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Liquid Crystals
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Liquid Crystals

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 (31 August 2009) | Viewed by 141369

Special Issue Editor

Prof. Dr. Kevin D. Belfield

E-Mail Website
Guest Editor
Department of Chemistry and Environmental Science, College of Science and Liberal Arts, New Jersey Institute of Technology, University Heights, Newark, NJ 07102, USA
Interests: multiphoton absorbing materials; two-photon photochemistry; in vivo and ex vivo two-photon fluorescence bioimaging; magnetic polymeric and sol-gel nanocomposites; site-specific fluorophore labeling; fluorescent-based sensors and bioimaging probes; photodynamic therapy agents; nanostructured functional organic and polymeric materials; two-photon based 3D high density optical data storage
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Since the first reported observation of a liquid crystalline behavior by the Austrian botanist Friedrich Reinitzer in 1888, liquid crystals have attracted immense scientific interest. Scientists have been drawn to the study of liquid crystals by both their unusual mesomorphic properties, being intermediate between the solid, crystalline state and the isotropic liquid phase, and the relative aesthetics attained upon observing the often spectacular mesophases between cross polarizers on an optical microscope. Over the past three to four decades, a number of unique properties exhibited by liquid crystalline materials in response to external stimuli have been exploited in a number of important technologies. For example, ferroelectric liquid crystals have been key components in the digital age, leading a revolution in display technology. Thermotropic liquid crystalline materials continue to find their place in numerous products including the healthcare field. Lyotropic liquid crystalline polymers have propelled the field of high strength, light weight materials for a number of military and civilian applications, including their important contribution in body armor. It is fitting that we have special issues in the Journal of Molecular Sciences and Materials dedicated to this still very intriguing class of materials that promises to continue to be an integral part of emerging technologies.

Prof. Dr. Kevin D. Belfield
Guest Editor

Keywords

  • liquid crystal
  • mesogen
  • mesomorphic
  • thermotropic
  • lyotropic
  • smectic
  • nematic
  • liquid crystalline polymers
  • cholesteric

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Related Special Issue

Published Papers (10 papers)

