture, besides this redox activity, the accompanying conformational change in the sensor material also appears to be responsible for the abnormal conductivity change. Polyaniline could, thus, recognize and expose the intermolecular interaction in the molecular pair of CH2Cl2 and CHCl3 like proteins through its chemically flexible unique characteristics of imine-amine groups and protonation-dependent conductivity. (c) 2004 Elsevier B.V. All rights reserved.