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Structural and Physical Properties of Liquid Crystals

A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Optical and Photonic Materials".

Deadline for manuscript submissions: 20 September 2025 | Viewed by 9882

Special Issue Editors


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Guest Editor
Centre for Organic and Nanohybrid Electronics, Silesian University of Technology, Konarskiego 22b, 44-100 Gliwice, Poland
Interests: organic synthesis; liquid crystals; supramolecular chemistry; delayed fluorescence; sensitizers; singlet oxygen; optoelectronics

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Guest Editor
Chemistry Institute, Federal University of Rio Grande do Sul, Bento Gonçalves 9500, Porto Alegre BR-91501970, RS, Brazil
Interests: organic synthesis; N-heterocyclic compounds; liquid crystals; polar self-assembly; photochromism; dye-sensitized solar cells; optoelectronic devices

Special Issue Information

Dear Colleagues,

Liquid crystals (LCs) are a fascinating class of soft matter that exhibit features of fluidity and long-range order. LCs have the intrinsic property of self-organization and give rise to unique physical and optical properties. This has inspired researchers to design and fabricate stimuli-responsive materials and devices for applications in a wide variety of areas.

Considering the outstanding importance of the development of new state-of-the-art liquid crystals, this Special Issue welcomes the submission of original research manuscripts, reviews embracing aspects of LC science and technology, and theoretical and experimental investigations ranging from mesogen design and synthesis to applications.

Potential topics include, but are not restricted to:

  • Design, synthesis and characterization of rod-like (calamitic), bent-core and discotic LCs
  • Functional liquid-crystalline polymers and supramolecular LCs
  • LC display science and technologies, optical alignment, switching materials, optical information processing and devices
  • Liquid crystalline properties beyond the biological applications
  • Liquid-crystalline sensitizers for singlet oxygen formation and solar cells applications
  • Investigation of triplet–triplet annihilation (TTA) in liquid crystals
  • Liquid-crystalline thermally activated delayed fluorescence (TADF) emitters
  • Environmental issues related to disposal of materials used in organic devices

Dr. Marli Ferreira
Prof. Dr. Aloir Antonio Merlo
Guest Editors

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Keywords

  • liquid crystals
  • smart soft materials
  • self-assembly
  • stimuli-responsive
  • delayed fluorescence
  • sensitizers
  • solar cells

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Published Papers (6 papers)