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Research

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13 pages, 499 KiB  
Article
Orientational Packing of a Confined Discotic Mesogen in the Columnar Phase
by Wenjun Zheng, Ya-Ting Hu, Cheng-Yan Chiang and Chi Wi Ong
Int. J. Mol. Sci. 2010, 11(3), 943-955; https://doi.org/10.3390/ijms11030943 - 8 Mar 2010
Cited by 15 | Viewed by 11919
Abstract
The stacking of discotic molecules (hexakis(alkoxy)diquinoxalino[2,3-a:2’,3’-c]phenazines) in the columnar phase sandwiched between two flat glass substrates has been studied. The surface free energy of the substrates, measured by means of sessile drop technique, is found to have significant influence on the way that [...] Read more.
The stacking of discotic molecules (hexakis(alkoxy)diquinoxalino[2,3-a:2’,3’-c]phenazines) in the columnar phase sandwiched between two flat glass substrates has been studied. The surface free energy of the substrates, measured by means of sessile drop technique, is found to have significant influence on the way that the discotic molecules anchor on the surface, and a steady thermal state of the system is crucial for a homogenous orientation of the discotic columns. On a surface of high free energy, the discotic molecules anchor with their disc-face toward the surface. A decrease in the surface free energy of the substrate causes the discotic columns to tilt away from the normal of the substrate. Full article
(This article belongs to the Special Issue Liquid Crystals)
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17 pages, 598 KiB  
Article
The Effect of Liquid Crystalline Structures on Antiseizure Properties of Aqueous Solutions of Ethoxylated Alcohols
by Marian Wlodzimierz Sulek and Anna Bak
Int. J. Mol. Sci. 2010, 11(1), 189-205; https://doi.org/10.3390/ijms11010189 - 12 Jan 2010
Cited by 14 | Viewed by 13806
Abstract
Aqueous solutions of ethoxylated alcohols which form lyotropic liquid crystals at high concentrations (40–80%) were selected as model lubricating substances. Microscopic studies under polarized light and viscosity measurements were carried out in order to confirm the presence of liquid crystalline structures in the [...] Read more.
Aqueous solutions of ethoxylated alcohols which form lyotropic liquid crystals at high concentrations (40–80%) were selected as model lubricating substances. Microscopic studies under polarized light and viscosity measurements were carried out in order to confirm the presence of liquid crystalline structures in the case of alcohol solutions with ethoxylation degrees of 3, 5, 7 and 10. Microscopic images and viscosity coefficient values characteristic of various mesophases were obtained. As expected, the viscosity of LLCs decreases considerably with an increase in shearing rate which is characteristic of liquid crystals being non-Newtonian liquids. Antiseizure properties were determined by means of a four-ball machine (T-02 Tester) and characterized by scuffing load (Pt), seizure load (Poz) and limiting pressure of seizure (poz). Alcohol ethoxylates forming mesophases in aqueous solutions have the strongest effect on the Pt values which are several times higher than those measured in the presence of water. Ethoxylates with higher degrees of ethoxylation exhibit higher values of scuffing load. Those changes have been interpreted as a result of higher cloud points at which those compounds lose their amphiphilic properties. In general, the presence of mesophases in the bulk phase and particularly in the surface phase may lead to the formation of a lubricant film which separates the frictionally cooperating elements of a friction pair. The antiseizure efficiency of alcohol solutions is highest up to the load value which does not exceed the scuffing load value. Full article
(This article belongs to the Special Issue Liquid Crystals)
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23 pages, 1037 KiB  
Article
Dendronized Polyimides Bearing Long-Chain Alkyl Groups and Their Application for Vertically Aligned Nematic Liquid Crystal Displays
by Yusuke Tsuda, Jae Min OH and Renpei Kuwahara
Int. J. Mol. Sci. 2009, 10(11), 5031-5053; https://doi.org/10.3390/ijms10115031 - 19 Nov 2009
Cited by 24 | Viewed by 15253
Abstract
Polyimides having dendritic side chains were investigated. The terphenylene diamine monomer having a first-generation monodendron, 3,4,5-tris(n-dodecyloxy)-benzoate and the monomer having a second-generation monodendron, 3,4,5-tris[-3’,4’,5’-tri(n-dodecyloxy)benzyloxy]benzoate were successfully synthesized and the corresponding soluble dendritic polyimides were obtained by polycondensation with conventional [...] Read more.
Polyimides having dendritic side chains were investigated. The terphenylene diamine monomer having a first-generation monodendron, 3,4,5-tris(n-dodecyloxy)-benzoate and the monomer having a second-generation monodendron, 3,4,5-tris[-3’,4’,5’-tri(n-dodecyloxy)benzyloxy]benzoate were successfully synthesized and the corresponding soluble dendritic polyimides were obtained by polycondensation with conventional tetracarboxylic dianhydride monomers such as benzophenone tertracarboxylic dianhydride (BTDA). The two-step polymerizations in NMP that is a general method for the synthesis of soluble polyimides is difficult; however, the expected dendritic polyimides can be obtained in aromatic polar solvents such as m-cresol and pyridine. The solubility of these dendoronized polyimides is characteristic; soluble in common organic solvents such as dichloromethane, chloroform, toluene and THF. These dendronized polyimides exhibited high glass transition temperatures and good thermal stability in both air and under nitrogen. Their application as alignment layers for LCDs was investigated, and it was found that these polyimides having dendritic side chains were applicable for the vertically aligned nematic liquid crystal displays (VAN-LCDs). Full article
(This article belongs to the Special Issue Liquid Crystals)
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17 pages, 3900 KiB  
Article
Synthesis, Characterization and Texture Observations of Calamitic Liquid Crystalline Compounds
by Maher A. Qaddoura and Kevin D. Belfield
Int. J. Mol. Sci. 2009, 10(11), 4772-4788; https://doi.org/10.3390/ijms10114772 - 4 Nov 2009
Cited by 14 | Viewed by 12270
Abstract
Several divinylic mesogenic monomers were synthesized based on coupling the monomer 4-(4-pentenyloxy)benzoic acid with chlorohydroquinone, 2,5-dihydroxyacetophenone, methylhydroquinone or 2-methoxyhydroquinone. This resulted in novel mesogens of phenylene esters with different lateral substituent groups. The effect of the lateral substituent group on the thermotropic phase [...] Read more.
Several divinylic mesogenic monomers were synthesized based on coupling the monomer 4-(4-pentenyloxy)benzoic acid with chlorohydroquinone, 2,5-dihydroxyacetophenone, methylhydroquinone or 2-methoxyhydroquinone. This resulted in novel mesogens of phenylene esters with different lateral substituent groups. The effect of the lateral substituent group on the thermotropic phase behavior for these liquid crystalline compounds was investigated using DSC and optical polarized microscopy. All the mesogens proved to have a wide nematic liquid crystalline range. Only the phenylene ester, which has a methoxy lateral substituent, exhibited both nematic and smectic phases. Structural confirmation of all new derivatives was accomplished by 1H- and 13C-NMR spectroscopic analysis, along with CH elemental analysis. Full article
(This article belongs to the Special Issue Liquid Crystals)
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18 pages, 1285 KiB  
Article
Time-Resolved Soft X-ray Diffraction Reveals Transient Structural Distortions of Ternary Liquid Crystals
by Wilson Quevedo, Christian Peth, Gerhard Busse, Mirko Scholz, Klaus Mann and Simone Techert
Int. J. Mol. Sci. 2009, 10(11), 4754-4771; https://doi.org/10.3390/ijms10114754 - 4 Nov 2009
Cited by 5 | Viewed by 13727
Abstract
Home-based soft X-ray time-resolved scattering experiments with nanosecond time resolution (10 ns) and nanometer spatial resolution were carried out at a table top soft X-ray plasma source (2.2–5.2 nm). The investigated system was the lyotropic liquid crystal C16E7/paraffin/glycerol/formamide/IR 5. [...] Read more.
Home-based soft X-ray time-resolved scattering experiments with nanosecond time resolution (10 ns) and nanometer spatial resolution were carried out at a table top soft X-ray plasma source (2.2–5.2 nm). The investigated system was the lyotropic liquid crystal C16E7/paraffin/glycerol/formamide/IR 5. Usually, major changes in physical, chemical, and/or optical properties of the sample occur as a result of structural changes and shrinking morphology. Here, these effects occur as a consequence of the energy absorption in the sample upon optical laser excitation in the IR regime. The liquid crystal shows changes in the structural response within few hundred nanoseconds showing a time decay of 182 ns. A decrease of the Bragg peak diffracted intensity of 30% and a coherent macroscopic movement of the Bragg reflection are found as a response to the optical pump. The Bragg reflection movement is established to be isotropic and diffusion controlled (1 μs). Structural processes are analyzed in the Patterson analysis framework of the time-varying diffraction peaks revealing that the inter-lamellar distance increases by 2.7 Å resulting in an elongation of the coherently expanding lamella crystallite. The present studies emphasize the possibility of applying TR-SXRD techniques for studying the mechanical dynamics of nanosystems. Full article
(This article belongs to the Special Issue Liquid Crystals)
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Graphical abstract

