Recent Advances in Liquid Crystals

Topic Information

Dear Colleagues,

Liquid crystals represent the fourth state of matter, being intermediate between the solid and liquid states. They are anisotropic fluids that flow like a liquid but maintain some of the ordered structure of crystals. Liquid crystals were first identified in the mid-to-late 18th century. The interest in both applied and academic topics in liquid crystals has been substantial. One of the best parts of the subject is the characterization of the different liquid crystal mesophases as the main technique, polarized optical microscopy. Liquid crystal molecules tend to be elongated and to orient in specific directions. As the phases are anisotropic, they are birefringent between crossed analyzer and polarizer. Liquid crystals have become an integral part of our commercial electronics world, and liquid crystal displays are a key part of most mobile, battery-powered electronic devices. The optical properties of liquid crystals depend on the direction light travels through a layer of the material. An electric field can change the orientation of molecules in a layer of liquid crystal and thus affect its optical properties. Such a process is termed as the electro-optical effect, and it forms the basis for liquid crystal displays. Liquid crystal materials that align either parallel or perpendicular to an applied field can be selected to suit particular applications. The small electric voltages necessary to orient liquid crystal molecules have been a key feature of the commercial success of liquid crystal displays.

The Special Issue will focus on a wide range of materials, including thermotropic, lyotropic, interfacial, chiral, ferroelectric, polymer, micro/nanocomposite, biological and related soft-matter liquid crystal systems. Additionally, it will explore techniques and challenges for liquid crystal physics, liquid crystal chemistry, liquid crystal optics, liquid crystal photonics, liquid crystal materials and devices, photo-aligning techniques for liquid crystals, micro/nanostructures of liquid crystals, 3D liquid crystal display, as well as flexible liquid crystal displays. It is intended that both extant and novel methods will be covered, ranging from traditional techniques to methods involving non-traditional technologies. The goal is to facilitate the dissemination of information on methods and outcomes that will benefit the broader community involved in the control of liquid crystals.

Dr. Jiatong Sun
Dr. Xiaoqian Wang
Topic Editors

Keywords

Participating Journals

Journal Name	Impact Factor	CiteScore	Launched Year	First Decision (median)	APC
Crystals crystals	2.4	4.2	2011	11.1 Days	CHF 2100
Liquids liquids	-	-	2021	23.4 Days	CHF 1000
Materials materials	3.1	5.8	2008	13.9 Days	CHF 2600
Molecules molecules	4.2	7.4	1996	15.1 Days	CHF 2700
Nanomaterials nanomaterials	4.4	8.5	2010	14.1 Days	CHF 2400

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Published Papers (10 papers)

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All Crystals Liquids Materials Molecules Nanomaterials

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15 pages, 3738 KiB  

Open AccessArticle

Estimation of Ionic Impurities in Poly(propylene Glycol) Diacrylate Monomers/Liquid Crystal E7 Mixtures Using Dielectric Spectroscopy

by Tayeb Benkouider, Yazid Derouiche, Lahcene Souli, Frédéric Dubois, Ana Barrera, Zohra Bouberka and Ulrich Maschke

Crystals 2024, 14(3), 286; https://doi.org/10.3390/cryst14030286 - 20 Mar 2024

Viewed by 1787

Abstract

The study investigated the effect of the molecular weight of three difunctional poly(propylene glycol) diacrylates on the temperature-dependent ionic conductivity of these monomers and their blends with an eutectic nematic liquid crystal mixture (E7). The results revealed two distinct regions. At low temperatures, [...] Read more.

