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

Deadline for manuscript submissions: closed (31 October 2020) | Viewed by 44889

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Special Issue Editors

Dr. Małgorzata Jasiurkowska-Delaporte

E-Mail Website
Guest Editor

Institute of Nuclear Physics, Polish Academy of Sciences, 31-342 Kraków, Poland
Interests: liquid crystals; broadband dielectric spectroscopy; molecular dynamics in bulk and under confinement; crystallization kinetics; glass transition; liquid crystalline composites

Dr. Łukasz Kolek

E-Mail Website
Co-Guest Editor

Department of Material Science, Rzeszow University of Technology, Rzeszów, Poland
Interests: liquid crystals, ferro-, antiferroelectric phases, dielectric spectroscopy, differential scanning calorimetry, nuclear magnetic resonance, phase transitions, glass transition, kinetics of crystallization, electro-optical methods, intra- and intermolecular dynamics

Special Issue Information

Dear Colleagues,

Due to their extraordinary physical properties liquid crystals (LCs) are of interest to a broad community of scientists and engineers. Although LCs are usually associated with display technology, they also have novel applications in a range of areas, including organic photovoltaics, sensing, pharmacy, and medicine. The simplest, and the most commonly used liquid crystalline state is the nematic phase (N), where the molecules are randomly positioned and oriented in a single direction. A special form of the nematic phase is the cholesteric phase composed of chiral molecules forming a helical superstructure.

The aim of this Special Issue is to combine the papers reporting fundamental and applied research related to nematic liquid crystals. The topics summarized under the keywords should be considered only as examples. The volume is open for any advanced topics in the field of nematic liquid crystals.

Dr. Małgorzata Jasiurkowska-Delaporte
Dr. Łukasz Kolek
Guest Editor

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Keywords

Synthesis and characterization of LCs
Molecular dynamics, glass transition, and crystallization kinetics in liquid crystals
Spectroscopic studies of LCs
Liquid crystals under confinement
Liquid crystals in life sciences
Applications of liquid crystals
Liquid crystalline polymers and elastomers
Liquid crystals/polymer composites
Liquid crystals dopped with nanoparticles
Liquid crystal colloidal dispersions

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Published Papers (13 papers)

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Editorial

Jump to: Research

2 pages, 172 KiB

Open AccessEditorial

Nematic Liquid Crystals

by Małgorzata Jasiurkowska-Delaporte and Łukasz Kolek

Crystals 2021, 11(4), 381; https://doi.org/10.3390/cryst11040381 - 6 Apr 2021

Cited by 3 | Viewed by 5679

Abstract

The discovery of liquid crystals (LCs) is dated to the year 1888, when Friedrich Reinitzer reported his observation of the double melting points of cholesterol benzoate [...] Full article

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

Research

Jump to: Editorial

14 pages, 14472 KiB

Open AccessArticle

Temperature Characterization of Liquid Crystal Dielectric Image Line Phase Shifter for Millimeter-Wave Applications

by Henning Tesmer, Rani Razzouk, Ersin Polat, Dongwei Wang, Rolf Jakoby and Holger Maune

Crystals 2021, 11(1), 63; https://doi.org/10.3390/cryst11010063 - 14 Jan 2021

Cited by 12 | Viewed by 3258

Abstract

In this paper we investigate the temperature dependent behavior of a liquid crystal (LC) loaded tunable dielectric image guide (DIG) phase shifter at millimeter-wave frequencies from 80

G

Hz

to 110

G

Hz

for future high data rate communications. The adhesive, necessary for [...] Read more.

In this paper we investigate the temperature dependent behavior of a liquid crystal (LC) loaded tunable dielectric image guide (DIG) phase shifter at millimeter-wave frequencies from 80

G

Hz

to 110

G

Hz

for future high data rate communications. The adhesive, necessary for precise fabrication, is analyzed before temperature dependent behavior of the component is shown, using the nematic LC-mixture GT7-29001. The temperature characterization is conducted by changing the temperature of the LC DIG’s ground plane between

- 10

^{\circ} C

and 80

^{\circ} C

. The orientation of the LC molecules, and therefore the effective macroscopic relative permittivity of the DIG, is changed by inserting the temperature setup in a fixture with rotatable magnets. Temperature independent matching can be observed, while the insertion loss gradually increases with temperature for both highest and lowest permittivity of the LC. At 80

