Controllable liquid crystal defect arrays induced by an in-plane electric field and their lithographic applications

Suh, Ah-Ram; Ahn, Hyungju; Shin, Tae Joo; Yoon, Dong Ki

doi:10.1039/c8tc06042h

Cited by 20 publications

(23 citation statements)

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“…Suh et al recently reported the dynamic modulation of disclination lines and FCDs in the N and SmA phases, respectively, by changing the magnitude of voltage ( Figure 8) [16]. The LC material having both N and SmA phases with positive dielectric anisotropy is confined under a hybrid anchoring condition with an applied electric field in the in-plane direction (y-axis).…”

Section: Electric Field Applicationmentioning

confidence: 99%

“…Passing through the golden age of the liquid crystal display (LCD) industry, nanotechnology based on liquid crystals (LCs) started gradually fading away from the prime line in industries once organic light-emitting diodes (OLEDs) and quantum dot technology appeared in display applications. Albeit not the most exciting material anymore, LCs are still indispensable due to their intrinsic physical properties that are easily switchable under various external stimuli, including light [1][2][3][4][5][6][7][8], temperature [9][10][11], and electric [12][13][14][15][16][17][18] and magnetic sources [19][20][21]. As the current era demands novel materials with tunable physical properties in an on/off but dynamic manner, LCs can still be one of the most appropriate media to satisfy the demand.…”

Section: Introductionmentioning

confidence: 99%

“…Even though extant research using LCs is commonly based on the uniaxial alignment of molecules, it limits the variety that LCs can offer as a tunable medium. In addition to a uniaxially ordered and randomly oriented state, LCs can form defect structures with a distorted arrangement, which would find a meaningful role in vortex generation [15,[22][23][24], diffraction grating [14,[25][26][27], lithographic tools [28][29][30], and particle manipulation [15,16,28,31,32]. The defects can be considered useful only when formed on a large scale with order and controlled with stimuli such as temperature, useful only when formed on a large scale with order and controlled with stimuli such as temperature, light, or external fields.…”

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

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Role of Stimuli on Liquid Crystalline Defects: From Defect Engineering to Switchable Functional Materials

Shin

Yoon

2020

Materials

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Achieving tunable physical properties is currently one of the most exciting research topics. In order to realize this goal, a medium that is responsive to external stimuli and can undergo a change in its physical property is required. Liquid crystal (LC) is a prominent candidate, as its physical and optical properties can be easily manipulated with various stimuli, such as surface anchoring, rubbing, geometric confinement, and external fields. Having broken away from the past devotion to obtaining a uniform domain of LCs, people are now putting significant efforts toward forming and manipulating ordered and oriented defect structures with a unique arrangement within. The complicated molecular order with tunability would benefit the interdisciplinary research fields of optics, physics, photonics, and materials science. In this review, the recent progress toward defect engineering in the nematic and smectic phases by controlling the surface environment and electric field and their combinational methods is introduced. We close the review with a discussion of the possible applications enabled using LC defect structures as switchable materials.

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Section: Electric Field Applicationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

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Role of Stimuli on Liquid Crystalline Defects: From Defect Engineering to Switchable Functional Materials

Shin

Yoon

2020

Materials

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“…Due to the high viscosity of smectics, a heating and cooling across the nematic‐smectic phase transition is employed to reach the new equilibrium. [ 26 ] When a voltage (20 V, 1 kHz) is applied, the w over electrodes decreases significantly (Figure 6e). As aforementioned, OSs occur at antagonistic boundary conditions, i.e., planar surface anchoring and air‐induced homeotropic anchoring.…”

Section: Figurementioning

confidence: 99%

Smectic Defect Engineering Enabled by Programmable Photoalignment

Chen

et al. 2020

Advanced Optical Materials

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Topological defects are vital for tailoring soft matter properties and inspiring remarkable applications. Arbitrary guiding and dynamic tuning of director distributions are highly pursued in defect engineering of liquid crystals. Till now, the orientation control of smectic defect walls remains a challenge. Here, photoalignment is adopted to preset the surface anchoring in order to guide smectic oily streaks. Flexible defect engineering such as deflecting, bending, and splaying is demonstrated. Based on their combination, more complicated defect arrays are realized in a predictable manner. After electric stimuli involved, new functions of tunability and rotatability are unlocked. This work brings new insights to soft matter architectures, and will upgrade the existing micromachines, nanoparticle manipulations and advanced photonic applications.