The study investigated the effect of the molecular weight of three difunctional poly(propylene glycol) diacrylates on the temperature-dependent ionic conductivity of these monomers and their blends with an eutectic nematic liquid crystal mixture (E7). The results revealed two distinct regions. At low temperatures, ionic conduction can be described by the Vogel–Tamman–Fulcher (VTF) equation, while at high temperatures, the conductivity data follow the prediction of the Arrhenius model. The Arrhenius and VTF parameters and their corresponding activation energies were determined using the least squares method. In addition, a conductivity analysis based on an ionic hopping model is proposed. Estimates of ion concentrations and diffusion constants were calculated. It was found that both the ionic concentration and the diffusion constant decrease with the increase in the molecular weight of the monomers. The static dielectric permittivity decreases in the following order: TPGDA, PPGDA540, and PPGDA900. This can be explained by the higher dipole moment of TPGDA, which is caused by an enhanced volume density of carbonyl groups. Full article

(This article belongs to the Topic Recent Advances in Liquid Crystals)

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12 pages, 6363 KiB  

Open AccessArticle

Defect Modes Generated in a Stack of Spin-Coated Chiral Liquid Crystal Layers

by Frederik Van Acker, Bo-Han Lin, Chun-Ta Wang, Kristiaan Neyts and Jeroen Beeckman

Crystals 2024, 14(3), 231; https://doi.org/10.3390/cryst14030231 - 28 Feb 2024

Cited by 3 | Viewed by 1574

Abstract

Nematic chiral liquid crystals (CLCs) are characterized by a helical arrangement of nematic LC molecules. A layer of CLC typically exhibits an optical reflection band due to Bragg reflection in the helical structure. When several layers of CLC are spin-coated and polymerized on [...] Read more.

Nematic chiral liquid crystals (CLCs) are characterized by a helical arrangement of nematic LC molecules. A layer of CLC typically exhibits an optical reflection band due to Bragg reflection in the helical structure. When several layers of CLC are spin-coated and polymerized on top of each other without a barrier layer in between, defect modes can form in their reflection spectrum. By comparing experimental results and simulations, we investigate the origin of the defect modes, thereby revealing details on the behavior of the materials at the interfaces during deposition. Simulations show that these defect modes can originate from the migration of chiral dopant leading to a layer with a smaller pitch or from a discontinuity in the director orientation at the interface between two layers. Full article

(This article belongs to the Topic Recent Advances in Liquid Crystals)

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13 pages, 2796 KiB  

Open AccessArticle

Macroscopic Biaxial Order in Multilayer Films of Bent-Core Liquid Crystals Deposited by Combined Langmuir–Blodgett/Langmuir–Schaefer Technique

by Francesco Vita, Fabrizio Corrado Adamo, Mario Campana, Blake Bordokas, Federica Ciuchi, Maria Penelope De Santo, Daniel Hermida-Merino, Angela Lisovsky, Michela Pisani, Diego Pontoni, Eric Scharrer and Oriano Francescangeli

Nanomaterials 2024, 14(4), 357; https://doi.org/10.3390/nano14040357 - 14 Feb 2024

Cited by 1 | Viewed by 1517

Abstract

Bent-core liquid crystals, a class of mesogenic compounds with non-linear molecular structures, are well known for their unconventional mesophases, characterized by complex molecular (and supramolecular) ordering and often featuring biaxial and polar properties. In the nematic phase, their unique behavior is manifested in [...] Read more.

Bent-core liquid crystals, a class of mesogenic compounds with non-linear molecular structures, are well known for their unconventional mesophases, characterized by complex molecular (and supramolecular) ordering and often featuring biaxial and polar properties. In the nematic phase, their unique behavior is manifested in the formation of nano-sized biaxial clusters of layered molecules (cybotactic groups). While this prompted their consideration in the quest for nematic biaxiality, experimental evidence indicates that the cybotactic order is only short-ranged and that the nematic phase is macroscopically uniaxial. By combining atomic force microscopy, neutron reflectivity and wide-angle grazing-incidence X-ray scattering, here, we demonstrate that multilayer films of a bent-core nematic, deposited on silicon by a combined Langmuir–Blodgett and Langmuir–Schaefer approach, exhibit macroscopic in-plane ordering, with the long molecular axis tilted with respect to the sample surface and the short molecular axis (i.e., the apex bisector) aligned along the film compression direction. We thus propose the use of Langmuir films as an effective way to study and control the complex anchoring properties of bent-core liquid crystals. Full article

(This article belongs to the Topic Recent Advances in Liquid Crystals)

