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Liquid Crystals 2011
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Liquid Crystals 2011

A special issue of International Journal of Molecular Sciences (ISSN 1422-0067). This special issue belongs to the section "Materials Science".

Deadline for manuscript submissions: closed (30 June 2011) | Viewed by 51939

Special Issue Editor

Prof. Dr. Wolfgang Haase

E-Mail Website
Guest Editor
Eduard-Zintl-Institut für Anorganische und Physikalische Chemie, Technische Universität Darmstadt, Petersenstrasse 20, D-64287 Darmstadt, Germany
Interests: liquid crystals; molecular magnetism; bioinorganic chemistry; nonlinear optics of functonal polymers
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

A Liquid Crystal can be considered as a truly multifunctional material being a thermotropic or lyotropic anisotropic fluid. Applications for Liquid Crystal Displays, for Photonics, for a broad range of Devices and Switchers, even for Analytical Tools or their functionalities in Life Science etc. are based essential on such anisotropic properties. The field of anisotropic properties is very rich, the physics of such anisotropic fluids is a hot topic, their design and chemical realization is still a challenge.
Basically most of the Liquid Crystals consist of All-Organic Compounds, but their existence is not restricted on those. By introducing closed or open shell metals as constitutive element the very interesting field of Metallomesogens opens a lot of pronounced and new properties.
Functionalized Nanomaterials doped in Liquid Crystals as for instance Au, BaTiO3, SWCNTs or MWCNTs lead to Nanocolloids with enhanced or quite new properties allowing nanostructuring.
Contributions to topics addressed above but not necessary limited are desirable.

Prof. Dr. W. Haase
Guest Editor

Keywords

  • anisotropic properties of liquid crystals in a broader sense
  • structural and chemical properties of liquid crystals
  • liquid crystals with special magnetic properties
  • liquid crystalline nanocolloids and LC-nanostructered systems
  • display related properties

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Related Special Issue

Published Papers (6 papers)

