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Crystals
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Liquid Crystal Research and Novel Applications in the 21st Century
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Liquid Crystal Research and Novel Applications in the 21st Century

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

Deadline for manuscript submissions: 31 December 2024 | Viewed by 10305

Special Issue Editor

Dr. Ingo Dierking

E-Mail Website
Guest Editor
Department of Physics and Astronomy, The University of Manchester, Oxford Road, Manchester M13 9PL, UK
Interests: liquid crystals; chiral liquid crystals; ferroelectric liquid crystals; polymer stabilized liquid crystals; nanoparticles in anisotropic fluids; liquid crystal-nanotube dispersions; defects and defect dynamics; phase ordering in soft matter; fractal structures
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

For many years, the main focus of liquid crystal (LC) research was on either the fundamental properties of anisotropic fluids or applications in liquid crystal displays (LCDs). This has changed quite dramatically in the last decade, since displays and monitors have matured considerably and have become the market’s dominating technology. From a physics point of view, fundamental LC research has spread into many other areas of soft matter science, such as polymers, colloids, biological materials, dispersions, medical and pharmaceutical systems, and fundamental phenomena in physics. From a chemistry point of view, increasingly complicated molecular structures have been developed; moreover, dendrimers, ionic liquid crystals, green chemistry approaches and recycling aspects of displays have emerged. In terms of applications, liquid crystals have expanded into the fields of adaptive optics, augmented reality, optical elements, telecommunication, optical solitons and lasers, as well as other devices outside the field of Liquid Crystal Displays.

This Special Issue will highlight the latest important developments in the research and applications of liquid crystal. It will include topics beyond the traditional liquid crystal investigations of past decades, focusing on recent studies that have propelled the field of soft matter systems and application development. Moreover, we anticipate that this collection of reviews, research papers, perspective articles and roadmaps will demonstrate the multi-disciplinarity, diversity and variety of liquid crystals, LC-related systems and composites, combining aspects of physics and chemistry with those of material science, mathematics, biology and medicine.

Given the broad range of liquid crystal-related topics covered in this collection, the submission deadline has been set to 30 June 2024 to give authors sufficient time to prepare their contributions.

Research areas include, but are not limited to:

  • New nematic systems (ferroelectric, biaxial and twist-bend nematics);
  • Active liquid crystals;
  • Instabilities, pattern formation, solitons and topological defects;
  • Nanostructured systems (PSLCs, PDLCs, elastomers, actuators and gels);
  • Colloidal liquid crystals (cellulose nanocrystals, graphene oxide LCs, clays, nano-rods, etc.);
  • Biological and bio-inspired liquid crystal systems;
  • Frustrated phases;
  • Photosensitive liquid crystals and surfaces;
  • Theory and simulation of liquid crystal-based systems;
  • Optics, photonics, and non-linear optical devices;
  • Conductive liquid crystal devices;
  • Optical films, gratings and smart devices;
  • LC lasers;
  • Drug delivery;
  • Liquid crystal-based sensors;
  • LCs in medicine.

Dr. Ingo Dierking
Guest Editor

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. Crystals is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2100 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

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Further information on MDPI's Special Issue polices can be found here.

Published Papers (8 papers)