^{\circ} C

the insertion loss is up to

1.3

d

B

higher and at

- 10

^{\circ} C

it is

0.6

d

B

lower than the insertion loss present at 20

^{\circ} C

. In addition, the achievable differential phase is reduced with increasing temperature. The impact of molecule alignment to this reduction is shown for the phase shifter and an estimated 85% of the anisotropy is still usable with an LC DIG phase shifter when increasing the temperature from 20

^{\circ} C

to 80

^{\circ} C

. Higher reduction of differential phase is present at higher frequencies as the electrical length of the phase shifter increases. A maximum difference in differential phase of 72

^{\circ}

is present at 110

G

Hz

, when increasing the temperature from 20

^{\circ} C

to 80

^{\circ} C

. Nevertheless, a well predictable, quasi-linear behavior can be observed at the covered temperature range, highlighting the potential of LC-based dielectric components at millimeter wave frequencies. Full article

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

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10 pages, 3349 KiB

Open AccessArticle

Effect of Ion Concentration on the Electro-Optic Response in Polymer-Stabilized Cholesteric Liquid Crystals

by Kyung M. Lee, Timothy J. Bunning, Timothy J. White, Michael E. McConney and Nicholas P. Godman

Crystals 2021, 11(1), 7; https://doi.org/10.3390/cryst11010007 - 23 Dec 2020

Cited by 12 | Viewed by 3300

Abstract

We have previously reported that the application of a DC field can adjust the position and/or bandwidth of the selective reflection notch in polymer-stabilized cholesteric liquid crystals (PSCLCs). The proposed mechanism of these electro-optic (EO) response is ion-facilitated electromechanical deformation of the polymer stabilizing network. Accordingly, the concentration of ions trapped within the polymer network should considerably influence the EO response of PSCLC. Our prior studies have indicated that photoinitiators can increase ion density in PSCLC by an order of magnitude. Here, we isolate the contribution of ionic impurities associated with liquid crystal monomers (LCMs) by utilizing initiator-less polymerization. PSCLCs prepared with LCM with low ion concentration show bandwidth broadening of the reflection band whereas PSCLCs prepared with LCM with high ion concentration exhibit a red shifting tuning of the reflection band. The extent of the tuning or bandwidth broadening of the CLC reflection band depends on the concentration of LCMs and the chirality of the LCM. Full article

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

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16 pages, 13052 KiB

Open AccessArticle

Chemical-Physical Characterization of a Binary Mixture of a Twist Bend Nematic Liquid Crystal with a Smectogen

by Abir Aouini, Maurizio Nobili, Edouard Chauveau, Philippe Dieudonné-George, Gauthier Damême, Daniel Stoenescu, Ivan Dozov and Christophe Blanc

Crystals 2020, 10(12), 1110; https://doi.org/10.3390/cryst10121110 - 4 Dec 2020

Cited by 16 | Viewed by 3439

Abstract

Nematic twist-bend phases (N_TB) are new types of nematic liquid crystalline phases with attractive properties for future electro-optic applications. However, most of these states are monotropic or are stable only in a narrow high temperature range. They are often destabilized under moderate cooling, and only a few single compounds have shown to give room temperature N_TB phases. Mixtures of twist-bend nematic liquid crystals with simple nematogens have shown to strongly lower the nematic to N_TB phase transition temperature. Here, we examined the behaviour of new types of mixtures with the dimeric liquid crystal [4′,4′-(heptane-1,7-diyl)bis(([1′,1″-biphenyl]4″-carbo-nitrile))] (CB7CB). This now well-known twist-bend nematic liquid crystal presents a nematic twist-bend phase below T ≈ 104 °C. Mixtures with other monomeric alkyl or alkoxy -biphenylcarbonitriles liquid crystals that display a smectic A (SmA) phase also strongly reduce this temperature. The most interesting smectogen is 4′-Octyl-4-biphenylcarbonitrile (8CB), for which a long-term metastable N_TB phase is found at room and lower temperatures. This paper presents the complete phase diagram of the corresponding binary system and a detailed investigation of its thermal, optical, dielectric, and elastic properties. Full article

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

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14 pages, 5398 KiB

Open AccessArticle

Characterization of Nematic Liquid Crystals at Microwave Frequencies

by Vicente Nova, Carmen Bachiller, Belén Villacampa, Rainer Kronberger and Vicente E. Boria

