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In Celebration of Noel A. Clark’s 80th Birthday
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In Celebration of Noel A. Clark’s 80th Birthday

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

Deadline for manuscript submissions: closed (30 June 2021) | Viewed by 39657

Special Issue Editor

Prof. Dr. Charles Rosenblatt

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Guest Editor
Ohio Eminent Scholar and Professor of Physics, Department of Physics, Case Western Reserve University, Cleveland, OH 44106-7079, USA
Interests: liquid crystals and complex fluids (electric and magnetic field effects, interfaces, phase transitions, colloidal inclusions); fluid interface instabilities; microgravity
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

This Special Issue is dedicated to Professor Noel A. Clark in celebration of his 80th birthday. 

Perhaps the most prolific and prominent soft matter experimentalist today, Prof. Noel Clark of the University of Colorado has pioneered many of the advances in liquid crystals that we now take for granted. These include ultrathin films and the crossover to two-dimensional behavior, ferroelectric and antiferroelectric liquid crystals, bent core molecular phases, ferromagnetic liquid crystals, chirality and polarizations in phases composed of achiral molecules, gravitational effects on liquid crystals, biomembranes, colloidal crystals, liquid crystals based on DNA, and liquid crystalline behavior in the origin of life. Prof. Clark has received numerous awards for his seminal contributions, among these the Oliver Buckley Condensed Matter prize of the American Physical Society, a Guggenheim fellowship, and the Humboldt Research award. He is also an Honored Member of the International Liquid Crystal Society, a Fellow of both the American Physical Society and the American Association for the Advancement of Science, and a member of the U.S. National Academy of Sciences. Having served as mentor to scores of students and a congenial colleague to as many researchers, Prof. Clark’s influence extends far and wide. As he approaches his 80th birthday on 17 December 2020, this issue brings together research articles by his colleagues and friends to honor his many contributions.

This Special Issue is intended to provide a unique international forum aimed at covering a broad description of research, both experimental and theoretical, involving liquid crystals.

Contributions to this special issue are by invitation only.

Prof. Dr. Charles Rosenblatt
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

  • Liquid crystals
  • Ferroelectricity
  • Liquid crystal thin films
  • Colloidal crystals

Published Papers (15 papers)

