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Chronic kidney disease (CKD) affects about 10% of all populations worldwide, with about 2 million people requiring dialysis. Although patients with CKD are at high risk of cardiovascular disease and events, they are often underrepresented or excluded in clinical trials, leading to important knowledge gaps about how to treat these patients. KDIGO (Kidney Disease: Improving Global Outcomes) convened the fourth clinical Controversies Conference on the heart, kidney and vasculature in Dublin, Ireland, in February 2020, entitled Central and Peripheral Arterial Diseases in Chronic Kidney Disease. A global panel of multidisciplinary experts from the fields of nephrology, cardiology, neurology, surgery, radiology, vascular biology, epidemiology, and health economics attended. The objective was to identify key issues related to the optimal detection, management, and treatment of cerebrovascular diseases, central aortic disease, renovascular disease, and peripheral artery disease in the setting of CKD. This report outlines the common pathophysiology of these vascular processes in the setting of CKD, describes best practices for their diagnosis and management, summarizes areas of uncertainty, addresses ongoing controversial issues, and proposes a research agenda to address key gaps in knowledge that, when addressed, could improve patient care and outcomes.

Custom acrylic multifaced pyramids were machined in-house and used to fabricate, in a single step, photonic crystals and quasicrystals on azobenzene molecular glass thin films with a surface area within the range of cm2. The obtained microcavity patterns have up to 8 -fold rotational symmetry depending on the number of pyramid faces used for laser inscription. The height of the resulting microcavities increases with the number of pyramid faces used and can even grow beyond the initial azobenzene film thickness. Furthermore, anisotropic and Moiré photonic structures were also fabricated upon changing the laser polarization and the number of exposures respectively.

Two-dimensional Resonant Waveguide Crossed Gratings (RWCG) were fabricated on azobenzene molecular glass thin films and their resonance behavior was studied once placed in between orthogonally aligned polarizers. Normally-incident polychromatic light was transmitted and/or reflected from these RWCGs only in narrow positive peaks. In addition, the central wavelength and transmitted intensity of these positive peaks were actively modulated by an external light source. Furthermore, a dynamic volume birefringence behavior related to the photomechanical effect of the azobenzene chromophores was observed. A mechanism to explain the polarization conversion of the resonant light using RWCGs at normal incidence was also proposed.

Surface plasmon resonance platforms based on laser inscribed azo polymer surface relief diffraction gratings were used to detect the binding of organic and biological molecules. Optical sensors were assembled to operate in transmission mode, resulting in a very simple setup. This new approach is observed to present a high sensitivity when compared to other systems, such as SPR-based biosensors using nanoholes. The corrugated surface provides a relatively large surface area and the improved sensitivity to binding events is related to resonant plasmon enhancement on the surface relief grating. It was found that varying the periodicity from 400 to 410 nm does not improve efficiency, however changing the groove depth from 30 to 65 nm, resulted in a two-fold increase in sensitivity. An interesting result is that sensors with higher energy surface plasmons present higher sensitivity when compared to lower energy ones. This result can drive further studies toward improved surface plasmon-based sensors.

The synthesis and structural characterization of optically active copolymers such as poly[(S)-(+)-MCPP-co-(S)-MAP-N] and poly[(S)-(+)-MCPP-co-(S)-MAP-C] has been performed in order to obtain a multifunctional photonic material for chiroptical switches and for optical storage applications. The observed chiroptical properties suggest the presence of ordered chiral conformations at least for the chain segments of the macromolecules. Spectroscopic, thermal and chiroptical characterization of these copolymers demonstrate the occurrence of significant electronic interactions between the carbazole chromophores and the azobenzene moieties. The photoinduction of birefringence of copolymer films has been investigated in order to evaluate their behavior as a material for optical data storage. Surface-relief gratings (SRG) have also been inscribed on the material. The results are interpreted in terms of copolymer composition, cooperative behavior and conformational stiffness of the chromophoric co-units.

