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A special issue of Symmetry (ISSN 2073-8994). This special issue belongs to the section "Chemistry: Symmetry/Asymmetry".

Deadline for manuscript submissions: closed (31 January 2023) | Viewed by 30594

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Special Issue Editors

Prof. Dr. Shoichi Ishihara

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Guest Editor

Department of Electrical and Electronic Engineering, Osaka Institute of Technology, Osaka 535-8585, Japan
Interests: chemical structure and physical properties; alignment control and device characteristics of liquid crystal molecules

Prof. Dr. Sadahito Uto

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Guest Editor

Department of Biomedical Engineering, Osaka Institute of Technology, Osaka 535-8585, Japan
Interests: ferroelectric liquid crystal; electrooptic effect

Special Issue Information

Dear Colleagues,

More than 50 years have passed since the liquid crystal (LC) display was proposed, and the market size is now growing to reach 100 billion US dollars. In addition, recently, research into the practical application of ferroelectric LC devices and cholesteric LC devices have been vigorously conducted. Examples of the former include a LiDAR (light detection and ranging) scanner and goggles for virtual reality entertainment, and an example of the latter includes an exhalation sensor that can detect diseases. However, many things have not yet been clarified in terms of LC configuration and physical properties.

In an LC in which a uniform layered structure or a helical structure is spatially modulated, or in an LC-polymer composite, by appropriately designing the coordination of the constituent molecules and units, it may be possible to obtain an ultra-fast response, bistability, or novel electro-optic effect that cannot be expected with conventional LC devices. In addition, it is said that human biomembranes have a smectic LC structure, and basic research in this field will lead to future bioelectronics applications.

This Special Issue of Symmetry features articles about LCs, or LC-polymer composites, with symmetry as the unifying theme. We are soliciting contributions that covering a broad range of topics, including the latest theory and experimental work on the formation of LC superstructures such as blue phase and cubic phase; dynamics of the phase separation of a composite system of LC and polymer; latest research on smectic, cholesteric, and ferroelectric LCs; molecular dynamics simulation of LC configuration and its physical properties; and symmetry and asymmetry seen in LC displays.

Submit your paper and select the Journal “Symmetry” and the Special Issue “Symmetry and Liquid Crystals” via: MDPI submission system. Our papers will be published on a rolling basis and we will be pleased to receive your submission once you have finished it.

Prof. Dr. Shoichi Ishihara
Prof. Dr. Sadahito Uto
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Symmetry is an international peer-reviewed open access monthly journal published by MDPI.

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Keywords

Latest LC technology on blue phase
New evolution of ferroelectric LC
Cholesteric LC devices
Molecular dynamics simulation
LC configuration and physical properties
LC configuration and device characteristics
Entropy and order parameter
Phase separation dynamics in a mixed system
Symmetry and asymmetry seen in LC displays

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Published Papers (12 papers)

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Editorial

Jump to: Research, Review

3 pages, 162 KiB

Open AccessEditorial

Symmetry and Liquid Crystals

by Shoichi Ishihara and Sadahito Uto

Symmetry 2023, 15(3), 691; https://doi.org/10.3390/sym15030691 - 10 Mar 2023

Cited by 4 | Viewed by 1448

Abstract

Liquid crystals are aggregates of individual molecules due to moderate intermolecular interactions, which are roughly divided into lyotropic liquid crystals and thermotropic liquid crystals [...] Full article

(This article belongs to the Special Issue Symmetry and Liquid Crystals)

Research

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10 pages, 2994 KiB

Open AccessArticle

The Missing Relationship between the Miscibility of Chiral Dopants and the Microscopic Dynamics of Solvent Liquid Crystals: A Molecular Dynamics Study

by Go Watanabe, Akane Yamazaki and Jun Yoshida

Symmetry 2023, 15(5), 1092; https://doi.org/10.3390/sym15051092 - 16 May 2023

Cited by 1 | Viewed by 1383

Abstract

Nematic liquid crystals (LCs) are known to undergo a phase transition to chiral nematic LCs possessing helices upon doping with enantiomeric molecules known as chiral dopants. The relationship between the helical pitch (

p

), the molar fraction (

x

), and the [...] Read more.

p

), the molar fraction (

x

), and the power of the chiral dopant to induce a helix in a nematic solvent (

β_{M}

) is expressed as

p = 1 / (x \cdot β_{M}) .

