An Oblique Orientation of Nematic Liquid Crystals on a Photosensitive Aligning Polymer

Dyadyusha, A.; Khizhnyak, A. I.; Marusii, Tatyana; Reznikov, Yuriy; Yaroshchuk, O.; Reshetnyak, Victor; Park, W.; Kwon, Soon‐Bum; Shin, Hyungsoon; Kang, Dong Jin

doi:10.1080/10587259508033600

Cited by 32 publications

(17 citation statements)

References 8 publications

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“…It gives the value of λ equal to (1 + 0.6 √ 30)/7. The results of numerical analysis reported in [31] shows that this heuristic procedure gives reasonably accurate approximation for correlators of the mean field distributions (26).…”

Section: Modelmentioning

confidence: 99%

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Photoinduced three-dimensional orientational order in side chain liquid crystalline azopolymers

et al. 2003

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We apply experimental technique based on the combination of methods dealing with principal refractive indices and absorption coefficients to study the photoinduced 3D orientational order in the films of liquid crystalline (LC) azopolymers. The technique is used to identify 3D orientational configurations of trans azobenzene chromophores and to characterize the degree of ordering in terms of order parameters. We study two types of LC azopolymers which form structures with preferred in-plane and out-of-plane alignment of azochromophores, correspondingly. Using irradiation with the polarized light of two different wavelengths we find that the kinetics of photoinduced anisotropy can be dominated by either photo-reorientation (angular redistribution of trans chromophores) or photoselection (angular selective trans-cis isomerization) mechanisms depending on the wavelength. At early stages of irradiation the films of both azopolymers are biaxial. This biaxiality disappears on reaching a state of photo-saturation. In the regime of photoselection the photo-saturated state of the film is optically isotropic. But, in the case of the photo-reorientation mechanism, anisotropy of this state is uniaxial with the optical axis dependent on the preferential alignment of azochromophores. We formulate the phenomenological model describing the kinetics of photoinduced anisotropy in terms of the isomer concentrations and the order parameter tensor. We present the numerical results for absorption coefficients that are found to be in good agreement with the experimental data. The model is also used to interpret the effect of changing the mechanism with the wavelength of the pumping light.

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Section: Modelmentioning

confidence: 99%

“…On the other hand, the problems related to the 3D orientational structures in polymeric films are currently of considerable importance in the development of new compensation films for liquid crystal (LC) displays [25] and the pretilt angle generation by the use of photoalignment method of LC orientation [26].…”

Section: Introductionmentioning

confidence: 99%

Photoinduced three-dimensional orientational order in side chain liquid crystalline azopolymers

et al. 2003

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“…UV−produced cross−linking of side fragments and their reorientation perpendicular to polarisation of UV−light are considered, the main mecha− nisms of formation of light−induced easy axis in these mate− rials [6]. At the same time we found a non−monotonic de− pendence of the pretilt of LC 4−n−pentyl−4'−cyanobiphenyl (5CB) on fluoro−polyvinyl−cinnamate (PVCN−F) [7] which cannot be explained by known models [9]. We assumed the observed increase in the pretilt at long UV−exposure to be caused by light−induced changes of polarity of the PVCN−F surface.…”

Section: Introductionmentioning

confidence: 78%

Exposure and temperature dependences of contact angle of liquid crystals on photoaligning surface

Gvozdovskyy¹,

Kurioz²,

Reznikov³

2009

Opto-Electronics Review

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We report on first studies of wetting of liquid crystal on photoaligning surface. We observed strong light-induced variations of a contact angle of a liquid LC 5CB on a photoaligning surface of fluoro-polyvinyl-cinnamate (PVCN-F) and we connected these variations with changes of PVCN-F polarity. We also present drastic changes of the contact angle of a nematic liquid crystal (MLC-6080) on the PVCN-F surface in a vicinity of temperature anchoring transition of liquid crystal from homeotropic orientation to planar one. We did not find any peculiarities in temperature dependence of the contact angle of isotropic liquid (glycerol) on PVCN-F and of nematic liquid crystal on pure glass in the same temperature range. It allows us to suggest that rearrangement of LC molecules and flexible fragments in the LC-polymer interface are responsible for the change of surface tensions both of LC and polymer and the observed jump of the contact angle.

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“…The pretilt angle can be controlled by attaching hydrophobic groups such as fluorine, alkyl, alkoxy, fluoroalkyl, fluoroalkoxy and others to photosensitive molecules. These groups can be attached as individual side chains [90,91], as terminal groups of photosensitive side chains [72,92] or fragments of main polymer chains. They can also be blended with the photoaligning materials [76,93,94].…”

Section: Photo-crosslinking In Cinnamic Side-chain Polymersmentioning

confidence: 99%

Photo-Alignment Technology

Lin

2014

Topics in Applied Physics

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LCDs are used in many everyday devices, including mobile phones, notebook computers and wide screen televisions. A typical LCD is composed of two glass substrates between which is a gap that is filled with LC. The arrangement of the LC is controlled by the boundary condition of an alignment film. A long-range orientational interaction causes the preferable alignment of a LC by the surface boundary to extend into the LC bulk. The alignment layer is typically rubbed with a special cloth to induce a unidirectional alignment of the LC. In the first devices based on twisted LCs, these LCs were aligned only by rubbing transparent electrodes. The rubbing technique became much more reliable when the glass substrate was covered with a rubbed polymer layer. The rubbing of polymers is a very simple technique and it is now extensively utilized in both small scientific laboratories and large LCD factories.Despite the extensive use of rubbing in LCD manufacturing, it has some serious shortcomings that arise from the contact involved in rubbing. These critically affect the production of the most recent generation of LCDs and miniature LC photonic devices. First, rotational rubbing for the polymer surface causes the accumulation of static charges and the formation of fine dust particles. The accumulation of static electricity may destroy the transistors or diodes in the LCD. The second shortcoming is the effect of decreasing in manufacturing yield. Rubbing for large and high-resolution active matrix LCDs (AMLCDs) involve additional difficulties that are associated with the precise control of the rubbing characteristics. Other problems are the difficulty of producing local structures with the required LC director alignment in the selected areas of the device. Finally, this method cannot be used to align LCs in closed volumes.For all of the above reasons, new alignment solutions and approaches are sought. There are some alternative methods of rubbing include laser writing, micro-rubbing, ion beam irradiation and photoalignment. Of these methods, the

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An Oblique Orientation of Nematic Liquid Crystals on a Photosensitive Aligning Polymer

Cited by 32 publications

References 8 publications

Photoinduced three-dimensional orientational order in side chain liquid crystalline azopolymers

Photoinduced three-dimensional orientational order in side chain liquid crystalline azopolymers

Exposure and temperature dependences of contact angle of liquid crystals on photoaligning surface

Photo-Alignment Technology

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