Photo-responsive Azopolymer Composites: Fabrication And Properties

In this thesis, several kinds of photo-responsive azopolymer-based composites are designed and fabricated. The stability, optically rewritable property and optical recording density of azopolymers in these composites are improved. New functionalities such as photo-controllable polarized luminescent properties, dual photochromism and photo-induced morphological transition are also observed in these composites. The contents of this thesis are as follows:1.The introduction of properties of azobenzene and composite materials.2.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.3. Extremely stable, high-density information storage media are prepared by connection of two azobenzene groups via hydrogen bonding to form supramolecular bisazopolymers. The supramolecular bisazopolymers contain 4-((4-hydroxyphenyl)diazenyl)benzonitrile (AzoCN) as a hydrogen bonding donor and poly(6-(4-(pyridin-4-yldiazenyl)phenoxy)hexyl methacrylate) (pAzopy) as a hydrogen bonding acceptor. High quality films of the supramolecular bisazopolymers pAzopy/(AzoCN)x (x=0.25,0.5,0.75,1.0) with different molar ratios of donor/acceptor are prepared by spin-casting. The supramolecular bisazopolymers spontaneously form lamellar structures with a periodic thickness of 7.1 nm. These samples exhibit optically induced birefringence. The birefringence and proportion of remnant birefringence increase from 0.0265 to 0.1 and 50.5% to 108%, respectively, as the content of AzoCN in the samples increases, which indicates a larger proportion of AzoCN enhances both the birefringence and its stability. We also use an azopolymer without pyridine groups (pAzoCH3) and AzoCN to do a control experiment, which shows that pAzoCH3/(AzoCN)10 do not show significant enhanced birefringence and its stability. The enhancements in pAzopy/(AzoCN)x are because of the unique structure of the supramolecular bisazopolymers. A new laser direct writing system has been developed for optical recording on the azopolymers. The pAzopy/(AzoCN)10 film is significantly better at image recording than the pAzopy film, because the optically recorded images on the pAzopy/(AzoCN)10 film are very clear after storage for four months whereas the optically recorded images on the pAzopy one disappear after just one day. Four-dimensional optical recording has been achieved by integrating the polarization and the intensity of the laser and the two dimensions of a plane. An information density of about 0.93 Gbit cm-2 could be optically recorded on the pAzopy/(AzoCN)10 film, which is about 20 times the information density of a normal DVD.4. We demonstrate photoinduced modulations of polarized fluorescence of a rare earth complex in azopolymer matrices.Two azopolymers (DACENO2 and DACEOCH3) with special structure are designed and synthesized. The azopolymer films doped with lanthanide complex Eu(TTA)3Phen are prepared by the casting method with the mixed solution of the azopolymer and lanthanide complex. UV-vis spectra shows absorption peaks of the predesigned azopolymers DACENO2 and DACEOCH3 are separated from that of Eu(TTA)3Phen. Under this circumstance, photo-induced anisotropy of the films could not be destroyed by excitation and emission during fluorescence measurement. Polarized luminescence of both oriented films is observed with polarization ratio 3.0 for DACENO2/Eu(TTA)3Phen film and 2.7 for DACEOCH3/Eu(TTA)3Phen film at 613 nm, respectively. The luminescent property of the film is found to be affected by the chemical structure of the azopolymer, the extent of the photo-induced alignment and the angle between the orientated direction of the film and the direction of the polarizer. All the results from this wok. reveal that the polarized luminescence from the azopolymer film doped with lanthanide complex can be controlled by extent of photo-induced alignment.5. Hydrogen bonding complex of a diacetylene TDA (10,12-tricosadiynoic acid) and an azopolymer pAzopy (poly(6-(4-(pyridin-4-yldiazenyl)phenoxy)hexyl methacrylate)) are prepared. TDA can be polymerized and become corresponding polydiacetylene pTDA in the hydrogen bonding complex. The morphology of the polymerized hydrogen bonding complex pAzopy/pTDA is different from both the hydrogen bonding donor pTDA and the hydrogen bonding acceptor pAzopy. We find that pTDA affect the photoisomerization of pAzopy.6. We demonstrate a new strategy for improved stabilization of polydiacetylene micelles. They show temperature induced colour changes, which are fully reversible even at varying pH. A novel azo chromophore functionalized amphiphilic diacetylene molecule is synthesized and used to prepare self-assembled cylindrical micelles. The micelles can be polymerized by 254 nm light irradiation. The azo chromophores form H- and J-like aggregates in the polydiacetylene micelles and increase the stability of the micelles, which leads to fully reversible thermochromism of the micelles in the temperature range between 20℃and 90℃and the pH range between 5.6 and 9.6.7. We investigate the effects of solvents on structure, morphology and photophysical properties of micelle-like assemblies of an azo chromophore-functionalized polydiacetylene (polyAzoDA) and polymerized tricosa-10,12-diynoic acid (polyTDA) for comparison. Using mixtures of water with glycol, DMSO, ethanol and THF, we systematically vary the solubility parameters and observe blue-to-red color changes of polydiacetylenes. Teas plots are used to estimate the strength of polymer-solvent interactions and explain the properties of polyAzoDA supramolecular assemblies in different solvent environments. In poor solvents, polyAzoDA forms rod-like micelles and the photoisomerization is strongly hindered by the aggregation of azo chromophores. At increasing content of organic solvents, polyAzoDA becomes gradually swollen, as indicated by the onsets of blue-to-red color changes, starting trans-cis isomerizations of the azo groups, and changes of the structures as seen in SEM images. At large ethanol content, we observe that photoisomerization of azobenzene groups induces a morphological transition and a color change of the polydiacetylene backbone.