Photoalignment Of Liquid Crystals Research Articles

Photoalignment of liquid crystals in a hydrogen‐bonding‐directed layer‐by‐layer ultrathin film

In this paper, a new type of hydrogen‐bonding‐directed layer‐by‐layer (LBL) ultrathin film with photosensitive cinnamoyl chromophores was prepared. It could induce uniform alignment of liquid crystals (LCs) after being irradiated by linearly polarised ultraviolet light (LPUVL). The hydrogen‐bonding‐directed formation of a photochromic multilayer film was achieved on the basis of an alternating assembly of poly(4‐vinylpyridine) (PVPy) and poly(4‐acryloyloxy)cinnamic acid (PCA). The assembly process was followed by UV–visible spectroscopy. The nature of the interaction between the two polymers was identified as a hydrogen bond through Fourier transform infrared spectroscopy. When the film was irradiated by LPUVL, the cinnamoyl units in the film underwent [2+2] cycloaddition along the electric vector direction of the LPUVL. The polarised UV–visible spectra proved that the film was anisotropic, and then the film could induce homogeneous alignment of nematic LCs. With the number increment of the bilayers, the alignment effect of the multilayer film was enhanced, and the contrast ratio became higher. The orientation direction of the LCs was always perpendicular to the electric vector of the irradiating LPUVL.

Photochemistry of Bis-Methacrylic Polymers and Alignment of Liquid Crystals

Photochemical processes leading to the photoinduced anisotropy and the excellent photoaligning properties of bis-methacrylic polymers are discussed. Comparing the data for bis-methacrylic polymers and a series of model compounds, we conclude that Fries rearrangements and crosslinking reactions taking place in bis-methacrylic polymers cause the photoinduced ordering in films of these polymers via the mechanism of photoselection. Thus, all of these photochemical processes contribute to the liquid crystal photoalignment. The induced alignment is thermally stable due to the crosslinking of methacryloyl groups which fix the induced anisotropy in aligning polymer films.

New properties and applications of rewritable azo‐dye photoalignment

Abstract—The rewritable azo‐dye photoalignment (ORW) of liquid crystals (LCs) for application in optical rewritable electronic paper has been investigated. It was observed that a periodic change in the azimuthal aligning direction with polarized UV light (365 nm) brings about homeotropic alignment, while utilization of visible light (450 nm) does not affect the LC tilt angle. The wavelength dependence of the ORW photoalignment result and the behavior of the photoinduced anisotropy was explored. The dark amplification of film anisotropy after exposure was observed, which is believed to be the relaxation process related to hydrogen bonding in azo‐dye film. New material, CD1, for azo‐dye rotation photoalignement that possesses a high azimuthal anchoring energy (about 2 × 10−4J/m2) was found.

Liquid‐crystal photoaligning by azo dyes (Invited Paper)

Abstract— Liquid‐crystal (LC) photoalignment using azo dyes is described. It will be shown that this photoaligning method can provide a highly uniform alignment with a controllable pretilt angle and strong anchoring energy of the LC cell, as well as a high thermal and UV stability. The application of LC photoalignment to the fabrication of various types of liquid‐crystal displays, such as VAN‐LCDs, FLCDs, TN‐LCDs, and microdisplays, on glass and plastic substrates is also discussed. Azo‐dye photoaligned super‐thin polarizers and phase retarders are considered as new optical elements in LCD production, in particular for transflective displays.

Cinnamate-functionalized hyperbranched polymer as liquid crystal photo-alignment layer

In this work, 4-methoxylcinnamoyl chloride was reacted with a commercial hyperbranched polymer (Boltorn∼TM H30) to prepare a hyperbranched photosensitive polymer (H30-Ci). The polymer was characterized by UV absorption spectrum and 1H-NMR spectrum. After processed by Linearly Polarized Polymerization (LPP) method, the spin-coated films of H30-Ci were used as photo-alignment layers to assemble liquid crystal (LC) cells containing nematic liquid crystal (5CB). The observation by polarized microscope showed that the H30-Ci blended with a linear polymer (BP-AN-Ci) photo-alignment layers could align LC molecules in a very uniform way.

