The influence of lipophilic additives on the emeraldine base–emeraldine salt transition of polyaniline

Abstract

The pH sensitivity of polyaniline (PANI) membranes containing potassium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (KTFPB), potassium tetrakis(4-chlorophenyl)borate (KTpClPB), cesium carborane (Cs-carborane), tetradodecylammonium tetrakis(4-chlorophenyl)borate (TDATpClPB, ETH 500) or tridodecylmethylammonium chloride (TDMACl) as the lipophilic additive have been studied in this work. It is shown with UV-Vis spectroscopy, potentiometry, energy dispersive X-ray analysis (EDXA) and dc conductivity measurements that the PANI membrane containing 30% (w/w) of the anionic additive KTFPB is in the electrically conducting emeraldine salt (ES) form still at pH 9 and that the film is insensitive to pH between 2 and 9. The reason for the unusual pH insensitivity is probably that the TFPB − anions prevent the pH dependent ES–emeraldine base (EB) transition from occurring by hindering the acid anions to leave the polymer chains and in this way locking PANI in the ES form. All membrane components were dissolved in tetrahydrofuran (THF) and the PANI membranes were prepared by drop casting on glassy carbon substrates. PANI was made soluble in THF either with the phosphoric acid dibutyl ester (DBP) or phosphoric acid dihexadecyl ester (DHDP).