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Special Issue "Structural, Optical and Hydrodynamic Properties of Liquid Crystals"

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A special issue of Symmetry (ISSN 2073-8994). This special issue belongs to the section "Chemistry: Symmetry/Asymmetry".

Deadline for manuscript submissions: closed (31 October 2023) | Viewed by 5882

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Prof. Dr. Alexandre Zakharov

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Guest Editor

Saint Petersburg Institute for Machine Sciences, The Russian Academy of Sciences, 199178 Saint Petersburg, Russia
Interests: liquid crystals; nanofluidics; optics of liquid crystals; hydrodynamics of liquid crystals; free-standing smectic films
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Liquid crystal (LC) materials are called curious, soft matter, but their influence on modern technologies is very impressive. The manipulation of tiny amounts of molecular liquids, such as LCs, has become a paradigm in various fields of applied chemistry, physics and biotechnology. The further development of LC applications requires the complex study of natural anisotropic soft materials through multicoupling interactions of internal fields initiated by external forces. Consisting of anisotropic molecules, LC materials interact with external fields and confined surfaces, which strongly influence their structure, optical and hydrodynamic properties. The problem of the externally driven manipulation of LC materials, especially by an externally applied electric field, has led to the development of an increasing number of integrated, small-scale microdevices used in displays, as well as LC sensors (LCSs) and LC actuators (LCAs). These LC materials have initiated a technological revolution in the display field. Widely used flat-panel twisted nematic (TN) displays consist of an LC film sandwiched between two plastic surfaces on a micrometer scale, through which voltage can be applied independently to each pixel of the liquid crystal display (LCD). This applied electric field can change the molecular configuration of the LC layer and thus change the optical characteristics of the LCD display. The advantages of TN include its low voltage requirements and ability to operate over a large wavelength range. With the development of the LC display market, a question concerning the further prospective applications of LC materials is raised. Perhaps there is no direction for LC materials more suitable than their application in LCSs and LCAs. They have various advantages compared other types of microsensors and microactuators, including their simple structure, high shape adaptability, easy downsizing and low driving voltages, due to their extreme sensitivity to external disturbances, and they can thus be used in the construction of stimuli-responsive devices.

We are inviting researchers to submit articles that discuss the structural, optical and hydrodynamic properties of liquid crystal compounds, as well as the applications of these compounds, from theoretical calculations to the study of materials and experimental viewing.

Prof. Dr. Alexandre Zakharov
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. Symmetry 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 2400 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
viscoelastic properties of liquid crystals
optics of liquid crystals
microfluidics

Related Special Issues

Structural, Optical and Hydrodynamic Properties of Liquid Crystals in Symmetry (6 articles)
Structural, Optical and Hydrodynamic Properties of Liquid Crystals in Symmetry (6 articles)

Published Papers (6 papers)

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Research

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36 pages, 6716 KiB

Open AccessFeature PaperArticle

Fluctuating Flexoelectric Membranes in Asymmetric Viscoelastic Media: Power Spectrum through Mechanical Network and Transfer Function Models

Edtson Emilio Herrera-Valencia

and

Alejandro D. Rey

Symmetry 2023, 15(5), 1004; https://doi.org/10.3390/sym15051004 - 29 Apr 2023

Cited by 1 | Viewed by 619

Abstract

Flexoelectric liquid crystalline membranes immersed in asymmetric viscoelastic media is a material system model with physiological applications such as outer hair cells (OHCs), where membrane oscillations generate bulk flow. Motivated by this physiological process, here we extend our previous work by characterizing the force transmission output of our model in addition to viscoelastic fluid flow, since solid–fluid interactions are an essential feature of confined physiological flow and flow in immersed elastic structures. In this work, the rigidity of the confinement results in a passive force reception, while more complete solid–fluid interactions will be considered in the future. A significant contribution of this work is a new asymmetry linear viscoelastic electro-rheological model and the obtained implicit relation between force transmission and flow generation and how this relation is modulated by electric field frequency and the material properties of the device. Maximal force and flow are found at resonant frequencies of asymmetry viscoelastic bulk phases, flexoelectric and dispersion mechanisms through the elastic and Womersley numbers. Full article

(This article belongs to the Special Issue Structural, Optical and Hydrodynamic Properties of Liquid Crystals)

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19 pages, 15696 KiB

Open AccessFeature PaperArticle

Photo-Induced Relief in Rheology of Liquid Crystals

Alexandre V. Zakharov

Sarah Loebner

and

Svetlana Santer

Symmetry 2023, 15(3), 722; https://doi.org/10.3390/sym15030722 - 14 Mar 2023

Cited by 1 | Viewed by 816

Abstract

In this paper, we report the first experimental results on capillary shear flows of a nematic liquid crystal 5CB (4-cyano-4′-pentylbiphenyl), arising due to interaction of the anisotropic liquid, correspondent to the continuous rotational symmetry, with photo-profiled polymer surfaces. The regular surface relief was obtained due to opto-mechanical deformation of azobenzene containing potoresponsive polymer film (PAZO) during irradiation with two-beam interference. Such surface treatment makes it possible to obtain a regular submicron profile with well-defined characteristics (direction, period, and height). The polarizing microscopy (PM) and dynamic light scattering (DLS) techniques were used to determine the direction of the surface orientation of LC and anchoring strength, which characterize the interaction of LC with the photo-profiled polymer surface. Two types of shear flows—spreading of LC droplets and capillary flow in a plane capillary, induced by the interaction of LC with one or two photo-profiled surfaces—were investigated for different directions of the flow relative to the direction of the relief. Strong anisotropy in the dynamics of the precursor film and contact line motion, as well as in the dynamical contact angle, was established. The experimental results were analyzed and compared with those previously obtained at the investigation of the spreading of LC droplets over a mechanically stamped submicron profile and capillary flows in plane capillaries with photo-aligned surfaces. Full article

