Problem of Photoalignment in the LCD's Development: Synthetic Routes in Its Solving

Vretik, L. O.; Syromyatnikov, V. G.; Zagniy, V. V.; Savchuk, E. A.; Yaroshchuk, O.

doi:10.1080/15421400801917395

Cited by 13 publications

(5 citation statements)

References 7 publications

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“…60 The majority of these materials undergo photo-crosslinking of a cycloaddition type. The [2 + 2] cycloaddition is typical for cinnamate, 8-10 coumarin, 21,61-63 chalconyl, 64 tetrahydrophthalimide 65 and maleimide 65,66 photosensitive groups. In some of these materials, such as cinnamates and chalcones, [2 + 2] cycloaddition is accompanied with trans-cis isomerization.…”

Section: Basic Photoaligning Materialsmentioning

confidence: 99%

Photoalignment of liquid crystals: basics and current trends

2012

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Section: Basic Photoaligning Materialsmentioning

confidence: 99%

Photoalignment of liquid crystals: basics and current trends

2012

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“…One of the most investigated class of materials for photoalignment of LCs are azobenzenes − , but low thermal stability and noncontrollable, random cis−trans relaxations severely limit implementation of azobenzene-derived photoalignment layers for display applications. Other compounds tethered to surfaces allowing for photoalignment of LCs include cinnamoyl-based chromophores ,− , the spyropyran-merocyanine isomer couple − , and coumarines − . Other polymers such polystyrene and oligosiloxanes − with hydrocarbon linkers to aromatic cores, such as naphthalene or pyridine, were also found very capable of imposing alignment onto nematic LCs, some requiring rubbing, others not.…”

Section: Introductionmentioning

confidence: 99%

Multiple Alignment Modes for Nematic Liquid Crystals Doped with Alkylthiol-Capped Gold Nanoparticles

Hegmann

2009

ACS Appl. Mater. Interfaces

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The ability of alkylthiol capped gold nanoparticles (Au NPs) to tune, alter, and reverse the alignment of nematic liquid crystals (LCs) has been investigated in detail. Adjusting the concentration of the suspended Au NPs in the nematic LC host, optimizing the sample preparation protocol, or providing different sample substrates (untreated glass slides, rubbed polyimide-coated LC test cell, or ITO-coated glass slides) results in several LC alignment scenarios (modes) including vertical alignment, planar alignment, and a thermally controlled alignment switch between these two alignment modes. The latter thermal switch between planar and homeotropic alignment was observed particularly for lower concentrations (i.e., around 1 to 2 wt %) of suspended NPs in the size regime of 1.5-2 nm and was found to be concentration-dependent and thermally reversible. Different scenarios are discussed that could explain these induced alignment modes. In one scenario, the NP-induced alignment is related to the temperature-dependent change of the order parameter, S, of the nematic phase (ordering in the bulk). In the second scenario, a change of the ordering of the nematic molecules around the NPs that reside at the interfaces is described. We also started to test spin coating as an alternative way of preparing nematic thin films with well-separated Au NPs on the substrate and found this to be a possible method for manufacturing of future NP-doped LC devices, as this method produced evenly distributed NPs on glass substrates. Together the presented findings continue to pave the way for LC display-related applications of Au NP-doped nematic LCs and provide insights for N-LC sensor applications.

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“…It is well known that vertical alignment of LCs can be induced by long‐alkyl‐chain‐terminated surfaces,1 but achieving reliable and cost‐effective planar alignment remains a challenge 12. Existing alignment methods, such as mechanical rubbing, photoalignment, and ion‐beam bombardment, all rely on nanometer‐scale topological or molecular/atomic anisotropy of the alignment surfaces, properties that are difficult to control uniformly on a macroscopic scale 12–16. Alignment with micropatterned isotropic surfaces, consisting of stripes of alternating random planar‐ and vertical‐aligning materials, has been suggested as a more reliable and cost‐effective technique 13, 17.…”

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Compartmentalized Multistable Liquid Crystal Alignment

Zhang¹,

Boamfa²,

Rowan³

et al. 2010

Advanced Materials

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Nematic liquid crystals (LCs) are anisotropic elastic fluids and their molecular orientation can be controlled by surfaces and external electric/magnetic fields. These properties make them highly attractive for fabrication of tunable devices such as displays, [1] spatial light modulators, [2] dynamic lenses [3] and artificial muscles, [4] and for the manipulation of guest materials as a tunable anisotropic host. [5][6][7][8] Here, we report a novel method for LC alignment based on micrometer-scale photolithographic patterning of a self-assembled monolayer (SAM) coated onto an indium tin oxide (ITO) surface. We use closed vertically aligned LC-boundary walls, induced by the SAM surfaces, to control planar alignment of LCs on the isotropic ITO surfaces. This simple approach not only presents a new concept of planar LC alignment, which, so far, has been achieved only by nanometer-scale anisotropic surfaces, but also provides a compartmentalization of those planar-aligned LC domains. This compartmentalization allows the planar domains to be switched independently by vertical electrical fields without the dynamic LC crosstalk (molecular orientation interference between neighboring switching LC domains), a serious problem that is known to degrade current LC devices. [9][10][11] Due to the symmetry of the SAM patterns, our compartmentalized LC cells show multistable states that are tunable by an in-plane bias. The described method, exploiting mature lithography techniques, is highly reliable and cost effective, and it opens new routes for the design and fabrication of multistable LC devices, switchable viewing angle displays, and tunable structures of guest materials within a LC host.It is well known that vertical alignment of LCs can be induced by long-alkyl-chain-terminated surfaces, [1] but achieving reliable and cost-effective planar alignment remains a challenge. [12] Existing alignment methods, such as mechanical rubbing, photoalignment, and ion-beam bombardment, all rely on nanometer-scale topological or molecular/atomic anisotropy of the alignment surfaces, properties that are difficult to control uniformly on a macroscopic scale. [12][13][14][15][16] Alignment with micropatterned isotropic surfaces, consisting of stripes of alternating random planar-and vertical-aligning materials, has been suggested as a more reliable and cost-effective technique. [13,17] The LC alignment with those stripe patterns suffers, however, from random defects [13,17] due to the finite elastic correlation length of LCs and the tilt degeneracy within the planar stripes. To solve these problems, it has been suggested to use oblique illumination in combination with photoactive SAMs, [13] yet this approach relies again on molecular-level anisotropy of the surfaces.We use patterned surfaces with random planar-aligning squares embedded in a vertical-aligning surface background. The closed vertically aligned LC boundaries induce well-defined planar LC alignment on the random planar squares. A macroscopic in-plane bias, such as a directional ...

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Problem of Photoalignment in the LCD's Development: Synthetic Routes in Its Solving

Cited by 13 publications

References 7 publications

Photoalignment of liquid crystals: basics and current trends

Photoalignment of liquid crystals: basics and current trends

Multiple Alignment Modes for Nematic Liquid Crystals Doped with Alkylthiol-Capped Gold Nanoparticles

Compartmentalized Multistable Liquid Crystal Alignment

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