The change in the transverse refractive indices of clamped transparent relaxor ferroelectric PLZT ceramics, having a composition of (9.5/65/35) and (9.0/65/35), were measured as a function of various ac and dc electric fields, as well as frequency and elapsed time, using an interferometric technique. It was found that the refractive index changed only in the same direction of the applied field, and that increasing dc fields decreased this refractive index, while increasing ac fields increased it, especially in composition (9.5/65/35). These results were explained on the basis of movement and creation of domain structures.

Changes in the refractive indices Δn1 and Δn3 of clamped transparent relaxor ferroelectric (9.5/65/35) and (9.0/65/35) PLZT ceramics were measured as a function of temperature ranging from −30 °C to 60 °C, and at various transversely applied DC electric fields E 3 DC . It was found that the refractive index of both PLZT compositions increased linearly with temperature under no DC bias, indicating a constant electronic polarizability of the samples in the tested temperature range. The rate of increase of Δn3 with temperature became higher for both compositions upon the application a DC bias field ( E 3 DC = 774 kV / m ) due to increased electronic polarizability of the samples, while the rate of increase of Δn1 with temperature remained unchanged and was independent of the DC field applied. The quadratic electro-optic coefficients of these two PLZT compositions were also obtained at 0, 20 and 40 °C, and a significant non-linearity was observed: an 85% decrease in the electro-optic coefficient of PLZT (9.5/65/35) was measured at 40 °C compared to 0 °C, while a similar 60% drop was measured for PLZT (9.0/65/35).

The synthesis of a novel optically active methacrylic monomer containing in the side chain the (S)-3-hydroxy-N-phenyl pyrrolidine ring linked to a 4-cyanophenylazocarbazole moiety [(S)- MCAPP-C] and of the analogous achiral monomer (MCAPE-C) is described. Both the monomers have been radically polymerized to produce the corresponding homopolymers as well as the copolymer at 50% molar composition. The photoinduction of birefringence has been assessed on thin films of the polymeric materials in order to evaluate their behavior as materials for optical data storage. Surface relief gratings (SRG) can also be inscribed over the material. The results are interpreted in terms of different cooperative performance and conformational stiffness of the chromophoric co-units in the polymeric derivatives.

A fluorescence study was conducted on commercial dyes (squaraines; triphenylmethane dyes; porphyrins and chlorins) in thin films of polyvinyl alcohol (PVA), poly (methyl methacrylate) (PMMA) and Hival 5108, a commercial polystyrene (PS) from Ashland. Fluorescence quantum yields were measured for dye–polymer system and compared to liquid- and solid-phase media values. All dyes were found to have fluorescent yields and stabilities that were dependent on the polymer film material. Squaraine dyes, SQ3 and OH-SQ, exhibited the highest quantum yields (Φf) when miscible in polymer films, reaching values as high as 0.89 in PS and 0.79 in PMMA. Acceptable Φf at wavelengths higher than 650 nm were observed for SQ3, OH-SQ, TPP and PP-IX-DME. Moreover, fluorescence decay was measured after 240 s of CW irradiation for all the dye–polymer films studied.

Azobenzene containing polymers are spin coated onto glass slides to form 200 to 400 nm thick films. The films are then poled by corona discharge to orient the azobenzene molecules in a direction perpendicular to the surface. A single infrared Nd-YAG laser beam at 1064 nm is incident on the film along the normal to the surface. This beam is within the transmission window of the film and is thus not highly absorbed. We have found that second harmonic SHG (at 532 nm) and third harmonic THG (at 354.7 nm) beams are generated and are emitted in the form of arcs behind the sample. These arcs are consistent with emission from periodic structures with a 700 nm spacing. If the sample is not poled then only the arc from the third harmonic is generated. We have also found that if the laser power is increased above a specific threshold then permanent surface ripples are formed on the polymer surface even though the laser power is well below the ablation threshold. We will also look at the effects of including...

The synthesis of a novel series of copolymers containing push−pull bisazobenzene (BAz) and monoazobenzene (MAz) groups with various N-alkyl donor groups and with spacers of two and four methylene u...

