Poly(3-alkylthiophenes) and polydiphenylamine copolymers: a comparative study using electrochemical impedance spectroscopy

Abstract

This study compares the electrical properties of two homopolymers, poly(3-methylthiophene) and poly(3-octylthiophene), and their copolymers with polydiphenylamine, previously synthesized electrochemically on a platinum wire electrode (average area 0.19 cm2) in 0.100 mol L−1 LiClO4 at 18 °C. Based on the cyclic voltammetry data from these systems, electrochemical impedance spectroscopy (EIS) was used to evaluate the resistive and capacitive properties of the homo- and copolymers using the open-circuit potential (OCP) and overvoltage potential methods. The copolymer of poly(3-methylthiophene) and polydiphenylamine showed lower resistivity between films obtained by OCP and overvoltage potential. For all EIS images obtained by overvoltage potential there was a drop in resistivity and lower variation among the capacitance values. Using a Bode plot, we observed two time constants related to the radical cation and dication species, as characterized by Raman spectroscopy. Using scanning electron microscopy, it was possible to observe the changes in the morphological structures of the copolymers by comparison with the homopolymers, confirming the influence of greater active area on the improved conductivity of the copolymers.