Photo-induced alignment

Advincula RC, Baba A, Kaneko F. 1999. Polymer ultrathin films via alternate self assembly adsorption of polyelectrolyte and azo dye molecules photo induced alignment and LC display properties. MRS Proc Spring Symp D Liquid Crystal Materials and Devices, San Francisco, 559. 

Rosenhauer R, Fischer T, Czapla S, Stumpe J, Vinuales A, Pinol M, Serrano JL. 2001. Photo induced alignment of LC polymers by photoorientation and thermotropic self organisation. Mol Cryst Liq Cryst 364 295 304. 

Wu Y, Demachi Y, Tsutsumi O, Kanazawa A, Shiono T, Ikeda T. 1998a. Photo induced alignment of pol5mer liquid crystals containing azobenzene moieties in the side chain. 1. Effect of light intensity on alignment behavior. Macromolecules 31 349 354. 

In addition, Zhao and coworkers [236] reported photo-induced alignment of ferroelectric hquid crystals using azobenzene polymer networks of polyethers and polyepoxides. Bulk alignment was achieved by polymerizing several divinyl ethers and diepoxide monomers bearing an azobenzene moiety. Here too, thermal polymerizations were conducted in solution within the ferroelectric hquid crystals, while exposing the reaction mixture to linearly polarized irradiation. The monomers can be shown as follows ... 

KoshibaY, Yamamoto M., Kinashi K., Misaki M., Ishida K., Oguchi Y, and Ueda Y, Photo-induced alignment behavior of azobenzene compound in thin film. Thin Solid Films, 518,805-809 (2009). 

Y. Wu, Q. Zhang, A. Kanazawa, T. Shiono, T. Ikeda, Y. Nagase, Photo induced alignment of polymer liquid crystals containing azobenzene moieties in the side chain. 5. Effect of the azo contents on alignment behavior and enhanced response. Macromolecules 32, 3951-3956 (1999)... 

Advincula, R., et al.. Photo-induced alignment of polymer ultrathin films fabricated by alternate self-assembly solution adsorption of polyelectrolytes and small azo dye chromophores. ACS Polymer Preprints, 1999. Spring p. 1-2. 

Figure 4.24 Optical scheme of three-step 3D substrate illumination (a) profiled substrate LC cell between crossed (b) and parallel (c) polarizers [68]. Reproduced from A. Muravsky, V. Chigrinov, S. Studentsov, V. Brezhnev, N. Zhukov, and B. Gorflnkel, Photo-induced alignment technology for 3-D surface profiles of LCD substrates. International Workshop on Liquid Crystals For Photonics, Gent, Belgium, 0-02 (2006)...

Fig. 15 Photo-induced current of aligned-DNA films (20 x 10 mm, thickness 30 5 irm) in which one acridine orange intercalates per ca. 10 base-pairs, a At 0.01 V, b 0.05 V, and c 0.1 V of applied voltage to the comb electrodes, in which the DNA strands are aligned perpendicular to the two electrodes, d DNA strands in the film placed parallel to the two electrodes at 0.1 V applied voltage. The pulse light above 380 nm was irradiated from a 150 W xenon lamp at 25 °C...

We have observed both dark and photo-induced one-dimensional currents along DNA strands aligned in the flexible film. The DNA-lipid film, in which aligned rod-like strands with hairy alkyl side chains occur, shows thermotropic liquid crystal properties. 

Recently, Chen and co-workers also presented a combination of photo- and nanoparticle-induced alignment, where the homeotropic alignment induced by POSS nanoparticles can be changed into planar alignment by adsorption of a photo-excited azo-dye [346-348]. 

In this section we show that photo-induced light scattering is a powerful tool, especially to obtain information about the polar structure in the crystal bulk. The polar structure in SBN Ce can be considered as the composition of different periodical and/or quasi-periodical assemblies of ferroelectric 180°-domains distributed in the bulk aligned along the c-axis. The existence of... 

Ishikawa J, et al. 2002. Photo induced in plane alignment of LC molecules on layer by layer self assembled films containing azo dyes evaluated by attenuated total reflection measurements. Colloids Surf A 198 200 917 922. 

Kaneko F, Kato T, Baba A, Shinbo K, Kato K, Advincula RC. 2002. Photo induced fabrication of surface relief gratings in alternate self assembled films eontaining azo dye and alignments of LC molecules. Coll Surf A 198 200 805 810. 

As discussed in Chapter 1, photo-polymers that have been unidirectionally modified by exposure to linearly polarized light have the ability to induce alignment of liquid crystals [37-41]. This works presumably via anisotropic van der Waals forces [38], similar to the alignment on conventionally rubbed polymer layers [18,22]. In spite of this similarity, generally there are large differences found between the surface anchoring strengths of these two types of... 

The monomers were then thermally polymerized and simultaneously irradiated with linearly polarized light. Two of the monomers were able to induce bulk alignment of the liquid crystals in direction perpendicular to the polarized light. Monomer 1 was effective in concentrations as low as 1%. It was also concluded from the experimental evidence that the photo-induced bulk alignment of the ferroelectric liquid crystals may take place by a mechanism that is different from one that takes place in achiral azopolymers. 

Corona poling technique in the wire to plane geometry as well as parallel electrode poling techniques have been used to pole these classes of polymers in film form. Poling is carried out prior to crosslinking to align the NLO units and possibly poise the photoreactive groups for photo-induced solid state reaction. 

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