Editorial

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Editorial: Special Issue “Liquid Crystals 2020”

by Viorel Cîrcu, Doina Manaila-Maximean and Valery A. Loiko

Molecules 2023, 28(8), 3359; https://doi.org/10.3390/molecules28083359 - 11 Apr 2023

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This Special Issue, entitled “Liquid Crystals 2020”, is a collection of ten original research papers, including two feature papers, on theoretical and experimental advanced studies of liquid crystal science and technology [...] Full article

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10 pages, 2487 KiB

Open AccessArticle

Multimode Robust Lasing in a Dye-Doped Polymer Layer Embedded in a Wedge-Shaped Cholesteric

by Tatevik M. Sarukhanyan, Hermine Gharagulyan, Mushegh S. Rafayelyan, Sergey S. Golik, Ashot H. Gevorgyan and Roman B. Alaverdyan

Molecules 2021, 26(19), 6089; https://doi.org/10.3390/molecules26196089 - 08 Oct 2021

Cited by 7 | Viewed by 2019

Abstract

Cholesteric liquid crystals (CLCs) with induced defects are one of the most prominent materials to realize compact, low-threshold and tunable coherent light sources. In this context, the investigation of optical properties of induced defect modes in such CLCs is of great interest. In [...] Read more.

Cholesteric liquid crystals (CLCs) with induced defects are one of the most prominent materials to realize compact, low-threshold and tunable coherent light sources. In this context, the investigation of optical properties of induced defect modes in such CLCs is of great interest. In particular, many studies have been devoted to the spectral control of the defect modes depending on their thickness, optical properties, distribution along the CLC, etc. In this paper, we investigate the lasing possibilities of a dye-doped polymer layer embedded in a wedge-shaped CLC. We show that multimode laser generation is possible due to the observed multiple defect modes in the PBG that enlarges the application range of the system. Furthermore, our simulations based on a Berreman 4 × 4 matrix approach for a wide range of CLC thickness show both periodic and continuous generation of defect modes along particular spectral lines inside the PBG. Such a robust spectral behaviour of induced defect modes is unique, and, to our knowledge, is not observed in similar CLC-based structures. Full article

(This article belongs to the Special Issue Liquid Crystals 2020)

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11 pages, 3867 KiB

Open AccessArticle

Defect Structures of Magnetic Nanoparticles in Smectic A Liquid Crystals

by Vladimíra Novotná, Lubor Lejček, Věra Hamplová and Jana Vejpravová

Molecules 2021, 26(18), 5717; https://doi.org/10.3390/molecules26185717 - 21 Sep 2021

Cited by 1 | Viewed by 1790

Abstract

Topological defects in anisotropic fluids like liquid crystals serve as a playground for the research of various effects. In this study, we concentrated on a hybrid system of chiral rod-like molecules doped by magnetic nanoparticles. In textures of the smectic A phase, we [...] Read more.

Topological defects in anisotropic fluids like liquid crystals serve as a playground for the research of various effects. In this study, we concentrated on a hybrid system of chiral rod-like molecules doped by magnetic nanoparticles. In textures of the smectic A phase, we observed linear defects and found that clusters of nanoparticles promote nucleation of smectic layer defects just at the phase transition from the isotropic to the smectic A (SmA) phase. In different geometries, we studied and analysed creation of defects which can be explained by attractive elastic forces between nanoparticles in the SmA phase. On cooling the studied hybrid system, clusters grow up to the critical dimension, and the smectic texture is stabilised. The presented effects are theoretically described and explained if we consider the elastic interaction of two point defects and stabilisation of prismatic dislocation loops due to the presence of nanoparticles. Full article

(This article belongs to the Special Issue Liquid Crystals 2020)

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9 pages, 2785 KiB

Open AccessArticle

Anomalous Lehmann Rotation of Achiral Nematic Liquid Crystal Droplets Trapped under Linearly Polarized Optical Tweezers

by Jarinee Kiang-ia, Rahut Taeudomkul, Pongthep Prajongtat, Padetha Tin, Apichart Pattanaporkratana and Nattaporn Chattham

Molecules 2021, 26(14), 4108; https://doi.org/10.3390/molecules26144108 - 06 Jul 2021

Cited by 4 | Viewed by 2087

Abstract

Continuous rotation of a cholesteric droplet under the heat gradient was observed by Lehmann in 1900. This phenomenon, the so-called Lehmann effect, consists of unidirectional rotation around the heat flux axis. We investigate this gradient heat effect using infrared laser optical tweezers. By [...] Read more.

