Fabrication and optical properties of dichroic polarizing films based on poly(vinyl alcohol)-heteropolyacid nanocomposites

Abstract

We report on a new type of poly(vinyl alcohol)(PVA)-based dichroic polarizing films whose visible dichroism is due to long-chain linear polyenes, –(CH=CH)n–, formed in the course of acid-catalyzed thermal dehydration of the polymer. The distinguishing feature of these films is that the solid acid catalyst (12-tungstophosphoric acid, TPA) is used instead of the liquid ones. Thin PVA films with embedded TPA nanoparticles were fabricated by solution casting technique. Subsequent stretching and annealing of these PVA/TPA nanocomposites produced PVA–polyene/TPA dichroic polarizing films with the thickness below 10 µm. Transmission electron microscopy, Fourier-transform infrared spectroscopy, and UV–Vis spectroscopy techniques were used to characterize the films at various stages of preparation. The fabricated polarizing films showed polarization efficiency exceeding 94% and transmittance higher than 40% in the visible range. The polarizing properties of the films did not deteriorate upon prolonged exposures to hot humid air (60 °C, 90% RH) and high temperature (90 °C). The nanocomposite polarizing film proposed in this study may have application potential in thin and flexible optoelectronic devices that must operate under harsh environmental conditions.