Holographic grating recording in azobenzene polymer films

The photo-induced birefringence grating and the surface grating in azobenzene polymer films were studied. The photo-induced birefringence (about 0.02 at 633 nm) was investigated at various intensities of laser (532 nm) beam. The effect of laser-induced heating has been introduced to the processes of photo-induced reorientation in azo polymer. The holographic grating period and the peak-to-peak value of the sinusoidal surface profile are 0.8 mm and 40 nm, respectively. The maximum diffractive efficiency of the grating is 2%. The mass diffusion responsible for the formation of the surface grating due to the temperature rise is analyzed.     

Time-resolved studies of photoinduced birefringence in azobenzene dye-doped polymer films

We measured transient photoinduced birefringence (delta n) in various azobenzene dye films by pumping with a nanosecond pulse at 532 nm and probing at 633 nm. The switch-on times for the photoinduced birefringence range from nanoseconds to milliseconds and are systematically related with the lowest optical transition energies for those films. Moreover, our results suggest that the transient photoinduced birefringence measurement is a convenient way to determine the relative energies of pi-pi(*) and n-pi(*) states in azo-based materials.     

Photomechanical response of azobenzene/organophilic mica complexes

To clarify whether photomechanical response is limited to the special combination of azobenzene (AzBz)/organophilic tetrasilicic mica (TSM) complexes, another swelling synthetic fluoro-mica, lithium taeniolite, was used as a starting host for AzBz/organophilic mica complexes. Basal spacings of organophilic taeniolites (o-TNs) prepared by the intercalation of trimethylalkylammonium (TMAA) into the TN increased linearly as alkyl chain length in TMAA increased from 2.44 to 2.86 nm. This indicates paraffin-type arrangement of TMAA in the TN gallery. Intercalation of AzBz to o-TN was performed via the gas phase at 100 °C. Photoresponses of AzBz/o-TN complexes were examined by XRD measurement under alternate UV and visible light irradiation. A decrease in basal spacing was observed under UV irradiation, and an increase was under visible light irradiation. Basal spacing change was 0.09–0.18 nm, which corresponds to 3–5% of the AzBz/o-TN basal spacing. These results indicate that reversible photomechanical response is a general phenomenon for AzBz/organophilic mica complexes.     

Light-induced optical activity in optically ordered amorphous side-chain azobenzene containing polymer

Abstract

We report the appearance of circular birefringence (optical activity) in amorphous side-chain azobenzene polymer films on illumination with circularly polarized light. The effect is observed only if an optical axis is previously created in the film with the help of linearly polarized light. The photoinduced optical activity is believed to be due to changes in the polymer structure initiated by a circular momentum transfer from the circularly polarized light to the azobenzene chromophores.     

Image storage based on circular-polarization holography in an azobenzene side-chain liquid-crystalline polymer

Image storage was investigated in a liquid-crystalline azobenzene polymer film based on circular-polarization holographic recording. An image was stored in pure polarization holograms using two orthogonal circularly polarized 532 nm beams and was reconstructed with a 633 nm beam. The polarization holograms showed high stability and a high diffraction efficiency of 31.8%. Moreover, the polarization holograms could convert arbitrary probe polarization state into circular polarization, and the diffraction efficiency was dependent on the probe polarization state, which was favorable for controlling the reconstructed images.     

新型含偶氮苯生色团聚合物的制备和性能

合成了含手性碳原子的新型偶氮苯生色团,通过酰氯化反应制备出含偶氮苯生色团的单体,将所合成的单体与丙烯酸酯类单体进行自由基共聚得到以偶氮苯生色团为侧基的高分子.利用1H NMR、FTIR、UV-Vis吸收光谱,对所合成的单体及聚合物进行了结构表征.研究了所制备的聚合物的全光开关效应.结果表明,在激发光的照射下,通过聚合物中偶氮苯基团的顺-反-顺异构循环在聚合物材料中可形成光致各向异性;在较低驱动光功率(28.1 mW)下这种聚合物具有良好的全光开关效应.     

Dielectric response of polymer relaxors

Dielectric response of vinylidene fluoride type ferroelectric polymers is dominated by that of segmental motions in the amorphous phase in temperature range 200–300 K and contributions related to the local mode and ferroelectric–paraelectric transition in the crystalline phase of the polymer at higher temperatures. Diffuse and frequency-dependent dielectric anomaly observed in fast electron irradiated polyvinylidene fluoride-trifluoroethylene P(VDF/TrFE) has been related to relaxor-like behavior induced in the semicrystalline ferroelectric copolymers. As random field and the response of polar nanosize clusters determine the relaxor behavior the effects of disorder and fast electron irradiation (below and above T _C) on the three contributions to the dielectric response of PVDF, P(VDF/TrFE)(75/25) and P(VDF/TrFE)(50/50) are shown. The processes involved in radiation-induced functionalization of PVDF-type polymers are discussed on the basis of results of ESR, IR and Raman spectroscopy studies.     

