Polymer‐TiO2 Nanocomposites: A Route Towards Visually Transparent Broadband UV Filters and High Refractive Index Materials

Abstract

Colloids of TiO 2, where rutile was the only crystal modification which could be detected, with ca. 2.5 nm average particle diameter were synthesized by hydrolysis of TiCl 4 in acidic solutions. The as‐prepared particles were incorporated in polymers such as poly(vinyl alcohol) (PVAL), partially hydrolyzed poly(vinyl acetate) (PVAC88), polyvinylpyrrolidone, and poly(4‐vinylpyridine). Nanocomposites transparent in the visible range were obtained. The highest TiO 2 contents in such materials were achieved with PVAL and PVAC88, with TiO 2 contents of ca. 35 wt.‐% (i.e. 10.5 vol.‐%). In particular, the nanocomposites with TiO 2 contents above 24 wt.‐% acted as efficient UV filters for radiation up to ca. 360 nm. At very low TiO 2 contents, an absorption maximum of the embedded TiO 2 particles was observed at 225 nm with an extinction coefficient of 140 000 cm−1 and a full width at half maximum of 45 nm, i.e. not only the absorption at the maximum at 225 nm but also at the flank of this band contributed significantly to the broadband UV absorption in the nanocomposites at higher TiO 2 fractions. The incorporation of TiO 2 enhanced the refractive index of the nanocomposites: for instance a refractive index of 1.609 was measured for a nanocomposite comprising 10.5 vol.‐% TiO 2 in PVAL, compared with 1.521 for the pristine polymer. TEM image of a section of a nanocomposite of poly(vinyl alcohol) and 11 wt.‐% TiO 2 (appearing dark). magnified imageTEM image of a section of a nanocomposite of poly(vinyl alcohol) and 11 wt.‐% TiO 2 (appearing dark).