Vertical alignment of liquid crystals without alignment layers

Kim, Ki-Han; Park, Byung Wok; Choi, Sun-Wook; Lee, Jihoon; Kim, Hoon; Shin, Kwang-Bok; Kim, Hee Seop; Yoon, Tae–Hoon

doi:10.1080/02678292.2012.754961

Cited by 32 publications

(13 citation statements)

References 11 publications

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“…The noncontact LC alignment systems consisting of nanoparticles or surface active agents dispersion in the LC host have been reported to achieve macroscopic homeotropic or homogeneous alignments 10−14 . Surface active agents (amphiphilic molecules) like hexadecyl trimethyl ammonium bromide (HTAB) in negative LC hosts interact with ITO substrates and results in homeotropic alignment due to molecular self-assembly at the interfaces 15 . The amphiphilic molecules usually contain a polar anchoring group and a flexible long alkyl chain, in which the polar anchoring group interacts with ITO surface, leaving the flexible long alkyl chain in the LC bulk to homeotropically align the LC molecules 16−18 .…”

Section: Introductionmentioning

confidence: 99%

Highly Stable, Pretilted Homeotropic Alignment of Liquid Crystals Enabled by In Situ Self-Assembled, Dual-Wavelength Photoalignment

Kumar

Jiang

et al. 2020

ACS Appl. Electron. Mater.

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Homeotropic alignment of liquid crystals (LCs) is one of the key modes used in commercial liquid crystal displays (LCDs) due to its advantages, such as high contrast ratios and fast response speed. Here, we report stable homeotropic LC alignment with a small pretilt angle in a nematic, negative LC host doped with additives including self-aligning agents, photoresponsive azo dyes and reactive mesogen via an in-situ self-assembled, dual-wavelength photoalignment approach. The underlying mechanism of stable, pretilted homeotropic LC alignment was further analyzed in detail. The achieved pretitled homeotropic LC cells are very stable against heat and UV light exposure and demonstrate excellent electro-optical characteristics. The experimental results show that such a noncontact, simple homeotropic alignment technique has big potential in many applications, such as high-quality LCDs, spatial light modulators, and other optoelectronic devices.

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Section: Introductionmentioning

confidence: 99%

Highly Stable, Pretilted Homeotropic Alignment of Liquid Crystals Enabled by In Situ Self-Assembled, Dual-Wavelength Photoalignment

Kumar

Jiang

et al. 2020

ACS Appl. Electron. Mater.

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“…In an another approach, K. H. Kim et al . described the vertical alignment of LCs on ITO substrate without the alignment layers, simply by mixing the LC with very small quantity (0.05%) of a surface active reagent namely, hexadecyltrimethylammonium bromide 22 . Similarly, an automatic vertical alignment of nematic LCs over an ITO substrate by using carbohydrate-based giant surfactants as alignment layers was reported by D. Y. Kim et al .…”

Section: Introductionmentioning

confidence: 99%

Vertical Alignment of Liquid Crystals Over a Functionalized Flexible Substrate

Sivaranjini

Mangaiyarkarasi

Ganesh

et al. 2018

Sci Rep

167

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A simple and effective approach for vertical alignment of liquid crystals (LCs) over a functionalized transparent flexible substrate is described. Surface characterization of this commercially available plastic substrate through X-ray photoelectron spectroscopy (XPS) and attenuated total reflection infrared spectroscopy (ATR-IR) indicated that cellulose acetate is main component of the transparent substrate. This substrate was chemically functionalized with a suitable LC compound. A trimethoxysilane terminated new rod-shaped mesogen is synthesized and covalently attached to the pre-treated film through silane condensation reaction. LC functionalization of the polymer film is confirmed through contact angle (CA), atomic force microscopy (AFM), XPS and ATR-IR spectroscopy studies. Versatility of the LC modified flexible substrates for the alignment of bulk LC sample at substrate-LC interface was assessed for nematic (N) and smectic A (SmA) phases. Remarkably, LC functionalized cellulose acetate films were found to be highly efficient in assisting a perfect homeotropic alignment of LCs (for both, a room temperature N and a high temperature SmA phase) over the entire area of the LC sample under observation indicating their superior aligning ability in comparison to their unmodified and octadecyltrimethoxysilane (OTS) modified counterparts. The demonstrated method of surface modification of flexible polymer film is easy, surface modified substrates are stable for several months, retained their aligning ability intact and more importantly they are reusable with maximum delivery.

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“…The doped LC cell had a faster rise time than the VA LC cell because cyclic dimers of the carboxylic acid group formed between the gelator molecules dispersed in the LC bulk [ 32 ]. The aggregated gelators functioned as the polymer sticks in polymer-stabilized LC (PSLC) cells [ 37 , 38 , 39 ], suppressing the optical bounce and improving the rise time of the cell.…”

Section: Resultsmentioning

confidence: 99%

Fast Response and Spontaneous Alignment in Liquid Crystals Doped with 12-Hydroxystearic Acid Gelators

Lin

Wang

et al. 2018

Materials

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The spontaneous vertical alignment of liquid crystals (LCs) in gelator (12-hydroxystearic acid)-doped LC cells was studied. Gelator-induced alignment can be used in both positive and negative LC cells. The electro-optical characteristics of the gelator-doped negative LC cell were similar to those of an LC cell that contained a vertically aligned (VA) host. The rise time of the gelator-doped LC cell was two orders of magnitude shorter than that of the VA host LC cell. The experimental results indicate that the gelator-induced vertical alignment of LC molecules occurred not only on the surface of the indium tin oxide (ITO) but also on the homogeneous alignment layer. Various LC alignments (planar, hybrid, multistable hybrid, and vertical alignments) were achieved by modulating the doped gelator concentrations. The multistable characteristic of LCs doped with the gelator is also presented. The alignment by doping with a gelator reduces the manufacturing costs and provides a means of fabricating fast-responding, flexible LC displays using a low-temperature process.

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Vertical alignment of liquid crystals without alignment layers

Cited by 32 publications

References 11 publications

Highly Stable, Pretilted Homeotropic Alignment of Liquid Crystals Enabled by In Situ Self-Assembled, Dual-Wavelength Photoalignment

Highly Stable, Pretilted Homeotropic Alignment of Liquid Crystals Enabled by In Situ Self-Assembled, Dual-Wavelength Photoalignment

Vertical Alignment of Liquid Crystals Over a Functionalized Flexible Substrate

Fast Response and Spontaneous Alignment in Liquid Crystals Doped with 12-Hydroxystearic Acid Gelators

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