Novel Surface-Stabilized Vertical Alignment Mode for Fast-Response Liquid Crystal Display

Lee, Jun Hyup; Oh, Keunchan; Kim, Hee Sub; Wu, Shin‐Tson

doi:10.1109/jdt.2011.2180358

Cited by 12 publications

(9 citation statements)

References 13 publications

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“…Therefore, other modes with wide viewing angles and high contrast ratios, including the in-plane switching (IPS) mode, fringe-field switching (FFS) mode, and vertical alignment (VA) modes have been developed [ 36 , 37 , 38 ]. Among these modes, the VA mode has an especially high contrast ratio owing to minimal retardation [ 39 , 40 , 41 ]. Additionally, nematic LCs, wherein the director is oriented vertically to the surface of the substrate, have been studied for sensor applications because of their susceptibility to small perturbations and any binding events [ 42 , 43 , 44 , 45 ], which can be observed not only with the naked eye but also with optical techniques such as polarized optical microscopy (POM) [ 46 , 47 ].…”

Section: Introductionmentioning

confidence: 99%

Vertical Orientation of Liquid Crystal on Polystyrene Substituted with n-Alkylbenzoate-p-oxymethyl Pendant Group as a 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 via polymer modification reactions. Thereafter, the orientation of the LC molecules on the polymer films, which possess part of the corresponding LC molecular structure, was investigated systematically. The precursors and the corresponding derivatives used in this study include ethyl-p-hydroxybenzoate (homopolymer P2BO and copolymer P2BO#, where # indicates the molar fraction of ethylbenzoate-p-oxymethyl in the side chain (# = 20, 40, 60, and 80)), n-butyl-p-hydroxybenzoate (P4BO), n-hexyl-p-hydroxybenzoate (P6BO), and n-octyl-p-hydroxybenzoate (P8BO). A stable and uniform vertical orientation of LC molecules was observed in LC cells fabricated with P2BO#, with 40 mol% or more ethylbenzoate-p-oxymethyl side groups. In addition, the LC molecules were oriented vertically in LC cells fabricated with homopolymers of P2BO, P4BO, P6BO, and P8BO. The water contact angle on the polymer films can be associated with the vertical orientation of the LC molecules in the LC cells fabricated with the polymer films. For example, vertical LC orientation was observed when the water contact angle of the polymer films was greater than ~86°. Good orientation stability was observed at 150 °C and with 20 J/cm2 of UV irradiation for LC cells fabricated with the P2BO film.

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Section: Introductionmentioning

confidence: 99%

Vertical Orientation of Liquid Crystal on Polystyrene Substituted with n-Alkylbenzoate-p-oxymethyl Pendant Group as a Liquid Crystal Precursor

Seo

Kang

2021

Polymers

View full text Add to dashboard Cite

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“…In order to achieve perfect vertical alignment, many methods have been taken to control the pretilt angle, such as rubbing vertical alignment [ 4 , 5 , 6 , 7 , 8 , 9 ], polymer-sustained vertical alignment (PSVA) [ 10 , 11 , 12 ], and photo-induced vertical alignment [ 13 , 14 , 15 , 16 , 17 ]. Among these alignment methods mentioned above, the PSVA technology showing strength through its fast response, high transmittance, and simple manufacturing process [ 18 ] has been widely investigated. Generally, this technology is conducted as follows: the LC cell containing LC and UV-curable monomers is UV-irradiated under a voltage larger than the Freedericksz transition voltage, and the pretilt angle is fixed by the polymer networks formed during UV irradiation.…”

Section: Introductionmentioning

confidence: 99%

Photo-Induced Vertical Alignment of Liquid Crystals via In Situ Polymerization Initiated by Polyimide Containing Benzophenone

et al. 2017

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Vertical alignment of liquid crystal (LC) was achieved in an easy and effective way: in situ photopolymerization of dodecyl acrylate (DA) monomers initiated by polyimide based on 3,3 ,4,4 -benzophenonetetracarboxylic dianhydride and 3,3 -dimethyl-4,4 -diaminodiphenyl methane (BTDA-DMMDA PI). The alignment behavior and alignment stabilities were characterized by a polarizing optical microscope (POM), which showed a stable vertical alignment after 12 h of thermal treatment. The chemical structures, morphology, and water contact angles of alignment films peeled from LC cells with and without DA monomers were analyzed by means of a Fourier transform infrared spectrometer (FTIR), a scanning electron microscope (SEM), and a contact angle tester, separately. The results confirmed that the DA monomers underwent self-polymerization and grafting polymerization initiated by the BTDA-DMMDA PI under ultraviolet irradiation, which aggregated on the surfaces of PI films. The water contact angles of the alignment films were about 15 • higher, indicating a relative lower surface energy. In conclusion, the vertical alignment of LC was introduced by the low surface free energy of PI films grafted with DA polymer and intermolecular interactions between LC and DA polymers.

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“…In general, pretilt angle results from the interaction between LC molecules and alignment film surface, which is subject to surface chemical properties, molecular structure of LC, surface morphology, and so on. There are several methods that have been developed for tuning LC pretilt angle in the cell, including using polymer alignment layer with long alkyl side chains or nonpolar groups, − tuning rubbing conditions, , application of surface modification, − or utilization of composite and new material alignment film. − Among numerous techniques, polymer-stabilized LC is one of the most promising methods. − To control the pretilt angle, monomers are doped into the LC solution. Polymerization is triggered while LC molecules are subjected to electric field, which guides the molecules into uniform alignment.…”

Section: Introductionmentioning

confidence: 99%

Role of Monomer Alkyl Chain Length in Pretilt Angle Control of Polymer-Stabilized Liquid Crystal Alignment System

2017

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The pretilt angle of liquid crystal (LC) molecules in LC cells was manipulated by adding a mixture of two photocurable monomers, alkyl acrylate and biphenyl diacrylate, into the LCs after the UV treatment. The hexyl acrylate and octadecyl acrylate were applied to examine the alkyl chain length effect on the pretilt angle control under the condition of a fixed concentration of biphenyl diacrylate. The LC alignment was continuously adjusted from homogeneous to homeotropic alignment in the polymer-stabilized LC system by simply increasing the alkyl acrylate concentration in the LCs. At a given molar concentration of alkyl acrylate, the addition of octadecyl acrylate exhibits higher pretilt angle than that of hexyl acrylate. Both the pretilt angle of the LCs and advancing contact angle of water on the inner surfaces of LC cells simultaneously changed due to surface chemical nature and surface roughness. The pretilt angle increases along with an increase in the advancing contact angle. As a consequence, the surface advancing contact angle acts as an index for pretilt angle control.

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Novel Surface-Stabilized Vertical Alignment Mode for Fast-Response Liquid Crystal Display

Cited by 12 publications

References 13 publications

Vertical Orientation of Liquid Crystal on Polystyrene Substituted with n-Alkylbenzoate-p-oxymethyl Pendant Group as a Liquid Crystal Precursor

Vertical Orientation of Liquid Crystal on Polystyrene Substituted with n-Alkylbenzoate-p-oxymethyl Pendant Group as a Liquid Crystal Precursor

Photo-Induced Vertical Alignment of Liquid Crystals via In Situ Polymerization Initiated by Polyimide Containing Benzophenone

Role of Monomer Alkyl Chain Length in Pretilt Angle Control of Polymer-Stabilized Liquid Crystal Alignment System

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