Crystals 2020, 10(12), 1106; https://doi.org/10.3390/cryst10121106 - 3 Dec 2020

Cited by 8 | Viewed by 3066

Abstract

The use of nematic liquid crystal (LC) mixtures for microwave frequency applications presents a fundamental drawback: many of these mixtures have not been properly characterized at these frequencies, and researchers do not have an a priori clear idea of which behavior they can expect. This work is focused on developing a new procedure for the extraction of the main parameters of a nematic liquid crystal: dielectric permittivity and loss tangent at 11 GHz under different polarization voltages; splay elastic constant

K_{11}

, which allows calculation of the threshold voltage (

V_{t h}

); and rotational viscosity

γ_{11}

, which allows calculating the response time of any arbitrary device. These properties will be calculated by using a resonator-based method, which is implemented with a new topology of substrate integrated transmission line. The LC molecules should be rotated (polarized) by applying an electric field in order to extract the characteristic parameters; thus, the transmission line needs to have two conductors and low electric losses in order to preserve the integrity of the measurements. This method was applied to a well-known liquid crystal mixture (GT3-23002 from MERCK) obtaining the permittivity and loss tangent versus bias voltage curves, the splay elastic constant, and the rotational viscosity of the mixture. The results validate the viability of the proposed method. Full article

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

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14 pages, 2147 KiB

Open AccessArticle

Study of Structural Changes in Nematic Liquid Crystals Doped with Magnetic Nanoparticles Using Surface Acoustic Waves

by Peter Bury, Marek Veveričík, František Černobila, Peter Kopčanský, Milan Timko and Vlasta Závišová

Crystals 2020, 10(11), 1023; https://doi.org/10.3390/cryst10111023 - 10 Nov 2020

Cited by 12 | Viewed by 2594

Abstract

The surface acoustic waves (SAWs) were used to study the effect of magnetic nanoparticles on nematic liquid crystal (NLC) behavior in weak magnetic and electric fields. The measurement of the attenuation of SAW propagating along the interface between piezoelectric substrate and liquid crystal is showed as an effective tool to study processes of structural changes. The magnetic nanoparticles Fe₃O₄ of nanorod shape and different low volume concentration were added to the NLC (4-(trans-4′-n-hexylcyclohexyl)-isothiocyanatobenzene (6CHBT)) during its isotropic phase. In contrast to undoped liquid crystals the distinctive different SAW attenuation responses induced by both magnetic and also electric fields in studied NLC samples were observed suggesting both structural changes and the orientational coupling between both magnetic and electric moments of nanoparticles and the director of the NLC molecules. Experimental measurements including the investigation under linearly increasing and/or jumped magnetic and electrical fields, respectively, as well as the investigation of temperature and time influences on structural changes were done. The investigation of the SAW anisotropy gives supplemental information about the internal structure of nanoparticles in investigated NLCs. In addition, some magneto-optical investigations were performed to support SAW results and study their stability and switching time. The analysis of observed SAW attenuation characteristics confirmed the role of concentration of magnetic nanoparticles on the resultant behavior of investigated NLC compounds. Obtained results are discussed within the context of previous ones. The theoretical background of the presented SAW investigation is introduced, too. Full article

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

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13 pages, 6541 KiB

Open AccessArticle

Molecular-Theory of High Frequency Dielectric Susceptibility of Nematic Nanocomposites

by Mikhail A. Osipov, Alexey S. Merekalov and Alexander A. Ezhov

Crystals 2020, 10(11), 970; https://doi.org/10.3390/cryst10110970 - 26 Oct 2020

Cited by 2 | Viewed by 1771

Abstract

A molecular-statistical theory of the high frequency dielectric susceptibility of the nematic nanocomposites has been developed and approximate analytical expressions for the susceptibility have been obtained in terms of the effective polarizability of a nanoparticle in the nematic host, volume fraction of the nanoparticles and the susceptibility of the pure nematic phase. A simple expression for the split of the plasmon resonance of the nanoparticles in the nematic host has been obtained and it has been shown that in the resonance frequency range the high frequency dielectric anisotropy of the nanocomposite may be significantly larger than that of the pure nematic host. As a result, all dielectric and optical properties of the nanocomposite related to the anisotropy are significantly enhanced which may be important for emerging applications. The components of the dielectric susceptibility have been calculated numerically for particular nematic nanocomposites with gold and silver nanoparicles as functions of the nanoparticle volume fraction and frequency. The splitting of the plasmon resonance has been observed together with the significant dependence on the nanoparticle volume fraction and the parameters of the nematic host phase. Full article

