Nanostructured alignment layer for liquid crystals

et al. 2015

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A novel discontinuous photoalignment surface with nano-domains for liquid crystal is developed. The formation of the discontinuous structure is created by self-organized dewetting, which is regarded as one of the most promising bottom-up approaches to fabricate nano-structure. Different dewetting conditions, such as surface roughness, thickness and viscosity, have been investigated. Such discontinuous photoalignment layer can be fabricated on top of another continuous alignment layer to form a new kind of heterogeneous nano-structured alignment surfacestacked alignment layers. This heterogeneous alignment surface can be used to produce arbitrary pretilt angles for the liquid crystal display. Simulation model has been built to understand the dewetting mechanism. Experiments using photo-aligned and photo-polymerisable polymer have been done to verify the dewetting theory. The produced stacked alignment layers are proved to be robust. Moreover, the dewetting processing is a fully controllable process and is compatible with existing manufacturing techniques.

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confidence: 99%

Nano‐domains formation on photoalignment thin film by self‐organized dewetting

et al. 2015

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“…At present, numerous methods had been proposed for generating pretilt angles in the range of 30°-60°. [1][2][3][4][5][6] However, there were only a few attempts to produce both variable pretilt and azimuth angles. [4][5][6] Jong et al 4 had proposed to control the pretilt angles via ion beam irradiation of silicon carbide (SiC) layers of various compositions.…”

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confidence: 99%

“…Liquid crystal (LC) alignment layer, which controls the LC molecule orientations on the panel surfaces, is one of the most important element to LC display. At present, numerous methods had been proposed for generating pretilt angles in the range of 30°–60° . However, there were only a few attempts to produce both variable pretilt and azimuth angles .…”

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confidence: 99%

Arbitrary pretilt and azimuth angles generation by stacked photoalignment layers

et al. 2015

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-We report a method of fabricating a nano-sized stack alignment layer. The stacked alignment layer consists of nano-domains of vertical and planar alignment materials. Experiments reveal that photoalignment thin film can undergo dewetting and form discrete nano-sized domains. Such selforganized structure creates a discontinuous layer stacked on top of a continuous layer and hence produces an inhomogeneous alignment surface. With two or more different principle alignment directions, this new alignment layer is capable of producing multiple pretilt and azimuth angle domains on a single substrate.Keywords -photoalignment, pretilt angle, azimuth angle, stacked layers, liquid crystal alignment, dewetting, nanostructured.DOI # 10.1002/jsid.374Liquid crystal (LC) alignment layer, which controls the LC molecule orientations on the panel surfaces, is one of the most important element to LC display. At present, numerous methods had been proposed for generating pretilt angles in the range of 30°-60°. 1-6 However, there were only a few attempts to produce both variable pretilt and azimuth angles.4-6 Jong et al. 4 had proposed to control the pretilt angles via ion beam irradiation of silicon carbide (SiC) layers of various compositions. The azimuth angle could be controlled by in-plane projection of the particle beam; but the produced pretilt angle only had a limited range of 67°to 90°. Yaroshchuk et al.5 had suggested using plasma beam irradiation to a fluorinated polyimide. Although the produced pretilt angle could be varied from 0°to 90°, the processing window for intermediate values, 30°-60°, was narrow. The transition was nonlinear and like a step function. The azimuth angle had also showed an abrupt change from parallel to perpendicular with respect to the plane of incidence of the plasma beam. In addition, the oblique irradiation might not be favorable to large-area substrate. The spatial reliability remained to be an issue. Ho et al.6 had attempted to generate variable pretilt angles by photoaligning a mixed polyimide. The nano-domains were formed by phase segregation during the drying of mixed fluids.7 The processing was rather simple, but the repeatability was unsatisfactory because of the uncertainty of the precipitation rate. Hence, in this paper, we would like to propose a stacked nanostructured surface that can fulfill this technology gap. The stacked nanostructured surface is preferable for large-area substrate and is highly reliable. The produced pretilt and azimuth angles can be varied from nearly 0°to 90°. In addition, the processing window is large as the angles are linearly proportional to the nano-domain area ratios. Moreover, we introduce thin film dewetting mechanism for self-generating the nano-domains without resorting to micro-fabrication techniques. The nano-domains of one alignment material are formed on top of another continuous alignment material. Hence, it has a stacked structure with only one additional coating step, which is compatible with existing manufacturing technique. The modeli...

“…Previously, our group had proposed three kinds of nano‐structured alignment surfaces . They contained nano‐sized alignment domains with both planar and vertical pretilt alignment properties.…”

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confidence: 99%

Bistable nano‐structured photoalignment surface by nanoimprint lithography

et al. 2015

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-A novel nano-structured photoalignment surface is proposed and demonstrated. Such alignment surface has bistable azimuthal alignment directions for the liquid crystal molecules. The new alignment surface has a structure of stacking a photo-polymerizable photoalignment polymer on top of a nano-sized groove surface. The photoalignment polymer and groove surface have different azimuthal alignment directions but the same azimuthal anchoring energies. The fabrication of the nano-sized groove is based on nano-imprint lithography. Hence, the size and depth are controllable, where no random process is involved. The alignment surface is robust, stable, reliable, reproducible and suitable for mass manufacturing. Such alignment surface can be applied to fabricate a π/2 bistable twisted nematic (π/2-BTN) display which has better optical performances than the traditional π-BTN display.