Liquid crystal pretilt angle control using adjustable wetting properties of alignment layers

Ahn, Hyung Jin; Kim, Jong-Bok; Kim, Kyung Chan; Hwang, Byoung Har; Kim, Jong-Tae; Baik, Hong Koo; Park, Jin Seol; Kang, Daeseung

doi:10.1063/1.2749843

Cited by 31 publications

(22 citation statements)

References 20 publications

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“…Fluorine-containing alignment layers are used widely to align LC molecules vertical with respect to the alignment layer surfaces because fluorinated groups can produce low surface energy layers. [63][64][65][66] This homeotropic LC alignment behavior of the polymers was found to be related to the surface energy values of polymer films discussed later in this paper. POM images of the LC cells made from polymer films and different LC molecules were also observed in order to compare the homeotropic LC aligning ability of the polystyrene derivatives containing fluorine side groups.…”

Section: Resultsmentioning

confidence: 99%

Liquid crystal alignment properties of polystyrene derivatives containing fluorinated side groups

2010

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The liquid crystal (LC) alignment properties of a series of polystyrene derivatives containing various fluorinated side chain terminal moieties, such as 4-fluorophenoxymethyl, 3,4,5-trifluorophenoxymethyl, pentafluorophenoxymethyl, and 4-trifluoromethoxyphenoxymethyl groups, were investigated. These polymers could induce homeotropic and/or homogeneous planar LC alignment on their surfaces by changing the LC molecules and rubbing conditions. For example, when a positive (MJ001929 from Merck) and negative dielectric anisotropic LC mixture (MLC-7026-000 from Merck) were used, homeotropic LC alignment was observed in the LC cells made from unrubbed films of pentafluorophenoxymethyl-and 4-trifluoromethoxyphenoxymethyl-substituted polystyrenes with a smaller surface energy, whereas random planar LC alignment was observed in those made from the other polymers with a larger surface energy. On the other hand, homeotropic LC alignment behavior was observed in all the LC cells made from unrubbed films of all the polystyrene derivatives when 5CB was used as the LC material.

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Section: Resultsmentioning

confidence: 99%

Liquid crystal alignment properties of polystyrene derivatives containing fluorinated side groups

2010

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“…[28][29][30] They include patterning techniques, such as polymer transfer printing, nanoimprinting with a rigiflex mold, and soft molding, and LC alignment mechanisms on an inorganic layer, for example, silicon carbide and diamond-like carbon. Among them, nanoimprinting with a rigiflex mold makes it possible to peel the mold off with directionality (directional peeling), which can induce orientation of the free end chain of the alignment layer because the directional peeling of the flat film affects the orientation of the free end chain of the polymer.…”

Section: Full Papermentioning

confidence: 99%

The Directional Peeling Effect of Nanostructured Rigiflex Molds on Liquid‐Crystal Devices: Liquid‐Crystal Alignment and Optical Properties

Kim

Lim

Park

et al. 2008

Adv Funct Materials

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We report a new strategy, the directional peeling of a rigiflex mold with a nanostructure, to overcome several problems with general patterning techniques for liquid‐crystal (LC) alignment. These include difficulty in generating the pretilt angle and in controlling the LC rising‐up direction, formation of local domains, and weak optical properties. The directional peeling of the rigiflex mold results in pretilt‐angle formation and controls the LC rising‐up direction. In addition, a nanostructure with small spacing aligns the LC with a high order parameter because of a strong confinement effect and suppresses diffraction due to its small spacing. Eventually, the nanostructure achieves improvements in the optical properties. In summary, while recent patterning techniques for LC alignment only solve one problem, the directional peeling of the rigiflex mold with a nanostructure simultaneously overcomes several problems with LC alignment and optical properties.

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“…Numerous polymers, including a variety of photoreactive functional groups for photoisomerization, photodimerization, and photodegradation have been studied as photoalignment layers [ 38 , 39 , 40 ]. The orientation of LC molecules on polymer films is dependent on the chemical composition of the polymer films [ 41 ]. Polystyrene (PS) surfaces producing planar LC orientation can be prepared at low temperatures suitable for the fabrication of flexible displays.…”

Section: Introductionmentioning

confidence: 99%

Vertical Orientation of Liquid Crystal on Comb-Like 4-(trans-4-alkylcyclohexyl)phenoxymethyl-substituted Polystyrene Containing Liquid Crystal Precursor

Seo

Kang

2021

Polymers

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We synthesized a series of polystyrene derivatives modified with precursors of liquid crystal (LC) molecules, including 4-(trans-4-ethylcyclohexyl)phenol (homopolymer PECH and copolymer PECH#; # = 5, 10, 15, 20, 40, 60, and 80, where # indicates the molar fraction of 4-(trans-4-ethylcyclohexyl)phenoxymethyl in the side chain), 4-(trans-4-propylcyclohexyl)phenol (PPCH), 4-(trans-4-butylcyclohexyl)phenol (PBCH), and 4-(trans-4-amylcyclohexyl)phenol (PAmCH) via polymer modification reactions in order to investigate the orientation of LC molecules on polymer films exhibiting part of the LC molecular structure. A stable and uniform vertical orientation of LC molecules was observed in LC cells fabricated with PECH#, having 15 mol% or more of 4-(trans-4-ethylcyclohexyl)phenoxymethyl side groups. In addition, the vertical orientation of LC molecules was observed in LC cells fabricated with homopolymers of PECH, PPCH, PBCH, and PAmCH. The water contact angle on the polymer films could be associated with the vertical orientation of the LC molecules in the LC cells fabricated with polymer films. For example, a vertical LC orientation was observed when the water contact angle of the polymer films was higher than ~81°. Good orientation stability was observed at 200 °C and 15 mW/cm2 of UV irradiation for LC cells fabricated with PECH films.

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Liquid crystal pretilt angle control using adjustable wetting properties of alignment layers

Cited by 31 publications

References 20 publications

Liquid crystal alignment properties of polystyrene derivatives containing fluorinated side groups

Liquid crystal alignment properties of polystyrene derivatives containing fluorinated side groups

The Directional Peeling Effect of Nanostructured Rigiflex Molds on Liquid‐Crystal Devices: Liquid‐Crystal Alignment and Optical Properties

Vertical Orientation of Liquid Crystal on Comb-Like 4-(trans-4-alkylcyclohexyl)phenoxymethyl-substituted Polystyrene Containing Liquid Crystal Precursor

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