&lt;title&gt;Oblique photoalignment of a nematic liquid crystal by modified polyvinylcinnamates&lt;/title&gt;

Dyadyusha, A.; Marusii, Tatyana; Reznikov, Yuri; Yaroshchuk, O.

doi:10.1117/12.230653

Cited by 10 publications

(7 citation statements)

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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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Section: Photo-crosslinking In Cinnamic Side-chain Polymersmentioning

confidence: 99%

Photo-Alignment Technology

Lin

2014

Topics in Applied Physics

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“…Photoalignment of nematic liquid crystals (NLCs) has been discovered almost three decades ago [1,2,3]. The process is not only an alternative to the standard aligning methods (e.g., mechanical rubbing of polyimide layers) ensuring the correct operation of devices based on NLCs, but also enables the reorientation of the liquid crystal director n in a contactless manner through light irradiation [4].…”

Section: Introductionmentioning

confidence: 99%

Photoalignment at the nematic liquid crystal - polymer interface: the importance of the liquid crystalline molecular structure

Nassrah¹,

Jánossy²,

Tóth-Katona³

2020

Preprint

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The influence of the molecular structure of the nematic liquid crystal (NLC) on the photoalignment process at the NLC -polymer interface has been investigated experimentally. NLCs having exclusively phenyl-, or cyclohexane rings in the rigid core, as well as NLCs containing both phenyl and cyclohexane groups have been considered. Substantial differences have been found in the photoalignment process depending on the molecular structure of the NLC, supporting the assumption that the polymer -NLC interface should be regarded as a coupled system, where the two components mutually influence each other. A phenomenological explanation is given for the observed differences.

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“…11,15,16 According to this method the cell is arranged between crossed polarizers so that the plane of the director-this is effectively the rubbing direction-makes an angle of 45°with respect to the polarization axes. The beam from a weak He-Ne laser passes through the first polarizer and is normally incident on the cell.…”

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confidence: 99%

“…For symmetric pretilt angles at the two surfaces, the intensity profile I vs ␤ is symmetric about ␤ϭ0; if the pretilt angles differ, the symmetry axis of I͑␤͒ is shifted by an angle ⌬␤. It can be shown that 15,16 ( PVCN ϩ PI )/2 Ϸ ⌬␤/(n e ϩn 0 ) , where PVCN is the pretilt angle of the PVCN-coated substrate and n e and n 0 are the refractive indices for ordinary and extraordinary light, respectively. Thus, a measurement of ⌬␤ facilitates a determination of the pretilt angle.…”

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confidence: 99%

“…Finally, we note that the magnetic field breaks rotational symmetry and thereby overcomes the problem of the twofold degeneracy of oblique alignment on photosensitive polymers. 15 Thus, the concomitant use of magnetic fields and UV-irradiation of a PVCN surface offers a nondestructive and controlled environment to achieve homogeneous alignment of liquid crystals. Such a technique may prove to be an effective alternative to mechanical buffing of the substrate.…”

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