Structural, morphological and spectroelectrochemical characterization of poly (2-ethyl aniline)

Journal of the Brazilian Chemical Society

Schemid, Andreia L.¹  Universidade Federal de São Carlos, São Carlos, Brazil¹  Torresi, Susana I. Córdoba de¹  Universidade de São Paulo, São Carlos, Brazil¹  Carlos, Ivani A.¹  Bassetto, Alessandra N.¹  Universidade de São Paulo, São Paulo, Brazil¹ 

关键词: polyaniline;    poly(2-ethylaniline);    spectroelectrochemistry;    DSC;    SEM.;   

DOI  :  10.1590/S0103-50532000000300020

学科分类：化学（综合）

来源: SciELO

【 摘 要 】

Conducting organic polymers have shown great potential for many applications, including rechargeable batteries, corrosion protection, light emitting diodes, molecular sensors, electrochromic devices and gas separation membranes1-6. For these applications, the polymers must be highly processable and chemically stable for long periods of time. Polyaniline (PANI) has been one of the most widely studied conducting polymers because of its chemical and oxidative stability. However, as it is common with other conjugated polymers, polyaniline is limited by poor thermal processability and solvent solubility7.Improved solubility can be achieved by introducing bulky alkyl substituents into the polyaniline backbone, but limitations are then imposed on the conductivity of the polymer produced. The conductivity of polyaniline and the solubility of substituted polyanilines can be achieved by copolymerization. A deep knowledge of the electrochemical properties and the study and characterization of the homopolymers is a very important path to find the route to synthesize copolymers with tailored properties.Polymeric films present many complicated mechanistic aspects due to electronic transfer through the film specially to sites which are far from the polymer/substrate interface. The movement of polymeric chains to allow the accommodation of different species like ions and solvent molecules inside the film, is very important. The form of the voltammograms strongly depends on counterion, solvent, thickness, etc., so a wide variety of E/i profiles have been found8.Kaufman et al.9 have proposed a model for charge transportation through polymeric films in the sense that propagation of charge takes place by auto exchange electronic reactions among oxidized and reduced species positioned at neighboring sites in the film. This model has been also suggested for PANI films in a recent paper10 dealing with the optical behavior of poly(2-ethyl aniline) films. It has been shown that a large substituent like ethyl and the chemical nature of the counterion are very important parameters in determining the energy of the electronic bands of PANI films. The presence of the substituent significantly perturbs the geometry of the chains, leading to a hypsochromic shift of the polaronic absorption band. It has been shown, that depending on the size of the counterion, the presence of an alkyl group in the ortho position influences the participation of this anion in the ionic exchange process due to steric hindrance. The electron-donating effect of the ethyl substituent is completely disregarded in comparison to the steric effect that produces an increase of the torsion angle between phenyl rings. The electronic effect is important in the second oxidation process and it is evidenced by the diminution of the redox potential of the emeraldine/pernigraniline couple.In this paper, a comparative structural and morphological study of poly(2-ethyl aniline) and polyaniline is presented. Besides, in order to reach a better understanding of the electrochromic phenomena of these materials, monochromatic absorption curves were obtained at different wavelengths, simultaneously with voltammetric recordings. By differentiating the absorption curves, it was possible to relate each electrochemical process with their absorption bands. This analysis is specially useful in the

【 授权许可】

Unknown