Optimized frequency regime for the electrohydrodynamic induction of a uniformly lying helix structure

Nian, Yu Lin; Wu, Po Chang; Lee, Wei

doi:10.1364/prj.4.000227

Cited by 22 publications

(20 citation statements)

References 25 publications

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“…Besides, in a special case where the frequency of the applied voltage is low enough to bring about electrohydrodynamic instability (EHDI), the ULH state can be obtained in a given voltage region. This phenomenon has been evidenced in some of the early works [17,18,30]. However, when the frequency varies from 1 kHz to 30 Hz in this study, the V-T% curve remains nearly unchanged as shown in Figure 1a.…”

Section: Methodssupporting

confidence: 73%

“…As illustrated in Figure 3, the obtained ULH can be readily switched back to the P state by triggering the cell with a single pulse of V = V H at f = f 2 , and to the FC state by a hybrid pulse at f 2 with amplitudes of V H for the leading component and V < V H for the succeeding component. The second way is to generate ULH via EHDI by elevating the temperature to promote the ionic effect rather than requiring the LC material to be ion-rich [17,18]. In this case, the cell is held in the H state at a temperature close to T c by the first portion of the pulse at V = 30 V rms and f 1 = 55 kHz.…”

Section: Frequency-modulated Textural and Phase Transitionsmentioning

confidence: 99%

“…On the basis of this method, Salter et al reported that the resulting ULH in a planar-aligned cell with 90 • -twisted rubbing is more uniform than those of hybrid-aligned cells and of the planar-aligned cells with parallel (0 • or 180 • ) rubbing [13]. Without undergoing the temperature-cooling process, voltage-generated ULH alignment has also been obtained in planar-aligned CLC cells by providing an extra mechanical force to induce shear flow in the meantime [14][15][16], using ion-rich positive nematic host to permit electrohydrodynamic flow by low-frequency voltages [17,18], controlling voltage conditions precisely to induce the nematic-to-CLC structural transition [19], optimizing the pretilt angle as well as the anchoring energy [20], or by designing a tri-electrode configuration [21,22]. For the surface-treatment method, the concept stems from the modification in surface morphology of alignment layers, enabling periodic anchoring for realizing the ULH structure spontaneously.…”

Section: Introductionmentioning

confidence: 99%

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Electro-Thermal Formation of Uniform Lying Helix Alignment in a Cholesteric Liquid Crystal Cell

Lee

2019

Crystals

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We demonstrated previously that the temperature of a sandwich-type liquid crystal cell with unignorable electrode resistivity could be electrically increased as a result of dielectric heating. In this study, we take advantage of such an electro-thermal effect and report on a unique electric-field approach to the formation of uniform lying helix (ULH) texture in a cholesteric liquid crystal (CLC) cell. The technique entails a hybrid voltage pulse at frequencies f1 and, subsequently, f2, which are higher and lower than the onset frequency for the induction of dielectric heating, respectively. When the cell is electrically sustained in the isotropic phase by the voltage pulse of V = 35 Vrms at f1 = 55 kHz or in the homeotropic state with the enhanced ionic effect at V = 30 Vrms and f1 = 55 kHz, our results indicate that switching of the voltage frequency from f1 to f2 enables the succeeding formation of well-aligned ULH during either the isotropic-to-CLC phase transition at f2 = 1 kHz or by the electrohydrodynamic effect at f2 = 30 Hz. For practical use, the aligning technique proposed for the first time in this study is more applicable than existing alternatives in that the obtained ULH is adoptable to CLCs with positive dielectric anisotropy in a simple cell geometry where complicated surface pretreatment is not required. Moreover, it is electrically switchable to other CLC textures such as Grandjean planar and focal conic states without the need of a temperature controller for the phase transition, the use of ion-rich LC materials, or mechanical shearing for textural transition.

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Section: Methodssupporting

confidence: 73%

Section: Frequency-modulated Textural and Phase Transitionsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Electro-Thermal Formation of Uniform Lying Helix Alignment in a Cholesteric Liquid Crystal Cell

Lee

2019

Crystals

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“…One of the CLCs changes the sign of its dielectric anisotropy upon varying the temperature of the sample while the other one used is a dual frequency CLC. The effect of various experimental and materials parameters on ULH structure formation and its stability has been given considerable attention …”

Section: Uniform Lying Helix Structurementioning

confidence: 99%

Stimuli‐Driven Control of the Helical Axis of Self‐Organized Soft Helical Superstructures

2018

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Supramolecular and macromolecular functional helical superstructures are ubiquitous in nature and display an impressive catalog of intriguing and elegant properties and performances. In materials science, self-organized soft helical superstructures, i.e., cholesteric liquid crystals (CLCs), serve as model systems toward the understanding of morphology- and orientation-dependent properties of supramolecular dynamic helical architectures and their potential for technological applications. Moreover, most of the fascinating device applications of CLCs are primarily determined by different orientations of the helical axis. Here, the control of the helical axis orientation of CLCs and its dynamic switching in two and three dimensions using different external stimuli are summarized. Electric-field-, magnetic-field-, and light-irradiation-driven orientation control and reorientation of the helical axis of CLCs are described and highlighted. Different techniques and strategies developed to achieve a uniform lying helix structure are explored. Helical axis control in recently developed heliconical cholesteric systems is examined. The control of the helical axis orientation in spherical geometries such as microdroplets and microshells fabricated from these enticing photonic fluids is also explored. Future challenges and opportunities in this exciting area involving anisotropic chiral liquids are then discussed.

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“…In our previous work, the tri-stable state CLC among ULH, P and FC states without specific structure by electrical and optical field are demonstrated, providing a functional, multi-stable device. However, the uniform and stable ULH is only existed by inducing the electrohydrodynamic effect under electrical field in specific frequency, limited short pitch (≤ 420 μm) and thin cell gap (7.5 μm) [14,15]. The specific condition thus limited the tolerance and optical performance in color information (P state) and the scattering performance (FC state) for advanced applications.…”

Section: Introductionmentioning

confidence: 99%

43‐1: Tri‐stable Cholesteric Liquid Crystal Smart Window

Tseng

Chen

et al. 2018

Symp Digest of Tech Papers

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Optimized frequency regime for the electrohydrodynamic induction of a uniformly lying helix structure

Cited by 22 publications

References 25 publications

Electro-Thermal Formation of Uniform Lying Helix Alignment in a Cholesteric Liquid Crystal Cell

Electro-Thermal Formation of Uniform Lying Helix Alignment in a Cholesteric Liquid Crystal Cell

Stimuli‐Driven Control of the Helical Axis of Self‐Organized Soft Helical Superstructures

43‐1: Tri‐stable Cholesteric Liquid Crystal Smart Window

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