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Liquid Crystals II

A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Materials Chemistry".

Deadline for manuscript submissions: 15 August 2024 | Viewed by 3780

Special Issue Editors

Department of Inorganic Chemistry, Faculty of Chemistry, University of Bucharest, Bucharest, Romania
Interests: liquid crystals; metallomesogens; luminescent materials; inorganic and coordination chemistry
Special Issues, Collections and Topics in MDPI journals
Department of Physics, Universitatea Politehnica din Bucuresti, Bucharest, Romania
Interests: liquid crystals; polymer-dispersed liquid crystals; nanocomposites; soft matter; dielectric properties; physical properties; optoelectronics; organic solar cells
Special Issues, Collections and Topics in MDPI journals
B.I. Stepanov Institute of Physics, National Academy of Sciences of Belarus, Minsk, Belarus
Interests: liquid crystals; polymer-dispersed liquid crystals; composite and smart materials; single and multiple scattering of waves in partially ordered disperse media; electro-optic devices; light propagation in metamaterials; photonic crystals; solar cells
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

This new Special Issue on “Liquid Crystals” will address recent progress in both experimental and theoretical aspects of liquid crystals science and technology, including molecular design, synthesis, processing, fabrication, characterization and engineering. With their unique combination of properties related to anisotropic fluids (anisotropy of physical properties and fast orientational response to external fields), liquid crystals are among the most versatile and dynamic soft materials of the present day, and they have found important indispensable applications, such as the manufacturing of display devices, molecular sensors and detectors, optical switches, spatial light modulators, and many others not mentioned here. Tremendous research efforts are also dedicated to the exploration of fundamental aspects related to self-assembly and supermolecular organization in thermotropic or lyotropic liquid crystals, contributing to the advancement of knowledge in liquid crystals science. This Special Issue will offer an appropriate opportunity to authors and research groups to make their studies visible to the liquid crystal scientific community. Contributions in the form of original research articles or comprehensive review papers from various fields are welcome, including submissions on biological, organic and inorganic liquid crystals; metallomesogens; ionic liquid crystals; and liquid crystalline polymers and liquid crystal composites, concerning both experimental and theoretical studies.

Prof. Dr. Viorel Circu
Prof. Dr. Doina Manaila-Maximean
Prof. Dr. Valery A. Loiko
Guest Editors

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. Molecules is an international peer-reviewed open access semimonthly 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 2700 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.

Keywords

  • liquid crystals
  • ionic liquid crystals
  • metallomesogens
  • nanoparticles
  • liquid crystal composites
  • polymer liquid crystals
  • lyotropic liquid crystals

Published Papers (5 papers)

