Polyaniline as pH-sensitive component in plasticized PVC membranes

The pH and redox sensitivity of electrically conducting polymer films consisting of a mixture of polyaniline (PANI) and plasticized poly(vinyl chloride) (PVC) have been studied with potentiometry, UV–vis spectroscopy and energy dispersive X-ray analysis (EDXA). It is well known that PANI is highly H⁺-selective and can easily be dissolved in many organic solvents with functionalized organic acids. PANI is therefore very suitable to be used as a H⁺-sensitive component in plasticized PVC membranes. In this work, we have studied the behaviour of PANI as the H⁺-sensitive component in plasticized PVC membranes as well as the influence of added lipophilic salts, tridodecylmethylammonium chloride (TDMACl) and potassium tetrakis(4-chlorophenyl)borate (KTpClPB), on the pH and redox sensitivity of these membranes. The pH sensitivity was studied between pH 2 and 9. The electrode membranes were prepared according to the all-solid-state electrode configuration by placing the membrane directly on a glassy carbon substrate. The PANI content in the membranes was varied from 0% to 100% (m/m) and the TDMACl and KTpClPB content from 0% to 40% (m/m). PANI was dissolved in tetrahydrofuran (THF) with phosphoric acid dihexadecyl ester. It was found that appropriate amounts of plasticized PVC decreases the hysteresis effect of pure PANI that was observed in the potentiometric measurements. It is also shown that TDMACl facilitates the emeraldine salt (ES)–emeraldine base (EB) transition of PANI while KTpClPB hinders it and allows PANI to stay in the conducting ES form even at pH 9. Differences in the redox sensitivity of membranes containing TDMACl and KTpClPB will also be discussed.