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Research

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15 pages, 3009 KiB  
Article
Local Orientation Transitions to a Lying Helix State in Negative Dielectric Anisotropy Cholesteric Liquid Crystal
by Ivan V. Simdyankin, Artur R. Geivandov, Irina V. Kasyanova and Serguei P. Palto
Crystals 2024, 14(10), 891; https://doi.org/10.3390/cryst14100891 - 13 Oct 2024
Viewed by 729
Abstract
Orientation transitions in a cholesteric liquid crystal (CLC) layer with negative dielectric anisotropy, under the influence of a non-uniform spatially periodic electric field created using a planar system of interdigitated electrodes, were studied experimentally and numerically. In the interelectrode space, transitions are observed [...] Read more.
Orientation transitions in a cholesteric liquid crystal (CLC) layer with negative dielectric anisotropy, under the influence of a non-uniform spatially periodic electric field created using a planar system of interdigitated electrodes, were studied experimentally and numerically. In the interelectrode space, transitions are observed from a planar Grandjean texture, with the helix axis perpendicular to the layer plane, to states with a lying helix, when the helix axis is parallel to the layer plane and perpendicular to the electrode stripes. It was found that the relaxation time of the induced state in the Grandjean zones, corresponding to two or more half-turns of the helix, significantly exceeded the relaxation time for the first Grandjean zone with one half-turn. An analysis of experimentally observed and numerically simulated textures shows that slow relaxation to the initial state in the second Grandjean zone, as well as in higher-order zones, is associated with the formation of local topologically equivalent states. In these states, the helix has a reduced integer number of helix half-turns throughout the layer thickness or unwound into the planar alignment state. Full article
(This article belongs to the Special Issue Liquid Crystal Research and Novel Applications in the 21st Century)
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17 pages, 3995 KiB  
Article
Density Functional Theory Calculations for Interpretation of Infra-Red Spectra of Liquid Crystalline Chiral Compound
by Aleksandra Deptuch, Natalia Górska, Michaela Murzyniec, Monika Srebro-Hooper, James Hooper, Magdalena Dziurka and Magdalena Urbańska
Crystals 2024, 14(7), 645; https://doi.org/10.3390/cryst14070645 - 13 Jul 2024
Viewed by 1146
Abstract
The experimental IR spectra of (S)-4′-(1-methylheptyloxycarbonyl) biphenyl-4-yl 4-[2-(2,2,3,3,4,4,4-heptafluorobutoxy) ethyl-1-oxy]-2-fluorobenzoate in the crystal phase are analyzed with the help of dispersion-corrected density functional theory (DFT+D3) calculations for isolated molecular monomer and dimer models, and a periodic model computed at the extended density [...] Read more.
The experimental IR spectra of (S)-4′-(1-methylheptyloxycarbonyl) biphenyl-4-yl 4-[2-(2,2,3,3,4,4,4-heptafluorobutoxy) ethyl-1-oxy]-2-fluorobenzoate in the crystal phase are analyzed with the help of dispersion-corrected density functional theory (DFT+D3) calculations for isolated molecular monomer and dimer models, and a periodic model computed at the extended density functional tight-binding (xTB) level of theory. It is found that the frequency scaling coefficients obtained with the results of the molecular calculations are good matches for the crystal phase, being close to 1. The molecular and periodic models both confirm that varied intra- and intermolecular interactions are crucial in order to reproduce the broadened shape of the experimental band related to C=O stretching; the key factors are the conjugation of the ester groups with the aromatic rings and the varied intermolecular chemical environments, wherein the C=O group that bridges the biphenyl and F-substituted phenyl groups seems particularly sensitive. The C=O stretching vibrations are investigated as a function of temperature, covering the range of the crystal, smectic CA*, smectic C* and isotropic liquid phases. The structure changes are followed based on the X-ray diffraction patterns collected in the same temperatures as the IR spectra. The experimental and computational results taken together indicate that the amount of weak C=O…H-C hydrogen bonds between the molecules in the smectic layers decreases with increasing temperature. Full article
(This article belongs to the Special Issue Liquid Crystal Research and Novel Applications in the 21st Century)
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9 pages, 2636 KiB  
Article
Polarization Coupling between Ferroelectric Liquids and Ferroelectric Solids: Effects of the Fringing Field Profile
by Stefano Marni, Raouf Barboza, Ayomide S. Oluwajoba, Riccardo Zamboni and Liana Lucchetti
Crystals 2024, 14(5), 425; https://doi.org/10.3390/cryst14050425 - 29 Apr 2024
Cited by 2 | Viewed by 953
Abstract
Recent experiments devoted to characterizing the behavior of sessile ferroelectric liquid droplets on ferroelectric solid substrates have shown the existence of a droplet electromechanical Rayleigh-like instability. The instability is induced by the bulk polarization of the ferroelectric fluid, which couples to the polarization [...] Read more.
Recent experiments devoted to characterizing the behavior of sessile ferroelectric liquid droplets on ferroelectric solid substrates have shown the existence of a droplet electromechanical Rayleigh-like instability. The instability is induced by the bulk polarization of the ferroelectric fluid, which couples to the polarization of the underlying substrate through its fringing field and solid–fluid interface coupling. With the aim of characterizing this phenomenon, namely the coupling between the polarizations of a fluid and a solid material, we studied the behavior of ferroelectric liquid droplets confined between two solid substrates, arranged in different configurations, realized to generate fringing fields with different profiles. The results show that the features of the droplets instability are indeed affected by the specific fringing field shape in a way dominated by the minimization of the electrostatic energy associated with the bulk polarization of the ferroelectric fluid. Full article
(This article belongs to the Special Issue Liquid Crystal Research and Novel Applications in the 21st Century)
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Graphical abstract