The helical pitch is easily controlled by the concentration of the chiral dopant when the dopant molecule is miscible with the host nematic LC. However, it has not yet been clarified what the miscibility of the chiral dopant molecules with the nematic LCs depends. Therefore, we performed all-atom molecular dynamics (MD) simulations for the system composed of both Δ and Λ isomers of a chiral dopant molecule dispersed in a nematic LC and investigated the relationship between the microdynamics of the chiral molecules and their miscibility with the nematic solvent. The miscibility of the chiral dopant molecules with the LC solvent was found to correlate with the diffusion coefficient of the LC solvent. In the system where the chiral dopant molecules with high miscibility were added, the diffusion coefficient of the LC solvents was comparable to that of the system in which the chiral molecule was not doped. Furthermore, it was confirmed that more elongated chiral dopants were more miscible with the nematic solvent consisting of calamitic molecules, and that these dopant molecules did not have a significant effect on the diffusion behavior of the LC molecules. Full article

(This article belongs to the Special Issue Symmetry and Liquid Crystals)

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9 pages, 2204 KiB

Open AccessArticle

Flexoelectric Polarization in Liquid Crystalline Elastomers Prepared by Cross-Linking under Horseshoe-Shaped Deformation

by Kazuyuki Hiraoka, Toshio Ishihara, Hiroyuki Minami, Shiori Taira, Katsumi Yamada and Toshihiro Hiejima

Symmetry 2023, 15(3), 616; https://doi.org/10.3390/sym15030616 - 1 Mar 2023

Cited by 1 | Viewed by 1537

Abstract

Flexoelectric polarization, which is caused by symmetry breaking in a distortion of material, was investigated in liquid crystalline elastomers composed of wedge-shaped mesogens prepared by cross-linking under horseshoe-shaped deformation. X-ray diffractometry suggested that splay distortion along the depth direction was induced in the pseudo-isotropic phase. While almost no electric charge was observed in the smectic A phase, an electric charge caused by polarization due to the flexoelectric effect appeared and reached −1367 pC/mm² in the pseudo-isotropic phase. We tentatively conclude that the macroscopic polarization due to the flexoelectric effect emerged and was fixed in the liquid crystalline elastomers by cross-linking under horseshoe-shaped deformation. Full article

(This article belongs to the Special Issue Symmetry and Liquid Crystals)

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11 pages, 4470 KiB

Open AccessArticle

Electro-Optical Characteristics of Quasi-Homogeneous Cell in Twisted Nematic Mode

by Rumiko Yamaguchi and Yoshiki Sakamoto

Symmetry 2023, 15(3), 597; https://doi.org/10.3390/sym15030597 - 26 Feb 2023

Cited by 1 | Viewed by 1585

Abstract

A liquid crystal (LC) director distribution was numerically analyzed in 90-degree twisted nematic (TN) LC cells with a symmetric and an asymmetric azimuthal anchoring strength of the alignment substrate and the influence of anchoring strength on the electro-optical property of the TN cell was evaluated. The twist angle decreased with decreasing azimuthal anchoring strength and the LC orientation changed to a homogeneous orientation with the twist angle of 0 degrees in the LC cell with asymmetric azimuthal anchoring strength, specifically with the strong anchoring substrate and the weak anchoring substrate below a critical strength. The asymmetric anchoring LC cell was fabricated by using a poly (vinyl cinnamate) alignment substrate as the weak anchoring surface and a polyimide alignment substrate as the strong anchoring surface. The LC cell performed the dark–bright–dark switching of the transmittance in the crossed polarizers, since the homogeneous LC orientation changed to the TN orientation again with increasing the applied voltage. Therefore, it was experimentally confirmed that LC molecules rotated at 90 degrees in the plane on the alignment surface by the electric field perpendicular to the weak anchoring substrate. Full article