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

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11 pages, 2648 KiB

Open AccessArticle

Vertical Alignment of Nematic Liquid Crystals Based on Spontaneous Alignment Layer Formation between Silver Nanowire Networks and Nonionic Amphiphiles

by Seung-Rak Son and Jun Hyup Lee

Crystals 2020, 10(10), 913; https://doi.org/10.3390/cryst10100913 - 9 Oct 2020

Cited by 5 | Viewed by 3162

Abstract

The vertical arrangement of nematic liquid crystals (LCs) in displays can be generally achieved by introducing a polyimide material onto indium tin oxide electrodes. However, this method requires multiple coating and deposition processes as well as high curing temperature, restricting the potential applicability to flexible displays. Thus, we herein propose the facile approach for homeotropic alignment of nematic LCs based on spontaneous alignment layer formation between silver nanowire networks and nonionic amphiphiles. The silver nanowires as transparent electrode materials were spin-coated on glass substrate and 4-(4-heptylphenyl)benzoic acids as nonionic amphiphiles were doped into the LC medium. The nonionic amphiphiles were spontaneously bonded to the polyvinylpyrrolidone capping layer of silver nanowire networks through polar interactions, creating the self-assembled alignment layer of nonionic amphiphiles on silver nanowire electrodes. In addition, the alkyl chains of the amphiphiles interacted with the LC molecules, leading to stable directional LC alignment along vertical direction. The electro-optical characteristics of the manufactured LC cell were comparable to those of conventional device including polyimide layer and indium tin oxide electrode. Overall, the combination of silver nanowire electrode and nonionic amphiphiles presents a new way to achieve the vertical alignment of nematic LCs without polyimide layer. Full article

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

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14 pages, 2945 KiB

Open AccessEditor’s ChoiceArticle

Large Angle Forward Diffraction by Chiral Liquid Crystal Gratings with Inclined Helical Axis

by Migle Stebryte, Inge Nys, Yera Ye. Ussembayev, Jeroen Beeckman and Kristiaan Neyts

Crystals 2020, 10(9), 807; https://doi.org/10.3390/cryst10090807 - 12 Sep 2020

Cited by 26 | Viewed by 5124

Abstract

A layer of chiral liquid crystal (CLC) with a photonic bandgap in the visible range has excellent reflective properties. Recently, two director configurations have been proposed in the literature for CLC between two substrates with periodic photo-alignment: one with the director parallel to the substrates and one with the director in the bulk parallel to the tilted plane. The transmission experiments under large angles of incidence (AOI) presented in this work prove that, in the bulk, the director does not remain parallel with the substrates. Because of the inclined helical axis, the full reflection band can be observed at a smaller AOI than in planar CLC. For sufficiently large AOI, the reflection of diffracted light is prohibited by total internal reflection and efficient diffraction occurs in the forward direction. Full article

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

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12 pages, 2785 KiB

Open AccessArticle

Tunable Polarization Gratings Based on Nematic Liquid Crystal Mixtures Photoaligned with Azo Polymer-Coated Substrates

by Mateusz Nieborek, Katarzyna Rutkowska, Tomasz Ryszard Woliński, Bartosz Bartosewicz, Bartłomiej Jankiewicz, Dariusz Szmigiel and Anna Kozanecka-Szmigiel

Crystals 2020, 10(9), 768; https://doi.org/10.3390/cryst10090768 - 31 Aug 2020

Cited by 12 | Viewed by 3266

Abstract

Liquid crystal polarization gratings are of great interest for optical communications as elements performing beam steering, splitting, multiplexing or beam combining. Material birefringence, cell thickness or a period of the liquid crystal director pattern influence, among other features, spectroscopic and electro-optical characteristics of fabricated devices, determining thus their functionality and applicability. Here, we report on liquid crystal polarization gratings that allow for complete maximization of the first-order diffraction efficiency (resulting in total elimination of the zeroth-order diffraction) for any wavelength of an incident beam from green to the near-infrared spectral region by applying a low electric voltage. The gratings with periods as small as 10 μm were obtained by holographic exposure of the cell substrates coated with light-sensitive azo polymer alignment layers, and then filled with three different liquid crystal mixtures. The influence of gold nanoparticle dopants in the liquid crystalline mixtures on spectroscopic and electro-optical properties of the devices is presented. Moreover, on the basis of the measured transmittance spectra of the fabricated gratings, the unknown birefringence of liquid crystal mixtures as well as their effective birefringence due to molecular reorientation in the electric field in the visible and near IR region were determined. Full article