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Research

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15 pages, 2018 KiB  
Article
Director Fluctuations in Two-Dimensional Liquid Crystal Disclinations
by Olaf Stenull and Tom C. Lubensky
Crystals 2022, 12(1), 1; https://doi.org/10.3390/cryst12010001 - 21 Dec 2021
Cited by 3 | Viewed by 2385
Abstract
We present analytical calculations of the energies and eigenfunctions of all normal modes of excitation of charge +1 two-dimensional splay (bend) disclinations confined to an annular region with inner radius R1 and outer radius R2 and with perpendicular (tangential) boundary [...] Read more.
We present analytical calculations of the energies and eigenfunctions of all normal modes of excitation of charge +1 two-dimensional splay (bend) disclinations confined to an annular region with inner radius R1 and outer radius R2 and with perpendicular (tangential) boundary conditions on the region’s inner and outer perimeters. Defects such as these appear in islands in smectic-C films and can in principle be created in bolaamphiphilic nematic films. Under perpendicular boundary conditions on the two surfaces and when the ratio β=Ks/Kb of the splay to bend 2D Frank constants is less than one, the splay configuration is stable for all values μ=R2/R1. When β>1, the splay configuration is stable only for μ less than a critical value μc(β), becoming unstable to a “spiral” mixed splay-bend configuration for μ>μc. The same behavior occurs in trapped bend defects with tangential boundary conditions but with Ks and Kb interchanged. By calculating free energies, we verify that the transition from a splay or bend configuration to a mixed one is continuous. We discuss the differences between our calculations that yield expressions for experimentally observable excitation energies and other calculations that produce the same critical points and spiral configurations as ours but not the same excitation energies. We also calculate measurable correlation functions and associated decay times of angular fluctuations. Full article
(This article belongs to the Special Issue In Celebration of Noel A. Clark’s 80th Birthday)
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13 pages, 2901 KiB  
Article
Topological Defect-Guided Regular Stacking of Focal Conic Domains in Hybrid-Aligned Smectic Liquid Crystal Shells
by JungHyun Noh and Jan P. F. Lagerwall
Crystals 2021, 11(8), 913; https://doi.org/10.3390/cryst11080913 - 04 Aug 2021
Cited by 4 | Viewed by 2608
Abstract
We study liquid crystal (LC) shells in hybrid configuration (director tangential to the inside but normal to the outside) as they slowly undergo a transition from a nematic (N) to a smectic-A (SmA) phase. Every shell has two antipodal +1 topological defects, at [...] Read more.
We study liquid crystal (LC) shells in hybrid configuration (director tangential to the inside but normal to the outside) as they slowly undergo a transition from a nematic (N) to a smectic-A (SmA) phase. Every shell has two antipodal +1 topological defects, at the thinnest and thickest points, respectively. On cooling from N to SmA, the symmetry axis connecting the defects gradually reorients from along gravity to perpendicular to it, reversibly and continuously, if the LC and aqueous phase are density matched at the N-SmA transition. This suggests reduced density near the defects—reflecting a local reduction in order—under the strong confinement with antagonistic boundary conditions. In the SmA phase, a regular array of focal conic domains (FCDs) develops, templated in position and orientation by the +1 defect at the thinnest point. Around this defect, a single complete toroidal FCD always develops, surrounded by incomplete FCDs. In contrast to similar FCD arrangements on flat aqueous interfaces, this is a stable situation, since the two +1 defects are required by the spherical topology. Our results demonstrate how the topological defects of LC shells can be used to template complex self-organized structures. With a suitable adaption of the LC chemistry, shells might serve as a basis for producing solid particles with complex yet highly regular morphologies. Full article
(This article belongs to the Special Issue In Celebration of Noel A. Clark’s 80th Birthday)
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15 pages, 2112 KiB  
Article
From Bend to Splay Dominated Elasticity in Nematics
by Davide Revignas and Alberta Ferrarini
Crystals 2021, 11(7), 831; https://doi.org/10.3390/cryst11070831 - 17 Jul 2021
Cited by 4 | Viewed by 2976
Abstract
In the past decade, much evidence has been provided for an unusually low cost for bend deformations in the nematic phase of bent-core mesogens and bimesogens (liquid crystal dimers) having a bent shape on average. Recently, an analogous effect was observed for the [...] Read more.
In the past decade, much evidence has been provided for an unusually low cost for bend deformations in the nematic phase of bent-core mesogens and bimesogens (liquid crystal dimers) having a bent shape on average. Recently, an analogous effect was observed for the splay mode of bent-core mesogens with an acute apical angle. Here, we present a systematic computational investigation of the Frank elastic constants of nematics made of V-shaped particles, with bend angles ranging from acute to obtuse. We show that by tuning this angle, the elastic behavior switches from bend dominated (K33>K11) to splay dominated (K11>K33), with anomalously low values of the splay and the bend constant, respectively. This is related to a change in the shape polarity of particles, which is associated with the emergence of polar order, longitudinal for splay and transversal for bend deformations. Crucial to this study is the use of a recently developed microscopic elastic theory, able to account for the interplay of mesogen morphology and director deformations. Full article
(This article belongs to the Special Issue In Celebration of Noel A. Clark’s 80th Birthday)
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16 pages, 7333 KiB  
Article
Synthesis and Characterization of Novel Bio-Chiral Dopants Obtained from Bio-Betulin Produced by a Fermentation Process
by Veridiana G. Guimarães, Anastasiia Svanidze, Tianyi Guo, Pawan Nepal, Robert J. Twieg, Peter Palffy-Muhoray and Hiroshi Yokoyama
Crystals 2021, 11(7), 785; https://doi.org/10.3390/cryst11070785 - 06 Jul 2021
Cited by 5 | Viewed by 2388
Abstract