A diffraction grating with a large diffraction efficiency (η = 25% on the first order) was inscribed on an azobenzene-containing polymer thin film, electrically poled, and characterized using spatially resolved Raman confocal microscopy and near-field scanning optical microscopy (NSOM) coupled with second-order nonlinear optical measurements. Linear (Raman) and nonlinear (second harmonic generation or SHG) polarized microscopic measurements were performed on a grating with ∼1.4 μm periodicity, revealing the molecular orientations in various regions of the sinusoidal relief surface. The most probable distribution functions f(θ) of the chromophore orientations were derived using the two first even parity Legendre polynomials 〈P2〉 and 〈P4〉 together with the two odd order parameters 〈P1〉 and 〈P3〉, as determined by Raman and SHG, respectively. These distribution functions show that the poling treatment is quite efficient and also emphasize the importance of determining both couples of the order parameters in s...

Circular dichroism and circular birefringence were induced in thin films of achiral polymer liquid crystals containing 7 or 15 mol % azobenzene chromophores by irradiation with circularly polarized light (CPL). Circular dichroism was observed not only for the azobenzene moieties but also for the nonphotoactive mesogens, cyanobiphenyl groups, due to a cooperative motion. CPL with opposite handedness produces enantiomeric structures, and a chiroptical switch can be achieved by alternating irradiation with left and right CPL. The level of photoinduced chirality depends on the incorporation methods (doped or chemically bound) of the azobenzene chromophores, the amount of azobenzene units, and the sample temperature. The photoinduced circular dichroism can be erased by heating the films above the clearing temperatures or by annealing the films in the liquid-crystalline phase.

A series of polyurethane elastomers containing aromatic azobenzene chromophore in the hard segment was synthesized by a one-step method. AFM surface study showed that particles on the order of 100 nm to several micrometers appeared after annealing the polymer films. Birefringence was induced in these polymer elastomers. The stability of the photoinduced birefringence could be improved significantly by annealing the polymer films. This also induced microphase separation. The effects of azo contents and molecular weight of soft segments were investigated. Dynamic study shows that photoinducing rate decreased while relaxation rate increased after annealing. Surface relief gratings could be induced only on the pure polyurethane and the elastomer containing 75% bis(azo)-diol. Only a reversible volume hologram was observed for the other elastomers.

Sinusoidally shaped surface relief gratings made of polymer films containing azobenzene moieties can be created by holographic illumination with laser light of about λ ≈ 500 nm. The remarkable material transport takes place at temperatures far (100 K) below the glass transition temperature of the material. As probed by visible light scattering the efficiency of grating formation crucially depends on the polarization state of the laser light and is maximal when circular polarization is used. In contrast to VIS light scattering X-ray diffraction is most sensitive for periodic surface undulations with amplitudes below 10 nm. Thus, combined in-situ X-ray and visible light scattering at CHESS were used to investigate the dynamics of surface relief grating formations upon laser illumination. The time development of grating peaks up to 9th order at laser power of P = 20 mW/cm2 could be investigated, even the onset of grating formation as a function of light polarization. A linear growth of grating amplitude was observed for all polarizations. The growth velocity is maximal using circularly polarized light but very small for s-polarized light.

The thermochromic properties of a series of liquid crystalline polymethacrylates, containing azobenzene side-chains with variable spacer lengths, were investigated. Annealing the amorphous polymer thin films above the glass transition temperature results in a rearrangement of the azobenzene moieties, causing a hypsochromic shift in the electronic absorption spectra. A detailed investigation of the spectral shift was performed by in situ UV–vis spectroscopy and indicated the formation of H-type aggregates by the side-chain chromophores above the glass transition temperature. The rate at which the hypsochromic shift occurs is faster for polymers with shorter spacers since their high glass transition temperature results in a higher thermal energy during the thermochromic effect. Experimentally determined activation energies show that the aggregation occurs primarily due to side-chain relaxation (β-relaxation) and main-chain relaxation (α-relaxation). Further annealing above the isotropization temperature resulted in the onset of deaggregation and in most cases showed that the chromophores were freed from the ordered state.Key words: liquid-crystalline polymer, thermochromic properties, chain relaxation, aggregation, thin films, azobenzene mesogens.