Continuous rotation of a cholesteric droplet under the heat gradient was observed by Lehmann in 1900. This phenomenon, the so-called Lehmann effect, consists of unidirectional rotation around the heat flux axis. We investigate this gradient heat effect using infrared laser optical tweezers. By applying single trap linearly polarized optical tweezers onto a radial achiral nematic liquid crystal droplet, trapping of the droplet was performed. However, under a linearly polarized optical trap, instead of stable trapping of the droplet with slightly deformed molecular directors along with a radial hedgehog defect, anomalous continuous rotation of the droplet was observed. Under low power laser trapping, the droplet appeared to rotate clockwise. By continuously increasing the laser power, a stable trap was observed, followed by reverse directional rotation in a higher intensity laser trap. Optical levitation of the droplet in the laser beam caused the heat gradient, and a breaking of the symmetry of the achiral nematic droplet. These two effects together led to the rotation of the droplet under linearly polarized laser trapping, with the sense of rotation depending on laser power. Full article

(This article belongs to the Special Issue Liquid Crystals 2020)

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12 pages, 3729 KiB

Open AccessArticle

Aptamer Laden Liquid Crystals Biosensing Platform for the Detection of HIV-1 Glycoprotein-120

by Amna Didar Abbasi, Zakir Hussain and Kun-Lin Yang

Molecules 2021, 26(10), 2893; https://doi.org/10.3390/molecules26102893 - 13 May 2021

Cited by 10 | Viewed by 2160

Abstract

We report a label-free and simple approach for the detection of glycoprotein-120 (gp-120) using an aptamer-based liquid crystals (LCs) biosensing platform. The LCs are supported on the surface of a modified glass slide with a suitable amount of B40t77 aptamer, allowing the LCs [...] Read more.

We report a label-free and simple approach for the detection of glycoprotein-120 (gp-120) using an aptamer-based liquid crystals (LCs) biosensing platform. The LCs are supported on the surface of a modified glass slide with a suitable amount of B40t77 aptamer, allowing the LCs to be homeotropically aligned. A pronounced topological change was observed on the surface due to a specific interaction between B40t77 and gp-120, which led to the disruption of the homeotropic alignment of LCs. This results in a dark-to-bright transition observed under a polarized optical microscope. With the developed biosensing platform, it was possible to not only identify gp-120, but obtained results were analyzed quantitatively through image analysis. The detection limit of the proposed biosensing platform was investigated to be 0.2 µg/mL of gp-120. Regarding selectivity of the developed platform, no response could be detected when gp-120 was replaced by other proteins, such as bovine serum albumin (BSA), hepatitis A virus capsid protein 1 (Hep A VP1) and immunoglobulin G protein (IgG). Due to attributes such as label-free, high specificity and no need for instrumental read-out, the presented biosensing platform provides the potential to develop a working device for the quick detection of HIV-1 gp-120. Full article

(This article belongs to the Special Issue Liquid Crystals 2020)

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13 pages, 2763 KiB

Open AccessFeature PaperArticle

Dielectric Spectroscopy Analysis of Liquid Crystals Recovered from End-of-Life Liquid Crystal Displays

by Ana Barrera, Corinne Binet, Frédéric Dubois, Pierre-Alexandre Hébert, Philippe Supiot, Corinne Foissac and Ulrich Maschke

Molecules 2021, 26(10), 2873; https://doi.org/10.3390/molecules26102873 - 12 May 2021

Cited by 16 | Viewed by 2402

Abstract

In the present work, the dielectric properties of recycled liquid crystals (LCs) (non-purified, purified, and doped with diamond nanoparticles at 0.05, 0.1, and 0.2 wt%) were investigated. The studied LC mixtures were obtained from industrial recycling of end-of-life LC displays presenting mainly nematic [...] Read more.

