White polyaniline as a time display: Reaction of polyaniline with gaseous oxygen

Electrically non-conductive ʹwhiteʹ polyaniline (WPANI) was obtained by the following successive processes: (A) polyaniline was prepared on the electrode by electro-oxidation of 0.5 M (l M = 1 mol dm−3) aniline in 2M HBF4 solution; (B) the polyaniline electrode was polarized in 2M HBF4 solution at −0.2 V (versus SCE); (C) the electrode was immersed in 2M HBF4 solution containing 1M hydrazine for 24h; (D) the electrode was treated with 30% hydrazine solution for 24h. The obtained WPANI film became gradually violet on exposure to air. The degree of the coloration increased linearly with the logarithm of the exposure time, and the film functioned as a time display. The coloration rate was probably related to the electron transfer between the original WPANI and the WPANI oxidized by the adsorbed oxygen.