The following article is a tribute to the late Almeria Natansohn and is based on a brief summary of her research in azopolymers. She showed that reversible trans–cis–trans photoisomerization of aromatic azo groups covalently bonded within polymers could trigger a variety of motions in the polymer materials at molecular, nanometer, and micrometer levels. The photoinduced motions could be limited only to the azo rigid chromophore or could involve many polymer chains and ordered domains. Some of the effects of these motions such as reversible photo-orientation of chromophores, amplification effects, photorefractive effects, formation of surface relief gratings (SRGs), and photoinduced chirality and switching in amorphous and liquid-crystalline (LC) polymer films are discussed in relation to the polymer structure and physical parameters. Possible photonic applications originating from these phenomena are also mentioned.

An amorphous polymer containing Disperse Red 1 (DR1) and crosslinkable acrylic groups as separate side groups was synthesized. Surface relief gratings were optically inscribed onto films of this polymer. Grating depths of 350 nm were obtained after 40 min of irradiation. The first-order diffraction was monitored during the laser irradiation, and an efficiency of about 22% was achieved. The polymer could be photocrosslinked at 80 °C under UV light. Although some photo-degradation due to UV irradiation of the azo chromophores was observed, the surface relief itself was fixed by the photocrosslinking, as observed by the improved thermal stability of the diffraction efficiency. Even after heating above the glass transition temperature ( T g ) for 2.0 h, significant diffraction was still present and the grating was still observed. In comparison with the photocrosslinked gratings, a non-crosslinked grating rapidly lost most of its shape when heated above T g . Thus, photocrosslinking is a useful method to improve the thermal stability of the gratings.

There has been recent interest in photoinduced chirality in azo polymers upon irradiation with circularly polarized light. The mechanism of ordering is thought to involve successive twisting of the achiral photoactive azo-containing side chains in response to the handedness of the pump polarization. In this study, a thin film of a liquid-crystalline azo polymer with a room-temperature nematic phase is irradiated with circularly polarized light and a circular Bragg reflection is observed in the absorption spectrum. When probed at normal incidence, the evolution of this selective reflection is monitored with increasing exposure. Then, the probing is carried out for various angles of incidence and the change in peak shape is studied. In the last experiment, the position of the Bragg reflection is monitored as the wavelength of the pump laser is varied. We propose that while the induced chirality is due to the circularly polarized light, the associated pitch may be large; the induced periodicity corresponding...

The formation of a surface relief grating (SRG) on polymer films containing azobenzene moieties has been inspected during exposure with counter-rotating circularly polarized light of λwrite=488 nm by probing the diffracting efficiency of a second low power laser. In particular, the growing SRG was observed at films of different film thickness and with low and high light power of the writing laser. Using probe lasers of two different wavelength (λprobe=514 and 670 nm) the grating formation was inspected near the film surface and within the whole film, respectively. At low writing power (P=50 mW) and small film thickness (d 300 nm) a density grating is also created within the film. The observations confirm the trends suggested by finite element calculations.

The development of light-induced polymer surface relief gratings (SRGs) inscribed onto polymer films containing photosensitive moieties is probed in situ by x-ray and visible (VIS) light scattering techniques. Both methods are complementary due to the different momentum transfer probed. The SRG appears with nearly perfect sinusoidal shape and amplitudes and is accompanied by a density grating (DG) below the surface. The time development of grating peak intensities for continuous and pulse like exposure is interpreted in terms of a new approach of kinematic scattering theory. The simulations demonstrate the extraordinary sensitivity of x-ray reflectivity for very small grating amplitudes (h

A series of poly{4‘-{(X-methacryloyloxyalkylene)methylamino}-4-nitroazobenzene} (pXMAN, where X is the number of methylene units and varies from 2 to 12) polymers with liquid crystalline (LC) prope...

