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Crystals
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Nematic Liquid Crystal
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Nematic Liquid Crystal

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

Deadline for manuscript submissions: closed (30 October 2023) | Viewed by 6649

Special Issue Editor

Dr. Stephen J. Cowling

E-Mail Website
Guest Editor
Department of Chemistry, The University of York, York YO10 5DD, UK
Interests: liquid crystals; ferroelectric; antiferroelectric; dichroic dye; smectic; nematic
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Nematic liquid crystals are the cornerstone of the liquid crystal display market, being used in twisted nematic, super-twist nematic, in-plane switching and vertically aligned devices, among others. There has always been a desire to improve the performance of the nematic liquid crystal to optimise its functionality and ensure it meets modern device requirements. 

There has been a recent resurgence of interest in nematic liquid crystals with the emergence of novel phases with nematic order, and several of these have shown interesting electro-optical behaviour. These new phases include the nematic twist-bend phase and the splay nematic phase (ferroelectric nematic). This Special Issue celebrates these novel nematic phases and the pursuit of new and interesting behaviours that continue to keep the nematic phase at the forefront of leading-edge liquid crystal research.

Dr. Stephen J. Cowling
Guest Editor

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. Crystals is an international peer-reviewed open access monthly 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 2600 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

  • nematic;
  • splay nematic;
  • ferroelectric nematic;
  • twist bend nematic;
  • liquid crystal;
  • bimesogen;
  • dimer

Published Papers (5 papers)