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Research

Jump to: Review

20 pages, 671 KB  
Article
Automatic Defect Detection for TFT-LCD Array Process Using Quasiconformal Kernel Support Vector Data Description
by Yi-Hung Liu and Yan-Jen Chen
Int. J. Mol. Sci. 2011, 12(9), 5762-5781; https://doi.org/10.3390/ijms12095762 - 9 Sep 2011
Cited by 17 | Viewed by 10648
Abstract
Defect detection has been considered an efficient way to increase the yield rate of panels in thin film transistor liquid crystal display (TFT-LCD) manufacturing. In this study we focus on the array process since it is the first and key process in TFT-LCD [...] Read more.
Defect detection has been considered an efficient way to increase the yield rate of panels in thin film transistor liquid crystal display (TFT-LCD) manufacturing. In this study we focus on the array process since it is the first and key process in TFT-LCD manufacturing. Various defects occur in the array process, and some of them could cause great damage to the LCD panels. Thus, how to design a method that can robustly detect defects from the images captured from the surface of LCD panels has become crucial. Previously, support vector data description (SVDD) has been successfully applied to LCD defect detection. However, its generalization performance is limited. In this paper, we propose a novel one-class machine learning method, called quasiconformal kernel SVDD (QK-SVDD) to address this issue. The QK-SVDD can significantly improve generalization performance of the traditional SVDD by introducing the quasiconformal transformation into a predefined kernel. Experimental results, carried out on real LCD images provided by an LCD manufacturer in Taiwan, indicate that the proposed QK-SVDD not only obtains a high defect detection rate of 96%, but also greatly improves generalization performance of SVDD. The improvement has shown to be over 30%. In addition, results also show that the QK-SVDD defect detector is able to accomplish the task of defect detection on an LCD image within 60 ms. Full article
(This article belongs to the Special Issue Liquid Crystals 2011)
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23 pages, 2150 KB  
Article
The Langmuir-Blodgett Technique as a Tool for Homeotropic Alignment of Fluorinated Liquid Crystals Mixed with Arachidic Acid
by Anna Modlińska and Danuta Bauman
Int. J. Mol. Sci. 2011, 12(8), 4923-4945; https://doi.org/10.3390/ijms12084923 - 3 Aug 2011
Cited by 25 | Viewed by 9060
Abstract
Some fluoro-substituted liquid crystals mixed with arachidic acid in monolayers formed at air-liquid (Langmuir films) and air-solid substrate (Langmuir-Blodgett films) interfaces were investigated. Molecular organization in Langmuir films was determined on the basis of the analysis of the shape of the surface pressure-mean [...] Read more.
Some fluoro-substituted liquid crystals mixed with arachidic acid in monolayers formed at air-liquid (Langmuir films) and air-solid substrate (Langmuir-Blodgett films) interfaces were investigated. Molecular organization in Langmuir films was determined on the basis of the analysis of the shape of the surface pressure-mean molecular area isotherm and observations made by means of a Brewster angle microscope. It was found that in the compression process the liquid crystal molecules are pushed out towards the top of the first monolayer being in direct contact with the subphase. Langmuir films were transferred onto the quartz substrates at various surface pressures and mono- and multilayered Langmuir-Blodgett films were obtained. The films were characterized using electronic absorption measurements. The conditions for obtaining the homeotropic orientation of the liquid crystal molecules were determined. Full article
(This article belongs to the Special Issue Liquid Crystals 2011)
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16 pages, 1528 KB  
Article
Steady State–Hopf Mode Interactions at the Onset of Electroconvection in the Nematic Liquid Crystal Phase V
by Gyanu Acharya, Gerhard Dangelmayr, James Gleeson and Iuliana Oprea
Int. J. Mol. Sci. 2011, 12(7), 4488-4503; https://doi.org/10.3390/ijms12074488 - 13 Jul 2011
Cited by 3 | Viewed by 7018
Abstract
We report on a new mode interaction found in electroconvection experiments on the nematic liquid crystal mixture Phase V in planar geometry. The mode interaction (codimension two) point occurs at a critical value of the frequency of the driving AC voltage. For frequencies [...] Read more.
We report on a new mode interaction found in electroconvection experiments on the nematic liquid crystal mixture Phase V in planar geometry. The mode interaction (codimension two) point occurs at a critical value of the frequency of the driving AC voltage. For frequencies below this value the primary pattern-forming instability at the onset voltage is an oblique stationary instability involving oblique rolls, and above this value it is an oscillatory instability giving rise to normal traveling rolls (oriented perpendicular to and traveling in the director direction). The transition has been confirmed by measuring the roll angle and the dominant frequency of the time series, as both quantities exhibit a discontinuous jump across zero when the AC frequency is varied near threshold. The globally coupled system of Ginzburg–Landau equations that qualitatively describe this mode interaction is constructed, and the resulting normal form, in which slow spatial variations of the mode amplitudes are ignored, is analyzed. This analysis shows that the Ginzburg–Landau system provides the adequate theoretical description for the experimentally observed phenomenon. The experimentally observed patterns at and higher above the onset allow us to narrow down the range of the parameters in the normal form. Full article
(This article belongs to the Special Issue Liquid Crystals 2011)
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Graphical abstract

12 pages, 910 KB  
Article
Continuous Spatial Tuning of Laser Emissions in a Full Visible Spectral Range
by Mi-Yun Jeong and Jeong Weon Wu
Int. J. Mol. Sci. 2011, 12(3), 2007-2018; https://doi.org/10.3390/ijms12032007 - 21 Mar 2011
Cited by 9 | Viewed by 9078
Abstract
In order to achieve a continuous tuning of laser emission, the authors designed and fabricated three types of cholesteric liquid crystal cells with pitch gradient, a wedge cell with positive slope, a wedge cell with negative slope, and a parallel cell. The length [...] Read more.
In order to achieve a continuous tuning of laser emission, the authors designed and fabricated three types of cholesteric liquid crystal cells with pitch gradient, a wedge cell with positive slope, a wedge cell with negative slope, and a parallel cell. The length of the cholesteric liquid crystal pitch could be elongated up to 10 nm, allowing the lasing behavior of continuous or discontinuous spatial tuning determined by the boundary conditions of the cholesteric liquid crystal cell. In the wedge cell with positive slope, the authors demonstrated a continuous spatial laser tuning in the near full visible spectral range, with a tuning resolution less than 1 nm by pumping with only a single 355 nm laser beam. This continuous tuning behavior is due to the fact that the concentration of pitch gradient matches the fixed helical pitch determined by the cell thickness. This characteristic continuous spatial laser tuning could be confirmed again by pumping with a 532 nm laser beam, over 90 nm in the visible spectral range. The scheme of the spatial laser tuning in the wedge cell bearing a pitch gradient enabled a route to designing small-sized optical devices that allow for a wide tunability of single-mode laser emissions. Full article
(This article belongs to the Special Issue Liquid Crystals 2011)
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Review