12 pages, 4848 KiB  
Article
Structural Study of Nematogenic Compound 5OS5
by Aleksandra Deptuch, Bartosz Sęk, Sebastian Lalik, Wojciech Zając, Mirosława D. Ossowska-Chruściel, Janusz Chruściel and Monika Marzec
Crystals 2024, 14(4), 367; https://doi.org/10.3390/cryst14040367 - 13 Apr 2024
Viewed by 1341
Abstract
The S-(4-pentylphenyl) 4-(pentyloxy)benzothioate, forming the nematic phase, is investigated by X-ray diffraction in temperatures between 263 K and 365 K, with the support of differential scanning calorimetry and polarizing optical microscopy. The microscopic observations show changes within the solid state, while X-ray diffraction [...] Read more.
The S-(4-pentylphenyl) 4-(pentyloxy)benzothioate, forming the nematic phase, is investigated by X-ray diffraction in temperatures between 263 K and 365 K, with the support of differential scanning calorimetry and polarizing optical microscopy. The microscopic observations show changes within the solid state, while X-ray diffraction does not indicate any transitions between the crystal phases. The Rietveld refinement shows that the crystal phase formed from the melt is the same monoclinic crystal phase with the P21/c space group as reported for a single crystal grown from an ethanol solution. The temperature dependence of the unit cell parameters in the 263–335 K range is determined and the coefficients of thermal expansion are obtained. The unit cell expands on heating along the longer ac-diagonal and b-axis while, along the shorter ac-diagonal, a very small shrinkage occurs. The diffraction patterns of the liquid crystalline nematic phase indicate the formation of dimers via hydrogen bonding. Density functional theory calculations (def2TZVPP basis set, B3LYP-D3(BJ) correlation-exchange functional) are applied for geometry optimization of an isolated molecule and selected dimers. Full article
(This article belongs to the Special Issue Liquid Crystal Research and Novel Applications in the 21st Century)
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15 pages, 1318 KiB  
Article
Analysing the Photo-Physical Properties of Liquid Crystals
by Jordan Hobbs, Johan Mattsson and Mamatha Nagaraj
Crystals 2024, 14(4), 362; https://doi.org/10.3390/cryst14040362 - 11 Apr 2024
Viewed by 1232
Abstract
Intrinsically fluorescent liquid crystals are highly sought after for a variety of applications. Most of the measurements of photo-physical properties of liquid crystals are made in dilute solutions, which is mainly due to the relative ease of both these measurements and the interpretation [...] Read more.
Intrinsically fluorescent liquid crystals are highly sought after for a variety of applications. Most of the measurements of photo-physical properties of liquid crystals are made in dilute solutions, which is mainly due to the relative ease of both these measurements and the interpretation of data. The fluorescence spectra depend on a number of parameters including the concentration in liquid crystal solutions, the device geometry, and the mesophase in which the spectra have been measured. Working with neat, or concentrated, liquid crystal samples adds experimental complexities such as the inner filter effect (IFE), which affects the collection of data, interpretation of the results, and accuracy of the conclusions. In this paper, we present a systematic study of the photo-physical properties of both a model reference material, Nile red, and a nematic liquid crystal, 4-cyano-4′-pentylbiphenyl (5CB). The influence on the emission spectra of an increasing solute concentration is investigated and discussed. Moreover, a detailed investigation of the influence of the used device geometry, as well as the choice of appropriate data fitting methodologies, are presented. Full article
(This article belongs to the Special Issue Liquid Crystal Research and Novel Applications in the 21st Century)
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11 pages, 2073 KiB  
Article
Reconfigurable Liquid Crystal Elastomer Director Patterns for Multi-Mode Shape Morphing
by Xianbing Zeng, Tianfeng Zhou, Lei Li, Juncai Song, Ruijue Duan, Xiang Xiao, Baiqian Xu, Guanghao Wu and Yubing Guo
Crystals 2024, 14(4), 357; https://doi.org/10.3390/cryst14040357 - 10 Apr 2024
Viewed by 1210
Abstract
Liquid crystal elastomers (LCEs) are a monolithic material with programmable three-dimensional (3D) morphing modes stemming from their designable non-uniform molecular orientations (or director). However, the shape morphing mode is generally fixed when director patterns of LCEs are determined. Multi-mode shape morphing is difficult [...] Read more.
Liquid crystal elastomers (LCEs) are a monolithic material with programmable three-dimensional (3D) morphing modes stemming from their designable non-uniform molecular orientations (or director). However, the shape morphing mode is generally fixed when director patterns of LCEs are determined. Multi-mode shape morphing is difficult to achieve since director patterns cannot be reconfigured. Herein, we demonstrate the ability to reconfigure LCE director patterns and initial shapes—and thus shape morphing modes—by the manual assembly and de-assembly of LCE pixels. We measured the mechanical properties of LCEs with and without UV glue and found their Young’s moduli were 9.6 MPa and 11.6 MPa. We firstly fabricate LCE pixels with designed director fields and then assemble 24 pixels with required director fields into an LCE film with a designed director pattern, which corresponds to a programmed shape morphing mode. We further exhibit that we can de-assemble the LCE film back into original pixels or new pixels with different shapes and then re-assemble them into a new film with a different initial shape and director pattern, which corresponds to a second programmed shape morphing mode. Principally, we can have a large amount of shape morphing modes if we have enough pixels. The demonstrated capability of multi-mode shape morphing enhances functions of LCEs, which broadens their applications in soft robotics, programmable origami/kirigami, responsive surfaces, and so on. Full article
(This article belongs to the Special Issue Liquid Crystal Research and Novel Applications in the 21st Century)
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Review