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Vertical Array of Graphite Oxide Liquid Crystal by Microwire Shearing for Highly Thermally Conductive Composites

Cao

et al. 2023

Advanced Materials

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10 W m −1 K −1 even at a high filler content (≈50 vol%). [3] Modulating vertical orientation of anisotropic nanofillers is a pronounced way for high throughplane thermal conductive composites. 2D nanosheets, such as graphene oxide and multilayer graphene, have been used as building blocks to form structurally anisotropic skeletons. [4] The highest throughplane thermal conductivity of such TIMs reaches 62.4 W m −1 K −1 with a graphene loading of 13.3 vol%. [5] However, achieving the higher through-plane thermal conductivity of TIMs under low filler contents remains challenging.Achieving high thermal conductivity of TIMs request high crystallite orientation, large crystallite size, and high density of skeleton. [6] Such perfect crystalline pathway of skeleton ensures high thermal conductivity of composites. [7] As a result, accurate control of vertical sheet alignment, high sheet content, and lower interface phonon scattering are three indispensable factors for producing advanced TIMs. 2D nanosheets typically have lateral dimensions less than 50 µm and a few atomic layer thicknesses. [8] The atom-thin and small-sized sheets render discontinuous crystalline domains and massive polymer/sheet interfaces when oriented vertically. In addition, the content of nanosheet liquid crystals is commonly below 30 mg g −1 because of strong steric and electrostatic repulsion. Low content of liquid crystals causes limited heat flux of skeleton, which rules out highly thermally conductive composites. Compared with colloidal nanosheets, giant sheets typically have much larger lateral dimensions of hundreds of microns and thicknesses of microns. [9] Selecting giant sheets as building blocks is promising, which provides a Excellent through-plane thermally conductive composites are highly demanded for efficient heat dissipation. Giant sheets have large crystalline domain and significantly reduce interface phonon scattering, making them promising to build highly thermally conductive composites. However, realizing vertical orientation of giant sheets remains challenging due to their enormous mass and huge hydrodynamic drag force. Here, we achieve highly vertically ordered liquid crystals of giant graphite oxide (more than 100 µm in lateral dimension) by microwire shearing, which endows the composite with a recorded through-plane thermal conductivity of 94 W m −1 K −1 . Microscale shearing fields induced by vertical motion of microwires conquer huge hydrodynamic energy barrier and vertically reorient giant sheets. The resulting liquid crystals exhibit extremely retarded relaxation and impart large-scale vertical array with bidirectional ordering degree as high as 0.82. The graphite array-based composites demonstrate an ultrahigh thermal enhancement efficiency of over 35 times per unit volume. Furthermore, the composites improve cooling efficiency by 93% for thermal management tests compared to commercial thermal interface materials. This work offers a novel methodology to precisely manipulate the orientation of giant particles and promo...

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Controllable liquid crystal defect arrays induced by an in-plane electric field and their lithographic applications

Abstract: We control the shape and arrangement of various kinds of liquid crystal (LC) defects in nematic (N) and smectic A (SmA) phases using an in-plane electric field.

Cited by 20 publications

References 44 publications

Role of Stimuli on Liquid Crystalline Defects: From Defect Engineering to Switchable Functional Materials

Role of Stimuli on Liquid Crystalline Defects: From Defect Engineering to Switchable Functional Materials

Smectic Defect Engineering Enabled by Programmable Photoalignment

Vertical Array of Graphite Oxide Liquid Crystal by Microwire Shearing for Highly Thermally Conductive Composites

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