Photoinduced Surface Relief Grating Research Articles

Photoresponsive behaviour of “T-type” azopolyimides. The unexpected high efficiency of diffraction gratings, modulations and stability of the SRG in azopoly(ether imide)

In this paper, we compare the light-induced properties of three “T-type“ polyimide containing azobenzene chromophores with the properties of their structural counterparts containing azopyridine moieties. The processes of photoinduced birefringence generation and surface relief grating (SRG) formation are efficient in azobenzene polyimides, while in the azopyridine analogues the processes are non-detectable. Density functional theory calculations performed to reveal a possible structural reason for the lack of optical response in the azopyridine materials showed a formation of intramolecular H-bonds. Azopoly(ether imide) with 2,2′-diphenylopropane structure despite relatively low chromophore content exhibited one of the highest diffraction efficiency (ca. 20%) and the largest modulation of the SRG (260 nm) as have ever been observed for azopolyimides. Two years after inscription, modulation of the SRG was still observed without a decrease in the relief depth, which is important in applications requiring long-term stability of SRGs.

Photo-triggered surface relief formation of polystyrene films based on the Marangoni flow driven by a surface photoresponsive skin layer

Surface relief gratings (SRGs) are widely investigated in azobenzene-containing polymer films. We have recently demonstrated that a photoresponsive azobenzene layer existing only at the surface of a non-photoresponsive liquid crystalline polymer film can induce mass migration by patterned UV light irradiation, resulting in the SRG structure. This process is explained by the Marangoni flow triggered by the photoinduced surface tension change of the surface layer. In this work, we newly propose that the same strategy is applicable to an amorphous polymer material of polystyrene. The results obtained here indicate that photoinduced SRG formation is expanded for general amorphous polymers.

Photoresponsive Behavior of Heterocyclic Azo Polymers with Various Functional Groups

Here, we report on efficiency of light-induced processes in a series of methacrylic polymers containing heterocyclic azo moieties covalently attached to the polymer backbone. The optical response of the polymers was investigated in experiments on photoinduced birefringence measurements and surface relief gratings inscription upon irradiation with polarized blue light. The experimental results indicate that the presence of acceptor-type (Br) substituent in the side benzene ring linked to the heterocyclic ring has a beneficial effect on efficiency of birefringence generation, while incorporation of donor-type (CH3, OCH3) substituents lowers the level of photoinduced birefringence. Moreover, the process of surface relief structure formation was successfully observed for all studied polymers. The obtained surface-modulation depth reached up to 100 nm for two out of four investigated materials. No straightforward relation between the induced azo chromophore alignment level and the efficiency of mass-transport process is observed.

Complex Dynamics of Photoinduced Mass Transport and Surface Relief Gratings Formation

The microscopic and semi-macroscopic mechanisms responsible for photoinduced mass transport in functionalized azo-polymers are far from deeply understood. To get some insight into those mechanisms on “microscopic” scale, we studied the directed photoinduced motion of single functionalized polymer chains under various types of polarized light illumination using Monte Carlo bond fluctuation model and our kinetic Monte Carlo model for photoinduced mass transport. We found sub-diffusive, diffusive and super-diffusive regimes of the dynamics of single chains at constant illumination and mostly super-diffusive regime for directed motion in the presence of the gradient of light intensity. This regime is more enhanced for long than for short chains and it approaches the ballistic limit for very long chains. We propose a physical picture of light-driven inscription of Surface Relief Gratings (SRG) as corresponding to a dynamical coexistence of normal and anomalous diffusion in various parts of the system. A simple continuous time random walk model of SRG inscription based on this physical picture reproduced the light-driven mass transport found in experiments as well as the fine structure of SRG.

Fabrication of fluorescent holographic micropatterns based on the rare earth complexes using azobenzene-containing poly(aryl ether)s as macromolecular ligands

In this work, on the basis of photoinduced surface relief gratings (SRGs) with the rare earth complexes using azo-polymers as macromolecular ligands, a series of novel materials for fabricating rewritable fluorescent two-dimensional micropatterns, whose color can be easily adjusted by changing the species of the rare earth ions, are demonstrated. The rare earth complexes are prepared using a series of poly(aryl ether)s containing azobenzene chromophores and carboxyl group as macromolecular ligands and 1,10-phenanthroline as co-ligands. The fluorescence properties of the rare earth complexes and the influence of the contents of azobenzene chromophores on the fluorescent intensity are investigated by means of fluorescence excitation and emission spectroscopy. By exposing the films of the rare earth complexes to an interference pattern laser beam, SRGs can be formed on the films. Under the excitation, fluorescent patterns of the SRGs can be observed by the measurement of fluorescence microscopy. © 2015 Wiley Periodicals, Inc. J. Polym. Sci. Part A: Polym. Chem. 2015, 53, 936–943

Properties of some azo-copolyimide thin films used in the formation of photoinduced surface relief gratings

The patterning of the free standing azo-copolyimide films under different irradiation conditions led to the uniform surface relief gratings.

