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State-of-the-Art Liquid Crystals Research in UK

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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 May 2022) | Viewed by 26349

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Special Issue Editor

Dr. Ingo Dierking

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Guest Editor

Department of Physics and Astronomy, The University of Manchester, Oxford Road, Manchester M13 9PL, UK
Interests: liquid crystals; chiral liquid crystals; ferroelectric liquid crystals; polymer stabilized liquid crystals; nanoparticles in anisotropic fluids; liquid crystal-nanotube dispersions; defects and defect dynamics; phase ordering in soft matter; fractal structures
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The United Kingdom has a proud history of liquid crystal research, from the formulation of the theory of nematic elasticity, as it is used today, via the Leslie–Erickson theory describing the viscosity of mesophases, to the discovery of the first room-temperature nematic and the related developments in the display industry, to name just a few of the pioneering contributions. Today, liquid crystal science in the UK is more diverse and multidisciplinary than ever, ranging from the synthesis of increasingly complex mesogenic molecules, via the physical properties of self-organised systems and composites of both the thermotropic and the lyotropic type, to a wide variety of applications outside of the traditional display sector. The field covers aspects of Chemistry, Physics, Material Sciences, Chemical Engineering, Mathematics, Biology and Device Engineering in an overarching effort to advance the fundamental understanding of these soft-matter materials and to promote their technological exploitation in the UK and worldwide. To this end, a large group of individuals and research groups from universities and industry in the UK are working together. Their achievements can be found in publications in top class journals and presentations at all large international conferences, in the development of new products, and as events for public engagement.

This Special Issue of the journal Crystals is dedicated to providing an overview of the state-of-the-art of current UK liquid crystals research, compiled from review papers and original research articles, highlighting the breadth of the field today. Research topics include, but are not limited to:

Synthesis of novel mesogens, self-assembly and novel phases;
Polymer- and nanoparticle-composites, elastomers;
Physical characterisation and electric and electrooptic effects;
Lyotropic and chromonic liquid crystals;
Bio-inspired systems;
Frustrated phases and topological defects;
Cellulose-based liquid crystalline materials;
Theory of liquid crystals;
Novel display and non-display applications;
Liquid-crystal-based adaptive optics and photonics.

The only restrictions are that the contribution is mostly devoted to liquid crystal research and that the main part of the study was conducted in the UK or by UK researchers.

We hope that this Special Issue will depict the current state-of-the-art liquid crystal research in the UK and offer an overview of what is being achieved in the field in the United Kingdom.

Dr. Ingo Dierking
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.

Published Papers (11 papers)

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Editorial

Jump to: Research, Review

7 pages, 2065 KiB

Open AccessEditorial

State-of-the-Art Liquid Crystals Research in UK

by Ingo Dierking

Crystals 2022, 12(12), 1725; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12121725 - 28 Nov 2022

Viewed by 1412

Abstract

A number of countries could reasonably produce a collection represented a name such as “State-of-the-Art Research in Liquid Crystals” [...] Full article

(This article belongs to the Special Issue State-of-the-Art Liquid Crystals Research in UK)

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Research

Jump to: Editorial, Review

18 pages, 3528 KiB

Open AccessArticle

Laser Written Stretchable Diffractive Optic Elements in Liquid Crystal Gels

by Bohan Chen, Zimo Zhao, Camron Nourshargh, Chao He, Patrick S. Salter, Martin J. Booth, Steve J. Elston and Stephen M. Morris

Crystals 2022, 12(10), 1340; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12101340 - 22 Sep 2022

Cited by 4 | Viewed by 2418

Abstract

Direct laser writing (DLW) in liquid crystals (LCs) enables a range of new stimuli-responsive functionality to be realized. Here, a method of fabricating mechanically tunable diffraction gratings in stretchable LC gels is demonstrated using a combination of two-photon polymerization direct laser writing (TPP-DLW) and ultraviolet (UV) irradiation. Results are presented that demonstrate the fabrication of a diffraction grating that is written using TPP-DLW in the presence of an electric field in order to align and lock-in the LC director in a homeotropic configuration. The electric field is subsequently removed and the surrounding regions of the LC layer are then exposed to UV light to freeze-in a different alignment so as to ensure that there is a phase difference between the laser written and UV illuminated polymerized regions. It is found that there is a change in the period of the diffraction grating when observed on a polarizing optical microscope as well as a change in the far-field diffraction pattern when the film is stretched or contracted. These experimental results are then compared with the results from simulations. The paper concludes with a demonstration of tuning of the far-field diffraction pattern of a 2-dimensional diffraction grating. Full article