In the present work, the dielectric properties of recycled liquid crystals (LCs) (non-purified, purified, and doped with diamond nanoparticles at 0.05, 0.1, and 0.2 wt%) were investigated. The studied LC mixtures were obtained from industrial recycling of end-of-life LC displays presenting mainly nematic phases. Dielectric measurements were carried out at room temperature on a frequency range from 0.1 to 10⁶ Hz using an impedance analyzer. The amplitude of the oscillating voltage was fixed at 1 V using cells with homogeneous and homeotropic alignments. Results show that the dielectric anisotropy of all purified samples presents positive values and decreases after the addition of diamond nanoparticles to the LC mixtures. DC conductivity values were obtained by applying the universal law of dielectric response proposed by Jonscher. In addition, conductivity of the doped LC mixtures is lower than that of the undoped and non-purified LC. Full article

(This article belongs to the Special Issue Liquid Crystals 2020)

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12 pages, 3349 KiB

Open AccessFeature PaperArticle

Liquid Crystals Based on the N-Phenylpyridinium Cation—Mesomorphism and the Effect of the Anion

by Jordan D. Herod and Duncan W. Bruce

Molecules 2021, 26(9), 2653; https://doi.org/10.3390/molecules26092653 - 01 May 2021

Cited by 4 | Viewed by 1560

Abstract

Families of symmetric, ionic, tetracatenar mesogens are described based on a rigid, N-phenylpyridinium core, prepared as their triflimide, octyl sulfate and dodecyl sulfate salts for a range of terminal chain lengths. The mesomorphism of the individual series is described before a comparison [...] Read more.

Families of symmetric, ionic, tetracatenar mesogens are described based on a rigid, N-phenylpyridinium core, prepared as their triflimide, octyl sulfate and dodecyl sulfate salts for a range of terminal chain lengths. The mesomorphism of the individual series is described before a comparison is drawn between the different families and then more broadly with (i) neutral tetracatenar materials and (ii) related bis(3,4-dialkoxystilbazole)silver(I) salts. For the octyl and dodecyl sulfates and the related triflates reported earlier, a SmA phase is seen at shorter chain lengths, giving way to a Col_h phase as the terminal chain lengthens. For the alkyl sulfate salts, an intermediate cubic phase is also seen and the terminal chain length required to cause the change from lamellar to columnar mesophase depends on the anion. Furthermore, there is an unexpected and sometime very large mesophase stabilisation seen on entering the columnar phase. All of the triflimide salts show a rectangular columnar (ribbon) phase. Full article

(This article belongs to the Special Issue Liquid Crystals 2020)

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12 pages, 3656 KiB

Open AccessArticle

Effective Permittivity of a Multi-Phase System: Nanoparticle-Doped Polymer-Dispersed Liquid Crystal Films

by Doina Manaila-Maximean

Molecules 2021, 26(5), 1441; https://doi.org/10.3390/molecules26051441 - 07 Mar 2021

Cited by 20 | Viewed by 2084

Abstract

This paper studies the effective dielectric properties of heterogeneous materials of the type particle inclusions in a host medium, using the Maxwell Garnet and the Bruggeman theory. The results of the theories are applied at polymer-dispersed liquid crystal (PDLC) films, nanoparticles (NP)-doped LCs, [...] Read more.

This paper studies the effective dielectric properties of heterogeneous materials of the type particle inclusions in a host medium, using the Maxwell Garnet and the Bruggeman theory. The results of the theories are applied at polymer-dispersed liquid crystal (PDLC) films, nanoparticles (NP)-doped LCs, and developed for NP-doped PDLC films. The effective permittivity of the composite was simulated at sufficiently high frequency, where the permittivity is constant, obtaining results on its dependency on the constituents’ permittivity and concentrations. The two models are compared and discussed. The method used for simulating the doped PDLC retains its general character and can be applied for other similar multiphase composites. The methods can be used to calculate the effective permittivity of a LC composite, or, in the case of a composite in which one of the phases has an unknown permittivity, to extract it from the measured composite permittivity. The obtained data are necessary in the design of the electrical circuits. Full article

(This article belongs to the Special Issue Liquid Crystals 2020)

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14 pages, 3940 KiB

Open AccessArticle

Phase Transitions and Hysteresis for a Simple Model Liquid Crystal by Replica-Exchange Monte Carlo Simulations

by Akie Kowaguchi, Paul E. Brumby and Kenji Yasuoka

Molecules 2021, 26(5), 1421; https://doi.org/10.3390/molecules26051421 - 05 Mar 2021

Cited by 5 | Viewed by 1937

Abstract

In this work, the advantages of applying the temperature and pressure replica-exchange method to investigate the phase transitions and the hysteresis for liquid-crystal fluids were demonstrated. In applying this method to the commonly used Hess–Su liquid-crystal model, heat capacity peaks and points of [...] Read more.