Cholesteric liquid crystals are frequently produced by the addition of chiral dopants to achiral nematic hosts. We report here the synthesis and performance of chiral dopants obtained from bio-betulin produced by a fermentation process. An important aspect of this work is to point [...] Read more.
Cholesteric liquid crystals are frequently produced by the addition of chiral dopants to achiral nematic hosts. We report here the synthesis and performance of chiral dopants obtained from bio-betulin produced by a fermentation process. An important aspect of this work is to point out that the fermentation process used to obtain the starting materials is much easier and cheaper when carried out in large volumes than isolating it from the natural product. The performance of the dopants obtained from bio-betulin is indistinguishable from those obtained from commercially available synthetic betulin. Full article
(This article belongs to the Special Issue In Celebration of Noel A. Clark’s 80th Birthday)
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9 pages, 25288 KiB  
Article
Azimuthal Anchoring Strength in Photopatterned Alignment of a Nematic
by H. Nilanthi Padmini, Mojtaba Rajabi, Sergij V. Shiyanovskii and Oleg D. Lavrentovich
Crystals 2021, 11(6), 675; https://doi.org/10.3390/cryst11060675 - 11 Jun 2021
Cited by 8 | Viewed by 3474
Abstract
Spatially-varying director fields have become an important part of research and development in liquid crystals. Characterization of the anchoring strength associated with a spatially-varying director is difficult, since the methods developed for a uniform alignment are seldom applicable. Here we characterize the strength [...] Read more.
Spatially-varying director fields have become an important part of research and development in liquid crystals. Characterization of the anchoring strength associated with a spatially-varying director is difficult, since the methods developed for a uniform alignment are seldom applicable. Here we characterize the strength of azimuthal surface anchoring produced by the photoalignment technique based on plasmonic metamsaks. The measurements used photopatterned arrays of topological point defects of strength +1 and −1 in thin layers of a nematic liquid crystal. The integer-strength defects split into pairs of half-integer defects with lower elastic energy. The separation distance between the split pair is limited by the azimuthal surface anchoring, which allows one to determine the strength of the latter. The strength of the azimuthal anchoring is proportional to the UV exposure time during the photoalignment of the azobenzene layer. Full article
(This article belongs to the Special Issue In Celebration of Noel A. Clark’s 80th Birthday)
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22 pages, 13524 KiB  
Article
The Beauty of Twist-Bend Nematic Phase: Fast Switching Domains, First Order Fréedericksz Transition and a Hierarchy of Structures
by Vitaly P. Panov, Jang-Kun Song, Georg H. Mehl and Jagdish K. Vij
Crystals 2021, 11(6), 621; https://doi.org/10.3390/cryst11060621 - 31 May 2021
Cited by 7 | Viewed by 2829
Abstract
The twist-bend nematic phase (NTB) exhibits a complicated hierarchy of structures responsible for several intriguing properties presented here. These are: the observation of a fast electrooptic response, the exhibition of a large electroclinic effect, and the observation of an unusual pattern [...] Read more.
The twist-bend nematic phase (NTB) exhibits a complicated hierarchy of structures responsible for several intriguing properties presented here. These are: the observation of a fast electrooptic response, the exhibition of a large electroclinic effect, and the observation of an unusual pattern of the temperature dependence of birefringence of bent-shaped bimesogens in parallel-rubbed planar-aligned cells. These unusual effects inspired the use of highly sophisticated techniques that led to the discovery of the twist-bend nematic phase. Results of the optical retardation of a parallel-rubbed planar-aligned cell show that the ‘heliconical angle’ (the angle the local director makes with the optical axis) starts increasing in the high temperature N phase, it exhibits a jump at the N–NTB transition temperature and continues to increase in magnitude with a further reduction in temperature. The liquid crystalline parallel-rubbed planar-aligned and twist-aligned cells in this phase exhibit fascinating phenomena such as a demonstration of the beautiful stripes and dependence of their periodicity on temperature. The Fréedericksz transition in the NTB phase is found to be of the first order both in rubbed planar and homeotropic-aligned cells, in contrast to the second order transition exhibited by a conventional nematic phase. This transition shows a significant hysteresis as well as an abrupt change in the orientation of the director as a function of the applied electric field. Hierarchical structures are revealed using the technique of polymer templating the structure of the liquid crystalline phase of interest, and imaging of the resulting structure by scanning electron microscopy. Full article
(This article belongs to the Special Issue In Celebration of Noel A. Clark’s 80th Birthday)
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11 pages, 1928 KiB  
Article
The Freedericksz Transition in a Spatially Varying Magnetic Field
by Tianyi Guo, Xiaoyu Zheng and Peter Palffy-Muhoray
Crystals 2021, 11(5), 541; https://doi.org/10.3390/cryst11050541 - 13 May 2021
Cited by 1 | Viewed by 2208
Abstract
Much is known about the Freedericksz transition induced by uniform electric and magnetic fields in nematic liquid crystals. In this work, we are interested in the effects of a spatially varying field on the transition. Specifically, we study the director configuration in a [...] Read more.
Much is known about the Freedericksz transition induced by uniform electric and magnetic fields in nematic liquid crystals. In this work, we are interested in the effects of a spatially varying field on the transition. Specifically, we study the director configuration in a homeotropic nematic cell in a spatially varying magnetic field with cylindrical symmetry. The experiment is conducted with a ring magnet which provides a radial magnetic field with magnitude monotonically decreasing to zero at the center. The nematic cell is positioned in the central plane of the ring, with the cell normal parallel to the ring normal. Interference patterns of the nematic cell between crossed polarizers were observed. The director configuration in the nematic cell is modeled with Frank–Oseen theory, and the computed interference pattern from the simulated director field are compared with experiment. We conclude that if the magnetic field strength varies with position in the plane of the cell, there is no Freedericksz transition. Full article