17 pages, 1483 KiB  
Article
In-TFT-Array-Process Micro Defect Inspection Using Nonlinear Principal Component Analysis
by Yi-Hung Liu, Chi-Kai Wang, Yung Ting, Wei-Zhi Lin, Zhi-Hao Kang, Ching-Shun Chen and Jih-Shang Hwang
Int. J. Mol. Sci. 2009, 10(10), 4498-4514; https://doi.org/10.3390/ijms10104498 - 22 Oct 2009
Cited by 14 | Viewed by 15777
Abstract
Defect inspection plays a critical role in thin film transistor liquid crystal display (TFT-LCD) manufacture, and has received much attention in the field of automatic optical inspection (AOI). Previously, most focus was put on the problems of macro-scale Mura-defect detection in cell process, [...] Read more.
Defect inspection plays a critical role in thin film transistor liquid crystal display (TFT-LCD) manufacture, and has received much attention in the field of automatic optical inspection (AOI). Previously, most focus was put on the problems of macro-scale Mura-defect detection in cell process, but it has recently been found that the defects which substantially influence the yield rate of LCD panels are actually those in the TFT array process, which is the first process in TFT-LCD manufacturing. Defect inspection in TFT array process is therefore considered a difficult task. This paper presents a novel inspection scheme based on kernel principal component analysis (KPCA) algorithm, which is a nonlinear version of the well-known PCA algorithm. The inspection scheme can not only detect the defects from the images captured from the surface of LCD panels, but also recognize the types of the detected defects automatically. Results, based on real images provided by a LCD manufacturer in Taiwan, indicate that the KPCA-based defect inspection scheme is able to achieve a defect detection rate of over 99% and a high defect classification rate of over 96% when the imbalanced support vector machine (ISVM) with 2-norm soft margin is employed as the classifier. More importantly, the inspection time is less than 1 s per input image. Full article
(This article belongs to the Special Issue Liquid Crystals)
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Review