Vortex retarders produced from photo-aligned liquid crystal polymers

We present developments using photo-aligned liquid crystal polymers for creating vortex retarders, halfwave retarders with a continuously variable fast axis. Polarization properties of components designed to create different polarization vortex modes are presented. We assess the viability of these components using the theoretical and experimental point spread functions and optical transfer functions in Mueller matrix format, point spread matrix (PSM) and optical transfer matrix (OTM). The measured PSM and OTM of these components in an optical system is very close to the theoretically predicted values thus showing that these components should provide excellent performance in applications utilizing polarized optical vortices. The impact of aberrations and of vortex retarder misalignment on the PSM and OTM are presented.

60.1: Optical Rewritable Electronic Paper with Fluorescent Dye Doped Liquid Crystal

AbstractNew optical rewritable (ORW) electronic paper is the joint result of advanced photoalignment of liquid crystals, optical engineering and flexible LCD technologies. We report improvement of both dark and bright states of reflective ORW e‐paper by doping LC with fluorescent dye, which absorb blue light & emit in green with high efficiency.

Problem of Photoalignment in the LCD's Development: Synthetic Routes in Its Solving

Hereinafter we discuss our last five years investigations in the field of new highly efficient polymers for liquid crystal (LC) photoalignment. New polymers finally proposed are based on methacryloylaminoarylmethacrylates with two methacryloyl groups of different reactivity. Fries rearrangement and photocrosslinking/photopolymeryzation are such photochemical reactions which take place in their films under the action of UV light. In a case of polarized light irradiation rearrangement results in LC photoalignment. The problem of pretilt angle and anchoring energy control as well as thermal stability of the induced alignment are discussed.

Effects of Dilution, Polarization Ratio, and Energy Transfer on Photoalignment of Liquid Crystals Using Coumarin-Containing Polymer Films

Orientation of a nematic liquid crystal, E-7, was investigated using coumarin-containing polymethacrylates to elucidate the roles played by the dilution of coumarin and the polarization ratio of irradiation. Dilution of coumarin by inert moieties had adverse effects on a nematic cell’s number density of disclinations and its orientational order parameter in the parallel but not the perpendicular regime. In addition, both dilution of coumarin and a decreasing polarization ratio resulted in a lower extent of coumarin dimerization at crossover, Xc. The significantly reduced Xc in a homopolymer comprising triphenylamine and coumarin was attributed to the dilution of coumarin and the diminished polarization ratio caused by competing absorption with simultaneous triplet energy transfer from triphenylamine to coumarin moieties.

Axially symmetric polarization converters based on photo-aligned liquid crystal films

This work demonstrates axially symmetric polarization converters based on photo-alignment in dye-doped liquid crystal (DDLC) films. A linear-shape and linearly polarized beam is applied onto a rotated homogeneous DDLC cell to achieve three axially symmetric polarizations - radial, azimuthal and vortical. Additionally, the spiral degree of the axially symmetric vortical polarization can be controlled by varying the polarization of the pumping light and the simulation results agree well with the experiment.

Creating vortex retarders using photoaligned liquid crystal polymers

We present developments using photoaligned liquid crystal polymers for creating vortex retarders, half-wave retarders with a continuously variable fast axis. Polarization properties of components designed to create different polarization vortex modes are presented. We assess the viability of these components by using the theoretical and experimental point spread functions in Mueller matrix format, or a point spread matrix (PSM). The measured PSM of these components in an optical system is very close to the theoretically predicted values, thus showing that these components should provide excellent performance in applications utilizing polarized optical vortices.

