Ag nanoparticle/azopolymer nanocomposites: In situ synthesis, microstructure, rewritable optically induced birefringence and optical recording

Ag nanoparticle/azopolymer nanocomposites are prepared with controlled concentration of Ag nanoparticles by in situ reduction of Ag(I) β-diketone complexes in an azopolymer matrix. The nanocomposites form an organic-inorganic network-like structure by interactions between the azopolymer matrix and the Ag nanoparticles. The Ag/azopolymer nanocomposites are homogeneous and highly transparent even when the content of Ag is as high as 5.6 wt%. Birefringence of the azopolymer without Ag and the nanocomposites can be optically induced and erased. However, after 5 cycles of optically writing-erasing processes, 9.7% decrease of the birefringence is observed for the azopolymer film without Ag and only 2.9% decrease of the birefringence is observed for the nanocomposite film with 5.6 wt% Ag, showing the stability of photo-induced birefringence of the nanocomposite is improved by introducing Ag nanoparticles into the azopolymer matrix. Relatively high concentration of Ag nanoparticles does not strongly hinder the mobility of azobenzene groups during photoisomerization and one-photon recording. In two-photon optical recording experiments, an image on the nanocomposite with 5.6 wt% Ag can be observed with writing power as low as 6 mW and no such an image can be observed in the azopolymer without Ag under the same two-photon recording condition.