Spectroelectrogravimetry of the electrical conductivity activation in poly(o-toluidine) films
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ORIGINAL PAPER
Spectroelectrogravimetry of the electrical conductivity activation in poly(o-toluidine) films Esteban Guillén 1 & Amparo Ferrer 1 & Jerónimo Agrisuelas 1
&
José J. García-Jareño 1 & Francisco Vicente 1
Received: 2 June 2020 / Revised: 2 July 2020 / Accepted: 3 July 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The study of the first stages of the transformation of conducting films from the insulating to the conducting form by oxidation is essential to understand the electrical conductivity activation of these kinds of films. This work examines this process induced by cyclic voltammetry in poly(o-toluidine) (POT) films synthesized in H2SO4 solution. In situ electrochemical quartz crystal microbalance (EQCM) and vis-NIR spectroscopy provide singular information complemented with the global response of current. We propose an electrochemical mechanism for the POT electrical conductivity activation by correlation of mass and spectroscopic data. On the one hand, anions are inserted during the formation of conducting polarons (PC), which have a spectral signal at 840 nm. On the other hand, protons are expulsed when the isolated polarons (P*) detected at 420 nm are oxidized. Keywords Conducting polymers . Poly(o-toluidine) . Electrical conductivity activation . Electrochemical quartz crystal microbalance . Spectroelectrochemistry
Introduction Conducting polymers (CPs) are smart materials used in different fields and technological applications such as sensors, supercapacitors, or electrochromic devices [1–6]. During electrochemical reactions, the electron transfer at the electrode|film interface leads to an increase of positive or negative defects in the polymeric structure, which are compensated by the exchange of ionic species to keep the electroneutrality [7, 8]. Simultaneously, structural changes such as conformational movements of the polymeric chains, swelling, shrinking, compaction, and relaxation processes induced by the electrochemical reactions can implicate the solvent transfer. Consequently, the voltammetric response of the film during the first half-cycle to the conductive state differs from the successive voltammetric profiles of the relaxed and activated film. This phenomenon is known as “first cycle effect,” “aging,” “slow relaxation,” “conformational relaxation,” or “memory effect,” and it is important for the fabrication of
* Jerónimo Agrisuelas [email protected] 1
Departament de Química Física, Universitat de València, C/ Dr. Moliner, 50, 46100, Burjassot, València, Spain
devices based on these polymers such as artificial muscles [9]. During the relaxing process, structural and molecular properties observed with several techniques often depend on the time the film is maintained in the insulating form (packing time or aging time) [10, 11]. Polyaniline and derivatives are one of the most investigated CPs [12–15]. Despite the considerable advances on the knowledge of the electrochemical reactions in this family of CPs, it is still generally assumed
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