We present the results of time-dependent x-ray scattering measurements during the formation of a buried, modulated density structure below polymer film surface created at temperatures above the glass transition temperature TG during the thermal erasure of a holographically written surface relief grating. The surface relief gratings are initially formed on polymer films containing azobenzene side groups by exposure to a polarization holographic pattern made using light at 488 nm. The material responds to the actinic light by forming a sinusoidal surface relief pattern in a one-step process. Theoretical predictions show that the surface relief grating formation is accompanied by a density grating just below the film surface. Upon annealing above polymers glass transition temperature the surface relief grating melts while some of the density modulation in the bulk remains and a nonsinusoidal density grating is rebuilt after long term annealing at a temperature approximately 30 K above the glass transition te...

In this study, an achiral liquid-crystalline azo polymer is irradiated with circularly polarized light, and the transmitted polarization data show evidence of photoinduced chirality. When the polarization of the laser is switched from left- to right-handed, the chirality of the polymer film is switched as well. In a more revealing experiment, the handedness of the laser is fixed and the evolution of the ordering is monitored. Two models are described to interpret this result, one based on a uniaxial arrangement with the observed circular anisotropy included on a phenomenological level; the other based on a helical arrangement of chromophores. These models were used to fit the polarization data in order to determine the anisotropic optical constants that characterize the structural arrangement. It was noticed that during the irradiation, the sense of the circular anisotropy switches. This is also discussed in relation to both models presented.

An azo-containing liquid crystalline polymer was irradiated with linearly polarized blue Ar+ light and the resulting linear birefringence and dichroism were monitored. In its amorphous phase, results obtained are typical for azo polymers of similar structure, with the optical constants largest along the direction perpendicular to the laser polarization. In its nematic phase, surprising results are obtained, including two changes in the sign of the dichroism measured at 632.8 nm and, at one point, a quadrupolar transmission profile. Dichroic visible spectra show evidence for two bands of opposite sign in the region of the nπ* transition, which are attributed to the trans and cis isomers. In addition to the conventional photoreorientation of azo groups along an axis perpendicular to the polarization direction of the pump, we propose that, under some conditions, a tendency toward parallel alignment occurs as a result of the optical Freedericksz transition.

Structural order often manifests itself in the anisotropic optical phenomena birefringence and dichroism. Such properties of a material cause changes in the polarization of a probe beam. Characterization of the optical anisotropy, and subsequent inference on the structural arrangement of molecules responsible, may be accomplished in two stages. First, Stokes polarimetry is used to determine the polarization change in the transmitted light. Next, a model of the polarization transfer is used to fit the data in order to obtain values of the birefringence and dichroism which may serve as quantitative order parameters. The technique may be applied to linear as well as circular anisotropy, but is perhaps most valuable for cases in which both types coexist and therefore need to be separated. Our polarimeter is simple in construction and may be assembled from common optical elements.

The transformation of a lateral surface relief grating inscribed on a polymer film containing azobenzene moieties into a density grating of equal spacing buried under a smooth surface was found for the polymer poly{(4-nitrophenyl)[4-[[2-(methacryloyloxy)-ethyl]ethylamino]phenyl]diazene} (pDR1M) using an X-ray scattering experiment. Annealing a polymer sample pre-inscribed with a surface grating for several hours above the glass transition temperature creates a nearly sinusoidal lateral density difference up to about 10%. The new state is stable between room temperature and the decomposition temperature of the original polymer when the formation was performed under the influence of VIS light. Growth of liquid-crystalline aggregates is proposed as a most probable explanation for the process.

