Photoinduced chirality in azopolymer-based nanocomposites with different TiO2 nanoparticles concentrations

Abstract

After its discovery, photoinduced chirality in azopolymer materials has been studied with growing interest because of its potential applications. According to our previous investigations, it is possible to induce chirality in an amorphous azopolymer with a high linear photoanisotropy by illumination with elliptically polarized light. In the present work, we studied the photoinduced chirality in thin nanocomposite films based on the azopolymer poly[1-[4-(3-carboxy-4-hydroxyphenylazo)benzenesulfonamido]-1,2-ethanediyl, sodium salt], shortly PAZO, doped with TiO2 nanoparticles with a size of about 20 nm. The thickness of the prepared films was approximately 550 nm and the concentration of the nanoparticles varied from 0 to 3 wt. %. A He-Cd laser beam (λ = 442 nm) was used, with the input ellipticity varying from –1 (left circularly polarized) to +1 (right circularly polarized). The ellipticity was set using a quarter-wave and a half-wave plates. We studied the dependences of the output ellipticity and the angle of self-rotation of the polarization azimuth on the input ellipticity. Based on the experimental data obtained, we could analyze the dependence of the self-rotation of the polarization azimuth on the concentration of the nanoparticles. The results show that small concentrations of nanoparticles lead to an enhancement of the self-rotation, hence, the chirality.