(This article belongs to the Special Issue Structural, Optical and Hydrodynamic Properties of Liquid Crystals)

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12 pages, 751 KiB

Open AccessArticle

Vortex Dynamics in a Hybrid Aligned Nematic Microvolume with an Orientational Defect

Izabela Śliwa

Pavel V. Maslennikov

and

Alex V. Zakharov

Symmetry 2023, 15(2), 324; https://doi.org/10.3390/sym15020324 - 23 Jan 2023

Viewed by 626

Abstract

The aim of this theoretical paper is to investigate the physical mechanism responsible for the appearance of vortex flow in a hybrid aligned nematic (HAN) microvolume with an orientational defect, excited by a temperature gradient

\nabla T

. This was done in the [...] Read more.

\nabla T

. This was done in the framework of the classical Ericksen-Leslie theory, supplemented by thermomechanical correction of the shear stress and Rayleigh dissipation function, as well as taking into account the entropy balance equation. We have carried out a numerical study of the system of hydrodynamic equations including director reorientation, fluid flow

v

, and the temperature redistribution across the HAN microvolume under the influence of

\nabla T

, when the HAN microvolume is heated from above. Calculations show that, due to the interaction between the gradient of the director field

\nabla \hat{n}

and

\nabla T

, the HAN microvolume settles down to a stationary complex vortex flow regime. Full article

(This article belongs to the Special Issue Structural, Optical and Hydrodynamic Properties of Liquid Crystals)

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27 pages, 5839 KiB

Open AccessFeature PaperArticle

Liquid Crystal-Based Geometric Phase-Enhanced Platform for Polarization and Wavefront Analysis Techniques with the Short-TeraHertz FEL Oscillator TerRa@BriXSinO

Marcello Rossetti Conti

Dario Giove

Verónica Vicuña-Hernández

Can Koral

Maria Rosaria Masullo

and

Symmetry 2023, 15(1), 103; https://doi.org/10.3390/sym15010103 - 30 Dec 2022

Cited by 3 | Viewed by 1355

Abstract

In this work, we propose to design a liquid crystal–based modular and extendable platform of cutting-edge optical technologies for studying materials based on the analysis of polarization and wavefront of light in the wavelength range of 10–50 μm, which is considered to work even in the longer wavelengths range. This platform will be driven by the future THz-FEL source TerRa@BriXSinO that produces high power radiation in THz-range from 6 THz up to 30 THz (Mid-/Far-IR). The lack of optical infrastructures in this range has been tackled by fabricating liquid crystal–based geometric phase components that have been specifically designed for this purpose. This is in order to optimally exploit all the source’s potential for maximum accuracy and efficiency in determining polarization- and wavefront-sensitive properties of materials. We present an overview of a few experiments for characterizing bulk inhomogeneities, dielectric anisotropy, surface roughness, cracks, impact damages, and stress and strain effects with special emphasis on non-destructive tests on composite structures. The tools for wavefront shaping developed within our platform will be exploited to add a further degree of freedom, i.e., orbital angular momentum, to nonlinear optics techniques, such as Terahertz Hyper-Raman spectroscopy, for investigating chiral agents’ properties. Full article

(This article belongs to the Special Issue Structural, Optical and Hydrodynamic Properties of Liquid Crystals)

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14 pages, 13055 KiB

Open AccessFeature PaperArticle

Optical Imaging and Analytical Design of Localized Topological Structures in Chiral Liquid Crystals

and

Symmetry 2022, 14(12), 2476; https://doi.org/10.3390/sym14122476 - 22 Nov 2022

Viewed by 1122

Abstract

We combine numerical modeling and analytical design techniques to study several of the most common localized topological structures in frustrated chiral nematic liquid crystal cells. An energy minimization procedure is applied to the lattice model to simulate the director field distributions. These distributions are also approximated using the suitably designed analytical ansatz. We present both simulated and approximated results for optical polarizing microscopy textures and different visualizations of director field structure such as distributions of the azimuthal director angle and isolines for the normal component of the director in coordinate planes. The ansatz correctly mimicked the geometry and optical properties of the solitonic structures under consideration. Full article

(This article belongs to the Special Issue Structural, Optical and Hydrodynamic Properties of Liquid Crystals)

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Review

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27 pages, 755 KiB

Open AccessReview

Electrically Driven Torsional Distortions in Twisted Nematic Volumes

Izabela Śliwa

Pavel V. Maslennikov

and

Alex V. Zakharov

Symmetry 2022, 14(11), 2365; https://doi.org/10.3390/sym14112365 - 09 Nov 2022

Cited by 1 | Viewed by 714

Abstract

The purpose of this review is to describe the physical mechanism responsible for the appearances of both traveling and non-traveling distortions in a twisted microsized nematic volume under the effect of a large electric field. Both experimental and theoretical works devoted to the excitation of structured periodic domains in initially homogeneously aligned liquid crystal systems under the effects of strong crossed electric and magnetic fields were analyzed. Electrically driven distortions in the microfluidic nematic capillary in the presence of a temperature gradient in it, based on the number of numerical results, were analyzed. We also focus on the description and explanation of the novel mechanism of excitation of the kink- and

π

-like distortion waves of the director field

\hat{n}

in a cylindrical nematic micro-volume under the effect of voltage U and temperature gradient

\nabla T

, set up between the cooler inner and hotter outer cylinders. Electrically driven torsional distortions in twisted nematic micro-volumes in the form of the kink-like running front based on the classical Ericksen–Leslie approach were considered. Full article

(This article belongs to the Special Issue Structural, Optical and Hydrodynamic Properties of Liquid Crystals)

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