Photochromism of Tungsten Oxide Film prepared by Sol-Gel Process II

Abstract

In the previous paper, we reported that efficiency of photochromism (PC) of amorphous tungsten oxide film was increased by lamination of PVA layer.
In this paper, we found the other some water soluble polymers ; polyacrylic acid (PAA), polyethylene glycol (PEG) and polyvinyl pyrrolidone (PVP) were effective for PC of tungsten oxide film by lamination of them. Among these polymers, PVP showed prominent PC efficiency.
Furthermore, we found that PVP did mix directly with H₂WO₄ sol freely. Tungsten oxide film made by this direct mixing was also very effective for PC and showed a stable repetition of coloration and of decoloration characteristics. An adequate adding PVP quantity for PC was found.
We paid attention to 2-pyrrolidone that was the side chain of PVP. PC of amorphous tungsten oxide film made by direct mixing of 2-pyrrolidone showed same behavior as that of PVP. As increasing mole ratio of 2-pyrrolidone for mol of WO₃, PC efficiency was improved up to around 0.3, over that enfeebled. It was found by AFM inspection that the grain size of amorphous tungsten oxide was controlled by addition of 2-pyrrolidone, the more mole ratio of 2-pyrrolidone, the less grain size. We recognized through FT-IR spectrum that tungsten oxide was linked to 2-pyrrolidone by hydrogen bond. A mechanism for coloration of tungsten oxide with 2-pyrrolidone was proposed.