(This article belongs to the Special Issue Symmetry and Liquid Crystals)

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11 pages, 6762 KiB

Open AccessArticle

New Diluter Solubilized in Liquid Crystal Compounds for High Stability and Fast Response Speed Liquid Crystal Displays

by Masanobu Mizusaki, Kazuo Okamoto and Toshihiro Shibata

Symmetry 2022, 14(8), 1620; https://doi.org/10.3390/sym14081620 - 6 Aug 2022

Cited by 2 | Viewed by 2902

Abstract

Diluters play a crucial role for reducing the rotational viscosity of liquid crystal (LC) materials for improving the response property of LC displays (LCDs). However, conventional diluters tend to deteriorate relatively easily under ultraviolet (UV) exposure, due to existence of vinyl groups. Hence, it was difficult to prepare polymer layers in the LC cells by exposing UV for polymerization regarding polymer-sustained vertically-aligned (PS-VA) and polyimide-free (PI-free) technologies. In this study, however, we succeeded to develop a high stable diluter, which shows a symmetrical structure and carries fluorinated groups for stable nematic phase and high affinity with other fluorinated LC compounds. With the use of the symmetrical-structured diluter, we developed the PS-VA and the PI-free in-plane switching cells with a fast response rate and high voltage holding ratio, by combining a reactive monomer including an azobenzene moiety. Full article

(This article belongs to the Special Issue Symmetry and Liquid Crystals)

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8 pages, 2022 KiB

Open AccessEditor’s ChoiceArticle

Analysis of Electro-Optical Behavior in Liquid Crystal Cells with Asymmetric Anchoring Strength

by Rumiko Yamaguchi

Symmetry 2022, 14(1), 85; https://doi.org/10.3390/sym14010085 - 6 Jan 2022

Cited by 11 | Viewed by 3646

Abstract

Liquid crystal director distributions have been numerically analyzed between asymmetric anchoring surfaces, that is, infinitely strong and very weak anchoring strength interfaces. In a hybrid aligned nematic (HAN) cell and a twisted nematic (TN) cell, HAN and TN orientations turn to a homogeneous orientation when the weak anchoring strength is lower than a critical one. Relationships between the anchoring strength and elastic constants of the liquid crystal were analyzed to be of a quasi-homogeneous orientation. The quasi-homogeneous orientation returned to the original HAN and TN orientations under voltage application. Low-driving electro-optical properties with no threshold voltage can be obtained in a quasi-homogeneous HAN cell. A unique voltage–transmission curve of 0–100–0% appeared in a quasi-homogeneous TN cell between the crossed polarizers. Full article

(This article belongs to the Special Issue Symmetry and Liquid Crystals)

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11 pages, 3266 KiB

Open AccessArticle

Polar Alkoxy Group and Pyridyl Effects on the Mesomorphic Behavior of New Non-Symmetrical Schiff Base Liquid Crystals

by Sayed Z. Mohammady, Daifallah M. Aldhayan, Mohammed A. Alshammri, Ayoub K. Alshammari, Mohammed Alazmi, Kanubhai D. Katariya, Mariusz Jaremko and Mohamed Hagar

