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

Abstract

International audienceThis 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

Complementary study on the electrical and structural properties of poly(3-alkylthiophene) and its copolymers synthesized on ITO by electrochemical impedance and Raman spectroscopy

“…This decrease in the R CT with the copolymerization was also seen between the P3ATs and the PDFA [18] and between P3ATs [3], both synthesized on platinum.…”

“…As seen for the films synthesized on platinum [3,18,25], the resistivity sequence between the homopolymer films on ITO also showed a decrease in the resistive behavior with the side chain of the polymer matrix, that is, a P3MT for having the smallest side chain among P3ATs with the lowest resistivity. Thus, it was found that resistive behavior of homopolymers in an open circuit potential behavior was dependent on the side chain in the polymer matrix.…”

“…1, a semicircle was seen in most graphs, with the exception of P3OT and CP3HT-OT, which had two semicircles. In previous work on these P3ATs and its copolymers, synthesized on platinum, only a semicircle was found [3,18]. The emergence of the two semicircles in the diagrams of the P3OT and CP3HT-OT films synthesized on ITO, is due to the charge transfer process between the ITO/polymer and polymer/solution interfaces [3,24].…”

“…Some studies have been developed using EIS at different overpotentials and open circuit potential (OCP) with the help of cyclic voltammetry (CV) to determine the charge transfer on films of poly(3-methylthiophene) (P3MT) and poly(3-octylthiophene) (P3OT) and its copolymers with poly diphenylamine (PDFA) synthesized in similar conditions on platinum. Variation in charge transfer resistance as the overpotential increase was seen in the Nyquist diagrams, and the different electrochemical behavior in OCP due to the structural changes that incurred in the polymer chain [4,18,19].…”

“…Marchesi et al [23] using CV and EIS techniques to understand the electrochemical degradation processes found, the decrease in the redox capacity of polymers with an increase in the number of voltammetric cycles and with the data from the Nyquist graph obtained by EIS, related to redox capacity variation with mobile ions along the polymer chain. Benedict et al [18] determined the variation in the resistivity values (R CT ) and double layer capacitance (C DL ) of P3MT and P3OT and their copolymers with the PDFA through the EIS in OCP and overpotential, and with Bode-phase diagram related to the two constants of the phase where the charge transfer processes occurred involving the radical and dication cation species.…”