Cyano azobenzene polymer films: Photo-induced reorientation and birefringence behaviors with linear and circular polarized light

Photo-induced behavior of polymethacrylate polymer, with cyano azobenzene side group, was studied. The photoisomerization process occurs in cyano azo polymer, by illumination of a film with polarized and unpolarized light. The illumination of the polymer film with light results in color change, the color of film gets darker. This is in opposition to common azo polymers in which the result of illumination is a photo-bleaching. Study of spectrum changes of a dilute polymer solution shows that the color change under pump beam illumination is not due to interaction between dye molecules. Time evaluation of probe beam absorption induced by Ar⁺ laser pump beam shows the fast change in population of isomers at higher light powers. Light induced birefringence (LIB) experiments with high power pump beams shows uncommon new features. A high long-term stability of LIB is demonstrated when the polymer film is kept in the dark. Not only a circular polarized light cannot erase the birefringence but it also induces anisotropy in polymer film. It appears that this is relevant of a phase transition in the polymer film.     

Fast response photorefractive guest-host polymer composite

Abstract

A film of composite poly(N-vinylzarbazole): [[4-(dodecanecyl-methylamino) phenyl]methylene]-propanedinitrile: C₆₀ was proven to possess attractive photorefractive properties with fast response time. The diffraction efficiency was fitted to the square of a biexponential formula and the fast response time was deduced to be 12 ms at an erasing beam intensity of 1 W/cm². Meanwhile, the strong photorefractive effect was maintained. An amplitude of index grating as large as 3.1 × 10^?3 at an electric field of 78 V/μ and fitted a two-beam coupling gain coefficient of 43 cm^?1 at 57 V/μ were observed.     

The immersed fatigue response of polymer composites

The effect of sea water on carbon/epoxy cross ply specimens is studied by consideration of fatigue data and failure modes. Tests were conducted using dry and saturated coupons fatigued in air, as well as pre-saturated coupons fatigued while immersed in sea water. The saturated coupons fatigued in air had the longest fatigue life, which was attributed to stress relief from sorption induced swelling. Saturated coupons fatigued in an immersed environment exhibited the shortest fatigue life, and also experienced significant deliminations prior to failure. Water trapped inside the transverse cracks during the load cycle provides a physical mechanism explaining this behavior. Analytical and numerical analyses are presented which show how moisture inside the transverse cracks can alter the coupon stress state and enhance delimination.     

On the mechanical response of short fibre reinforced polymer composites

In this paper, a generalized Mori-Tanaka scheme is applied to evaluate the elastic response of short fibre composite materials. Numerical predictions are compared with experimental measurements performed on short fibreglass reinforced thermoplastics with a wide range of fibre concentrations, including the range characteristic of usual industrial applications with non-trivial fibre orientation distribution.     

Removal of azobenzene from water by kaolinite

The use of natural kaolinite clay to remove azobenzene from aqueous solutions under different pHs, ionic strengths, initial solid mass used, and initial solution concentrations was investigated. Batch kinetic experiments showed that the adsorption of azobenzene onto kaolinite followed a pseudo-second-order kinetics with an initial rate of 7.2 mg/g-h and a rate constant of 0.19 g/mg-h. The equilibrium azobenzene adsorption on kaolinite was well described by the Langmuir and Freundlich isotherms with an adsorption capacity of 11 mg/g, or 60 mmol/kg, corresponding to a monolayer adsorption on the surface of kaolinite. Adsorption increased with decreases in solution pH and increases in solution ionic strength. The enthalpy change of adsorption was −38 kJ/mol, suggesting that both physical and chemical adsorption was responsible for the retention of azobenzene on kaolinite. The high affinity of azobenzene for siloxane and gibbsite surfaces was attributed to the attractive Coulombic and van der Waals’ forces between the surface and the planar structure of the organic molecule.     

Preparation of single conjugated polymer nanofibers with high opto-electric response

Single pristine poly(p-phenylene vinylene) (PPV) nanofibers were prepared by electrospinning. The fibers were characterized by fluorescence microscopy, scanning electron microscopy, and polarized fluorescence spectra. The results indicated that the fibers were stretched and oriented toward to rollup direction during the electrospinning process and PPV polymer molecules were oriented with their conjugated backbones along the PPV fiber direction. The parallel array of countable PPV nanofibers was assembled into a photoconductor device. The device shows much higher sensitivity to photo detection than device with PPV film, indicating efficient carrier transport in the well-oriented polymer fibers. This facile, easily operated method for the fabrication of well-oriented fibers indicates its potential application in optoelectronic devices.     

Correlating yield response with molecular architecture in polymer glasses

The yield response of nine architecturally different glassy networks is investigated under several stress states, strain rates, and temperatures, and correlations are made among them. Differences in molecular architecture are quantified through two proposed governing parameters; the glass transition temperature, T _g, capturing network stiffness and the cohesive energy density, E _c, reflecting network strength. Cohesive energy density is estimated using molecular modeling techniques and supported by solvent swelling experiments. The limits of the correlations made between molecular architecture and yield behavior are further studied with attempts to relate yielding in thermoplastic glasses and heterogeneous networks.     