Two copolymers, poly{4‘-[[[2-(methacryloyloxy)ethyl]ethyl]amino]-4-nitroazobenzene}-co-[(methacryloyloxy)-4-nitrophenyl-(S)-prolinol] (poly(DR1M-co-(S)-NPPMMA)) and poly{4-[2-methacryloyloxy)ethyl]azobenzene-co-[(methacryloyloxy)-4-nitrophenyl-(S)-prolinol] (poly(MEA-co-(S)-NPPMMA)), were synthesized and characterized. They contain side chain azobenzene chromophores (DR1 and MEA, respectively) and a prolinol-based chiral side chain group (NPP). Photoinduced birefringence, polarized absorption spectroscopy, and chiroptical properties (optical rotation and circular dichroism) in films were measured, and the results are discussed in relation to the structure of these copolymers. Cooperative motion of the chiral structural unit is observed for the photoinduced birefringence. Chirality is, however, not transmitted from the chiral structural unit to the azobenzene structural unit at the 1:1 compositions investigated here.

Two new amorphous high-Tg azobenzene-containing polymers: poly{4-[(2-(methacryloyloxy)ethyl)ethylamino]-4'-(methylsulfonyl)azobenzene} (pDRSAM) and poly{4-[(2-(methacryloyloxy)ethylsulfonyl]-4'-(diethylamino)azobenzene}(pDRASM), having side group dipoles of the same strength but differently bound to the main chain, and a series of copolymers of various compositions, have been synthesized.

The design of polymeric materials with optimized photoconductivity and nonlinear optical properties is of major interest for emerging optical applications using photorefractive properties. This paper reports the synthesis and preliminary optical characterization of a series of novel, fully functionalized, photorefractive polymers. They were synthesized by a post azo coupling reaction of a polyether carbonate polymer based on the charge transport N,N,N‘,N‘-tetraphenyl-diaminobiphenyl group with 4-nitrobenzene-diazonium tetrafluoroborate by phase transfer catalysis. The amount of the inserted 4-nitro-phenyl-azo group was between 0.1 and 1.7 per structural unit. These polymers absorb in the UV−vis range, because of the presence of donor−acceptor substituted azobenzene chromophores. Light induced change of the refractive index was studied by birefringence measurements (λprobe = 632.8 nm) as a function of azo content in thin films with thickness ranging from 200 to 500 nm. Surface relief grating inscription wa...

Three novel polyurethanes with V-shaped bisazo groups (PU1 and PU2) or rodlike monoazo groups (PU3) in the main chain were synthesized. On irradiation with a linearly polarized laser beam, birefringence was induced in the three films to the level of 0.035, 0.037, and 0.044 for PU1, PU2, and PU3, respectively. The stable birefringence obtained at Tg − T = 33 °C was 71%, 46%, and 19% of that achieved at room temperature for PU1, PU2, and PU3, respectively. The relative stability of the photoinduced birefringence of PU3 decreased linearly with the increase of temperature, while that of PU1 and PU2 was constant even close to Tg. Surface relief gratings with high diffraction efficiency were inscribed on these main-chain polymers. The photoinduced gratings are only partially erasable by heating above the Tg of the polymers.

The well-known trans–cis–trans photoisomerization of azobenzenes produces at least three different kinds of motion in the polymer materials to which the azobenzenes are bound. The first is a photoinduced motion of the azobenzene groups only, and they can align in a selected position with respect to the light polarization. The second is a macroscopic motion of huge amounts of polymeric material, producing surface deformation, and the third is a reorganization of smectic domains in liquid crystalline polymers. These motions and their consequences are briefly discussed in relation to the polymer structure and some possible photonic applications are mentioned.Key words: photoinduced orientation, azobenzene polymers, surface gratings, photonics, thermochromism, photochromism, photorefractivity, photoinduced chirality and switching.

