A method for liquid crystal alignment using <i>in situ</i> ultraviolet exposure during imidization of polyimide

Kim, Jae-Hoon; Acharya, Bharat R.; Kumar, Satyendra; Ha, Ki Ryong

doi:10.1063/1.122754

Cited by 31 publications

(17 citation statements)

References 6 publications

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“…This photoalignment method is still studied actively, [9][10][11][12][13][14] but photodecomposition may cause lowering of the inherent stability of polyimide films. [15][16][17] On the other hand, Park et al reported an alignment method based on the photoisomerization reaction of polyamic acid containing azobenzene in the backbone structure ͑azo-PAA͒. 18 Since this method contains no decomposition reaction of polyimide, the inherent stability of the polyimide film is maintained.…”

Section: Introductionmentioning

confidence: 99%

Photoinduced inclination of polyimide molecules containing azobenzene in the backbone structure

Sakamoto

Usami

Kanayama

et al. 2003

Journal of Applied Physics

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Articles you may be interested inPhotoinduced magnetic uniaxial anisotropy and molecular orientation of polymer containing azobenzene side groups with free radical end J. Appl. Phys. 93, 4392 (2003); 10.1063/1.1559634 Alignment of polyamic acid molecules containing azobenzene in the backbone structure: Effects of polarized ultraviolet light irradiation and subsequent thermal imidizationWe have investigated the inclined alignment of polyimide molecules ͑containing azobenzene in the backbone structure͒ induced by oblique angle irradiation of ultraviolet ͑UV͒ light. The UV irradiation was performed for a polyamic acid film, which then was thermally converted into a polyimide film. The orientation of the polyimide backbone structure was determined by measuring the polarized infrared absorption spectra as a function of the angle of incidence. We confirmed that inclined alignment of the polyimide backbone structures is obtained by oblique angle UV irradiation, and that this also induces tilted homogeneous liquid crystal ͑LC͒ alignment. For the UV irradiation conditions used in the present study, the average inclination angle of the polyimide backbone structure was about 4°from the surface plane. The pretilt angle of the LC molecules was 0.9°.

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Section: Introductionmentioning

confidence: 99%

Photoinduced inclination of polyimide molecules containing azobenzene in the backbone structure

Sakamoto

Usami

Kanayama

et al. 2003

Journal of Applied Physics

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“…The targets of these reactions are normally aromatic fragments of main or side polymer chains. Apart from PIs [17,93,97,98], polysilanes [99,100], polystyrene, polyesters and some other aromatic polymers [101] undergo photoalignment upon photodestruction. Photodestroyable PIs usually have a sufficiently high anchoring energy of 10 −5 J/m 2 [102,103].…”

Section: Photo-degradation In Polyimide Filmsmentioning

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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“…Many researchers have reported a rubbing-free method for LC alignment [13][14][15][16]. Most recently, the LC alignment and pretilt angle generation using the in-situ photoalignment method on a PI surface for homogeneous alignment have been reported [17]. The in-situ photoalignment method produces a higher thermal stability of LC alignment than that produced using the conventional photoalignment method.…”

Section: Introductionmentioning

confidence: 99%

Alignment Properties and EO Performances of Flexible TN-LCD UsingIn-SituPhotoalignment Method with the Polymer Film

Hwang

Nam

Seo

2005

Molecular Crystals and Liquid Crystals

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We have investigated the generation of pretilt angle for a nematic liquid crystal (NLC) alignment with in-situ photoalignment method on polyimide (PI) surfaces using polymer films. Especially, we studied in-situ photoalignment changing heating temperature from 50 C to 120 C on the polymer film. The LC aligning capabilities and pretilt angle on the polymer substrates were better than those on the glass substrate using in-situ photoalignment method. It is considered that this increase in pretilt angle may be attributed to the roughness of the micro-groove substrate induced by the in-situ photoalignment. As temperature of heated subtrate and UV exposure time increases, pretilt angle of the cell used polymer film increased. It is considered that the heating temperature of substrate is attributed to generate pretilt angle. Also, EO performances of the in-situ photoaligned TN cell using the polymer substrate are almost the same as that of the TN cell using the glass substrate.

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A method for liquid crystal alignment using in situ ultraviolet exposure during imidization of polyimide

Cited by 31 publications

References 6 publications

Photoinduced inclination of polyimide molecules containing azobenzene in the backbone structure

Photoinduced inclination of polyimide molecules containing azobenzene in the backbone structure

Photo-Alignment Technology

Alignment Properties and EO Performances of Flexible TN-LCD UsingIn-SituPhotoalignment Method with the Polymer Film

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