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16 pages, 2072 KiB  
Review
Chiral, Topological, and Knotted Colloids in Liquid Crystals
by Ye Yuan and Ivan I. Smalyukh
Crystals 2024, 14(10), 885; https://doi.org/10.3390/cryst14100885 - 11 Oct 2024
Viewed by 840
Abstract
The geometric shape, symmetry, and topology of colloidal particles often allow for controlling colloidal phase behavior and physical properties of these soft matter systems. In liquid crystalline dispersions, colloidal particles with low symmetry and nontrivial topology of surface confinement are of particular interest, [...] Read more.
The geometric shape, symmetry, and topology of colloidal particles often allow for controlling colloidal phase behavior and physical properties of these soft matter systems. In liquid crystalline dispersions, colloidal particles with low symmetry and nontrivial topology of surface confinement are of particular interest, including surfaces shaped as handlebodies, spirals, knots, multi-component links, and so on. These types of colloidal surfaces induce topologically nontrivial three-dimensional director field configurations and topological defects. Director switching by electric fields, laser tweezing of defects, and local photo-thermal melting of the liquid crystal host medium promote transformations among many stable and metastable particle-induced director configurations that can be revealed by means of direct label-free three-dimensional nonlinear optical imaging. The interplay between topologies of colloidal surfaces, director fields, and defects is found to show a number of unexpected features, such as knotting and linking of line defects, often uniquely arising from the nonpolar nature of the nematic director field. This review article highlights fascinating examples of new physical behavior arising from the interplay of nematic molecular order and both chiral symmetry and topology of colloidal inclusions within the nematic host. Furthermore, the article concludes with a brief discussion of how these findings may lay the groundwork for new types of topology-dictated self-assembly in soft condensed matter leading to novel mesostructured composite materials, as well as for experimental insights into the pure-math aspects of low-dimensional topology. Full article
(This article belongs to the Special Issue Liquid Crystal Research and Novel Applications in the 21st Century)
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30 pages, 9007 KiB  
Review
The Role of Liquid Crystal Elastomers in Pioneering Biological Applications
by Faeze Shiralipour, Yeganeh Nik Akhtar, Ashley Gilmor, Gisele Pegorin, Abraham Valerio-Aguilar and Elda Hegmann
Crystals 2024, 14(10), 859; https://doi.org/10.3390/cryst14100859 - 29 Sep 2024
Viewed by 1514
Abstract
Liquid crystal elastomers have shown an attractive potential for various biological applications due to their unique combination of mechanical flexibility and responsiveness to external stimuli. In this review, we will focus on a few examples of LCEs used with specific applications for biological/biomedical/environmental [...] Read more.
Liquid crystal elastomers have shown an attractive potential for various biological applications due to their unique combination of mechanical flexibility and responsiveness to external stimuli. In this review, we will focus on a few examples of LCEs used with specific applications for biological/biomedical/environmental systems. So far, areas of innovation have been concentrating on the integration of LCEs to enhance stability under physiological conditions, ensure precise integration with biological systems, and address challenges related to optical properties and spatial control of deformation. However, several challenges and limitations must still be addressed to fully realize their potential in biomedical and environmental fields, and future research should focus on continuing to improve biocompatibility, response to the environment and chemical cues, mechanical properties, ensuring long-term stability, and establishing cost-effective production processes. So far, 3D/4D printing appears as a great promise to develop materials of high complexity, almost any shape, and high production output. However, researchers need to find ways to reduce synthesis costs to ensure that LCEs are developed using cost-effective production methods at a scale necessary for their specific applications’ needs. Full article
(This article belongs to the Special Issue Liquid Crystal Research and Novel Applications in the 21st Century)
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