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13 pages, 5116 KiB  

Open AccessArticle

Self-Consistent Explanation of the Untwist Alignment of Ferroelectric Nematic Liquid Crystals with Decreasing Cell Thickness and Deviation of the Surface Easy Axis Experimented upon Using the Brewster Angle Reflection Method

by Sakunosuke Abe, Yosei Shibata, Munehiro Kimura and Tadashi Akahane

Crystals 2024, 14(2), 157; https://doi.org/10.3390/cryst14020157 - 31 Jan 2024

Cited by 5 | Viewed by 1931

Abstract

The huge dielectric constant of ferroelectric nematic liquid crystals (FNLCs) seems to bring about a difficulty of molecular alignment control in exchange for a potential device application. To obtain a satisfactory level of uniform molecular alignment, it is essential to understand how the [...] Read more.

The huge dielectric constant of ferroelectric nematic liquid crystals (FNLCs) seems to bring about a difficulty of molecular alignment control in exchange for a potential device application. To obtain a satisfactory level of uniform molecular alignment, it is essential to understand how the molecules near the alignment surface are anchored. In this study, bulk molecular alignment with an anti-parallel rubbing manner, which has not yet been investigated extensively, is explained using a conventional torque balance model introducing a polar anchoring function, and it is shown that the disappearance of the bulk twist alignment with decreasing cell thickness can be explained self-consistently. To validate this estimation for a room-temperature FNLC substance, the Brewster angle reflection method was attempted to confirm the surface director’s deviation from the rubbing direction caused by the polar surface anchoring. Full article

(This article belongs to the Topic Recent Advances in Liquid Crystals)

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34 pages, 22932 KiB  

Open AccessReview

The Formation of Supramolecular Chiral Materials from Achiral Molecules Using a Liquid-Crystallin System: Symmetry Breaking, Amplification, and Transfer

by Atsushi Yoshizawa

Crystals 2024, 14(1), 97; https://doi.org/10.3390/cryst14010097 - 21 Jan 2024

Cited by 1 | Viewed by 3863

Abstract

Recently, the formation of chiral materials by the self-organization of achiral small molecules has attracted much attention. How can we obtain chirality without a chiral source? Interesting approaches, such as mechanical rotation, circularly polarized light, and asymmetric reaction fields, have been used. We [...] Read more.

Recently, the formation of chiral materials by the self-organization of achiral small molecules has attracted much attention. How can we obtain chirality without a chiral source? Interesting approaches, such as mechanical rotation, circularly polarized light, and asymmetric reaction fields, have been used. We describe recent research developments in supramolecular chirality in liquid crystals, focusing primarily on our group’s experimental results. We present the following concepts in this review. Spontaneous mirror symmetry breaking in self-assembled achiral trimers induces supramolecular chirality in the soft crystalline phase. Two kinds of domains with opposite handedness exist in non-equal populations. The dominant domain is amplified to produce a homochiral state. Chirality is transferred to a polymer film during the polymerization of achiral monomers by using the homochiral state as a template. Finally, we discuss how the concepts obtained from this liquid crystal research relate to the origin of homochirality in life. Full article

(This article belongs to the Topic Recent Advances in Liquid Crystals)

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11 pages, 2640 KiB  

Open AccessArticle

Tunable Reflection through Size Polydispersity of Chiral-Nematic Liquid Crystal Polymer Particles

by Tomoki Shigeyama, Kohsuke Matsumoto, Kyohei Hisano and Osamu Tsutsumi

Molecules 2023, 28(23), 7779; https://doi.org/10.3390/molecules28237779 - 25 Nov 2023

Cited by 3 | Viewed by 1948

Abstract

Micro-sized chiral-nematic liquid crystal (N* LC) polymer particles have attracted considerable interest as versatile reflective colorants with selective circularly polarized light (CPL) properties. However, challenges in achieving the desired size distribution of N* LC particles have led to an incomplete understanding of their [...] Read more.

