Spectro-Electro-Gravimetry of Poly (o-toluidine)
Authors: Agrisuelas Jeronimo , Ferrer Amparo , Frau Antonello F , García Jose , Vicente Francisco 
Published: February 2020

Polyaniline and derivatives are one of ICPs most investigated [1-4]. Despite the considerable advances on the knowledge of the electrochemical reactions in this family of ICPs, it is still generally assumed that a “simple” transition from insulating form (leucoemeraldine or LE) to conductor form (emeraldine or E) by anion doping takes place with the formation of polaron centers [5]. Nekrasov et al and Hillman et al have proven that this transition is more complex than assumed or discussed in literature. On the one hand, Hillman et al have suggested a slow-moving solvent counter flux with a fast anion insertion together with a proton expulsion during this transition, at least, in HClO4 solution [6,7]. On the other hand, Nekrasov et al have proven that two different species are generated and coexist during this transition: (i) the isolated polarons or radical cations (P*) with a spectral response around 420 nm and the (ii) the conducting polarons which are coil structures due to the strong interaction of anions with the C-NH+-C group (PC) with a spectral response around 840 nm [8-10].

We present a more detailed electrochemical mechanism for the insulating to conductor transformation of POT films. During the relaxation, protons are expulsed when the isolated polarons (P*) detected at 420 nm are oxidized. Isolated polarons could be formed because of trapped anions when the film is reducing and shrinking (packing). Anions are inserted during the formation of conducting polarons (PC), which consist in coil structures due to the strong interaction of anions with the C-NH+-C group of polymer detected at 840 nm.

[1] A. Syed, M. Dinesan, Polyaniline - a Novel Polymeric Material - Review, Talanta. 38 (1991) 815–837. doi:10.1016/0039-9140(91)80261-W.

[2] T.H. Qazi, R. Rai, A.R. Boccaccini, Tissue engineering of electrically responsive tissues using polyaniline based polymers: A review, Biomaterials. 35 (2014) 9068–9086. doi:10.1016/j.biomaterials.2014.07.020.

[3] R.Y. Suckeveriene, E. Zelikman, G. Mechrez, M. Narkis, Literature review: conducting carbon nanotube/polyaniline nanocomposites, Reviews in Chemical Engineering. 27 (2011) 15–21. doi:10.1515/REVCE.2011.004.

[4] J. Lai, Y. Yi, P. Zhu, J. Shen, K. Wu, L. Zhang, J. Liu, Polyaniline-based glucose biosensor: A review, Journal of Electroanalytical Chemistry. 782 (2016) 138–153. doi:10.1016/j.jelechem.2016.10.033.

[5] G. Ćirić-Marjanović, Recent advances in polyaniline research: Polymerization mechanisms, structural aspects, properties and applications, Synthetic Metals. 177 (2013) 1–47. doi:10.1016/j.synthmet.2013.06.004.

[6] M.J. Henderson, A.R. Hillman, E. Vieil, Ion and Solvent Transfer Discrimination at a Poly(o-toluidine) Film Exposed to HClO4 by Combined Electrochemical Quartz Crystal Microbalance (EQCM) and Probe Beam Deflection (PBD), J. Phys. Chem. B. 103 (1999) 8899–8907. doi:10.1021/jp9910845.

[7] M. J. Henderson, A. Robert Hillman, E. Vieil, A combined electrochemical quartz crystal microbalance (EQCM) and probe beam deflection (PBD) study of a poly(o-toluidine) modified electrode in perchloric acid solution, Journal of Electroanalytical Chemistry. 454 (1998) 1–8. doi:10.1016/S0022-0728(98)00245-9.

[8] A.A. Nekrasov, V.F. Ivanov, A.V. Vannikov, Analysis of the structure of polyaniline absorption spectra based on spectroelectrochemical data, J. Electroanal. Chem. 482 (2000) 11–17. doi:10.1016/S0022-0728(00)00005-X.

[9] A.A. Nekrasov, V.F. Ivanov, A.V. Vannikov, Effect of pH on the structure of absorption spectra of highly protonated polyaniline analyzed by the Alentsev-Fock method, Electrochimica Acta. 46 (2001) 4051–4056. doi:10.1016/S0013-4686(01)00693-4.

[10] A.A. Nekrasov, V.E. Ivanov, O.L. Gribkova, A. Vannikov, Voltabsorptometric study of “structural memory” effects in polyaniline, Electrochimica Acta. 50 (2005) 1605–1613. doi:10.1016/j.electacta.2004.10.030.

Part of this work was supported by MINECO-FEDER CTQ2015-71794-R.