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Photoactive polymers are important for fundamental studies and applications in several area of photonics such as data storage and holography and nonlinear optics and photomechanics. The latter is perhaps one of the most important applications of such materials, since they act as light to mechanical energy transducers and move under light action. For example, azo-polymers irradiated by inhomogeneous resonant ultra-violet or visible light undergo molecular and macroscopic motion, at sub-glass transition temperatures by photoisomerization of the azo dyes. Our recent research in this field highlighted the fundamentals of mobility enhancement by light, including light-induced viscosity change and acceleration of relaxation times, and photomechanics, encompassing motions in gradients of actinic light leading to surface structuring and actuation. In this paper, we present an original model which predicts the creation of mechanical pressure, i.e., motion, by a photo-induced change in the occupied volume and length of anisometric isomers, and we give simple analytical expressions describing the dynamics of volume as well as strain change upon polarized light irradiation of photomechanic samples.

Ubiquitous surface wrinkling has been well‐studied theoretically and experimentally. How to modulate the stress state of a liquid‐supported system for the unexploited wrinkling capabilities remains a challenge. Here we report a simple linearly‐polarized‐light illumination to spatiotemporally trigger ultrasensitive in situ dynamic wrinkling on a floating azo‐film. The smart combination of the liquid substrate with photoresponsive azo‐moieties leads to the light‐induced ultrafast wrinkling evolution, accompanied by unprecedented sequential wrinkling orientation conversion (from polarization‐parallel to polarization‐perpendicular). The involved different polarization‐dependent sequential photo‐orientation for azo side chains and azo‐grafted main chains of azopolymers is disclosed experimentally for the first time. Meanwhile, programmable dynamic wrinkling with all‐optical switchable surface topographies is available, which has wide application potentials in photoresponsive soft photonics. [ABSTRACT FROM AUTHOR]

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In this communication, we summarise our results related to light-induced orientational phenomena at liquid crystal-polymer interfaces. We investigated photoalignment for various nematics at the interface with the photosensitive polymer layer polymethyl methacrilate functionalised with azo dye Disperse Red 1. It was found that the efficiency of photoalignment exhibits marked differences depending on the structure of the rigid core of the liquid crystal molecules. It was demonstrated that the photo-orientation process is also significantly affected by the type of mesophase in which irradiation is carried out. The observations highlight the importance of the mutual influence of the polymer and the liquid crystal in light-induced processes.

The explicit dependence of the rate of photoinduced ordering (photo-orientation) of an azobenzene-containing liquid-crystalline polymer on the photostationary concentration of cis-azobenzene has been predicted theoretically and found experimentally. The employed kinetic model based on the photoinduced rearrangement of the domain structure of a liquid-crystalline material predicts the maximum rate of photo-orientation at ca. 50% content of the cis-isomer in the photostationary state of irradiation. For experimental fine tuning of the photostationary trans-cis ratio, the simultaneous irradiation of material with two beams of light with different wavelengths was employed. The excellent agreement of theory and experiment indicates that the difference of photostationary fractions of cis-azobenzene fragments in adjacent domains of different orientations is the driving force of photoinduced ordering.