(This article belongs to the Special Issue State-of-the-Art Liquid Crystals Research in UK)

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21 pages, 4883 KiB

Open AccessArticle

Defect Dynamics in Anomalous Latching of a Grating Aligned Bistable Nematic Liquid Crystal Device

by J. C. Jones, S. A. Jones, Z. R. Gradwell, F. A. Fernandez and S. E. Day

Crystals 2022, 12(9), 1291; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12091291 - 13 Sep 2022

Viewed by 1528

Abstract

Deliberate manipulation of topological defects is of particular interest for liquid crystal applications. For example, surface bistability occurs in the grating aligned Zenithal Bistable Device due to the stabilisation of ±½ defects at the points of high surface curvature. Conventional latching between continuous and defect states has previously been simulated satisfactorily using Q-tensor models that include the effect of weak-anchoring and flexoelectricity. However, experimental studies show that some arrangements lead to anomalous latching regimes. The Q-tensor model is used to show that such effects occur when the defects become detached from the surface and have more complex paths in the bulk of the sample. Full article

(This article belongs to the Special Issue State-of-the-Art Liquid Crystals Research in UK)

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15 pages, 3713 KiB

Open AccessArticle

Reappraisal of The Optical Textures of Columnar Phases in Terms of Developable Domain Structures with Relaxed Constraints and a Rationale for The Striated Texture

by John E. Lydon

Crystals 2022, 12(8), 1180; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12081180 - 22 Aug 2022

Viewed by 1531

Abstract

Optical textures pictured in the seminal 1974 textbook, The Microscopy of Liquid Crystals, by Norman Hartshorne, have been reappraised. Some of these, which were described by Hartshorne (and many others) as confused focal conics, were of chromonic and discotic phases, which had not been identified at that time—and would now be recognized as developable domain structures of columnar phases. It is suggested that the rigorous constraint of isometry in these is relaxed in regions of the director field under high stress. A rationale for the characteristic striated appearance of columnar textures is proposed, in which the molecular columns are bundled together, forming twisted ropes within the domains. It is also suggested that the regular alternation of opposing domains in M ribbons minimizes the slippage of columns required as the mesophase develops, and an explanation of the characteristic multi-pole appearance of the brushes in the optical textures of columnar structures is proposed. Full article

(This article belongs to the Special Issue State-of-the-Art Liquid Crystals Research in UK)

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12 pages, 2584 KiB

Open AccessArticle

Ferroelectric Smectic Liquid Crystals as Electrocaloric Materials

by Peter John Tipping and Helen Frances Gleeson

Crystals 2022, 12(6), 809; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12060809 - 08 Jun 2022

Cited by 1 | Viewed by 2110

Abstract

The 1980s saw the development of ferroelectric chiral smectic C (SmC*) liquid crystals (FLCs) with a clear focus on their application in fast electro-optic devices. However, as the only known fluid ferroelectric materials, they also have potential in other applications, one of which is in heat-exchange devices based on the electrocaloric effect. In particular, ferroelectric liquid crystals can be both the electrocaloric material and the heat exchanging fluid in an electrocaloric device, significantly simplifying some of the design constraints associated with solid dielectrics. In this paper, we consider the electrocaloric potential of three SmC* ferroelectric liquid crystal systems, two of which are pure materials that exhibit ferroelectric, antiferroelectric, and intermediate phases and one that was developed as a room-temperature SmC* material for electro-optic applications. We report the field-induced temperature changes of these selected materials, measured indirectly using the Maxwell method. The maximum induced temperature change determined, 0.37 K, is currently record-breaking for an FLC and is sufficiently large to make these materials interesting candidates for the development for electrocaloric applications. Using the electrocaloric temperature change normalised as a function of electric field strength, as a function of merit, the performances of FLCs are compared with ferroelectric ceramics and polymers. Full article

(This article belongs to the Special Issue State-of-the-Art Liquid Crystals Research in UK)