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Research

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20 pages, 4814 KiB  
Article
Solvent Evaporation-Induced Self-Assembly of Flexible Cholesteric Liquid Crystal Elastomers: Fabrication, Performance Tuning, and Optimization
by Jinying Zhang, Yexiaotong Zhang, Zhongwei Gao, Jiaxing Yang and Xinye Wang
Materials 2025, 18(9), 1927; https://doi.org/10.3390/ma18091927 - 24 Apr 2025
Viewed by 150
Abstract
The realization of broad-wavelength tunability of the structural color in Double layered Cholesteric Liquid Crystal Elastomers (DCLCEs), along with good flexibility and processability, presents a significant challenge. This research introduces a facile and effective fabrication technique, Solvent Evaporation-Induced Self-Assembly (SEISA), for the production [...] Read more.
The realization of broad-wavelength tunability of the structural color in Double layered Cholesteric Liquid Crystal Elastomers (DCLCEs), along with good flexibility and processability, presents a significant challenge. This research introduces a facile and effective fabrication technique, Solvent Evaporation-Induced Self-Assembly (SEISA), for the production of DCLCEs exhibiting broad wavelength tunability, superior flexibility, and robust mechanical characteristics. Focusing on initial color tuning, bubble defect minimization, UV photopolymerization, and coating procedures, this research systematically optimizes the fabrication process through experimental investigation of factors like chiral dopant amount, temperature, UV exposure duration, coating thickness, and speed. The method enabled the successful fabrication of DCLCEs with uniform and controllable coloration, demonstrating the effectiveness of this controlled synthesis approach in significantly enhancing structural color features. Upon stretching to 2.8 times its original length, the center wavelength shifted from 613 nm to 404 nm, yielding a tunable bandwidth of up to 209 nm across the visible spectrum. Full article
(This article belongs to the Special Issue Structural and Physical Properties of Liquid Crystals)
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16 pages, 5265 KiB  
Article
Overlooked Ionic Contribution of a Chiral Dopant in Cholesteric Liquid Crystals
by Hassanein Shaban, Po-Chang Wu, Yi-Fei Jia and Wei Lee
Materials 2024, 17(20), 5080; https://doi.org/10.3390/ma17205080 - 18 Oct 2024
Cited by 1 | Viewed by 1202
Abstract
This study focuses on the ionic contribution by a chiral dopant added into a nematic host for preparing cholesteric liquid crystals (CLCs). Chiral structures were designated by individually incorporating two enantiomers, R5011 and S5011, into the nematic E44 to construct right- and left-handed [...] Read more.
This study focuses on the ionic contribution by a chiral dopant added into a nematic host for preparing cholesteric liquid crystals (CLCs). Chiral structures were designated by individually incorporating two enantiomers, R5011 and S5011, into the nematic E44 to construct right- and left-handed CLCs, respectively. Characterized by the space-charge polarization, the dielectric spectra of the CLCs were investigated in the low-frequency regime, where f  ≤  1 kHz. The role of the individual chiral dopant, R5011 or S5011, at concentrations of 0–4.0 wt.% in altering the ionic properties of the CLC material was analyzed by deducing the electrical conductivity, ion density, and ion diffusivity. Regardless of the cell structure to be antiparallel or twisted by 90°, a significant ionic response was observed in the right-handed CLCs in comparison with the left-handed counterparts, suggesting that excess ions originating from our R5011 were introduced into the mesogenic mixtures. This work alarms the potential contribution of notorious impurity ions by a chiral dopant, which is often ignored in fabricating CLCs for electro-optical applications. Full article
(This article belongs to the Special Issue Structural and Physical Properties of Liquid Crystals)
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14 pages, 4390 KiB  
Article
Photoinduced Phase Transitions of Imine-Based Liquid Crystal Dimers with Twist–Bend Nematic Phases
by Yuki Arakawa and Yuto Arai
Materials 2024, 17(13), 3278; https://doi.org/10.3390/ma17133278 - 3 Jul 2024
Cited by 2 | Viewed by 1335
Abstract
Photoisomerizable molecules in liquid crystals (LCs) allow for photoinduced phase transitions, facilitating applications in a wide variety of photoresponsive materials. In contrast to the widely investigated azobenzene structure, research on the photoinduced phase-transition behavior of imine-based LCs is considerably limited. We herein report [...] Read more.
Photoisomerizable molecules in liquid crystals (LCs) allow for photoinduced phase transitions, facilitating applications in a wide variety of photoresponsive materials. In contrast to the widely investigated azobenzene structure, research on the photoinduced phase-transition behavior of imine-based LCs is considerably limited. We herein report the thermal and photoinduced phase-transition behaviors of photoisomerizable imine-based LC dimers with twist–bend nematic (NTB) phases. We synthesize two homologous series of ester- and thioether-linked N-(4-cyanobenzylidene)aniline-based bent-shaped LC dimers with an even number of carbon atoms (n = 2, 4, 6, 8, and 10) in the central alkylene spacers, namely, CBCOOnSBA(CN) and CBOCOnSBA(CN), possessing oppositely directed ester linkages, C=OO and OC=O, respectively. Their thermal phase-transition behavior is examined using polarizing optical microscopy and differential scanning calorimetry. All dimers form a monotropic NTB phase below the temperature of the conventional nematic (N) phase upon cooling. Remarkably, the NTB phases of CBCOOnSBA(CN) (n = 2, 4, 6, and 8) and CBOCOnSBA(CN) (n = 6 and 8) supercool to room temperature and vitrify without crystallization. In addition, the phase-transition temperatures and entropy changes of CBCOOnSBA(CN) are lower than those of CBOCOnSBA(CN) at the same n. Under UV light irradiation, the NTB and N phases transition to the N and isotropic phases, respectively, and reversibly return to their initial LC phases when the UV light is turned off. Full article
(This article belongs to the Special Issue Structural and Physical Properties of Liquid Crystals)
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13 pages, 9516 KiB  
Article
Comparative Study of the Optical and Dielectric Anisotropy of a Difluoroterphenyl Dimer and Trimer Forming Two Nematic Phases
by Evangelia E. Zavvou, Chris Welch, Georg H. Mehl, Alexandros G. Vanakaras and Panagiota K. Karahaliou
Materials 2024, 17(11), 2555; https://doi.org/10.3390/ma17112555 - 25 May 2024
Cited by 1 | Viewed by 1286
Abstract
We present a comparative study of the optical and dielectric anisotropy of a laterally fluorinated liquid crystal dimer and its homologous trimer, both exhibiting two nematic phases. In the high-temperature nematic phase, both oligomers exhibit positive optical anisotropy with similar magnitude, which, however, [...] Read more.
We present a comparative study of the optical and dielectric anisotropy of a laterally fluorinated liquid crystal dimer and its homologous trimer, both exhibiting two nematic phases. In the high-temperature nematic phase, both oligomers exhibit positive optical anisotropy with similar magnitude, which, however, is lower in comparison with the optical anisotropy of the monomer. In the same temperature range, the dielectric permittivity along and perpendicular to the nematic director, measured on magnetically aligned samples, reveals negative dielectric anisotropy for both oligomers, which saturates as the temperature approaches the N–N phase transition temperature. Comparison of the dielectric anisotropies of the oligomers with the corresponding anisotropy of the monomer indicates a systematic variation of its magnitude with the number of the linked mesogenic units. Results are compared with the corresponding anisotropies of the cyanobiphenyl dimers, the archetypal compounds with two nematic phases, and are discussed in terms of the dipolar structure of the mesogens and the dipolar correlations in their nematic phases. Full article
(This article belongs to the Special Issue Structural and Physical Properties of Liquid Crystals)
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Review

