[Show abstract][Hide abstract] ABSTRACT: In this paper, we investigated the effect of light driving force induced surface deformation on azobenzene-containing polymers. The surface deformation is attributed to light-induced mass migration inside the polymers. Circular cap arrays are firstly fabricated by high power laser ablation via polarization controlled three-beam interference. The circular caps are subsequently exposed to polarization controlled two-beam interfering field. The results illuminate that when the interfering laser beams are both set to P polarization, the circular caps are deformed. While the laser beams are of other interfering modes like (S, S) and (+45° , -45°), the caps are seldom deformed. The circular caps are also exposed to single intensity-homogeneous linearly polarized laser beam. The deformation of the caps keeps the same direction as the irradiating polarization. A model based on the focusing effect of the circular caps is addressed to explain the origin of the light driving force for mass migration in azopolymers. The all-optical approach for the production of deformed caps can be used to generate aspherical lens, which may be applied to many domains.
Full-text · Article · Aug 2011 · Physical Chemistry Chemical Physics
[Show abstract][Hide abstract] ABSTRACT: 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 5.6wt%. 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 5.6wt% 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 5.6wt% Ag can be observed with writing power as low as 6mW and no such an image can be observed in the azopolymer without Ag under the same two-photon recording condition.
[Show abstract][Hide abstract] ABSTRACT: In this paper, we report the localized surface plasmon resonance of silver nanoparticles on the photo-induced alignment properties of azopolymers. Two series of azopolymer films doped with silver nanoparticles (SNPs) were prepared with different contents of SNPs, in which two side chain azopolymers, with cyano group (AzoCN) and methyl group (AzoCH3) as substitutes, respectively, were designed and synthesized because of the different interaction between SNPs and each kind of substitute. Tapping-mode atomic force microscope imaging was used to characterize the distribution of SNPs in azopolymer films, from which it was found that in AzoCN film SNPs were almost uniformly distributed, whereas in AzoCH3 film several decades of single SNP aggregated into a cluster. Photo-induced alignment of azopolymer films doped with SNPs was performed under irradiation of linearly polarized light at 442 nm. The experimental results reveal that there is an obvious difference in photo-induced alignment behavior between two series of azopolymer films. For AzoCN, the alignment rate decreased with the increase of SNPs concentration, and when the SNPs' concentration achieved 0.24% the ratio of alignment rate reached the minimum, about 77% of that of the undoped sample. For AzoCH3, the alignment rate increased along with the increase of the content of SNPs, showing that the alignment rate, at least for “fast” process, could be enhanced by doping SNPs. This phenomenon resulted from localized surface plasmon resonance of SNPs and was also found to be affected by the chemical structure and the condensed state of azopolymers doped with SNPs.
[Show abstract][Hide abstract] ABSTRACT: Three series of amorphous copolymers containing azobenzene groups with various substituents and certain amounts of crosslinkable acrylic groups were prepared. The cross-linked polymer films were obtained by thermal polymerization of the acrylic groups in the copolymers, during which, by controlling the time of cross-linking reaction, the films can be made with different cross-linking degree (from 0 to 32%, which was monitored by FT-IR spectra measurement). Photo-induced alignment process of the films was performed under irradiation with linearly polarized light at 442 nm, and the effect of cross-linking degree on the photo-induced alignment rate was investigated. The dynamics of the photo-induced alignment was analyzed with biexponential curve fitting. The photo-induced alignment rate and the maximum transmittance of the films decreased because of the cross-linking. Furthermore, for the cross-linked samples, it was found that their saturated value of transmittances keep constant after repeated 'writing' and 'erasing' cycles. The findings reveal that the cross-linking of the film can effectively restrain the phototactic mass transport of azopolymer during irradiation by polarized light. The relationship between the cross-linking degree and the photo-induced alignment behavior of azopolymer is discussed in detail.
No preview · Article · Dec 2008 · Chinese journal of chemical physics
[Show abstract][Hide abstract] ABSTRACT: We demonstrate a new strategy for improved stabilization of polydiacetylene micelles. They show temperature-induced color 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 °C and the pH range between 5.6 and 9.6.
[Show abstract][Hide abstract] ABSTRACT: Pure polarization grating without surface topology on crosslinked azopolymer film was fabricated upon exposure to an interference pattern of orthogonal linearly polarized beams from a He–Cd laser without any subsequent processing steps. The grating structure was investigated using atomic force microscopy and polarization optical microscopy. A regular spaced grating but without surface relief was observed. The grating was stable at ambient conditions and can endure repeated writing–erasing processes. The interference mode of writing beam had a significant effect on grating formation and was investigated by using the two patterns of orthogonal linearly polarized beams (polarization-modulated mode) and parallel linearly polarization beams (intensity-modulated mode). The effect of material crosslinking was also studied by comparing the surface relief depth on the grating formation process between crosslinked and non-crosslinking azopolymer films. Experiment results demonstrated that the surface relief grating was observed on non-crosslinking azopolymer film. For intensity-modulated interference mode, whatever crosslinked and non-crosslinking azopolymer films, the surface relief gratings were fabricated.
Full-text · Article · Aug 2008 · Optical Materials
[Show abstract][Hide abstract] ABSTRACT: Two azopolymers (DACENO2 and DACEOCH3) with a special structure were designed and synthesized. The azopolymer films doped with the lanthanide complex Eu(TTA)3Phen were prepared by a casting method with a mixed solution of the azopolymer and lanthanide complex. UV-vis spectra show that the absorption peaks of the predesigned azopolymers DACENO2 and DACEOCH3 are separated from that of Eu(TTA)3Phen. Under this circumstance, the photo-induced anisotropy of the films could not be destroyed by excitation and emission during fluorescence measurements. Polarized luminescence of both oriented films was observed with polarization ratios of 3.0 for the DACENO2–Eu(TTA)3Phen film and 2.7 for the DACEOCH3–Eu(TTA)3Phen film at 613 nm, respectively. The luminescent properties of the film were 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 work revealed that the polarized luminescence from the azopolymer film doped with a lanthanide complex can be controlled by the extent of photo-induced alignment.
[Show abstract][Hide abstract] ABSTRACT: A series of polymer films containing azo groups and silver nanoparticles were prepared. Photo-induced reorientation of the film was conducted under irradiation of polarized light with wavelength at 365 nm, 442 nm and 532 nm, respectively. The influence of the concentration of dopant silver on the reorientation of the azo groups was studied. An enhancement of about 50% for the reorientation rate and about 70% for the reorientation amplitude was achieved. From a comparison of the enhancement obtained by irradiating with three different light sources, it was realized that the mechanism for enhancement of reorientation of azo groups is due to plasmon resonance of silver nanoparticles doped in the polymer films.
No preview · Article · Jun 2007 · Thin Solid Films
[Show abstract][Hide abstract] ABSTRACT: A cross-linked azopolymer with high optical and thermal stability was prepared. A pure polarization grating without surface topology was fabricated from cross-linked azopolymer by polarization holography by use of orthogonal linearly polarized beams from a He-Cd laser with a power density of 60 mW/cm(-2). The surface relief structure was investigated by atomic-force microscopy, and the polarization grating was observed by polarization optical microscopy. The grating spacing is 1.5 microm. The grating is stable at room temperature and can endure repeated writing-erasing.