(This article belongs to the Special Issue In Celebration of Noel A. Clark’s 80th Birthday)
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10 pages, 3494 KiB  
Communication
Synchrotron Microbeam Diffraction Studies on the Alignment within 3D-Printed Smectic-A Liquid Crystal Elastomer Filaments during Extrusion
by Marianne E. Prévôt, Senay Ustunel, Benjamin M. Yavitt, Guillaume Freychet, Caitlyn R. Webb, Mikhail Zhernenkov, Elda Hegmann and Ron Pindak
Crystals 2021, 11(5), 523; https://doi.org/10.3390/cryst11050523 - 08 May 2021
Cited by 9 | Viewed by 3183
Abstract
3D printing of novel and smart materials has received considerable attention due to its applications within biological and medical fields, mostly as they can be used to print complex architectures and particular designs. However, the internal structure during 3D printing can be problematic [...] Read more.
3D printing of novel and smart materials has received considerable attention due to its applications within biological and medical fields, mostly as they can be used to print complex architectures and particular designs. However, the internal structure during 3D printing can be problematic to resolve. We present here how time-resolved synchrotron microbeam Small-Angle X-ray Diffraction (μ-SAXD) allows us to elucidate the local orientational structure of a liquid crystal elastomer-based printed scaffold. Most reported 3D-printed liquid crystal elastomers are mainly nematic; here, we present a Smectic-A 3D-printed liquid crystal elastomer that has previously been reported to promote cell proliferation and alignment. The data obtained on the 3D-printed filaments will provide insights into the internal structure of the liquid crystal elastomer for the future fabrication of liquid crystal elastomers as responsive and anisotropic 3D cell scaffolds. Full article
(This article belongs to the Special Issue In Celebration of Noel A. Clark’s 80th Birthday)
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13 pages, 4073 KiB  
Article
Observation of Backflow during the Anihilation of Topologocal Defects in Freely Suspended Smectic Films
by Amine Missaoui, Emmanuelle Lacaze, Alexey Eremin and Ralf Stannarius
Crystals 2021, 11(4), 430; https://doi.org/10.3390/cryst11040430 - 16 Apr 2021
Cited by 6 | Viewed by 2158
Abstract
Freely suspended films in the smectic C phase are excellent templates for the study of topological defect dynamics. It is well known that, during the annihilation of a pair of disclinations with strengths +/−1, the +1 defect moves faster because it is carried [...] Read more.
Freely suspended films in the smectic C phase are excellent templates for the study of topological defect dynamics. It is well known that, during the annihilation of a pair of disclinations with strengths +/−1, the +1 defect moves faster because it is carried towards its opponent by backflow, whereas the flow in the vicinity of the −1 defect is negligibly small. This backflow pattern is created by the defect motion itself. An experimental confirmation of this theoretical prediction and its quantitative characterization is achieved here by fluorescence labeling. Film regions near the defect positions are labeled and their displacements are tracked optically. Full article
(This article belongs to the Special Issue In Celebration of Noel A. Clark’s 80th Birthday)
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12 pages, 2225 KiB  
Article
Modeling of the Resonant X-ray Response of a Chiral Cubic Phase
by Timon Grabovac, Ewa Gorecka, Damian Pociecha and Nataša Vaupotič
Crystals 2021, 11(2), 214; https://doi.org/10.3390/cryst11020214 - 21 Feb 2021
Cited by 2 | Viewed by 2074
Abstract
The structure of a continuous-grid chiral cubic phase made of achiral constituent molecules is a hot topic in the field of thermotropic liquid crystals. Several structural models have been proposed so far. Resonant X-ray scattering (RXS), which gives information on the molecular orientation [...] Read more.
The structure of a continuous-grid chiral cubic phase made of achiral constituent molecules is a hot topic in the field of thermotropic liquid crystals. Several structural models have been proposed so far. Resonant X-ray scattering (RXS), which gives information on the molecular orientation in the unit cell, could be applied to select the most appropriate model. We modeled the RXS response for the recently proposed chiral cubic phase structure with an all-hexagon chiral continuous grid. A tensor form factor of a unit cell is constructed, which enables calculation of intensities of peaks for all Miller indices. We find that all the symmetry allowed peaks are resonantly enhanced, and their intensity is much stronger than the intensity of the symmetry forbidden (resonant) peaks. In particular, we predict that a strong resonant enhancement of the symmetry allowed peaks (011) and (002), not observed in a nonresonant scattering, could be observed by RXS at the carbon absorption edge. By RXS at the sulfur absorption edge, one might observe a resonant peak (113) and resonantly enhanced peak (233), and resonant enhancement of all the peaks that are observed in a nonresonant scattering, which probably hide the rest of the predicted resonant peaks. Full article
(This article belongs to the Special Issue In Celebration of Noel A. Clark’s 80th Birthday)
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11 pages, 1682 KiB  
Article
Impact of the Liquid Crystal Director Twisting on Two-Beam Energy Exchange in a Hybrid Photorefractive Inorganic-Liquid Crystal Cell
by Victor Yu. Reshetnyak, Igor P. Pinkevych, Michael E. McConney, Jonathan E. Slagle and Dean R. Evans
Crystals 2020, 10(12), 1104; https://doi.org/10.3390/cryst10121104 - 03 Dec 2020
Cited by 1 | Viewed by 1591
Abstract
We studied the energy transfer between light beams on the director grating in a hybrid photorefractive liquid crystal (LC) cell assuming the propagation of light waves in the cell to be in the Mauguin regime. This approach makes it possible to trace the [...] Read more.