Easily crosslinkable side-chain azobenzene polymers for fast and persistent fixation of surface relief gratings

A facile and highly efficient approach to achieve rapid and persistent fixation of the photoinduced surface relief gratings is described.

Controllable alignment of liquid crystals based on the surface relief gratings from a photocross-linkable organic monomer

The orientational control of liquid crystal (LC) molecules is essential for high-quality liquid crystal displays, and the photo-induced surface relief grating (SRG) is a facile and effective non-contact process. Here, SRGs with different period and depth were prepared with a photocross-linkable organic monomer 4-propyldiphenylacetylenecarboxylic acid cinnamyl ester (PDACE), and the LC alignment induced by SRG was studied. It is found that both the surface topography and the chemical nature of the surface are responsible for the LC alignment, which is strongly dependent on the groove geometry of the gratings. Furthermore, the patterned LC cell was fabricated with the patterned SRG surface. These results demonstrate that the planar, perpendicular and patterned orientations of LC can be easily photo-controllably obtained with PDACE, which have important applications in optical devices.

Photolithographic periodic patterning of gold using azobenzene-functionalized polymers

Metal micro- and nanostructures for optical and electronic applications are typically fabricated by means of interferometric optical or electron-beam lithographies using conventional photo- or electron-beam resists. In this work, we report on fabrication of periodic nanostructures of gold by exploiting photoinduced surface-relief gratings in an azobenzene-functionalized polymer film as masks for reactive ion etching of the metal. The proposed technique provides a convenient, fast and flexible alternative to photoresist-based lithography for fabricating metal nanostructures of large surface area. Owing to the fact that the azo-polymer is sensitive to the polarization rather than the intensity modulation of the exposing light, the technique is particularly suitable for patterning highly reflective surfaces.

Influence of temperature on the relaxation kinetics of spontaneous pattern formation in an azo–polymer film

The relaxation dynamics of photoinduced spontaneous surface relief gratings (SRG) printed on an azo polymer films has been investigated using pulsed exposure. The λ=532nm line of a diode-pumped solid-state (DPSS) laser is used as an inscription beam. The formation of spontaneous SRG is monitored using the intensity of the diffracted beam of a He–Ne laser (632.8nm). By switching off the recording beam, a sharp enhancement occurs, that is followed by a slow relaxation process. Surprisingly, by switching on the writing beam, a sharp decrease occurs, that is followed by an increase under further illumination. These sharp variations strongly depend on the temperature. The temperature dependence of spontaneous SRG formation is presented. The orientation and motion mechanism of azo–chormophores is enhanced by thermal effects. However, at temperatures around Tg glass transition, the mass transport vanishes.

Cyclic Main-Chain Phenylazo Naphthalene Polymers: Topological Effect on Fluorescence Emission and Photoinduced Surface Relief Grating Formation

Cyclic Main-Chain Phenylazo Naphthalene Polymers: Topological Effect on Fluorescence Emission and Photoinduced Surface Relief Grating Formation

Redox‐Active, Organometallic Surface‐Relief Gratings from Azobenzene‐Containing Polyferrocenylsilane Block Copolymers

Organometallic gratings: the ionic self-assembly of metal-containing block-copolymer polyelectrolytes and azobenzene chromophores is exploited for the efficient production of stable photo-induced surface-relief gratings. We show that feature sizes can be tuned using simple redox chemistry, and that the chromophores can be removed during plasma treatment to yield ceramic-based optical materials.

Single-layer one-dimensional nonpolarizing guided-mode resonance filters under normal incidence

We demonstrate that properly designed one-dimensional guided-mode resonance filters (GMRFs) with only one grating layer can exhibit a nonpolarizing resonant filtering effect under normal incidence. A sinusoidal profile nonpolarizing GMRF is realized by photoinduced surface-relief grating formation on thin films of polymer-azobenzene complexes and subsequent atomic layer deposition, showing the feasibility of fabrication of such compact GMRFs.