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24 pages, 10307 KiB

Open AccessArticle

Molecular Simulation Approaches to the Study of Thermotropic and Lyotropic Liquid Crystals

by Mark R. Wilson, Gary Yu, Thomas D. Potter, Martin Walker, Sarah J. Gray, Jing Li and Nicola Jane Boyd

Crystals 2022, 12(5), 685; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12050685 - 10 May 2022

Cited by 10 | Viewed by 3549

Abstract

Over the last decade, the availability of computer time, together with new algorithms capable of exploiting parallel computer architectures, has opened up many possibilities in molecularly modelling liquid crystalline systems. This perspective article points to recent progress in modelling both thermotropic and lyotropic systems. For thermotropic nematics, the advent of improved molecular force fields can provide predictions for nematic clearing temperatures within a 10 K range. Such studies also provide valuable insights into the structure of more complex phases, where molecular organisation may be challenging to probe experimentally. Developments in coarse-grained models for thermotropics are discussed in the context of understanding the complex interplay of molecular packing, microphase separation and local interactions, and in developing methods for the calculation of material properties for thermotropics. We discuss progress towards the calculation of elastic constants, rotational viscosity coefficients, flexoelectric coefficients and helical twisting powers. The article also covers developments in modelling micelles, conventional lyotropic phases, lyotropic phase diagrams, and chromonic liquid crystals. For the latter, atomistic simulations have been particularly productive in clarifying the nature of the self-assembled aggregates in dilute solution. The development of effective coarse-grained models for chromonics is discussed in detail, including models that have demonstrated the formation of the chromonic N and M phases. Full article

(This article belongs to the Special Issue State-of-the-Art Liquid Crystals Research in UK)

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14 pages, 584 KiB

Open AccessArticle

Anatomy of a Discovery: The Twist–Bend Nematic Phase

by David Dunmur

Crystals 2022, 12(3), 309; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12030309 - 22 Feb 2022

Cited by 7 | Viewed by 1902

Abstract

New fluid states of matter, now known as liquid crystals, were discovered at the end of the 19th century and still provide strong themes in scientific research. The applications of liquid crystals continue to attract attention, and the most successful so far has been to the technology of flat panel displays; this has diversified in recent years and LCDs no longer dominate the industry. Despite this, there is plenty more to be uncovered in the science of liquid crystals, and as well as new applications, novel types of liquid crystal phases continue to be discovered. The simplest liquid crystal phase is the nematic together with its handed or chiral equivalent, named the cholesteric phase. In the latter, the aligned molecules of the nematic twist about an axis perpendicular to their alignment axis, but in the 1970s a heliconical phase with a tilt angle of less than 90° was predicted. The discovery of this phase nearly 40 years later is described in this paper. Robert Meyer proposed that coupling between a vector order parameter in a nematic and a splay or bend elastic distortion could result in spontaneously splayed or bent structures. Later, Ivan Dozov suggested that new nematic phases with splay–bend or twist–bend structures could be stabilised if the appropriate elastic constants became negative. Theoretical speculation on new nematic phases and the experimental identification of nematic–nematic phase transitions are reviewed in the paper, and the serendipitous discovery in 2010 of the nematic twist–bend phase in 1″,7″-bis(4-cyanobiphenyl-4′-yl)heptane (CB7CB) is described. Full article

(This article belongs to the Special Issue State-of-the-Art Liquid Crystals Research in UK)

Review

Jump to: Editorial, Research

27 pages, 12030 KiB

Open AccessReview

Liquid Crystal Dimers and Smectic Phases from the Intercalated to the Twist-Bend

by Corrie T. Imrie, Rebecca Walker, John M. D. Storey, Ewa Gorecka and Damian Pociecha

Crystals 2022, 12(9), 1245; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12091245 - 02 Sep 2022