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Research

12 pages, 1925 KiB  
Communication
Alignment of Nematic Liquid Crystal 5CB Using Graphene Oxide
by Grazia Giuseppina Politano, Francesco Filice and Carlo Versace
Crystals 2023, 13(10), 1500; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst13101500 - 15 Oct 2023
Cited by 1 | Viewed by 1070
Abstract
In this article, we employed the saturation voltage method (SVM) to investigate the interaction between a nematic liquid crystal (NLC) and a graphene oxide (GO) substrate. The SVM approach involved applying a potential difference (ΔV) to the cell containing the NLC (specifically, 5CB) [...] Read more.
In this article, we employed the saturation voltage method (SVM) to investigate the interaction between a nematic liquid crystal (NLC) and a graphene oxide (GO) substrate. The SVM approach involved applying a potential difference (ΔV) to the cell containing the NLC (specifically, 5CB) to reorient the nematic director (n) from a parallel to a perpendicular configuration with respect to the cell’s surface. By utilizing sandwich cells with indium–tin oxide semi-transparent electrodes covered by GO, we measured the anchoring energy between the NLC and the thin GO film. To evaluate the strength of this anchoring energy, we compared the results with two other cells: one exhibiting strong anchoring energy (polyimide cell) and the other demonstrating weak anchoring energy (formvar cell). The influence of GO thin films on the alignment of nematic 5CB was distinctly observed. Full article
(This article belongs to the Special Issue Nematic Liquid Crystal)
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9 pages, 3636 KiB  
Article
Collective Relaxation Processes in Nonchiral Nematics
by Neelam Yadav, Yuri P. Panarin, Wanhe Jiang, Georg H. Mehl and Jagdish K. Vij
Crystals 2023, 13(6), 962; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst13060962 - 16 Jun 2023
Viewed by 879
Abstract
Nematic–nematic transitions in a highly polar nematic compound are studied, in thick cells in which the molecules are aligned parallel to the substrates but perpendicular to the applied electric field, using dielectric spectroscopy in the frequency range 1 Hz to 10 MHz over [...] Read more.
Nematic–nematic transitions in a highly polar nematic compound are studied, in thick cells in which the molecules are aligned parallel to the substrates but perpendicular to the applied electric field, using dielectric spectroscopy in the frequency range 1 Hz to 10 MHz over a wide temperature range. The studied compound displays three nematic phases under cooling from the isotropic phase: ubiquitous nematic N; high polarizability NX; and ferroelectric nematic NF. Two collective processes were observed. The dielectric strength and relaxation frequency of one of the processes P2 showed a dependence on the thickness of the cell. The process P1 is the amplitude mode, while the process P2 is the phason mode. Full article
(This article belongs to the Special Issue Nematic Liquid Crystal)
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10 pages, 2045 KiB  
Article
In Silico Interactome of a Room-Temperature Ferroelectric Nematic Material
by Richard J. Mandle
Crystals 2023, 13(6), 857; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst13060857 - 23 May 2023
Cited by 3 | Viewed by 1140
Abstract
The ferroelectric nematic (NF) phase, characterised by the combination of orientational and polar order, offers unique properties that are challenging to replicate in other systems. Understanding the molecular structure requirements for generating the NF phase is crucial for the design [...] Read more.
The ferroelectric nematic (NF) phase, characterised by the combination of orientational and polar order, offers unique properties that are challenging to replicate in other systems. Understanding the molecular structure requirements for generating the NF phase is crucial for the design of new materials with enhanced properties. This study investigates UUQU-4-N, a room-temperature NF material, using fully atomistic molecular dynamics simulations. UUQU-4-N does not spontaneously form an apolar nematic phase in silico, but exhibits a stable polar nematic configuration akin to the NF phase. The polar order remains significant and near saturation throughout the simulations. The study also examines the cylindrical pair correlation functions, providing insights into the preferred pairing modes and intermolecular interactions which we can then attribute to specific molecular features. We then simulate structural variants of UUQU-4-N, highlighting the potential for developing further examples of near-room-temperature ferroelectric nematic materials via the manipulation of the fluorination pattern, variations in terminal chain length, and replacement of the difluoromethyleneoxy linker. Full article
(This article belongs to the Special Issue Nematic Liquid Crystal)
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16 pages, 1353 KiB  
Article
Computer Simulations of a Twist Bend Nematic (NTB): A Coarse-Grained Simulation of the Phase Behaviour of the Liquid Crystal Dimer CB7CB
by Mark R. Wilson and Gary Yu
Crystals 2023, 13(3), 502; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst13030502 - 15 Mar 2023
Cited by 2 | Viewed by 1489
Abstract
In recent years, a number of achiral liquid crystal dimer molecules have been shown to exhibit nematic–nematic phase transitions. The lower temperature phase has been identified as the NTB phase, which demonstrates emergent chirality in the spontaneous formation of a heliconical structure. [...] Read more.
In recent years, a number of achiral liquid crystal dimer molecules have been shown to exhibit nematic–nematic phase transitions. The lower temperature phase has been identified as the NTB phase, which demonstrates emergent chirality in the spontaneous formation of a heliconical structure. Recent fully atomistic simulations of the molecule CB7CB (1,7-bis-4-(4′-cyanobiphenyl) heptane), a dimer with an odd number of carbon spacers between the mesogenic parts of the molecule, have captured the NTB–N–I phase sequence, providing a picture of the order at a molecular level. In this paper, we use atomistic simulations of CB7CB to develop a coarse-grained model using systematic coarse graining in the NTB phase. We use both force matching (in the form of the MS-CG method) and iterative Boltzmann inversion (IBI) methodologies. Both techniques capture the heliconical order within the NTB phase. Moreover, the model developed via force matching is shown to provide an excellent representation of the atomistic simulation reference model and, remarkably, demonstrates good transferability across temperatures, allowing the NTB–N and N–I phase transitions to be simulated. We also compare results with those of a Martini 3-based coarse-grained model. Full article
(This article belongs to the Special Issue Nematic Liquid Crystal)
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22 pages, 21002 KiB  
Article
Temperature Dependence of the Electroclinic Effect in the Twist-Bend Nematic Phase
by Claire Meyer, Patrick Davidson, Geoffrey R. Luckhurst, Irena Dokli, Anamarija Knežević, Andreja Lesac, Daniel A. Paterson, Rebecca Walker, John M. D. Storey, Corrie T. Imrie and Ivan Dozov
Crystals 2023, 13(3), 465; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst13030465 - 08 Mar 2023
Viewed by 1454
Abstract
The twist-bend nematic (NTB) phase of bent-shaped molecules has recently attracted much attention due to the spontaneous bend of its director field and the doubly-degenerate chirality of its heliconical structure. Despite intensive experimental and theoretical investigation worldwide, the main structural characteristics [...] Read more.
The twist-bend nematic (NTB) phase of bent-shaped molecules has recently attracted much attention due to the spontaneous bend of its director field and the doubly-degenerate chirality of its heliconical structure. Despite intensive experimental and theoretical investigation worldwide, the main structural characteristics (pitch and conical angle) and elastic properties of the phase are still barely understood. This is mainly due to the difficulty in growing large single domains of the NTB phase, which prevents the application of the powerful electro-optical techniques developed for the nematic (N) phase. Moreover, the twist and bend distortions of the optic axis are forbidden by the pseudo-layered structure of the NTB phase, which makes its response to the field smectic-like instead of nematic-like. Therefore, the only macroscopic electric effect that can be observed deep in the NTB phase is the smectic-like “electroclinic” effect (ECENTB). Here, we achieve large monochiral NTB domains which remain uniform over a wide temperature range (20–60 °C) in thin (1.5 µm) planar cells, thus avoiding the so-called stripe- and rope-like textural instabilities. This allowed us to experimentally determine, using electro-optical measurements, the temperature dependence of the ECENTB response in four different NTB materials: namely the dimers CB7CB, CB9CB, CB6OCB, and BNA76. For all compounds, the thermal dependences of conical angle and pitch in the vicinity of the N-NTB transition follow the theoretically predicted power law behaviour. However, the agreement between the measured and predicted power law exponents remains only qualitative, which calls for improvement of the theoretical models. Full article
(This article belongs to the Special Issue Nematic Liquid Crystal)
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