Electrochromic Properties of Polyaniline-Based Hybrid Organic/Inorganic Materials

Abstract

Hybrid materials based on polyaniline (PAni) were obtained by in situ polymerization of aniline with chitosan and/or organically modified clay (nanomer I-24) in HCl. The samples were characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM) and direct current (DC) electrical conductivity. Thin films of PAni, PAni-clay, PAni-chitosan and PAni-chitosan-clay were prepared by casting a solution of each sample in N-methyl-2-pyrrolidone (NMP) onto indium tin oxide (ITO)/glass electrodes and their electrochromic properties were investigated. It was observed color variation from transparent yellow in the reduced state (E = −0.2 V vs. Ag/AgCl), green in the intermediate state (E = 0.5 V) and dark blue in the oxidized state (E = 0.8 V) for all samples. The color changes of each material in function of the applied potential were tracked using the Commission Internationale de l'Eclairage (CIE) system of colorimetry, in which the color change was much more significant for PAni-clay film.Keywords: conjugated polymer, hybrid material, polyaniline, chitosan, organophilic clay IntroductionConjugated polymers have attracted the attention of academia and industries mainly because of their electrical, magnetic, and optical properties, which make them useful for applications in organic optoelectronic devices. Currently, the development of new hybrid materials based on conjugated polymers have afforded materials with excellent characteristics for application in organic light emitting diodes (OLEDs), 1,2 organic field effect transistors (OFETs), 3 organic solar cells (OSCs), 4 and electrochromic devices (ECDs). [5][6][7] Electrochromic materials based on conjugated polymers show many interesting properties such as multicolor, fast switching speed, flexibility and easy to optimize their properties through molecular tailoring. 8,9 Among the organic polymeric electrochromic materials, polyaniline (PAni) has been widely studied due to many advantageous properties including high optical contrast (∆%T), environmental stability, easy synthesis, as well as comparatively low cost.8 Furthermore, the high pseudocapacitance arising from the versatile redox reactions and its corresponding color changes make PAni promising candidate for electrochemical capacitors 10,11 and ECDs. 12,13 However, the difficulties in processing of PAni into films due to its very low solubility in most of the available solvents and the relatively poor mechanical properties decrease its performances and utilities in such applications.Despite PAni can be synthesized by chemical 14 or electrochemical 15 polymerization methods described in the literature, PAni films with good mechanical properties and adherence to a surface are not usually achieved from the conventional chemical methods of synthesis, which yield PAni as an insoluble and infusible bulky powder. 16 In order to increase the processability and mechanical properties of PAni, significant efforts have been done in preparation of blends based on PA...

Polyaniline-based electrospun polycaprolactone nanofibers: preparation and characterization

“…PAni was synthesized according to the method described by Silva et al [10] , in which 1.0 mL of freshly distilled aniline was dissolved in 10.0 mL of 1.0 mol L −1 HCl and the solution was cooled to −10 °C in an ice, NaCl and ethanol bath. Then, a solution containing 3.0 g of (NH 4 ) 2 S 2 O 8 dissolved in 40 mL of 1.0 mol L −1 HCl was slowly poured into the monomer solution, under vigorous stirring.…”

“…The FTIR spectra of neat Pani, electrospun PCL, and PCL/PAni mats are presented in Figure 4. The PAni FTIR spectrum shows the characteristic bands at 1584 cm -1 and 1488 cm -1 , which are assigned to the stretching vibration of quinoid rings and the stretching mode of benzonoid rings [9,10,34] , respectively. The bands at 1321 cm -1 refer to C-N stretching bonds of secondary amine group [35] , whilst the bands at 1158 and 829 cm -1 are attributed to the in-plane C-H bending of quinoid structure and the out-of-plane bending of C-H bonds in the aromatic ring.…”

“…However, the processability of PAni to produce films or fibers is rather difficult because it is infusible and insoluble in common solvents, and thus, its practical use is limited. Significant efforts have been made in order to overcome such drawbacks and to improve the solubility, processability and mechanical properties of PAni by changing the dopant agent [7] , blending it with other polymers [8] or preparing hybrid organic/inorganic composites [8][9][10] .…”

“…Our research group has synthesized and characterized a series of PAni-based hybrid materials for application as electrochromic materials and optical sensors, and found interesting results, such as enhanced electrochromic properties with an intense color variation from yellow to green and blue in function of the applied potential, from blending PAni with chitosan with the incorporation of nanoclay fillers [9,10] . Therefore, the use of biopolymers along with PAni aroused considerable interest in the preparation of electrospun nanofibers for several applications in addition to the biological ones.…”

Clay Hybrid Materials

“…However, they can be made oleophilic by exchanging the cations with organic ions like cetyl trimethyl ammonium bromide ions or cetyl trimethyl ammonium pyridinium ions etc., producing organoclay composites or polymer clay nanocomposites (PCNs). These composites are extremely investigated in material science and find widespread applications as adsorbents for heavy metal ions [2][3][4], ceramics and thin films [5], building materials [6], photocatalysts for wastewater treatment [7,8], drug delivery vehicle [9], bio-inspired materials [10], optoelectronic devices [11], ferrofluids [12], and hydrogel clay hybrids for pesticide and nutrient retention [13].…”