Cited by 27 | Viewed by 2459

Abstract

In this review we consider the relationships between molecular structure and the tendency of liquid crystal dimers to exhibit smectic phases, and show how our application of these led to the recent discovery of the twist-bend, heliconical smectic phases. Liquid crystal dimers consist of molecules containing two mesogenic groups linked through a flexible spacer, and even- and odd-membered dimers differ in terms of their average molecular shapes. The former tend to be linear whereas the latter are bent, and this difference in shape drives very different smectic behaviour. For symmetric dimers, in which the two mesogenic groups are identical, smectic phase formation may be understood in terms of a microphase separation into distinct sublayers consisting of terminal chains, mesogenic units and spacers, and monolayer smectic phases are observed. By contrast, intercalated smectic phases were discovered for nonsymmetric dimers in which the two mesogenic units differ. In these phases, the ratio of the layer spacing to the molecular length is typically around 0.5 indicating that unlike segments of the molecules overlap. The formation of intercalated phases is driven by a favourable interaction between the different liquid crystal groups. If an odd-membered dimer possesses sufficient molecular curvature, then the twist-bend nematic phase may be seen in which spontaneous chirality is observed for a system consisting of achiral molecules. Combining the empirical relationships developed for smectogenic dimers, and more recently for twist-bend nematogenic dimers, we show how dimers were designed to show the new twist-bend, heliconical smectic phases. These have been designated SmC_TB phases in which the director is tilted with respect to the layer plane, and the tilt direction describes a helix on passing between layers. We describe three variants of the SmC_TB phase, and in each the origin of the symmetry breaking is attributed to the anomalously low-bend elastic constant arising from the bent molecular structures. Full article

(This article belongs to the Special Issue State-of-the-Art Liquid Crystals Research in UK)

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20 pages, 6647 KiB

Open AccessReview

Steroid-Based Liquid Crystalline Polymers: Responsive and Biocompatible Materials of the Future

by Bartlomiej Czubak, Nicholas J. Warren and Mamatha Nagaraj

Crystals 2022, 12(7), 1000; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12071000 - 19 Jul 2022

Cited by 3 | Viewed by 2334

Abstract

Steroid-based liquid crystal polymers and co-polymers have come a long way, with new and significant advances being made every year. This paper reviews some of the recent key developments in steroid-based liquid crystal polymers and co-polymers. It covers the structure–property relationship between cholesterol and sterol-based compounds and their corresponding polymers, and the influence of chemical structure and synthesis conditions on the liquid crystalline behaviour. An overview of the nature of self-assembly of these materials in solvents and through polymerisation is given. The role of liquid crystalline properties in the applications of these materials, in the creation of nano-objects, drug delivery and biomedicine and photonic and electronic devices, is discussed. Full article

(This article belongs to the Special Issue State-of-the-Art Liquid Crystals Research in UK)

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31 pages, 6735 KiB

Open AccessEditor’s ChoiceReview

Conception, Discovery, Invention, Serendipity and Consortia: Cyanobiphenyls and Beyond

by John W. Goodby and Stephen J. Cowling

Crystals 2022, 12(6), 825; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12060825 - 10 Jun 2022

Cited by 7 | Viewed by 2678

Abstract

In the 1960s, a world-wide change in electronic devices was about to occur with the invention of integrated circuits. The chip was upon us, which instantly created the need for a revolution in visual communication displays. From the watch to the computer monitor, to TVs, to the phone, nearly all everyday applications were affected. A strange connection in technology underpinned these changes; the linkage between silicon semiconductors and organic compounds that did not know if they were solids or liquids. Liquid crystals had been known since 1888 and had seen little usage until they were inserted between conducting glass slides and an applied electric field. Suddenly, the possibility of driving images with low voltage fields became obvious. Many major companies took up the challenge of commercialisation, but in the UK a curious combination of government research facilities, electronic companies and one small university came together in 1970 to form a consortium and within two years the basis for new technologies had been founded. Chemistry is part of this story, with new conceptions, discoveries and inventions, and the luck to be in the right place at the right time. Full article

(This article belongs to the Special Issue State-of-the-Art Liquid Crystals Research in UK)

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17 pages, 4993 KiB

Open AccessEditor’s ChoiceReview

Recent Progresses on Experimental Investigations of Topological and Dissipative Solitons in Liquid Crystals

by Yuan Shen and Ingo Dierking

Crystals 2022, 12(1), 94; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst12010094 - 11 Jan 2022

Cited by 12 | Viewed by 2555

Abstract

Solitons in liquid crystals have received increasing attention due to their importance in fundamental physical science and potential applications in various fields. The study of solitons in liquid crystals has been carried out for over five decades with various kinds of solitons being reported. Recently, a number of new types of solitons have been observed, among which, many of them exhibit intriguing dynamic behaviors. In this paper, we briefly review the recent progresses on experimental investigations of solitons in liquid crystals. Full article

(This article belongs to the Special Issue State-of-the-Art Liquid Crystals Research in UK)

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