Matched elastic constants for a perfect helical planar state and a fast switching time in chiral nematic liquid crystals

Yu, Meina; Zhou, Xiaochen; Jiang, Jinghua; Yang, Huai; Yang, Deng‐Ke

doi:10.1039/c6sm00546b

Cited by 29 publications

(12 citation statements)

References 29 publications

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“…This transient structure quickly transforms into another transient structure that resembles a normal cholesteric with a pitch that is larger than the equilibrium cholesteric pitch.Yu et al (M. Yu et al 2016) used CB7CB as a dopant to a cholesteric mixture and demonstrated that the decrease of the bend elastic constant in these mixtures can speed up the transition from the homeotropic to intrinsic planar cholesteric state, with a response time on the order of tens of milliseconds. Furthermore, the transient conical and planar states help to improve the quality of the resulting planar structure, avoiding defects such as dislocations and oily streaks (M Yu et al 2016…”

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confidence: 99%

Physics of liquid crystals of bent-shaped molecules

2018

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Thermotropic liquid crystals can be formed by various molecular shapes, some discovered over 125 years ago. The simplest and most-studied liquid crystals are made of rodshaped molecules and led to today's omnipresent LCDs. While applied scientists and engineers have been perfecting LCDs, a large group of liquid crystal scientists have become excited about liquid crystals of bent-shaped (banana-shaped) molecules. These compounds were first reported 20 years ago, and since then have taken center stage in current liquid crystal science. The "banana-mania" is due to the fact that even a small kink in the molecular shape leads to fundamentally new properties and phases. In this review we summarize the large variety of novel structures and physical properties, and describe the underlying physics. We emphasize that macroscopic properties depend on both the shape of the molecules and the flexibility of the central core. Most rigid bent-core molecules form smectic and sometimes columnar structures; only a minority forms nematic phases. By contrast, most flexible bent-core molecules form nanostructured nematic phases, including the twist-bend nematic phase discovered very recently.

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confidence: 99%

Physics of liquid crystals of bent-shaped molecules

2018

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“…A wider viewing angle in the infrared spectrum region for a graphene glass-based ChLC device (Figure i) is thus achieved compared with the above-mentioned device with a PVA-polymer alignment layer. It should be noted that the visible light reflection of ChLCs is also possible through the optimization of parameters such as viscosity, , elastic constants, and the appropriate graphene nanostructures with controlled patterns of lines or dots. − …”

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confidence: 99%

Graphene Glass Inducing Multidomain Orientations in Cholesteric Liquid Crystal Devices toward Wide Viewing Angles

et al. 2018

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The photonic reflection of a cholesteric liquid crystal (ChLC) device depends on the spatial distribution of the orientations of their helical axes, and many orientation techniques have been developed so far. In this study, we select the hybrids of graphene directly grown on quartz glass as platforms to construct ChLC-based devices. This special design makes graphene serve as both an alignment layer and a conductive layer, thus affording a more simplified device fabrication route. We reveal that multidomain structures can be evolved for ChLCs on polycrystalline monolayer graphene on quartz glass, as evidenced by polarized optical microscope characterizations. The disparate orientations of the helical axes of ChLCs and the formation of multidomain structures are proposed to be induced by the different domain orientations of graphene, leading to a wide viewing angle of the ChLC-based devices. Moreover, the pitch of ChLCs is also observed to play a key role in the relative orientations of ChLCs. A wide viewing angle of the ChLC-based device is also detected especially in the infrared spectrum region. Briefly, this work should provoke the application of graphene glass as a perfect transparent electrode in the fabrication of liquid-crystal-based devices showing broad application potentials in intelligent laser protection and energy-saving smart windows.

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“…The validity of the Grandjean planar texture in the RM50-CLC sample after voltage treatment has been double-checked by the visible light transmission spectrum without any polarizer, which shows transmittance of ~80% on average compared to that of ITO glass used (data not shown). The resultant Grandjean planar texture with high transparency in visible light might be attributable to the CB7CBdoped CLC host with matched bend and twist elastic constants so that the nucleation process for the transition from the transient planar state to the initial Grandjean state was reduced [34]. Subsequently, a continuous voltage waveform comprising V = 100 V rms at 5 kHz for 3 s and V = 0 for 7 s in a period was designated to repeatedly unwind and rewind the CLC helix.…”

Section: Stability and Recoverability Of Pn-ulh Texturesmentioning

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Polymer Stabilization of Uniform Lying Helix Texture in a Bimesogen-Doped Cholesteric Liquid Crystal for Frequency-Modulated Electro-Optic Responses

Lee

2022

Materials

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A polymer network (PN) can sustain the uniform lying helix (ULH) texture in a binary cholesteric liquid crystal (LC) comprising a calamitic LC and a bimesogenic LC dimer. Upon copolymerization of a bifunctional monomer with a trifunctional monomer at a concentration of 5-wt% to create the desired polymer network structure, the PN-ULH was obtained with high stability and recoverability even when cycles of helical unwinding-to-rewinding processes were induced after the electrical or thermal treatment. Utilizing dielectric spectroscopy, the flexoelectric-polarization-dominated dielectric relaxation in the PN-ULH state was characterized to determine two frequency regions, f < fflexo and f > fdi, with pronounced and suppressed flexoelectric effect, respectively. It is demonstrated that the cell in the PN-ULH state can operate in the light-intensity modulation mode by the flexoelectric and dielectric effects at f < fflexo and phase-shift mode by the dielectric effect at f > fdi. Moreover, varying the voltage frequency from f < fflexo to f > fdi results in a frequency dispersion of transmittance analogous to that of flexoelectric-polarization-dominated dielectric relaxation. The unique combination of the bimesogen-doped cholesteric LC with a stable and recoverable PN-ULH texture is thus promising for developing a frequency-modulated electro-optic device.

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Matched elastic constants for a perfect helical planar state and a fast switching time in chiral nematic liquid crystals

Cited by 29 publications

References 29 publications

Physics of liquid crystals of bent-shaped molecules

Physics of liquid crystals of bent-shaped molecules

Graphene Glass Inducing Multidomain Orientations in Cholesteric Liquid Crystal Devices toward Wide Viewing Angles

Polymer Stabilization of Uniform Lying Helix Texture in a Bimesogen-Doped Cholesteric Liquid Crystal for Frequency-Modulated Electro-Optic Responses

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