In situ electrochemical and surface plasmon resonance (SPR) studies of aniline-carboxylated aniline copolymers

Abstract

Self-doped conducting polyanilines (PAn) were fabricated by electrochemical copolymerization of aniline and carboxylated anilines in acidic aqueous solution using cyclic voltammetry. The comparative studies of carboxyl substituted and unsubstituted polyanilines show that only the copolymers from aniline (An) and 2-anthranilic acid (AA) with appropriate monomer fractions retain a high electroactivity and stability on electrodes in neutral aqueous solution. The polymerization process, the redox properties and the stability of the copolymers in comparison with those of polymers on gold electrodes were thoroughly investigated by in situ electrochemistry and surface plasmon resonance spectroscopy (SPR). The “self-inhibiting effect” and the “autocatalytic effect” were observed in the substituted and the unsubstituted polyanilines separately during the polymerization processes monitored by SPR. The combination of electrochemical and SPR techniques provides the direct information about the changes of dielectric properties and film thickness of the polymers in their redox processes. Comparing with those of PAn and copolymers, the dielectric constants of the substituted polyaniline play a minor role in the SPR reflectivity when it changes between different redox states. The comparable electroactivity of these copolymers obtained from aniline and its substituted analogues in acidic environments indicates the presence of a similar conjugated structure of the copolymer and the polyaniline, which is further confirmed by total internal reflection FTIR (TIR-IR).