A series of amorphous copolymers containing disperse red 1 and crosslinkable acrylic groups were prepared. The crosslinked polymers were prepared in thin films by thermal polymerization of the acrylic groups in the copolymers. The orientation induced by irradiation with a linearly polarized laser was measured as birefringence at several temperatures, and the effect of crosslinking on the photoinduced orientation was investigated. Crosslinking enhanced the stability of the photoinduced birefringence. In particular, crosslinking helped to maintain the birefringence both at high temperatures and after the linearly polarized laser was turned off. The birefringence dynamics was analyzed with biexponential curve fitting. Crosslinking influenced not only the birefringence levels but also its rate of growth. The growth rate of the photoinduced birefringence decreased by crosslinking, whereas the relaxation was not significantly affected. Although crosslinking restrained the mobility of the azo chromophores, a certain fraction could orient or move randomly even in highly crosslinked polymer networks. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1686–1696, 2001

Irradiation with circularly polarized light of a film of an achiral azobenzene liquid crystalline polymer induces chirality. Circularly polarized light with opposite handedness produces enantiomeric structures. A chirooptical switch based on this phenomenon is reported.

A series of azobenzene-containing side chain liquid crystalline polymers with various spacer lengths (pXMAN, where X, the number of methylene units, varies from 4 to 12) have been synthesized and characterized. Phases and aggregation have been studied by UV-visible spectroscopy as a function of temperature. Polarized spectra were measured before and after irradiation with a resonant pump light at 488 nm. The annealing process on polymers with short spacers (p4MAN-p8MAN) induces a hypsochromic shift while, for longer spacers (p9MAN-p12MAN), it induces a large bathochromic shift. These effects may be due to the strong dipolar interaction and interdigitation of the side chain chromophores in an antiparallel orientation. The irradiation of such organized films with either circularly or linearly polarized light induces a bathochromic shift by breaking the antiparallel organization. This is a consequence of the angular reorientation of the azobenzene moieties as a result of trans-cis photoisomerization. To estimate the orientation of the side chain azobenzene photoactive group, of the aliphatic spacer and of the main chain, linear dichroism in the infrared spectral range was measured using the polarization-modulation technique with in situ irradiation. From these experiments, a high and stable value of photoinduced linear dichroism reveals a strong interaction and self-organization of azobenzene side chain molecules during the relaxation process. The anisotropic reorientation of the polymer main chain and of the spacer is small when compared to the reorientation of the azobenzene side chains, which become perpendicular to the linearly polarized pump beam. Additional birefringence measurements were carried out with in situ irradiation followed by a relaxation cycle for the whole series of polymers in various phases. The stability and the rate of the induced birefringence depend on the initial degree of organization within the thin film and on its thermal history. It is noteworthy that annealing can lead to a significant improvement of the birefringence level (+44%). The results obtained on photoinduced orientation and phase organization are correlated with the polymer properties.

We have developed a liquid crystal (LC) device that is totally controlled using light. The initial alignment is made by optically buffing the azopolymer film with two coherent argon laser beams. Surface relief gratings have been optically induced on an assembled cell filled with LC. A single linearly polarized argon laser beam is then employed to irradiate the sample and photoinduce a twisted alignment structure. This can then be erased by a circularly polarized beam. The alignment information can also be erased by heating to the glass transition temperature of the azopolymer film.

The synthesis and optical properties of a series of amorphous polyesters with amino-sulfone azobenzene chromophores in the main chain are presented. The condensation of alkyl diacid chlorides with 4-[(2-hydroxyethyl)ethylamino]-4′-(2-hydroxyethylsulfonyl)azobenzene (7) gave polymers that showed low and unstable photoinduced birefringence because of their low glass-transition temperature. The condensation of 7 with mixtures of adipoyl chloride and terephthaloyl chloride gave a polymer with a higher glass-transition temperature and a stable reversible photoinduced birefringence. A photostationary birefringence of 0.07 was observed. Surface profile gratings were optically inscribed and produced diffraction efficiencies less than or equal to 19%. Photostationary, long-term stable birefringence and surface-grating efficiency increased with polymer rigidity. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2245–2253, 2000