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Research

22 pages, 36782 KiB  
Article
Preparation and Application of Polymer-Dispersed Liquid Crystal Film with Step-Driven Display Capability
Molecules 2024, 29(5), 1109; https://doi.org/10.3390/molecules29051109 - 01 Mar 2024
Viewed by 213
Abstract
The realization of multifunctional advanced displays with better electro-optical properties is especially crucial at present. However, conventional integral full drive-based transparent display is increasingly failing to meet the demands of the day. Herein, partitioned polymerization as a novel preparation method was introduced innovatively [...] Read more.
The realization of multifunctional advanced displays with better electro-optical properties is especially crucial at present. However, conventional integral full drive-based transparent display is increasingly failing to meet the demands of the day. Herein, partitioned polymerization as a novel preparation method was introduced innovatively into polymer-dispersed liquid crystals (PDLC) for realizing a step-driven display in agreement with fluorescent dye to solve the above drawback. At first, the utilization of fluorescent dye to endow the PDLC film with fluorescent properties resulted in a reduction in the saturation voltage of the PDLC from 39.7 V to 25.5 V and an increase in the contrast ratio from 58.4 to 96.6. Meanwhile, the experimental observations and theoretical considerations have elucidated that variation in microscopic pore size can significantly influence the electro-optical behavior of PDLC. Then, the step-driven PDLC film was fabricated through the exposure of different regions of the LC cell to different UV-light intensities, resulting in stepwise voltage–transmittance (V–T) responses of the PDLC film for the corresponding regions. Consequently, under appropriate driving voltages, the PDLC can realize three different states of total scattering, semi-transparent and total transparent, respectively. In addition, the PDLC film also embodied an outstanding anti-aging property and UV-shielding performance, which makes it fascinating for multifunctional advanced display applications. Full article
(This article belongs to the Special Issue Liquid Crystals II)
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10 pages, 2873 KiB  
Article
Electrically Induced Structural Transformations of a Chiral Nematic under Tangential-Conical Boundary Conditions
Molecules 2023, 28(23), 7842; https://doi.org/10.3390/molecules28237842 - 29 Nov 2023
Viewed by 501
Abstract
In this study, structural transformations induced by an electric field in the chiral nematic under tangential-conical boundary conditions have been considered. The composition influence of the orienting polymer films on the director tilt angles, the formation of orientational structures in the LC layer, [...] Read more.
In this study, structural transformations induced by an electric field in the chiral nematic under tangential-conical boundary conditions have been considered. The composition influence of the orienting polymer films on the director tilt angles, the formation of orientational structures in the LC layer, as well as the electro-optical response and relaxation processes have been studied. It has been shown that the poly(tert-butyl methacrylate) concentration change in the orienting polymer mixture allows for smoothly controlling the director tilt angle without fixing its azimuthal orientation rigidly. Full article
(This article belongs to the Special Issue Liquid Crystals II)
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14 pages, 5408 KiB  
Article
Exploring the Impact of Intermolecular Interactions on the Glassy Phase Formation of Twist-Bend Liquid Crystal Dimers: Insights from Dielectric Studies
Molecules 2023, 28(21), 7441; https://doi.org/10.3390/molecules28217441 - 06 Nov 2023
Viewed by 725
Abstract
The formation of the nematic to twist-bend nematic (NTB) phase has emerged as a fascinating phenomenon in the field of supramolecular chemistry, based on complex intermolecular interactions. Through a careful analysis of molecular structures and dynamics, we elucidate how these intermolecular [...] Read more.
The formation of the nematic to twist-bend nematic (NTB) phase has emerged as a fascinating phenomenon in the field of supramolecular chemistry, based on complex intermolecular interactions. Through a careful analysis of molecular structures and dynamics, we elucidate how these intermolecular interactions drive the complex twist-bend modulation observed in the NTB. The study employs broadband dielectric spectroscopy spanning frequencies from 10 to 2 × 109 Hz to investigate the molecular orientational dynamics within the glass-forming thioether-linked cyanobiphenyl liquid crystal dimers, namely, CBSC7SCB and CBSC7OCB. The experimental findings align with theoretical expectations, revealing the presence of two distinct relaxation processes contributing to the dielectric permittivity of these dimers. The low-frequency relaxation mode is attributed to an “end-over-end rotation” of the dipolar groups parallel to the director. The high-frequency relaxation mode is associated with precessional motions of the dipolar groups about the director. Various models are employed to describe the