Feature Articles in Liquid Crystals from Our Editorial Board Members and Their Colleagues, 2022/2023

A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Liquid Crystals".

Deadline for manuscript submissions: closed (30 June 2023) | Viewed by 13815

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Guest Editor
Ohio Eminent Scholar and Professor of Physics, Department of Physics, Case Western Reserve University, Cleveland, OH 44106-7079, USA
Interests: liquid crystals and complex fluids (electric and magnetic field effects, interfaces, phase transitions, colloidal inclusions); fluid interface instabilities; microgravity
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Special Issue Information

Dear Colleagues,

The field of liquid crystals is incredibly diverse, involving the active participation of physicists, chemists, biologists, and engineers. Their research spans length scales from the molecular to the cosmic; their techniques are experimental, theoretical, and computational; and their work ranges from understanding the fundamental aspects of nature to the creation of mass-market consumer products. The Editorial Board of the Liquid Crystals section of Crystals is composed of a stellar group of scientists and engineers, all of whom interact with other outstanding researchers. In this special issue, we will collect a number of articles written by members of our Editorial Board and their colleagues that cover the breadth of topics in liquid crystals research today. I hope that you will find these works, which will be incorporated in our special issue “Feature Articles in Liquid Crystals from Our Editorial Board Members and Their Colleagues, 2022/2023” to be informative and compelling.

Prof. Dr. Charles Rosenblatt
Guest Editor

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Keywords

  • liquid crystals
  • liquid crystal thin films
  • liquid crystal displays
  • nematic
  • smectic
  • liquid crystal optics

Published Papers (9 papers)