Symmetry 2021, 13(10), 1832; https://doi.org/10.3390/sym13101832 - 1 Oct 2021

Cited by 15 | Viewed by 2118

Abstract

A series of non-symmetrical Schiff base liquid crystals were prepared and investigated. Schiff bases of p-alkyloxy aniline derivatives and 4-phenyl pyridine-4′-carbaldehyde were synthesized. The terminal alkoxy groups substituting aniline are of varied chain length, namely C6, C8, and C16. The structures of the compounds were confirmed via ¹H NMR and ¹³C NMR spectroscopy. Different mesophases of the samples were thermally and optically characterized by differential thermal analysis (DSC) and polarized optical microscopy (POM). All samples revealed enantiotropic smectic B (SmB) and smectic A (SmA) mesophases. The results obtained were further correlated with the density functional theory (DFT) theoretical calculations. The results are compared to a series of compounds bearing biphenyl moiety in their mesogens. The thermal stabilities of the different mesophase reduced upon the increment of the alkoxy chain length. The temperature ranges of both the smectic mesophases of new compounds bearing the 4-phenyl pyridine moiety are generally expanded higher than the other series. In addition, the total mesophase range is greater in the new compounds when compared to their biphenyl analogues. The DFT results were investigated in terms of the molecular geometries and the frontier molecular orbitals as well as the charge distribution mapping to show and illustrate the difference in the mesomorphic properties. Full article

(This article belongs to the Special Issue Symmetry and Liquid Crystals)

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9 pages, 2152 KiB

Open AccessArticle

Generation of Geometric Extra Phase and Accompanying Temporal Effects in Asymmetric Optically Compensated IPS-LCDs and FFS-LCDs

by Shunsuke Kobayashi, Tomohiro Miyama, Hidenari Akiyama, Atsushi Ikemura and Michio Kitamura

Symmetry 2021, 13(7), 1143; https://doi.org/10.3390/sym13071143 - 26 Jun 2021

Cited by 4 | Viewed by 1657

Abstract

This paper reports the generation of an extra phase and the accompanying temporal effects in an asymmetric optically compensated in-pane-switching (IPS) liquid crystal (LC) system and a fringe-field-switching (FFS) liquid crystal display (LCD) exhibiting a twofold faster response speed in the switching-off process compared with that in single and symmetric IPS-LCDs and FFS LCDs for the first time. To explain the experimental results, we derived an approximate analytical formula for the optical output intensity that includes an extra phase advancement and conducted simulations to achieve normally black operation using a dynamic optical retarder. Full article

(This article belongs to the Special Issue Symmetry and Liquid Crystals)

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14 pages, 6667 KiB

Open AccessArticle

A Novel Technique for Determination of Residual Direct-Current Voltage of Liquid Crystal Cells with Vertical and In-Plane Electric Fields

by Msanobu Mizusaki and Shoichi Ishihara

Symmetry 2021, 13(5), 816; https://doi.org/10.3390/sym13050816 - 7 May 2021

Cited by 5 | Viewed by 2568

Abstract

Generation of residual direct-current (DC) voltage (V_rDC) induces serious image sticking of liquid crystal displays (LCDs). In this study, a novel technique to determine the V_rDC of LC cells is proposed. We found that the V_rDC could be determined from a current-voltage (I-V) curve obtained by the application of triangular voltage. In the case of a vertically aligned twisted nematic (VTN) mode LC cell, where a vertical electric field is applied, the I-V curve shows maximum and minimum current peaks owing to rotation of an LC director, and the V_rDC is able to be determined from an average value of the two peaks. On the other hand, in the case of a fringe field switching (FFS) mode LC cell, where an in-plane (lateral) electric field is applied from comb electrodes, the current peaks derived from the rotation of the LC director do not appear. Therefore, we could not adopt the same way with that of the VTN mode LC cell. However, we found that there were two minimum current peaks derived from minimum capacitances of the FFS mode LC cell, and could determine the V_rDC by using these two current peaks. The proposed technique would be useful for the evaluation of the V_rDC of the LCDs, where the electric field is applied both vertically and laterally. Full article

(This article belongs to the Special Issue Symmetry and Liquid Crystals)

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11 pages, 4501 KiB

Open AccessArticle

Enhancement of Polymer Structural Ordering in Polymer-Stabilised Blue Phases for Improved Electro-Optical Properties

by Hirotsugu Kikuchi, Takahiro Ashimine, Zehui Qin, Hiroki Higuchi, Shizuka Anan and Yasushi Okumura