Polymethacryloylaminoarylmethacrylates: New Concept of Photoalignment Materials for Liquid Crystals

New class of highly efficient polymers for liquid crystal (LC) photoalignment is proposed. These polymers are based on methacryloylaminoarylmethacrylates having two methacryloyl groups of different reactivity. The more active O-methacryloyl group is subjected to polymerization, while the less active NH-methacryloyl group undergoes photocrosslinking reaction in combination with Fries rearrangement. The latter process is anisotropic in case of polarized light irradiation that results in LC photoalignment with readily controlled pretilt angle and anchoring energy. The induced alignment shows high thermal and photo-stability.

Quantitative Assessment of Coumarin-Containing Polymer Film's Capability for Photoalignment of Liquid Crystals

The photoalignment of a nematic fluid, E-7, and a glassy-nematic oligofluorene, F(MB)5, was investigated on films of Polymers 1 and 2 in the parallel regime. Polarized absorption spectroscopy and computational chemistry were employed to characterize coumarin monomer's and dimer's molar extinction coefficients and to locate absorption dipoles as parallel to their long molecular axes. Moreover, their orientational order parameters, Sm and Sd, were experimentally determined as functions of the extent of dimerization. Higher Sd and Yd, coumarin dimer's mole fraction, were achieved in films of Polymer 1 than in Polymer 2 because of the greater coumarin mobility of the former. The ability of a coumarin-containing photoalignment film to orient a spin-cast F(MB)5 film was found to improve with increasing YdSd to an extent comparable to that of a rubbed polyimide film. Because of the relatively short lengths of its constituent molecules, E-7 was oriented equally well on both polymer films regardless of the YdSd va...

New Photoalignment Materials in LCD's Development: Liquid Crystal Pretilt Angle Variations By Using Fluoroalkylmethacrylates

Fluorinated copolymers based on 4-(N-methacryloylamino)phenyl methacrylate are proposed as materials for the liquid crystal (LC) photoalignment with a wide range of variations of a pretilt angle. As fluorinated chains, 2,2,3,3-tetrafluoropropylmethacrylate and 2,2,3,3,4,4,5,5-octafluoropenthylmethacrylate are used. The growth of a pretilt angle with the concentration of fluorinated chains, more pronounced in a series with longer fluorinated chain, is observed. The pretilt angle of TN LC ZLI 2293 is smoothly varied in the range 0°–20°. Additionally, the uniform high pretilt angle (89°–90°) alignment is realized for VA LC MJ961180.

P‐129: Rejuvenated Photoalignment of Liquid Crystal on Cinnamoil‐Containing Polymers

AbstractWe report on easy orientation axis alternation in new photoaligning polymers (PG materials) based on cellulose backbone containing photosensitive cinnamoil groups. Materials have strong application potential due to high aligning quality and photosensitivity, strong anchoring energy, small sticking effect. Rejuvenation of polymer after UV‐irradiation makes PG attractive for various applications.

Surface-Assisted Photoalignment of Discotic Liquid Crystals by Nonpolarized Light Irradiation of Photo-Cross-Linkable Polymer Thin Films

In this article, we describe the surface-assisted photoalignment of discotic liquid crystals (DLCs) on thin films of photo-cross-linkable polymers with cinnamoyl moieties as the side chains. Oblique irradiation of the polymer thin films with nonpolarized UV light at 313 nm brought about inclined orientation of the cinnamoyl residues as a result of their direction-selective photoisomerization and photodimerization. The DLC molecules on the photoirradiated polymer films were aligned in a tilted hybrid manner. This means that the DLC directors are continuously altered from the substrate to the DLC film surface so as to minimize the elastic free energy. Interestingly, we found that the tilted direction of aligned DLC molecules is clearly influenced by the chemical structures of the cinnamate-containing polymers. When a poly(vinyl cinnamate) thin film was obliquely exposed to nonpolarized UV light, the DLCs were inclined to the direction opposite to the UV light propagation. In a keen contrast, the thin film of poly(methacrylate)s tethering cinnamoyl groups, which was obliquely exposed to nonpolarized UV light in advance, provided the tilting DLC direction in parallel with the light propagation. The results were supported by tilted orientation of calamitic (rod-shaped) liquid crystal on the obliquely irradiated polymer films. Such photoalignment behavior of the DLCs can be rationalized by anchoring balance between intermolecular interaction of the DLC molecules with the photodimers of polymer films and those with the remaining E-isomers of cinnamoyl side chains at the film interface. The present technique of DLC photoalignment opens promising ways not only to understand anisotropic physical properties of DLCs, but also to design and fabricate novel nanodevices for photonics and electronics applications.

