Molecular Orientation of Liquid Crystals on Topographic Nanopatterns

Ryu, Seong Ho; Yoon, Dong Ki

doi:10.1021/acsami.6b05568

Cited by 15 publications

(10 citation statements)

References 45 publications

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“…The 8CB molecule shows two distinct LC phases, N and SmA phases, on cooling. Generally, LC molecules in the N phase have a long-range orientation order, and the rubbing method becomes a powerful tool to orient LC molecules along the rubbing direction in this phase, whose effect is considerably maintained even in the arrangement of SmA layers. , As a result, one dimensionally oriented LC molecules in the N phase are developed to have layers in the SmA phase, thereby generating different types of textures (Figure S1). To investigate the surface anchoring- and rubbing-dependent molecular arrangement, pristine or rubbed substrates coated with both types of PI were prepared to make three different anchoring conditions, which are PA, VA, and hybrid anchoring systems with a cell gap of 5 μm (Figures and S1).…”

Section: Resultsmentioning

confidence: 99%

Directed Self-Assembly of Topological Defects of Liquid Crystals

2018

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One of the alluring aspects of liquid crystals (LCs) is their readily controllable self-assembly behavior, leading to comprehension of complex topological structures and practical patterning applications. Here, we report on manipulating various kinds of topological defects by adopting an imprinted polymer-based soft microchannel that simultaneously imposes adjustable surface anchoring, confinement, and uniaxial alignment. Distinctive molecular orientation could be achieved by varying the surface anchoring conditions at the sidewall polymer and the rubbing directions on the bottom layer. On this pioneering platform, a common LC material, 8CB (4'-n-octyl-4-cyano-biphenyl), was placed where various topological defect domains were generated in a periodic arrangement. The experimental results showed that our platform can change the packing behavior and even the shape of topological defects by varying the rubbing condition. We believe that this facile tool to modulate surface boundary conditions combined with topographic confinement can open a way to use LC materials in potential optical and patterning applications.

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Section: Resultsmentioning

confidence: 99%

Directed Self-Assembly of Topological Defects of Liquid Crystals

2018

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“…In addition, there have been many attempts to develop the materials for controlling the pretilt angle of an LC alignment layer because different LC modes based on the control of the pretilt angle are required for electro-optical performance according to the customer's needs. [12][13][14] Until now, the development of materials for the control of the LC pretilt angle has been conducted through thermal and surface treatment, [14,15] mixture of functional materials, [16,17] both of which can control the surface characteristics, thereby controlling the pretilt angle of the LCs. However, thermal treatment sensitively reacts with the LC surface characteristic within a narrow temperature range (220-300 °C).…”

Section: Introductionmentioning

confidence: 99%

Selective Liquid Crystal Driving Mode Achieved by Controlling the Pretilt Angle via a Nanopatterned Organic/Inorganic Hybrid Thin Film

Song

Jeong

Lee

et al. 2021

Advanced Optical Materials

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Behavior of liquid crystal (LC) is a result of interaction between the geometrical shape restrictions of the adjacent surface and molecular forces among LCs or adjacent surface. For years, continuous efforts have been made to control LC orientation and anchoring with pretilt angle for modulating the electro‐optical characteristics. For now, diverse driving modes have been developed including twisted nematic, optically compensated bend, electrically controlled birefringence, and vertical alignment. However, it has the limitation that different fabrication process should be adopted in different driving mode such as materials of alignment layer and techniques for aligning the LCs. Herein, selective LC modes are achieved by controlling the LC pretilt angle using nanopatterned organic/inorganic hybrid thin films composed of polyimide (PI) and tin oxide (SnO). It is possible to control the surface wettability according to the composition ratio between PI and SnO, thereby adjusting the pretilt angle of the LCs. Fabrication of SnO combined with PI applied via embossing allows for the large‐scale replication for LC alignment and based on consumer demand, devices can be manufactured in various modes through simple configuration changes. Therefore, an inorganic compound combined with an organic one permits designing addressable LC driving modes.

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“…Liquid crystals (LCs), as a group of unique materials with special phase states between solids and liquids, have been drawing huge attention since their discovery in 1888 . They combined both rigidity and fluidity of materials and infused them with long-ranged orders and confined mobilities. − At the molecular level, liquid crystals must be highly geometrically anisotropic in structures and are believed to possess potential applications in lubrication. − Moreover, the orientation of the liquid crystal molecules can be changed by outer external stimuli, such as temperature, electric field, or even light, making them perfect candidates for controllable tribological applications.…”

Section: Introductionmentioning

confidence: 99%

Cholesteryl Liquid Crystals as Oil-Based Lubricant Additives: Effect of Mesogenic Phases and Structures on Tribological Characteristics

Gao

Jiang

et al. 2019

Langmuir

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Mechanical operation could be seriously affected by friction and controlling it by oil lubrication has been considered as an effective way. Good lubricant additives are very necessary to avoid the friction damages, and to find or design new additives is always a challenge. In this study, a systematic investigation of using cholesteryl liquid crystals (LCs) as lubricant additives to obtain exceptional tribological behaviors was performed. In total, four cholesteryl LC compounds were synthesized targetedly and their thermal and mesogenic properties were studied to see the inherent relationship between the mesogenic phases and antifriction and antiwear performance. Through a series of tribological and related tests, including the UMT TriboLab test, three-dimensional optical microscopy, oil film thickness and viscosity tests, etc., the effect of the mesogenic phases and structures of the synthesized cholesteryl LCs on their tribological properties as lubricant additives was investigated and a related mechanism was analyzed. The result showed that within and close to the mesogenic phase temperature ranges, which we called as effective temperature ranges of LC additives (T EF), the LCs presented better tribological behaviors, meaning they could be used in special lubrication applications that need to be confined in certain temperature scopes; however, the ester groups with long alky tails could help dissolve in base oils and adsorb onto the friction pairs. Among the four LCs, LC-D with a long perfluoroalkyl tail brought widest mesogenic phase with considerably enhanced lubrication performance and increased oil film thickness, viscosity, and thermal stability, indicating that the perfluoroalkyl group could be well used in the structural modification of LC additives to give unexpected tribological performance. This study, in conjunction with our experimental data, suggested that the liquid crystals may be evaluated as potential friction modifiers for temperature-controllable lubrication and also shed a fresh light on the development of novel liquid crystal lubrication materials.

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Molecular Orientation of Liquid Crystals on Topographic Nanopatterns

Cited by 15 publications

References 45 publications

Directed Self-Assembly of Topological Defects of Liquid Crystals

Directed Self-Assembly of Topological Defects of Liquid Crystals

Selective Liquid Crystal Driving Mode Achieved by Controlling the Pretilt Angle via a Nanopatterned Organic/Inorganic Hybrid Thin Film

Cholesteryl Liquid Crystals as Oil-Based Lubricant Additives: Effect of Mesogenic Phases and Structures on Tribological Characteristics

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