temperature-dependent behavior of the relaxation times for both modes. Particularly, the critical-like description via the dynamic scaling model seems to give not only quite good numerical fittings, but also provides a consistent physical picture of the orientational dynamics in accordance with findings from infrared (IR) spectroscopy. Here, as the longitudinal correlations of dipoles intensify, the m1 mode experiences a sudden upsurge in enthalpy, while the m2 mode undergoes continuous changes, displaying critical mode coupling behavior. Interestingly, both types of molecular motion exhibit a strong cooperative interplay within the lower temperature range of the NTB phase, evolving in tandem as the material’s temperature approaches the glass transition point. Consequently, both molecular motions converge to determine the glassy dynamics, characterized by a shared glass transition temperature, Tg. Full article
(This article belongs to the Special Issue Liquid Crystals II)
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14 pages, 2401 KiB  
Article
Multilayer, Broadband Infrared Reflectors Based on the Photoinduced Preparation of Cholesteric Liquid Crystal Polymers
Molecules 2023, 28(20), 7063; https://doi.org/10.3390/molecules28207063 - 12 Oct 2023
Viewed by 692
Abstract
This paper focuses on preparing broadband reflective liquid crystal films through the diffusion of monofunctional and bifunctional monomers in a photoinduced trilayer system. By combining the hydrophilic and hydrophobic liquid crystal glass surface treatment technologies, the polymer network of polymer-stabilized cholesteric liquid crystal [...] Read more.
This paper focuses on preparing broadband reflective liquid crystal films through the diffusion of monofunctional and bifunctional monomers in a photoinduced trilayer system. By combining the hydrophilic and hydrophobic liquid crystal glass surface treatment technologies, the polymer network of polymer-stabilized cholesteric liquid crystal (PSCLC) itself serves as a diffusion channel to form a trilayer cholesteric liquid crystal composite system containing bifunctional monomers, a nematic liquid crystal composite system, and a cholesteric liquid crystal composite system containing monofunctional monomers. Utilizing the difference in the polymerization rates of monofunctional and difunctional polymerizable monomers, the monomers and chiral compounds diffuse relative to each other, so that the liquid crystal pitch exhibits a gradient distribution, and the broadened reflective width can reach up to 1570 nm. There is no doubt that new and improved processes and technologies offer important possibilities for preparing and applying PSCLC films. Full article
(This article belongs to the Special Issue Liquid Crystals II)
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20 pages, 6353 KiB  
Article
Columnar Liquid Crystals of Copper(I) Complexes with Ionic Conductivity and Solid State Emission
Molecules 2023, 28(10), 4196; https://doi.org/10.3390/molecules28104196 - 19 May 2023
Viewed by 1145
Abstract
Two neutral copper(I) halide complexes ([Cu(BTU)2X], X = Cl, Br) were prepared by the reduction of the corresponding copper(II) halides (chloride or bromide) with a benzoylthiourea (BTU, N-(3,4-diheptyloxybenzoyl)-N′-(4-heptadecafluorooctylphenyl)thiourea) ligand in ethanol. The two copper(I) complexes show a very [...] Read more.
Two neutral copper(I) halide complexes ([Cu(BTU)2X], X = Cl, Br) were prepared by the reduction of the corresponding copper(II) halides (chloride or bromide) with a benzoylthiourea (BTU, N-(3,4-diheptyloxybenzoyl)-N′-(4-heptadecafluorooctylphenyl)thiourea) ligand in ethanol. The two copper(I) complexes show a very interesting combination of 2D supramolecular structures, liquid crystalline, emission, and 1D ionic conduction properties. Their chemical structure was ascribed based on ESI–MS, elemental analysis, IR, and NMR spectroscopies (1H and 13C), while the mesomorphic behavior was analyzed through a combination of differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and powder X-ray diffraction (XRD). These new copper(I) complexes have mesomorphic properties and exhibit a hexagonal columnar mesophase over a large temperature range, more than 100 K, as evidenced by DSC studies and POM observations. The thermogravimetric analysis (TG) indicated a very good thermal stability of these samples up to the isotropization temperatures and over the whole temperature range of the liquid crystalline phase existence. Both complexes displayed a solid-state emission with quantum yields up to 8% at ambient temperature. The electrical properties of the new metallomesogens were investigated by variable temperature dielectric spectroscopy over the entire temperature range of the liquid crystalline phase. It was found that the liquid crystal phases favoured anhydrous proton conduction provided by the hydrogen-bonding networks formed by the NH…X moieties (X = halide or oxygen) of the benzoylthiourea ligand in the copper(I) complexes. A proton conductivity of 2.97 × 10−7 S·cm−1 was achieved at 430 K for the chloro-complex and 1.37 × 10−6 S·cm−1 at 440K for the related bromo-complex. Full article
(This article belongs to the Special Issue Liquid Crystals II)
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