Photoalignment of liquid crystals using a covalently attached self-assembled ultrathin film fabricated from diazoresin and cinnamate polyelectrolyte

Download options Please wait... Article information DOI https://doi.org/10.1039/B703598E Article type Paper Submitted 09 Mar 2007 Accepted 04 May 2007 First published 15 May 2007 Download Citation J. Mater. Chem., 2007,17, 3015-3022 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions Photoalignment of liquid crystals using a covalently attached self-assembled ultrathin film fabricated from diazoresin and cinnamate polyelectrolyte L. Zhang, Z. Peng, L. Yao, F. Lv and L. Xuan, J. Mater. Chem., 2007, 17, 3015 DOI: 10.1039/B703598E To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Search articles by author Lingli Zhang Zenghui Peng Lishuang Yao Fengzhen Lv Li Xuan

Photoalignment of liquid crystals by cinnamate polyelectrolyte layer-by-layer ultrathin film

In this paper, a new layer-by-layer (LBL) ultrathin film with photosensitive cinnamoyl chromophores was prepared. It could induce uniform alignment of liquid crystals (LC) after irradiated by linearly polarized ultraviolet (LPUV) light. First, a photosensitive polycation containing cinnamoyl side groups was synthesized. Then a layer-by-layer ultrathin film was prepared in an aqueous solution of the polycations and poly (sodium 4-styrenesulphonate). The spectra of UV–vis absorption and ellipsometric measurement showed that the LBL film was uniform and suitable for the photoalignment of LC. When the film was irradiated by LPUV light, the cinnamoyl units in the film underwent [2+2] cycloaddition along the electric vector direction of the LPUV light. The polarized UV–vis spectra also proved that the film was anisotropic, and then the film could induce the homogeneous alignment of nematic LC. With the number of bilayers increasing, the alignment effect of multilayer film became better, and the contrast ratio became higher.

Effect of Molecular Weight on Liquid Crystal Photoalignment byPhotosensitive Polyester Containing Thrifluoromethyl Moieties

We investigate the liquid-crystal (LC) alignment direction onphotoalignment films formed from photosensitive polyestercontaining thrifluoromethyl moieties (PPDA) with various molecularweights by crossed polarized optical microscopy. It isfound that LC alignment behaviour changes with molecular weight ofPPDA. The LC alignment on PPDA irradiated films with the highestmolecular weight is homogeneous, while those with low and intermediatemolecular weights are homeotropic. However, surface morphologies showweak dependence on molecular weight. The surfaces are smooth and thereis no clear morphological anisotropy on these aligned films observed byan atomic force microscope. The surface energies of the irradiatedfilms are also measured by using an indirect contact-angle method whereboth surface energy and its polar component increase with increasingmolecular weight. Different polar surface energies can be considered asa main reason for different alignment characteristics.

Light-Controlled Alignment of Cholesteric Liquid Crystals on Photosensitive Materials

We report on investigation of photoalignment of cholesteric liquid crystal on phenylone-based photosensitive material as aligning layer. We found that reflective and electro-optical characteristics of cholesteric cells strongly depended on the dose of irradiation of a photoaligning layer with polarized UV light. Irradiation resulted in orientation of initially chaotically oriented planar domains in a direction determined with incident UV-light polarization and in narrowing of the dependence of light scattering by a planar structure on the scattering angle. The long enough exposure resulted in scattering and electro-optical characteristics not worse than obtained with standard rubbing technology. The photosensitive orientant possesses evident advantages of the effective control of cholesteric textures.