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Research

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14 pages, 4839 KiB  
Article
Photoaligned Tunable Liquid Crystal Lenses with Parabolic Phase Profile
by Svitlana P. Bielykh, Liana Lucchetti and Victor Yu. Reshetnyak
Crystals 2023, 13(7), 1104; https://doi.org/10.3390/cryst13071104 - 15 Jul 2023
Cited by 2 | Viewed by 905
Abstract
We present a theoretical model of a cylindrical tunable liquid crystal lens based on the modulation of anchoring energy. The latter can be easily obtained using photoalignment techniques. The liquid crystal cell we propose exhibits strong anchoring at the top substrate and anchoring [...] Read more.
We present a theoretical model of a cylindrical tunable liquid crystal lens based on the modulation of anchoring energy. The latter can be easily obtained using photoalignment techniques. The liquid crystal cell we propose exhibits strong anchoring at the top substrate and anchoring energy with a parabolic profile at the bottom substrate. The model describes the dependence of the focal length on the applied voltage and presents a theoretical study of the lens aberrations. The results obtained are of general relevance and can be used to optimize the performances of every type of liquid crystal lens with a parabolic profile. Full article
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21 pages, 7219 KiB  
Article
TIC Reorientation under Electric and Magnetic Fields in Homeotropic Samples of Cholesteric LC with Negative Dielectric Anisotropy
by Patrick Oswald, Guilhem Poy and Jordi Ignés-Mullol
Crystals 2023, 13(6), 957; https://doi.org/10.3390/cryst13060957 - 15 Jun 2023
Viewed by 650
Abstract
In this paper, we numerically and experimentally show that the director field orientation degeneracy within the Translationally Invariant Configuration (TIC) of a cholesteric liquid crystal under an electric field can be lifted by imposing a magnetic field B parallel to the electrodes. [...] Read more.
In this paper, we numerically and experimentally show that the director field orientation degeneracy within the Translationally Invariant Configuration (TIC) of a cholesteric liquid crystal under an electric field can be lifted by imposing a magnetic field B parallel to the electrodes. The configuration can be either parallel or perpendicular to the magnetic field depending on the values of the sample thickness, pitch, and applied voltage, with two equiprobable orientations in each case. The transition between the parallel and perpendicular orientations has hysteresis, suggesting that it is first order. When B is slightly tilted with respect to the electrode plane, the indeterminacy on the TIC orientation is removed when the TIC is directed along B. Full article
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11 pages, 7321 KiB  
Article
Reconfiguration of Nematic Disclinations in Plane-Parallel Confinements
by Saša Harkai, Charles Rosenblatt and Samo Kralj
Crystals 2023, 13(6), 904; https://doi.org/10.3390/cryst13060904 - 01 Jun 2023
Cited by 1 | Viewed by 964
Abstract
We study numerically the reconfiguration process of colliding m=1/2 strength disclinations in an achiral nematic liquid crystal (NLC). A Landau–de Gennes approach in terms of tensor nematic-order parameters is used. Initially, different pairs m1,m2 of [...] Read more.
We study numerically the reconfiguration process of colliding m=1/2 strength disclinations in an achiral nematic liquid crystal (NLC). A Landau–de Gennes approach in terms of tensor nematic-order parameters is used. Initially, different pairs m1,m2 of parallel wedge disclination lines connecting opposite substrates confining the NLC in a plane-parallel cell of a thickness h are imposed: {1/2,1/2}, {−1/2,−1/2} and {−1/2,1/2}. The collisions are imposed by the relative rotation of the azimuthal angle θ of the substrates that strongly pin the defect end points. Pairs {1/2,1/2} and {−1/2,−1/2} “rewire” at the critical angle θc1=3π4 in all cases studied. On the other hand, two qualitatively different scenarios are observed for {−1/2,1/2}. In the thinner film regime h<hc, the disclinations rewire at θc2=5π4. The rewiring process is mediated by an additional chargeless loop nucleated in the middle of the cell. In the regime h>hc, the colliding disclinations at θc2 reconfigure into boojum-like twist disclinations. Full article
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17 pages, 3002 KiB  
Article
New Liquid Crystalline Elastomeric Films Containing a Smectic Crosslinker: Chemical and Physical Properties
by Andraz Resetic, Jerneja Milavec, Alexej Bubnov, Damian Pociecha, Vera Hamplova, Ewa Gorecka, Bostjan Zalar and Valentina Domenici
Crystals 2023, 13(1), 96; https://doi.org/10.3390/cryst13010096 - 04 Jan 2023
Cited by 2 | Viewed by 1683
Abstract
Side-chain liquid crystal elastomers (SC-LCEs) have been designed by using a new smectic crosslinker. Two types of monodomain films were prepared based on polysiloxane chains, with a different relative concentration of both crosslinker and mesogenic comonomers. The mesomorphic behavior of the two SC-LCE [...] Read more.
Side-chain liquid crystal elastomers (SC-LCEs) have been designed by using a new smectic crosslinker. Two types of monodomain films were prepared based on polysiloxane chains, with a different relative concentration of both crosslinker and mesogenic comonomers. The mesomorphic behavior of the two SC-LCE systems was investigated by differential scanning calorimetry and polarized optical microscopy showing a different mesomorphic behavior: in one case, we obtained a nematic SC-LCE film, in the other case, a Smectic A SC-LCE film. In both systems, the mesophases were stable in a wide temperature range. Moreover, the SC-LCE films possess a relatively high orientation at room temperature. The physical-chemical properties, such as the local orientational ordering, structural organization, and dynamics of SC-LCEs’ constituents were studied by means of static and dynamic 2H NMR experiments, small-angle X-ray, and wide-angle X-ray diffractions. The relevant physical properties, such as the thermo-elastic and thermo-mechanic behaviors, are reported and discussed in view of the practical applications. Full article
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8 pages, 2143 KiB  
Article
Effect of Rod-like Nanoparticles on the Dielectric Susceptibility of Nematic Nano-Composites: A Molecular Theory
by Mikhail A. Osipov, Alexey S. Merekalov and Alexander A. Ezhov
Crystals 2022, 12(12), 1827; https://doi.org/10.3390/cryst12121827 - 15 Dec 2022
Viewed by 1540
Abstract
The effect of rod-like nanoparticles on the high-frequency dielectric susceptibility of the nematic nano-composites has been investigated in the framework of a molecular theory. Analytical expressions for the components of the effective polarizability of a rod-like nanoparticle in the nematic host have been [...] Read more.
The effect of rod-like nanoparticles on the high-frequency dielectric susceptibility of the nematic nano-composites has been investigated in the framework of a molecular theory. Analytical expressions for the components of the effective polarizability of a rod-like nanoparticle in the nematic host have been obtained and used in the calculations of the dielectric susceptibility of the composites as functions of the nanoparticle volume fraction. Numerical calculations of the susceptibility have been undertaken using the nematic liquid crystal 5CB as a host doped with either gold or silver particles for different values of the concentration of nanoparticles. It has been shown that the rod-like nanoparticles have a much stronger effect on the components of the dielectric susceptibility of the nano-composites including, in particular, the one with gold nanoparticles in the vicinity of the plasmon resonance. The main conclusion is that at sufficiently large concentration of nanoparticles, the anisotropy of the dielectric susceptibility of the nano-composites may even change the sign with an increasing concentration which may be important for various applications. Full article
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8 pages, 301 KiB  
Article
Effective Chiral Interactions between Nonchiral Rigid Macromolecules in a Chiral Solvent and the Induced Cholesteric Liquid Crystal Phase
by Mikhail A. Osipov and Alexey S. Merekalov
Crystals 2022, 12(9), 1318; https://doi.org/10.3390/cryst12091318 - 18 Sep 2022
Cited by 1 | Viewed by 1560
Abstract
It has been shown that a nonchiral anisotropic macromolecule embedded in a chiral dielectric solvent possesses an effective optical activity proportional to the optical activity of the solvent. As a result, there exists an effective chiral interaction between the macromolecules, which creates a [...] Read more.
It has been shown that a nonchiral anisotropic macromolecule embedded in a chiral dielectric solvent possesses an effective optical activity proportional to the optical activity of the solvent. As a result, there exists an effective chiral interaction between the macromolecules, which creates a torque acting on the primary axes of the two interacting molecules. A general expression for the effective chiral interaction potential has been derived in terms of the effective polarizability and the effective gyration tensor of the macromolecule in the chiral solvent. Explicit expressions for the components of the effective polarizability and the gyration have been obtained using the model of a hard rod filled with anisotropic dielectric and embedded into the isotropic chiral dielectric medium. The theory predicts the formation of the cholesteric helical structure in the nematic polymer liquid crystal phase induced by a chiral solvent. Full article
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11 pages, 18128 KiB  
Article
Achievement of Unidirectional Aluminum Tin Oxide/UV-Curable Polymer Hybrid Film via UV Nanoimprinting Lithography for Uniform Liquid Crystal Alignment
by Dong-Wook Lee, Dong-Hyun Kim, Jonghoon Won, Jin-Young Oh and Dae-Shik Seo
Crystals 2022, 12(6), 855; https://doi.org/10.3390/cryst12060855 - 17 Jun 2022
Viewed by 1575
Abstract
A uniform unidirectional nanostructure composed of aluminum tin oxide and ultraviolet (UV)-curable polymer is introduced herein. The nanostructure was produced by UV-nanoimprint lithography (UV-NIL), and the fabricated hybrid film was used as a uniform liquid crystal (LC) alignment layer. Atomic force microscopy and [...] Read more.
A uniform unidirectional nanostructure composed of aluminum tin oxide and ultraviolet (UV)-curable polymer is introduced herein. The nanostructure was produced by UV-nanoimprint lithography (UV-NIL), and the fabricated hybrid film was used as a uniform liquid crystal (LC) alignment layer. Atomic force microscopy and line profile analysis were performed to confirm a well-ordered nanostructure with 760 nm periodicity and 30 nm height. X-ray photoelectron spectroscopy analysis was also conducted to examine the chemical modifications to the hybrid film surface during UV exposure. Optical transmittance investigation of the nanopatterned hybrid film revealed its compatibility for LC device application. Stable, uniform, and homogeneous LC alignment on the hybrid film was confirmed by polarized optical microscopy observance and analysis of LC pretilt angle. The unidirectional structure on the film surface enabled uniform LC orientation along with surface anisotropy property. Hence, we expect that the proposed UV-NIL process can be applied to fabricate high-resolution unidirectional nanostructures with various inorganic/organic hybrid materials and that these nanostructures have high potential for next-generation LC systems. Full article
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9 pages, 1675 KiB  
Article
Influence of Surface Relief on Orientation of Nematic Liquid Crystals: Polyimide Doped with WS2 Nanotubes
by Natalia Kamanina, Andrey Toikka, Yaroslav Barnash, Alla Zak and Reshef Tenne
Crystals 2022, 12(3), 391; https://doi.org/10.3390/cryst12030391 - 14 Mar 2022
Cited by 8 | Viewed by 2182
Abstract
Among the different methods for orienting liquid crystal (LC) molecules, adding nanoparticles into the matrix of the substrate material towards modifying its surface, is actively pursued. In this context, the influence of the nanoparticle content on the texture of the surface of polymer [...] Read more.
Among the different methods for orienting liquid crystal (LC) molecules, adding nanoparticles into the matrix of the substrate material towards modifying its surface, is actively pursued. In this context, the influence of the nanoparticle content on the texture of the surface of polymer film used as the substrate for the LC orientation is of particular interest. Thus, in the current paper, WS2 nanotubes were used to dope the polyimide (PI) substrate-film in order to modify and control its surface morphology/roughness and properties. The modified organic surface structure is applied in order to achieve a new means for controlling the orientation of the LC molecules. This tool adds to the classical methods for controlling the orientation of the LC molecules, such as the display technique. Full article
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Review