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41 pages, 5307 KB  
Review
Review of Crystalline Structures of Some Selected Homologous Series of Rod-Like Molecules Capable of Forming Liquid Crystalline Phases
by Peter Zugenmaier
Int. J. Mol. Sci. 2011, 12(11), 7360-7400; https://doi.org/10.3390/ijms12117360 - 28 Oct 2011
Cited by 7 | Viewed by 7084
Abstract
The crystal structures of four homologous series of rod-like molecules are reviewed, two of which form hydrogen bonds and two with a symmetric chemical constitution. Many of the compounds investigated turn into liquid crystalline phases upon temperature increase. It is of valuable interest [...] Read more.
The crystal structures of four homologous series of rod-like molecules are reviewed, two of which form hydrogen bonds and two with a symmetric chemical constitution. Many of the compounds investigated turn into liquid crystalline phases upon temperature increase. It is of valuable interest to know possible conformations and possible packing arrangements as prerequisites to model liquid crystalline structures. The hydrogen bonds of homologous series of pure 4-(ω-hydroxyalkyloxy)-4′-hydroxybiphenyl (HnHBP, n the alkyloxy tail length) are realized through head to tail arrangements of the hydroxyl groups and crystallize except one compound in chiral space groups without the molecules containing any asymmetric carbon. The hydrogen bonds of the homologous series of 4-substituted benzoic acids with various lengths of the tail provide dimers through strong polar bonding of adjacent carboxyl groups and thus provide the stiff part of a mesogenic unit prerequisite for liquid crystalline phases. The homologous series of dialkanoyloxybiphenyls (BP-n, n = 1, 19), of which nine compounds could be crystallized, show liquid crystalline behavior for longer alkane chain lengths, despite the high mobility of the alkane chain ends already detectable in the crystal phase. A single molecule, half a molecule or two half molecules form the asymmetric unit in a centrosymmetric space group. The homologous series of 1,4-terephthalidene-bis-N-(4′-n-alkylaniline) (TBAA-n) exhibit a large variety of packing arrangements in the crystalline state, with or without relying on the symmetry center within the molecules. Full article
(This article belongs to the Special Issue Liquid Crystals 2011)
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21 pages, 855 KB  
Review
Structure and Dynamics of Reentrant Nematics: Any Open Questions after Almost 40 Years?
by Marco G. Mazza and Martin Schoen
Int. J. Mol. Sci. 2011, 12(8), 5352-5372; https://doi.org/10.3390/ijms12085352 - 22 Aug 2011
Cited by 19 | Viewed by 8386
Abstract
Liquid crystals have attracted enormous interest because of the variety of their phases and richness of their application. The interplay of general physical symmetries and specific molecular features generates a myriad of different phenomena. A surprising behavior of liquid crystals is the reentrancy [...] Read more.
Liquid crystals have attracted enormous interest because of the variety of their phases and richness of their application. The interplay of general physical symmetries and specific molecular features generates a myriad of different phenomena. A surprising behavior of liquid crystals is the reentrancy of phases as temperature, pressure, or concentration are varied. Here, we review the main experimental facts and the different theoretical scenarios that have guided the understanding of bulk reentrant nematics. Recently, some computer simulations of a system confined to nanoscopic scales have found new dynamical features of the reentrant nematic phase. We discuss this prediction in relation with the available experimental evidence on reentrant nematics and with the dynamics of liquids in strongly confined environments. Full article
(This article belongs to the Special Issue Liquid Crystals 2011)
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