In this work, the advantages of applying the temperature and pressure replica-exchange method to investigate the phase transitions and the hysteresis for liquid-crystal fluids were demonstrated. In applying this method to the commonly used Hess–Su liquid-crystal model, heat capacity peaks and points of phase co-existence were observed. The absence of a smectic phase at higher densities and a narrow range of the nematic phase were reported. The identity of the crystalline phase of this system was found to a hexagonal close-packed solid. Since the nematic-solid phase transition is strongly first order, care must be taken when using this model not to inadvertently simulate meta-stable nematic states at higher densities. In further analysis, the Weighted Histogram Analysis Method was applied to verify the precise locations of the phase transition points. Full article

(This article belongs to the Special Issue Liquid Crystals 2020)

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12 pages, 599 KiB

Open AccessArticle

Ferroelectric Particles in Nematic Liquid Crystals with Soft Anchoring

by Cristina Cirtoaje

Molecules 2021, 26(4), 1166; https://doi.org/10.3390/molecules26041166 - 22 Feb 2021

Cited by 3 | Viewed by 1875

Abstract

A theoretical evaluation of the electric Freedericksz transition threshold and saturation field is proposed for a liquid crystals composite with ferroelectric particles. Existing models consider a strong anchoring of nematic molecules on the glass support of the cell, but in this paper a [...] Read more.

A theoretical evaluation of the electric Freedericksz transition threshold and saturation field is proposed for a liquid crystals composite with ferroelectric particles. Existing models consider a strong anchoring of nematic molecules on the glass support of the cell, but in this paper a soft molecular anchoring of molecules on the glass support and also on the ferroelectric nanoparticle’s surface is assumed. Thus, a finite saturation field was obtained in agreement with real systems. Calculations are made for planar configuration of positive dielectric anisotropy liquid crystals. The results are compared with data obtained on similar systems from different publications and the differences are discussed. Full article

(This article belongs to the Special Issue Liquid Crystals 2020)

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19 pages, 5285 KiB

Open AccessArticle

Impact of Substitution Pattern and Chain Length on the Thermotropic Properties of Alkoxy-Substituted Triphenyl-Tristriazolotriazines

by Thorsten Rieth, Natalie Tober, Daniel Limbach, Tobias Haspel, Marcel Sperner, Niklas Schupp, Philipp Wicker, Stefan Glang, Matthias Lehmann and Heiner Detert

Molecules 2020, 25(23), 5761; https://doi.org/10.3390/molecules25235761 - 07 Dec 2020

Cited by 7 | Viewed by 3041

Abstract

Tristriazolotriazines (TTTs) with a threefold alkoxyphenyl substitution were prepared and studied by DSC, polarized optical microscopy (POM) and X-ray scattering. Six pentyloxy chains are sufficient to induce liquid-crystalline behavior in these star-shaped compounds. Thermotropic properties of TTTs with varying substitution patterns and a [...] Read more.

Tristriazolotriazines (TTTs) with a threefold alkoxyphenyl substitution were prepared and studied by DSC, polarized optical microscopy (POM) and X-ray scattering. Six pentyloxy chains are sufficient to induce liquid-crystalline behavior in these star-shaped compounds. Thermotropic properties of TTTs with varying substitution patterns and a periphery of linear chains of different lengths, branching in the chain and swallow-tails, are compared. Generally, these disks display broad and stable thermotropic mesophases, with the tangential TTT being superior to the radial isomer. The structure–property relationships of the number of alkyl chains, their position, length and structure were studied. Full article

(This article belongs to the Special Issue Liquid Crystals 2020)

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