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13 pages, 2507 KiB  
Review
Photosensitive Alignment: Advanced Electronic Paper-Based Devices
by Vladimir Chigrinov, Aleksey Kudreyko and Jiatong Sun
Crystals 2022, 12(3), 364; https://doi.org/10.3390/cryst12030364 - 09 Mar 2022
Cited by 5 | Viewed by 1925
Abstract
In this review we describe the reversible photoalignment effect imposed on the director in nematic liquid crystals that provides an approach for fabrication of advanced optically addressed devices. Several new concepts have been developed to render photosensitive materials during the past decade. Functional [...] Read more.
In this review we describe the reversible photoalignment effect imposed on the director in nematic liquid crystals that provides an approach for fabrication of advanced optically addressed devices. Several new concepts have been developed to render photosensitive materials during the past decade. Functional soft azo dye compounds exhibiting distinct functionalities in response to polarized light are highly desirable for fabrication of optically rewritable electronic paper. An optically rewritable element base using simple and inexpensive materials can potentially enable the development of novel environmentally friendly, paper-like gadgets with improved functionality over regular electronic paper. We argue that an optically rewritable technique is relevant for some applications, where conventional paper might be irrelevant. In particular, we have tested and discussed several techniques of color and 3D image formation. This strategy for fabrication of novel devices offers versatile methods for visualization. We also show that the intensity modulation of the irradiation light has a potential to generate improved grayscale visualization. This principle is based on the statistical distribution control of photosensitive azo dye molecules, driven by the incident polarized light. Additionally, we discuss the functional characteristics of the developed prototypes. Full article
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