The effect of temperature on the viscoelastic response of polymer melts

Observations are reported in isothermal torsional oscillation tests on melts of isotactic polypropylene (iPP) and low-density polyethylene (LDPE) in the intervals of temperature between 190 and 250 °C (iPP) and between 120 and 190 °C (LDPE). With reference to the concept of transient networks, constitutive equations are developed for the viscoelastic response of polymer melts at three-dimensional deformations with small strains. A melt is treated as an equivalent network of strands bridged by temporary junctions (entanglements and physical cross-links whose life-times exceed the characteristic time of deformation). The time-dependent behavior of the network is modelled as detachment of active strands from their junctions and merging of dangling strands with the network. The network is assumed to be strongly heterogeneous in the sense that different junctions have different activation energies for separation of strands. The stress–strain relations involve three adjustable parameters (the plateau modulus, the average activation energy for rearrangement of strands and the standard deviation of activation energies) that are determined by matching the dependencies of storage and loss moduli on frequency of oscillations. The difference in the effects of temperature on the material constants of iPP and LDPE is associated with the difference in their molecular architecture.     

主链型偶氮苯改性聚芳酰胺的合成及表征

在以N,N二甲基乙酰胺为溶剂,三乙胺为酸吸收剂的条件下,将自制的反式-4,4'-偶氮苯二甲酰氯与对苯二胺进行低温缩聚反应,合成了1种新型的反式偶氮苯聚芳酰胺.用红外光谱、示差热扫描量热分析,热重分析,偏光显微镜,紫外光谱对其结构及性能进行了表征.合成的聚合物表现出了一定的结晶性能,聚合物的稀溶液呈现出溶致液晶行为.     

Dynamics of photoinduced motions in azobenzene grafted polybutadienes

The goal of the investigations was to measure the dynamics of photoinduced motions in semicrystalline polybutadiene backbone based polymer grafted with various degree of mesogenic thiols. We studied the influence of the grafting degree of the azobenzene-containing side groups and the length of terminal oxyaliphatic substituent in the side groups on the dynamics of the laser holographic volume and surface gratings recording. Measurements were performed in a typical laser degenerate two-wave mixing experiment, in which light self-diffraction efficiency during holographic recording was monitored. Mathematical model for grating formation based on coupling of three gratings has been assumed to elaborate the obtained results. Theoretical estimations and experimental results have shown very good agreement.     

Broadband magneto-dielectric response of particulate ferrite polymer composite at microwave frequencies

Complex permittivity and permeability of a magneto-dielectric composite material is studied using shielded, conductor-backed coplanar waveguide technique over X-band. The propagation constant over the test frequency range is evaluated using element-to-element correspondence of the ABCD matrix computed from scalar scattering parameters without modifying the coplanar structure. The mathematical formulation is verified by performing permittivity and permeability measurements for air over the range 9.5–12.045 GHz. Nano-sized nickel ferrite particles was synthesized using co-precipitation technique at different sintering temperatures. Average crystallite diameter is found to be 6.63–17.55 nm. The composite with 2% and 4% volume fractions is fabricated by reinforcing 6.63 nm ferrite particles in low density polyethylene matrix. The complex permittivity and permeability of the composite obtained from this method are also verified with cavity perturbation technique. The composite shows low saturation magnetization of 1.8745 emu/g and reduced hysteresis loss at room temperature.     

Effective dielectric response of polymer composites with ceramic coated silver flakes

High permittivity polymer composites were prepared using Bisphenol A epoxy resin and low loss alumina (Al₂O₃) coated silver (Ag) flakes for embedded passives. The uniformity and thickness of the Al₂O₃ layer were studied using both scanning and transmission electron microscopy (SEM and TEM). SEM was also used to investigate the morphology of the composites and the particle distribution. The dielectric properties of the composites were measured as a function of frequency and temperature. The composites showed a high relative permittivity of 370 with a low loss tangent of 0.07 at 1 MHz and a temperature coefficient of permittivity ~160 ppm/K.     

Aggregation and self-organization of hydrophilic azobenzene dye Langmuir-Blodgett films

Langmuir-Blodgett (LB) films of azobenzene dye of 2-hydroxyl-3-(4-methoxyl)-naphthanilide-azodiphenyl (AS-RL) and its hybrid films with behenic acid (BA) and octadecylamine (ODA) were investigated by tapping mode atomic force microscopy and ultraviolet visible light absorption spectroscopy. Wavy line-shaped or fingerprint-like dye aggregates were observed in the pure dye LB films. BA and ODA were used to modulate and control the structure of the dye aggregates and different patterns resulted in changing the molar ratio of dye molecules in the composites films, such as long lines (AS-RL/BA = 1:2), sheets (AS-RL/ODA = 1:2), wide lines (AS-RL/ODA = 1:1), and ordered lines (AS-RL/ODA = 2:1).