Micro-sized chiral-nematic liquid crystal (N* LC) polymer particles have attracted considerable interest as versatile reflective colorants with selective circularly polarized light (CPL) properties. However, challenges in achieving the desired size distribution of N* LC particles have led to an incomplete understanding of their reflective characteristics. In this study, we successfully synthesized N* LC particles via dispersion polymerization, enabling precise control over size polydispersity by manipulating the composition of the polymerization solvent. Our investigation revealed that monodisperse N* LC particles displayed distinct reflection bands with high CPL selectivity, while polydisperse particles exhibited broader reflection with lower CPL selectivity. These findings underscore the potential to synthesize N* LC particles with tailored reflective properties using identical monomeric compounds. Furthermore, we demonstrated the production of multifunctional reflective colorants by blending N* LC particles with varying reflection colors. These discoveries hold significant promise for advancing the development of reflective colorants and anti-counterfeiting printing techniques utilizing micro-sized N* LC particles. Full article

(This article belongs to the Topic Recent Advances in Liquid Crystals)

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13 pages, 1519 KiB  

Open AccessReview

Oral Drug Delivery via Intestinal Lymphatic Transport Utilizing Lipid-Based Lyotropic Liquid Crystals

by Linh Dinh and Bingfang Yan

Liquids 2023, 3(4), 456-468; https://doi.org/10.3390/liquids3040029 - 20 Nov 2023

Cited by 9 | Viewed by 4404

Abstract

Lyotropic liquid crystals (LLCs) are liquids that have crystalline structures. LLCs as drug delivery systems that can deliver hydrophobic, hydrophilic, and amphiphilic agents. Due to their unique phases and structures, LLCs can protect both small molecules and biologics from the gastrointestinal tract’s harsh [...] Read more.

Lyotropic liquid crystals (LLCs) are liquids that have crystalline structures. LLCs as drug delivery systems that can deliver hydrophobic, hydrophilic, and amphiphilic agents. Due to their unique phases and structures, LLCs can protect both small molecules and biologics from the gastrointestinal tract’s harsh environment, thus making LLCs attractive as carriers for oral drug delivery. In this review, we discuss the advantages of LLCs and LLCs as oral formulations targeting intestinal lymphatic transport. In oral LLC formulations, the relationship between the micelle compositions and the resulting LLC structures as well as intestinal transport and absorption were determined. In addition, we further demonstrated approaches for the enhancement of intestinal lymphatic transport: (1) lipid-based LLCs promoting chylomicron secretion and (2) the design of LLC nanoparticles with M cell-triggered ligands for targeting the M cell pathway. In this review, we introduce LLC drug delivery systems and their characteristics. Our review focuses on recent approaches using oral LLC drug delivery strategies targeting the intestinal lymphatic system to enhance drug bioavailability. Full article

(This article belongs to the Topic Recent Advances in Liquid Crystals)

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13 pages, 2726 KiB  

Open AccessArticle

Physical and Thermal Characterizations of Newly Synthesized Liquid Crystals Based on Benzotrifluoride Moiety

by Fowzia S. Alamro, Hoda A. Ahmed, Mohamed A. El-Atawy, Muna S. Khushaim, Noha S. Bedowr, Rawan AL-Faze and Nada S. Al-Kadhi

Materials 2023, 16(12), 4304; https://doi.org/10.3390/ma16124304 - 10 Jun 2023

Cited by 7 | Viewed by 1680

Abstract

The mesomorphic stability and optical activity of new group-based benzotrifluoride liquid crystals, (E)-4-(((4-(trifluoromethyl) phenyl) imino) methyl) phenyl 4-(alkyloxy)benzoate, or In, were investigated. The end of the molecules connected to the benzotrifluoride moiety and the end of the phenylazo benzoate moiety have terminal [...] Read more.

The mesomorphic stability and optical activity of new group-based benzotrifluoride liquid crystals, (E)-4-(((4-(trifluoromethyl) phenyl) imino) methyl) phenyl 4-(alkyloxy)benzoate, or In, were investigated. The end of the molecules connected to the benzotrifluoride moiety and the end of the phenylazo benzoate moiety have terminal alkoxy groups which can range in chain length from 6 to 12 carbons. The synthesized compounds’ molecular structures were verified using FT-IR, ¹H NMR, mass spectroscopy, and elemental analysis. Mesomorphic characteristics were verified using differential scanning calorimetry (DSC) and a polarized optical microscope (POM). All of the homologous series that have been developed display great thermal stability across a broad temperature range. Density functional theory (DFT) determined the examined compounds’ geometrical and thermal properties. The findings showed that every compound is entirely planar. Additionally, by using the DFT approach, it was possible to link the experimentally found values of the investigated compounds’ investigated compounds’ mesophase thermal stability, mesophase temperature ranges, and mesophase type to the predicted quantum chemical parameters. Full article