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

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13 pages, 398 KiB

Open AccessArticle

Freedericksz Transitions in Twisted Ferronematics Subjected to Magnetic and Laser Field

by Cristina Cirtoaje, Gabriela Iacobescu and Emil Petrescu

Crystals 2020, 10(7), 567; https://doi.org/10.3390/cryst10070567 - 1 Jul 2020

Cited by 4 | Viewed by 2850

Abstract

The influence of the anchoring forces on the Freedericksz transition in twisted ferronematics simultaneously subjected to magnetic and laser fields is studied in this work. Using the elastic continuum theory and Gouchen model for molecular anchoring on the cell support plates, the critical field and the saturation field were calculated as a function of the laser intensity and anchoring strength for two types of ferronematics based on 5CB and CCN-37 liquid crystals. Full article

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

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17 pages, 3678 KiB

Open AccessArticle

‘Quasi-Tricritical’ and Glassy Dielectric Properties of a Nematic Liquid Crystalline Material

by Aleksandra Drozd-Rzoska

Crystals 2020, 10(4), 297; https://doi.org/10.3390/cryst10040297 - 13 Apr 2020

Cited by 14 | Viewed by 2590

Abstract

Results of dielectric studies in the nematic and isotropic liquid phases of pentylcyanobiphenyl (5CB), a model rod-like liquid crystalline material, are shown. They are based on the discussion of the evolution of dielectric constant (

ε

), its changes under the strong electric [...] Read more.

ε

), its changes under the strong electric field (nonlinear dielectric effect, NDE), and finally, the primary relaxation time. It is shown that changes in

ε (T)

and NDE are entirely dominated by the impact of pretransitional fluctuations (pre-nematic and pre-isotropic, respectively) which are associated with the weakly discontinuous character of the isotropic–nematic phase transition. This influence also extends for the low-frequency, ionic species dominated, region. Notable, that the derivative-based and distortions sensitive analysis revealed the tricritical nature of the I-N transition. Although the glass transition in 5CB occurs in the deeply supercooled state at

T_{g} \approx - 68 ° C

, the dynamics (changes of the primary relaxation time) follow a previtreous pattern both in the isotropic and in the nematic phase. Finally, the discussion of the ’molecular’ vs. ‘quasi-critical’ characterizations of the isotropic and nematic phases is presented. It shows the evident prevalence of the ‘quasi-critical-picture’, which offers the consistent temperature parameterization in the total tested temperature range. Full article

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

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19 pages, 5977 KiB

Open AccessArticle

Interplay between Convective and Viscoelastic Forces Controls the Morphology of In Vitro Paclitaxel-Stabilized Microtubules

by Eftihia Barnes, Xin Guan, Erik M. Alberts, Travis L. Thornell, Christopher M. Warner and Kevin R. Pilkiewicz

Crystals 2020, 10(1), 43; https://doi.org/10.3390/cryst10010043 - 17 Jan 2020

Cited by 2 | Viewed by 2648

Abstract

Microtubules (MTs) are self-assembling, high-aspect-ratio tubular nanostructures formed from the polymerization of tubulin protein. MTs are capable of globally assembling into optically birefringent morphologies, but there is disagreement on the mechanisms driving this behavior. We investigated the temporal evolution of paclitaxel (PTX)-stabilized MT solutions under a range of in vitro conditions. Significant morphological differences were observed in the polymerized PTX-MT solutions as a consequence of varying the orientation of the reaction vessel (vertical vs. horizontal), the type of heating source (hot plate vs. incubator), the incubation time, and the concentration of PTX (high vs. low). The most robust birefringent patterns were found only in vertically oriented cuvettes that were heated asymmetrically on a hot plate, suggesting dependence upon a convective flow, which we confirmed with a combination of optical and thermal imaging. Higher concentrations of PTX led to denser PTX-MT domain formation and brighter birefringence, due to more complete polymerization. Combining our experimental observations, we conclude that birefringent patterns arise principally through a combination of convective and viscoelastic forces, and we identify the sequence of dynamical stages through which they evolve. Full article

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

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