We studied the energy transfer between light beams on the director grating in a hybrid photorefractive liquid crystal (LC) cell assuming the propagation of light waves in the cell to be in the Mauguin regime. This approach makes it possible to trace the change of the gain coefficient dependence on the director grating spacing with the change of the LC director twist. Conditions for the LC flexoelectric parameters and the director helix pitch necessary for transformation the gain coefficient dependence from the nematic to cholesteric type are obtained. The influence of the director splay and bend deformations on the gain coefficient is also studied. Full article
(This article belongs to the Special Issue In Celebration of Noel A. Clark’s 80th Birthday)
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13 pages, 1519 KiB  
Article
The Genetic Algorithm: Using Biology to Compute Liquid Crystal Director Configurations
by S. Yang and Peter J. Collings
Crystals 2020, 10(11), 1041; https://doi.org/10.3390/cryst10111041 - 16 Nov 2020
Cited by 5 | Viewed by 2039 | Correction
Abstract
The genetic algorithm is an optimization routine for finding the solution to a problem that requires a function to be minimized. It accomplishes this by creating a population of solutions and then producing “offspring” solutions from this population by combining two “parental” solutions [...] Read more.
The genetic algorithm is an optimization routine for finding the solution to a problem that requires a function to be minimized. It accomplishes this by creating a population of solutions and then producing “offspring” solutions from this population by combining two “parental” solutions in much the way that the DNA of biological parents is combined in the DNA of offspring. Strengths of the algorithm include that it is simple to implement, no trial solution is required, and the results are fairly accurate. Weaknesses include its slow computational speed and its tendency to find a local minimum that does not represent the global minimum of the function. By minimizing the elastic, surface, and electric free energies, the genetic algorithm is used to compute the liquid crystal director configuration for a wide range of situations, including one- and two-dimensional problems with various forms of boundary conditions, with and without an applied electric field. When appropriate, comparisons are made with the exact solutions. Ways to increase the performance of the algorithm as well as how to avoid various pitfalls are discussed. Full article
(This article belongs to the Special Issue In Celebration of Noel A. Clark’s 80th Birthday)
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13 pages, 3653 KiB  
Article
Annihilation of Highly-Charged Topological Defects
by Eva Klemenčič, Pavlo Kurioz, Milan Ambrožič, Charles Rosenblatt and Samo Kralj
Crystals 2020, 10(8), 673; https://doi.org/10.3390/cryst10080673 - 03 Aug 2020
Viewed by 2109
Abstract
We studied numerically external stimuli enforced annihilation of a pair of daughter nematic topological defect (TD) assemblies bearing a relatively strong topological charge |m|=3/2. A Landau- de Gennes phenomenological approach in terms of tensor nematic order [...] Read more.
We studied numerically external stimuli enforced annihilation of a pair of daughter nematic topological defect (TD) assemblies bearing a relatively strong topological charge |m|=3/2. A Landau- de Gennes phenomenological approach in terms of tensor nematic order parameter was used in an effectively two-dimensional Cartesian coordinate system, where spatial variations along the z-axis were neglected. A pair of {m=3/2,m=−3/2} was enforced by an appropriate surface anchoring field, mimicking an experimental sample realization using the atomic force microscope (AFM) scribing method. Furthermore, defects were confined within a rectangular boundary that imposes strong tangential anchoring. This setup enabled complex and counter-intuitive annihilation processes on varying relevant parameters. We present two qualitatively different annihilation paths, where we either gradually reduced the relative surface anchoring field importance or increased an external in-plane spatially homogeneous electric field E. The creation and depinning of additional defect pairs {12,−12} mediated the annihilation in such a geometry. Furthermore, we illustrate the absorption of TDs by sharp edges of the confining boundary, accompanied by m=±1/4↔∓1/4 winding reversal of edge singularities, and also E-driven zero-dimensional to one-dimensional defect core transformation. Full article
(This article belongs to the Special Issue In Celebration of Noel A. Clark’s 80th Birthday)
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15 pages, 2649 KiB  
Article
Multiple Twisted Chiral Nematic Structures in Cylindrical Confinement
by Milan Ambrožič, Apparao Gudimalla, Charles Rosenblatt and Samo Kralj
Crystals 2020, 10(7), 576; https://doi.org/10.3390/cryst10070576 - 04 Jul 2020
Cited by 2 | Viewed by 2326
Abstract
In this article, we theoretically and numerically study the chirality and saddle-splay elastic constant ( K 24 ) -enabled stability of multiple twist-like nematic liquid crystal (LC) structures in cylindrical confinement. We focus on the so-called radially z-twisted (RZT) and radially twisted (RT) [...] Read more.
In this article, we theoretically and numerically study the chirality and saddle-splay elastic constant ( K 24 ) -enabled stability of multiple twist-like nematic liquid crystal (LC) structures in cylindrical confinement. We focus on the so-called radially z-twisted (RZT) and radially twisted (RT) configurations, which simultaneously exhibit twists in different spatial directions. We express the free energies of the structures in terms of dimensionless wave vectors, which characterise the structures and play the roles of order parameters. The impact of different confinement anchoring conditions is explored. A simple Landau-type analysis provides an insight into how different model parameters influence the stability of structures. We determine conditions for which the structures are stable in chiral and also nonchiral LCs. In particular, we find that the RZT structure could exhibit macroscopic chirality inversion upon varying the relevant parameters. This phenomenon could be exploited for the measurement of   K 24 . Full article
(This article belongs to the Special Issue In Celebration of Noel A. Clark’s 80th Birthday)
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Review