(This article belongs to the Topic Recent Advances in Liquid Crystals)

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11 pages, 3964 KiB  

Open AccessArticle

Difluorovinyl Liquid Crystal Diluters Improve the Electro-Optical Properties of High-∆n Liquid Crystal Mixture for AR Displays

by Jiaxing Tang, Zihao Mao, Zhongwei An, Ran Chen, Xinbing Chen and Pei Chen

Molecules 2023, 28(6), 2458; https://doi.org/10.3390/molecules28062458 - 8 Mar 2023

Cited by 4 | Viewed by 2021

Abstract

A liquid crystal (LC) mixture in liquid crystal on silicon (LCoS) is the core material for augmented reality (AR) displays. However, a LC mixture with high birefringence (Δn) and large dielectric anisotropy (Δε) possesses high viscosity (γ₁ [...] Read more.

A liquid crystal (LC) mixture in liquid crystal on silicon (LCoS) is the core material for augmented reality (AR) displays. However, a LC mixture with high birefringence (Δn) and large dielectric anisotropy (Δε) possesses high viscosity (γ₁), which results in a slow response time of LCoS devices for AR displays. This work proposes to apply difluorovinyl-based LC diluters to fine balance the low viscosity, high ∆n, and large ∆ε of the LC mixture for a fast response time. Through studying their effects on the key electro-optical properties of a high-∆n LC mixture, it is found that doping these diluter molecules to a high-∆n LC mixture can decrease the viscoelastic coefficient (γ₁/K₁₁), increase ∆ε and the figure of merit, maintain a wide nematic phase temperature range, a high clearing point, and ∆n. It also means that these diluters could effectively regulate the relationship between ∆n, ∆ε, and γ₁ in the LC mixtures to achieve a fine balance of various excellent properties and further improve the LC device’s response time. The widespread applications of these liquid crystal diluters in emerging liquid crystal optical devices are foreseeable. Full article

(This article belongs to the Topic Recent Advances in Liquid Crystals)

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10 pages, 2203 KiB  

Open AccessArticle

Liquid-Crystalline Order in the Phosphorus-Containing DenDrimers

by Victor Furer, Alexandr Vandyukov, Jean-Pierre Majoral, Anne-Marie Caminade and Valery Kovalenko

Molecules 2022, 27(23), 8214; https://doi.org/10.3390/molecules27238214 - 25 Nov 2022

Viewed by 1676

Abstract

The structure of phosphorus-containing dendrimers has been studied by IR spectroscopy and optical polarization microscopy. The repeating units of dendrimer molecules are mesogens. This property arises from the conjugation of the aromatic ring and the hydrazone group. An analysis of the IR spectra [...] Read more.

The structure of phosphorus-containing dendrimers has been studied by IR spectroscopy and optical polarization microscopy. The repeating units of dendrimer molecules are mesogens. This property arises from the conjugation of the aromatic ring and the hydrazone group. An analysis of the IR spectra showed that, with an increase in the generation number, the width of the stretching vibration bands ν(PN) and ν(PO) increases. Difficulties in packing molecules of higher generations cause conformational diversity. The shape of the dendrimer molecules was determined by analyzing the increments of dipole moments. Additionally, the modeling of the stacking of repeating links was performed. The spherical model of molecules does not satisfy the experimental dipole moments of the dendrimers. The flat disk model is more suitable for explaining step changes in dipole moments. The liquid-crystalline ordering of dendrimers under the action of applied pressure was found. With simultaneous heating and uniaxial compression, optical anisotropy appears in dendrimers. It is associated with the formation of liquid-crystalline order. However, a thermodynamically stable liquid-crystalline phase is not formed in this case. Dendrimers most likely have disk-shaped molecules. Full article

(This article belongs to the Topic Recent Advances in Liquid Crystals)

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