Nanochromics: old materials, new structures and architectures for high performance devices

Abstract

Com o desenvolvimento da nanociência, o estudo do fenômeno do eletrocromismo desperta forte e continuado interesse devido à possibilidade de obter maiores eficiências eletrocrômicas, contrastes cromáticos, sintonização de cores e baixos tempos de resposta por meio da montagem de nanomateriais. Estas vantagens são possíveis devido à alta área superficial que os nanomateriais possuem e a enorme quantidade de moléculas orgânicas eletrocrômicas que podem ser facilmente ligadas a nanopartículas inorgânicas como TiO 2 ou SiO 2 . Somado a isto, o contato direto entre o eletrólito e os nanomateriais produz altas velocidades de transferência iônica, com a concomitante compensação de carga rápida, o que é essencial para preparar eletrodos eletrocrômicos de alto desempenho. Recentemente a técnica de deposição eletrostática camada por camada foi apresentada como uma maneira interessante de preparar diferentes arquiteturas combinando nanopartículas e polímeros. O presente trabalho mostra alguns dos últimos avanços em nanocromismo.Due to the development of nanoscience, the interest in electrochromism has increased and new assemblies of electrochromic materials at nanoscale leading to higher efficiencies and chromatic contrasts, low switching times and the possibility of color tuning have been developed. These advantages are reached due to the extensive surface area found in nanomaterials and the large amount of organic electrochromic molecules that can be easily attached onto inorganic nanoparticles, as TiO 2 or SiO 2 . Moreover, the direct contact between electrolyte and nanomaterials produces high ionic transfer rates, leading to fast charge compensation, which is essential for high performance electrochromic electrodes. Recently, the layer-by-layer technique was presented as an interesting way to produce different architectures by the combination of both electrochromic nanoparticles and polymers. The present paper shows some of the newest insights into nanochromic science. Keywords: nanochromics, nanoparticles, layer-by-layer, viologensAbbreviations ECM (ox) : electrochromic material in oxidized form; ECM (red) : electrochromic material in reduced form; CV: cyclic voltammetry; : electrochromic efficiency, defined by the relation between change in absorbance and the electric charge spent in the process; A: change in absorbance; T %: change in transmittance or contrast; : response time, the time required for a total or partial change in contrast; q: electric charge; ITO: Sn-doped indium oxide; transparent conducting material used for electrochromic measures; PB, Prussian blue: [Fe III Fe II (CN) 6 ] − , iron hexacyanoferrate; viologens: organic molecules based on 1,1-"disubstituted-4,4-bipyridinium salts"; ECP: electronic conducting polymer; MLCT; metal-ligand charge transfer; PEDOT: poly(3,4-ethylenedioxythiophene); LbL: Layer-by-Layer deposition; technique based on adsorption of alternate charged species; PANI: poly(aniline); HWCVD: hot wire chemical vapour deposition; LPEI/PB: polyethyleneimine/Prussian blue; PAH: poly(al...

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