Titania-PMMA nanohybrids of enhanced nanocrystallinity

Abstract

Nanohybrid thin films consisting of titania nanoparticles embedded in a suitable polymer matrix represent a new class of functional materials for optoelectronic applications. For instance, our previous studies show that titania-poly(methylmethacrylate) or TiO2-PMMA nanohybrids derived from in situ sol-gel technique are promising as nonlinear optical materials since they can demonstrate a very fast recovery time of ∼1.5 picosecond and a large third-order nonlinear susceptibility, χ(3) up to 1.93 × 10-9 esu, as observed by pump-probe and Z-scan techniques. However, it was realized that the conventional in situ sol-gel technique employed led to a largely amorphous TiO2 phase in the PMMA matrix. In order to overcome this limitation, we have performed two modification approaches making use of high pressure water vapor, i.e.: pre-and post-hydrothermal treatments applied on the sol-gel precursors. The degree of TiO2 crystallinity in the resulting nanohybrids was studied by XRD, FTIR, and TEM. Both approaches can enhance the nanocrystallinity TiO2 phase considerably and at the same time preserve the integrity of polymer matrix. It was found, however, that while the nanohybrid thin films derived from the pre-hydrothermal treatment show a high absorption in the visible length, those derived from the post-hydrothermal treatment are highly transparent. Nonlinear optical measurement using the Z-scan technique on the latter sample shows a significant enhancement in χ(3) as high as 5.27 × 10-9 esu. © Springer Science + Business Media, LLC 2006.