Star-like polyaniline : synthesis, layer-by-layer assembly and electrochromism
Date of Issue2011
School of Materials Science and Engineering
Electrochromism is a phenomenon related to reversible color transformation of a material produced by the application of an external electric field. Electrochromic contrast and switching speed are the key performance indicators for an electrochromic material. The motivation of this work is to make use of cyclotriphosphazene (CP) and polyhedral oligomeric silsesquioxane (POSS) to synthesize novel star-like electrochromic conjugated polymers and study the synergistic effect of star-like structure and film fabrication techniques on electrochromic properties. Firstly, a new series of electrochromic hexa(4-aminophenoxy) cyclotriphosphazene-polyaniline copolymers (HACP-PANI) were synthesized. Dodecylbenzenesulfonic acid (DBSA) doped 4.0%HACP-PANI (4%HACP-PANI/DBSA) exhibits a significant enhancement in electrochromic contrast as compared with DBSA-doped homopolyaniline (PANI/DBSA). The contrast enhancement can be attributed to the easier diffusion of cations in the film of 4%HACP-PANI/DBSA, as evidenced by a significant increase in ionic conductivity, whereas the switching speed of 4%HACP-PANI/DBSA is not improved significantly due to the excessive external dopants. In order to avoid using excessive amounts of doping acid, HACP-PANI and POSS-PANI copolymers in emeraldine base form were synthesized and fabricated into multilayer thin films with poly(2-acrylamido-methane-2-propanesulfonic acid) (PAMPS) via layer-by-layer (LbL) assembly. However, the contrast and switching kinetics of 4%HACP-PANI/PAMPS is not improved compared with those of PANI/PAMPS under dynamic switching because of its densely packed structure brought by the flexible -O- linkage in HACP-PANI.