Electrochemical study of charge transfer in conducting polymers

Abstract

Aspectos cinético e termodinâmico da transferência de carga em polímeros condutores foram investigados. Um modelo de difusão restrita foi impregado para interpretar os da dos obtidos por cronopotenciometria com pulso. Em filmes de poli 3-metiltiofeno, o coeficiente de difusão aparente diminuiu em função da espessura do filme mas ficou constante com a concentração eletrolítica. Em filmes finos, usando-se voltametria cíclica, caracterizou-se mudanças termodinâmicas, como em par tic u lar, a deconvolução das duas transferências eletrônicas envolvidas no processo. Usando-se um modelo nernstiano incluindo potenciais de interação, conseguiu-se descrever a reação para as duas etapas eletroquímicas. Finalmente, como esperado, uma correlação en tre o raio iônico dos dopantes e o coeficiente de difusão aparente foi estabelecida em filmes de polipirrol.The ki net ics and ther mo dy namic as pects of charge trans fer in con duct ing poly mers were in ves ti gated. A re stricted dif fu sion model was used to an a lyze ki netic data ob tained from pulse-chronopotentiometric ex per i ments. In poly 3-methylthiophene, the ap par ent dif fu sion co ef fi cient de creased with the film thick ness, whereas it re mained con stant with the elec tro lyte con cen tra tion. In thin films, ther mo dy namic changes were char ac ter ized by cy clic voltammetry, spe cif i cally, the deconvolution of the two elec tronic trans fers in volved in the pro cess. Using a Nernstian model in clud ing in ter ac tion po ten tials, the two elec tro chem i cal steps were well de scribed. Finally, as ex pected, a cor re la tion be tween the ionic ra dius of the dop ants and the ap par ent dif fu sion co ef fi cient was es tab lished in polypyrrole films. Key words: con duct ing poly mer, charge trans fer, chronopotentiometry, dif fu sion In tro duc tionCon ducting poly mers be long to a class of quite ver satile 1 ma te ri als of in ter est be cause of their pros pect in techno log i cal ap pli ca tions 2 . The in su la tor/con duc tor tran si tion plays a fun da men tal role which mo ti vates the study of the re dox re ac tion in these ma te ri als (charge trans fer and ac cumu la tion), in or der to de ter mine pa ram e ters such as dop ing level, re vers ibil ity, or ki netic fac tors.The dif fi culty in un der stand ing the prop er ties of these ma te ri als co mes from the fact that the work is usu ally carried out on poly mers with vari able struc tures, us ing dif ferent char ac ter iza tion tech niques, some of which are not very suit able for these pur poses. It is gen er ally rec og nized that in all kinds of con duct ing poly mers the oxido-reduction reac tion is equiv a lent to a two-step elec tro chem i cal pro cess that does not fol low the Nernst model. It is com monly attrib uted to high intersite in ter ac tions and other non-ideality fac tors 3 . On the other hand, it is also known that a sim ple ki netic model of dif fu sion does not ex actly fit the dop ing pro cess of the electroactive films. This is mainly be cause the poly mer suf...

Conducting Polymers for the Design of Tactile Sensors

“…Some studies concluded that the ionic diffusion coefficient decreases with the thickness of the polymer film, and it is slightly influenced by the electrolyte concentration. Focusing on the cationic doping of Ppy, it was possible to observe a change in the diffusion speed as a function of the ionic radius of the dopant [ 83 ]. Such a conclusion was obtained despite different polymerization methods, namely, galvanostatic, potentiostatic, and potentiodynamic, being applied for Ppy layer production.…”

“…Pulsed current polymerization undoubtedly leads to more compact and adherent films. It was found that the reversibility of the redox process of the films decreased, and the thickness could not be simply related to the polymerization charge [ 83 ]. This observation is very important for different applications of conducting polymers, especially for sensors, where a thin and compact layer of polymer is needed.…”

Desenvolvimento e aplicação de células eletroquímicas em camada delgada

“…Ilustra-se a seguir, na Figura 4, o efeito de K 0 sobre a reversibilidade um processo quasi-reversível. partir dos dados voltamétricos obtidos à baixa velocidade de varredura de potencial 14 , os dados cronopotenciométricos podem ser ajustados usando-se as equações acima, o que permite a determinação de D ap .…”

Biomimetic Dual Sensing-Actuators Based on Conducting Polymers. Galvanostatic Theoretical Model for Actuators Sensing Temperature

“…Several attempts exist for the description of voltammetric responses to cyclic potential sweeps − or for chronoamperometric responses to potential steps. − Chronopotentiometric responses have been modeled from impedance results using equivalent electrical circuits. , As far as we know, only Micka et al tried to propose a self-supporting model (without adjustable parameters) for polyacetylene oxidation based on the empirical dependence of the electrical conductivity and the stationary potential on the degree of doping, not considering experimental chemical variables. The evolution of the potential at open circuit was studied by Pernaut et al employing pulse chronopotentiometric experiments and concepts from diffusion …”

“…The evolution of the potential at open circuit was studied by Pernaut et al employing pulse chronopotentiometric experiments and concepts from diffusion. 63 In this paper we propose an initial physicochemical approach to the description of the actuating-sensing properties of conducting polymers, materials, and devices, working under galvanostatic control. Theoretical and experimental results will be presented for self-supported polypyrrole responses at different temperatures and compared with those existing for artificial muscles sensing temperature (the actuator, an artificial muscle, sense ambient temperature) while working.…”