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13 pages, 5845 KiB  
Review
Graphene–Liquid Crystal Synergy: Advancing Sensor Technologies across Multiple Domains
by Mohammad A. Adeshina, Abdulazeez M. Ogunleye, Hakseon Lee, Bharathkumar Mareddi, Hyunmin Kim and Jonghoo Park
Materials 2024, 17(17), 4431; https://doi.org/10.3390/ma17174431 - 9 Sep 2024
Cited by 1 | Viewed by 1857
Abstract
This review explores the integration of graphene and liquid crystals to advance sensor technologies across multiple domains, with a focus on recent developments in thermal and infrared sensing, flexible actuators, chemical and biological detection, and environmental monitoring systems. The synergy between graphene’s exceptional [...] Read more.
This review explores the integration of graphene and liquid crystals to advance sensor technologies across multiple domains, with a focus on recent developments in thermal and infrared sensing, flexible actuators, chemical and biological detection, and environmental monitoring systems. The synergy between graphene’s exceptional electrical, optical, and thermal properties and the dynamic behavior of liquid crystals leads to sensors with significantly enhanced sensitivity, selectivity, and versatility. Notable contributions of this review include highlighting key advancements such as graphene-doped liquid crystal IR detectors, shape-memory polymers for flexible actuators, and composite hydrogels for environmental pollutant detection. Additionally, this review addresses ongoing challenges in scalability and integration, providing insights into current research efforts aimed at overcoming these obstacles. The potential for multi-modal sensing, self-powered devices, and AI integration is discussed, suggesting a transformative impact of these composite sensors on various sectors, including health, environmental monitoring, and technology. This review demonstrates how the fusion of graphene and liquid crystals is pushing the boundaries of sensor technology, offering more sensitive, adaptable, and innovative solutions to global challenges. Full article
(This article belongs to the Special Issue Structural and Physical Properties of Liquid Crystals)
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26 pages, 12445 KiB  
Review
Amorphous Blue Phase III: Structure, Materials, and Properties
by Atsushi Yoshizawa
Materials 2024, 17(6), 1291; https://doi.org/10.3390/ma17061291 - 11 Mar 2024
Cited by 1 | Viewed by 2980
Abstract
Blue phases (BPs) have a frustrated structure stabilized by chirality-dependent defects. They are classified into three categories: blue phase I (BPI), blue phase II (BPII), and blue phase III (BPIII). Among them, BPIII has recently attracted much attention due to its elusive amorphous [...] Read more.
Blue phases (BPs) have a frustrated structure stabilized by chirality-dependent defects. They are classified into three categories: blue phase I (BPI), blue phase II (BPII), and blue phase III (BPIII). Among them, BPIII has recently attracted much attention due to its elusive amorphous structure and high-contrast electro-optical response. However, its structure has remained unelucidated, and the molecular design for stabilizing BPIII is still unclear. We present the following findings in this review. (1) BPIII is a spaghetti-like tangled arrangement of double-twist cylinders with characteristic dynamics. (2) Molecular biaxiality and flexibility contribute to stabilize BPIII. (3) BPIII exhibits submillisecond response, high contrast, and wide-viewing angle at room temperature without surface treatment or an optical compensation film. It was free from both hysteresis and residual transmittance. The electro-optical effects are explained in relation to the revealed structure of BPIII. Finally, we discuss the memory effect of a polymer network derived from the defects of BPIII. Full article
(This article belongs to the Special Issue Structural and Physical Properties of Liquid Crystals)
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