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21 pages, 15430 KiB  
Review
Introduction to Colloidal and Microfluidic Nematic Microstructures
by Simon Čopar, Miha Ravnik and Slobodan Žumer
Crystals 2021, 11(8), 956; https://doi.org/10.3390/cryst11080956 - 16 Aug 2021
Cited by 15 | Viewed by 3227
Abstract
In this brief review, we give an introduction to selected colloidal and microfluidic nematic microstructures, as enabled by the inherent anisotropy and microscopic orientational ordering in complex liquid crystalline materials. We give a brief overview of the mesoscopic theory, for equilibrium and dynamics, [...] Read more.
In this brief review, we give an introduction to selected colloidal and microfluidic nematic microstructures, as enabled by the inherent anisotropy and microscopic orientational ordering in complex liquid crystalline materials. We give a brief overview of the mesoscopic theory, for equilibrium and dynamics, of nematic fluids, that provides the framework for understanding, characterization, and even prediction of such microstructures, with particular comment also on the role of topology and topological defects. Three types of nematic microstructures are highlighted: stable or metastable structures in nematic colloids based on spherical colloidal particles, stationary nematic microfluidic structures, and ferromagnetic liquid crystal structures based on magnetic colloidal particles. Finally, this paper is in honor of Noel A. Clark, as one of the world pioneers that helped to shape this field of complex and functional soft matter, contributing at different levels to works of various groups worldwide, including ours. Full article
(This article belongs to the Special Issue In Celebration of Noel A. Clark’s 80th Birthday)
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