Methacrylate copolymers with substituted azobenzene side groups: synthesis, characterization and photo-induced birefringence properties

AbstractWell-defined copolymer of methyl methacrylate (MMA) and 2-methylacrylic- acid-2-{ethyl-[4-(4-methoxy-phenylazo)-3-methyl-phenyl]-amino}-ethyl ester (MAMP) bearing pendent azobenzene groups, was synthesized via reversible addition-fragmentation chain transfer polymerization (RAFT). Copolymers with different contents of azobenzene moieties, e. g. from 12 mol % to 100 mol %, were obtained by varying the feed molar ratios of MAMP and MMA. The reactivity ratios of these two monomers were measured and calculated via the modified Kelen- Tüdos method. Glass transition temperature of the copolymers was measured by differential scanning calorimetry (DSC). Photoinduced trans-cis isomerization of azobenzene moieties in the copolymer was studied at room temperature. Films cast from the functional copolymers were characterized by photo-induced birefringence and surface relief grating (SRG).

Sensing Diffraction Gratings of Antigen‐Responsive Hydrogel for Human Immunoglobulin‐G Detection

Sensing diffraction gratings of antigen-responsive hydrogel were developed for human immunoglobulin-G (H-IgG) detection. The IgG-sensing gratings were fabricated by soft lithographic duplication of photoinduced surface relief gratings on azo polymer films to the hydrogel surfaces. The quantitative detection of H-IgG was achieved by detecting modulation of the diffraction efficiency when the gratings were exposed to antigen solutions. The gratings showed high sensitivity and specificity for the H-IgG detection. The detection could be performed at a reasonably fast rate with good reusability. In the process, no fluorophore labeling or additional signal enhancement was required.

Photoinduced Surface Relief Grating Formation for a Single Crystal of 4-Aminoazobenzene

Photoinduced surface relief grating (SRG) formation for a single crystal of 4-aminoazobenzene was investigated. It was found that SRG could be inscribed on the (001) surface of the crystal, which might suggest that the photoinduced SRG formation is a general phenomenon observed for single crystals of azobenzene-based molecules as well as for azobenzene-based amorphous systems. In addition, the dependences of the SRG formation upon the orientation of the sample crystal and upon the polarization of the writing beams were found to be different from those observed for previously reported crystalline systems.

Alternating photoinduced mass transport triggered by light polarization in azobenzene containing sol-gel films

Combined shear-force and near-field optical microscopies are used for real-time monitoring of the formation of photoinduced surface relief gratings in photochromic thin films containing azobenzene derivatives. The correlated optical and topographical images provide evidence that the direction of the photoinduced matter migration is defined by the light polarization pattern and that, for a given light intensity pattern, modulating the polarization between two orthogonal states gives rise to alternating mass transport.

Photoinduced surface-relief gratings in films of supramolecular polymer–bisazobenzene complexes

We demonstrate that hydrogen-bonded polymer–azobenzene complexes, containing nonpolar bisazobenzene chromophores, yield efficient photoinduced surface-relief gratings over a wide chromophore concentration range. The efficient grating formation is thought to be enabled by the lack of spacer between the chromophores and the polymer backbone, which prevents the formation of liquid-crystalline phases even at high chromophore concentrations. The surface-modulation depth can be tuned by varying the chromophore content, and the deepest gratings (625 nm) are obtained, when every second polymer repeat unit is occupied by a chromophore. The gratings are thermally erasable by heating the samples above their glass-transition temperature, and no irreversible photodegradation of the chromophores is observed.

Fabrication of Fluorescent Holographic Micropatterns Based on Azobenzene-Containing Host−Guest Complexes

On the basis of photoinduced surface relief gratings (SRGs) with fluorophore/azo-complexes, a novel and facile method for fabricating stable and bright fluorescent two-dimensional micropatterns, whose color could be easily adjusted by changing the corresponding fluorophores, was developed for the first time.

Weak anchoring of nematic liquid crystals on photo-induced surface relief gratings of organic polysilane

Surface relief gratings on organic polysilane thin films are fabricated by holographic exposure of ultra-violet light, and Au gratings are subsequently prepared on polysilane gratings by vapor deposition of Au. The anchoring energies of 4-pentyl-4′-cyanobiphenyl (5CB) nematic liquid crystal on the fabricated gratings are determined with a saturation voltage method. The anchoring energies of Au gratings are weaker than those of organic polysilane gratings because of suppression of π–π interaction between the liquid crystal and the alignment layer. The polar anchoring energies of Au gratings are also weaker than those reported in literature.