Symmetry 2021, 13(5), 772; https://doi.org/10.3390/sym13050772 - 29 Apr 2021

Cited by 2 | Viewed by 2137

Abstract

Polymer-stabilised blue phase (PSBP) could be employed in novel fast response optical and photonic devices. It is inferred that inside PSBPs, the polymers are selectively aggregated by location in −1/2 disclinations, which are defects coexisting with the blue phase as a periodic lattice, thereby extending the temperature range of the blue phase. The polymer aggregate structure in PSBPs strongly affects their physical properties. In this study, we employed a non-destructive synchrotron ultra-small-angle X-ray diffraction analysis to investigate the effect of polymerisation rates on the polymer aggregate structure in PSBPs prepared with monomers of different polymerisation rates and examined the structure formation process of the polymer during polymerisation. When methacrylate monomers, which exhibit a relatively low polymerisation rate, were used to form polymers in PSBP, the resulting polymer was more selectively aggregated at disclinations in the PSBP. Furthermore, the electro-optical effect in the PSBP was successfully improved by reducing the polymer concentration in the PSBPs prepared with the optimised monomer combinations. Full article

(This article belongs to the Special Issue Symmetry and Liquid Crystals)

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Review

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14 pages, 4922 KiB

Open AccessReview

Blue Phase Liquid Crystals with Tailored Crystal Orientation for Photonic Applications

by SeongYong Cho and Masanori Ozaki

Symmetry 2021, 13(9), 1584; https://doi.org/10.3390/sym13091584 - 27 Aug 2021

Cited by 5 | Viewed by 3537

Abstract

Blue phase (BP) liquid crystals, which self-assemble into soft three-dimensional (3D) photonic crystals, have attracted enormous research interest due to their ability to control light and potential photonic applications. BPs have long been known as optically isotropic materials, but recent works have revealed that achieving on-demand 3D orientation of BP crystals is necessary to obtain improved electro-optical performance and tailored optical characteristics. Various approaches have been proposed to precisely manipulate the crystal orientation of BPs on a substrate, through the assistance of external stimuli and directing self-assembly processes. Here, we discuss the various orientation-controlling technologies of BP crystals, with their mechanisms, advantages, drawbacks, and promising applications. This review first focuses on technologies to achieve the uniform crystal plane orientation of BPs on a substrate. Further, we review a strategy to control the azimuthal orientation of BPs along predesigned directions with a uniform crystal plane, allowing the 3D orientation to be uniquely defined on a substrate. The potential applications such as volume holograms are also discussed with their operation principle. This review provides significant advances in 3D photonic crystals and gives a huge potential for intelligent photonic devices with tailored optical characteristics. Full article

(This article belongs to the Special Issue Symmetry and Liquid Crystals)

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19 pages, 7145 KiB

Open AccessReview

Chiral Liquid Crystalline Electronic Systems

by Masahiro Funahashi

Symmetry 2021, 13(4), 672; https://doi.org/10.3390/sym13040672 - 13 Apr 2021

Cited by 14 | Viewed by 3502

Abstract

Liquid crystals bearing extended π-conjugated units function as organic semiconductors and liquid crystalline semiconductors have been studied for their applications in light-emitting diodes, field-effect transistors, and solar cells. However, studies on electronic functionalities in chiral liquid crystal phases have been limited so far. Electronic charge carrier transport has been confirmed in chiral nematic and chiral smectic C phases. In the chiral nematic phase, consisting of molecules bearing extended π-conjugated units, circularly polarized photoluminescence has been observed within the wavelength range of reflection band. Recently, circularly polarized electroluminescence has been confirmed from devices based on active layers of chiral conjugated polymers with twisted structures induced by the molecular chirality. The chiral smectic C phase of oligothiophene derivatives is ferroelectric and indicates a bulk photovoltaic effect, which is driven by spontaneous polarization. This bulk photovoltaic effect has also been observed in achiral polar liquid crystal phases in which extended π-conjugated units are properly assembled. In this manuscript, optical and electronic functions of these chiral π-conjugated liquid crystalline semiconductors are reviewed. Full article

(This article belongs to the Special Issue Symmetry and Liquid Crystals)

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