The physical origin of surface relief patterning on amorphous polymer films containing azobenzene-side chains induced by holographic exposure with visible light of about 450 nm is not yet fully understood. To understand the nature of the induced material transport is of special interest to describe the dynamic processes occurring in thin films below the glass transition temperature TG. Thus, we investigated films made from the polar (poly {4′-[2-(methacryloxy) ethyl]-ethyl}amino-4-nitroazobenzene, TG=129 °C) and less polar {poly[4-(2-methacryloxy)-ethyl] azobenzene, TG=80 °C} azobenzene side-chain homopolymers and performed temperature-resolved coherent x-ray and visible (VIS) light scattering measurements of the thermally induced erasure of the surface gratings. The simultaneous use of x-ray synchrotron light (λ=0.14 nm) and VIS laser light (λ=633 nm) allows the detection of the material flow on different lengths scales. We did not find remarkable differences in the thermal behavior of polar and nonpolar...

A series of copolymers of 4'-[[[2-(methacryloyloxy)ethyl]ethyl]amino]-4-nitroazobenzene (DR1M) and an optically "inert" styrene comonomer were tested for photoinduced birefringence. The level of saturated birefringence increased linearly with the content of DR1M in the copolymer. The birefringence per mole of azo chromophore was constant along the copolymer series.Key words: azobenzene, photoinduced birefringence, copolymers, trans-cis isomerization.

An azocarbazole-based polyimide was synthesized from an azocarbazole diamine monomer and 4,4‘-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) by a two-step polycondensation reaction. Birefringence experiments have been performed on the pure polyimide and on the polyimide mixed with small azo chromophores. Because of its high Tg, the polyimide has a very stable induced birefringence (only 14% loss during the relaxation process). The stability of the mixtures is also very high. Surface relief diffraction gratings were inscribed on these systems. The measured diffraction efficiency was about 0.25% for a diamine-doped polyimide exposed for 1 h to an irradiance of 200 mW/cm2. The surface profile studied by atomic force microscopy showed an amplitude of 30 nm and a regular spacing of 700 nm on a 255 nm thick film. The photoinduced gratings had a high stability without further surface deformation after baking at 240 °C for 1 h in air.

This paper concerns itself with photoinduced anisotropy in two azobenzene-functionalized polymers. A simple physical model of the process that considers only three possible states of azo chromophores is proposed. This model predicts an equilibrium level of anisotropy that depends on the pump irradiance and temperature. Each of these influences is examined in turn, with experimental illustrations from the two polymers poly[4-[2-(methacryloxy)-ethyl-ethyl]azobenzene] (pMEA) and poly[4prime-[[2-(methacryloxy)ethyl]-ethyl]amino-4-nitroazobenzene] (pDR1M).Key words: azobenzene polymers, photoinduced orientation, irradiance, temperature.

Based on Newtonian fluid dynamic relations, a model is constructed to describe laser-induced mass transport in thin films of polymers containing isomerizable azobenzene chromophores, in which surface profile diffraction gratings can be inscribed with an interference pattern of coherent light. The Navier–Stokes equations for laminar flow of a viscous fluid are developed to relate velocity components in the film to pressure gradients in the polymer film, by definition of boundary layer conditions. This general laminar flow model is applicable to the formation of surface gratings through a variety of mechanisms. Considering the mechanism of an isomerization-driven free volume expansion to produce internal pressure gradients, a specific model is developed to describe polymer flow resulting from laser-induced isomerization of the bulky chromophores. This yields an expression relating the time evolution of the surface gratings to properties which could be varied experimentally, such as those of the irradiating ...

Amorphous copolymers with rigid azobenzene and ester side groups form films in which birefringence can be induced using linearly polarized light. When both the azobenzene and the ester groups are p...

This paper concerns itself with photo-induced anisotropy in two azobenzene functionalized polymers. A simple physical model of the process which considers only three possible states of azo chromophores is proposed. This model predicts an equilibrium level of anisotropy which depends on the pump irradiance and temperature. Each of these influences is examined in turn, with experimental illustrations from the two polymers poly 4-2-(METHACRYLOXY)-ETHYLazobenzene (pMEA) and poly4'-2-(METHACRYLOXY)ETHYLamino-4-nitroazobenzene (pDR1M).