As part of continuing efforts to deepen the understanding of photo-induced mass transport in azo-containing polymers, we compared the diffraction efficiency (DE) during surface-relief grating (SRG) inscription, photo-induced molecular orientation (< P 2 >), and thermal stability in two sets of supramolecular azopolymer complexes, namely, hydrogen-bonded (H-bonded) and ionically bonded (i-bonded) complexes, both as a function of the polymer degree of polymerization (DP). To that end, poly(4-vinylpyridine) (P4VP) polymers with DPs of 41, 480, and 1900 were H-bonded at an equimolar ratio with 4-hydroxy-4'-dimethylaminoazobenzene (azoOH), and the fully quaternized derivatives of the three P4VPs (P4VPMe) were i-bonded via ion exchange to sodium 4-[(4-dimethylamino)-phenylazo]benzene sulfonate (azoSO 3 ), also known as methyl orange, where the OH functionality of azoOH is replaced by a sulfonate group. The i-bonded complexes show much better DE performances and < P > curves by a biexponential equation leads to two parameters associated with a fast trans-cis or angular hole burning (AHB) process and a slow angular redistribution (AR) process of the azo, respectively. It is found that AHB is predominant in the H-bonded complexes, whereas the AR contribution is much greater in the i-bonded complexes, assuring their superior SRG efficiency that is enabled by the anisotropic free volume created mainly by the AR process. In each set of complexes, the SRG efficiency is much better for the lowest DP complex, while the AR contribution is constant (and low) for the H-bonded complexes and increases roughly linearly with the decrease in DP for the i-bonded complexes. The latter difference might be related to the presence of entanglements in the complexes with DPs 480 and 1900, which slow down the macroscopic movement during SRG inscription but not the molecular-scale movement in photo-orientation.2 > levels than those of H-bonded complexes, which we relate to the liquid crystal structure of the former complexes. Fitting the < P 2 > curves by a biexponential equation leads to two parameters associated with a fast trans-cis or angular hole burning (AHB) process and a slow angular redistribution (AR) process of the azo, respectively. It is found that AHB is predominant in the H-bonded complexes, whereas the AR contribution is much greater in the i-bonded complexes, assuring their superior SRG efficiency that is enabled by the anisotropic free volume created mainly by the AR process. In each set of complexes, the SRG efficiency is much better for the lowest DP complex, while the AR contribution is constant (and low) for the H-bonded complexes and increases roughly linearly with the decrease in DP for the i-bonded complexes. The latter difference might be related to the presence of entanglements in the complexes with DPs 480 and 1900, which slow down the macroscopic movement during SRG inscription but not the molecular-scale movement in photo-orientation.

Synthesis and investigation of the phase behavior and photo-optical properties of two chiral liquid-crystalline polymers with azobenzene-containing side groups having different spacer lengths, 6 and 10 methylene groups (PMAzo-6 and PMAzo-10, respectively) are described. Formation of different smectic phases and high-temperature cholesteric phase is studied by polarizing optical microscope, differential scanning calorimetry, and X-ray investigations. It is shown that UV-irradiation induces effective reversible E-Z photoisomerization in polymer solutions and films. Atomic force microscopy (AFM) study reveals substantial changes in the surface topography of the polymer PMAzo-6 film after UV-irradiation, whereas PMAzo-10 surface remains the same. Irradiation by polarized light (457 nm) results in photo-orientation process in polymer films consequential in significant alignment of the chromophores in direction perpendicular to the polarization plane of the incident light. A significant difference is found in thermal stability of the photoinduced alignment; an annealing of PMAzo-10 irradiated samples results in a slight decrease of dichroism values (down to 0.57); whereas the dichroism increases up to very high values (0.91) for PMAzo-6. [ABSTRACT FROM AUTHOR]

Traditional aerial triangulation has long relied on control points for orientating the photo models into a ground-based coordinate system, reducing the distortion effect when tying photos by imperfect photo measurements, and calibrating camera parameters. Field surveys to provide an adequate number of control points and manual measurements of the control points afterwards in the photos incur considerable cost both in labor and expense. The past decade has seen the development of digital photogrammetry as a result of integrating into the photogrammetric discipline both the advantages of image processing techniques and the rapid computational efficiency of the computer. Such a development has made possible database-supplied control entities, as well as the automation of matching control data between object space and image space. Inspired by this capability, we employ a control patches database where the control points are found on older imagery and matched in the new photo. The successful implementation of the proposal lies in an effective control patches database, robust matching methodology, and a reliable orientation approach. Single photo resection is applied whenever no less than three matched control patches are available. The experiments under this project suggest the potential efficiency of automatic control point measurements from the control patches database and a reliable photo orientation solution. [ABSTRACT FROM AUTHOR]

The evolution of the domain structure of two azobenzene-containing materials during irradiation with polarized light was monitored using polarized optical microscopy with additional λ-waveplate for discerning the domains oriented parallel and perpendicular to irradiating light polarization. It is shown that the process of photo-orientation consists in growth of perpendicularly oriented domains and diminishing of parallel domains via the movement of domain boundaries. These data confirm the mechanism of photo-orientation via domain structure rearrangement.