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16 pages, 451 KiB  
Review
Application of Δ- and Λ-Isomerism of Octahedral Metal Complexes for Inducing Chiral Nematic Phases
by Hisako Sato and Akihiko Yamagishi
Int. J. Mol. Sci. 2009, 10(10), 4559-4574; https://doi.org/10.3390/ijms10104559 - 23 Oct 2009
Cited by 16 | Viewed by 13475
Abstract
The Δ- and Λ-isomerism of octahedral metal complexes is employed as a source of chirality for inducing chiral nematic phases. By applying a wide range of chiral metal complexes as a dopant, it has been found that tris(β-diketonato)metal(III) complexes exhibit an extremely high [...] Read more.
The Δ- and Λ-isomerism of octahedral metal complexes is employed as a source of chirality for inducing chiral nematic phases. By applying a wide range of chiral metal complexes as a dopant, it has been found that tris(β-diketonato)metal(III) complexes exhibit an extremely high value of helical twisting power. The mechanism of induction of the chiral nematic phase is postulated on the basis of a surface chirality model. The strategy for designing an efficient dopant is described, together with the results using a number of examples of Co(III), Cr(III) and Ru(III) complexes with C2 symmetry. The development of photo-responsive dopants to achieve the photo-induced structural change of liquid crystal by use of photo-isomerization of chiral metal complexes is also described. Full article
(This article belongs to the Special Issue Liquid Crystals)
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14 pages, 159 KiB  
Review
Liquid Crystals in Tribology
by Francisco-José Carrión, Ginés Martínez-Nicolás, Patricia Iglesias, José Sanes and María-Dolores Bermúdez
Int. J. Mol. Sci. 2009, 10(9), 4102-4115; https://doi.org/10.3390/ijms10094102 - 18 Sep 2009
Cited by 83 | Viewed by 16874
Abstract
Two decades ago, the literature dealing with the possible applications of low molar mass liquid crystals, also called monomer liquid crystals (MLCs), only included about 50 references. Today, thousands of papers, conference reports, books or book chapters and patents refer to the study [...] Read more.
Two decades ago, the literature dealing with the possible applications of low molar mass liquid crystals, also called monomer liquid crystals (MLCs), only included about 50 references. Today, thousands of papers, conference reports, books or book chapters and patents refer to the study and applications of MLCs as lubricants and lubricant additives and efforts are made to develop new commercial applications. The development of more efficient lubricants is of paramount technological and economic relevance as it is estimated that half the energy consumption is dissipated as friction. MLCs have shown their ability to form ordered boundary layers with good load-carrying capacity and to lower the friction coefficients, wear rates and contact temperature of sliding surfaces, thus contributing to increase the components service life and to save energy. This review includes the use of MLCs in lubrication, and dispersions of MLCs in conventional polymers (PDMLCs). Finally, new lubricating system composed of MLC blends with surfactants, ionic liquids or nanophases are considered. Full article
(This article belongs to the Special Issue Liquid Crystals)
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24 pages, 1235 KiB  
Review
Experimental and Computational Characterization of Biological Liquid Crystals: A Review of Single-Molecule Bioassays
by Kilho Eom, Jaemoon Yang, Jinsung Park, Gwonchan Yoon, Young Soo Sohn, Shinsuk Park, Dae Sung Yoon, Sungsoo Na and Taeyun Kwon
Int. J. Mol. Sci. 2009, 10(9), 4009-4032; https://doi.org/10.3390/ijms10094009 - 10 Sep 2009
Cited by 14 | Viewed by 13559
Abstract
Quantitative understanding of the mechanical behavior of biological liquid crystals such as proteins is essential for gaining insight into their biological functions, since some proteins perform notable mechanical functions. Recently, single-molecule experiments have allowed not only the quantitative characterization of the mechanical behavior [...] Read more.
Quantitative understanding of the mechanical behavior of biological liquid crystals such as proteins is essential for gaining insight into their biological functions, since some proteins perform notable mechanical functions. Recently, single-molecule experiments have allowed not only the quantitative characterization of the mechanical behavior of proteins such as protein unfolding mechanics, but also the exploration of the free energy landscape for protein folding. In this work, we have reviewed the current state-of-art in single-molecule bioassays that enable quantitative studies on protein unfolding mechanics and/or various molecular interactions. Specifically, single-molecule pulling experiments based on atomic force microscopy (AFM) have been overviewed. In addition, the computational simulations on single-molecule pulling experiments have been reviewed. We have also reviewed the AFM cantilever-based bioassay that provides insight into various molecular interactions. Our review highlights the AFM-based single-molecule bioassay for quantitative characterization of biological liquid crystals such as proteins. Full article
(This article belongs to the Special Issue Liquid Crystals)
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38 pages, 865 KiB  
Review
The Influence of Disorder on Thermotropic Nematic Liquid Crystals Phase Behavior
by Vlad Popa-Nita, Ivan Gerlič and Samo Kralj
Int. J. Mol. Sci. 2009, 10(9), 3971-4008; https://doi.org/10.3390/ijms10093971 - 10 Sep 2009
Cited by 23 | Viewed by 13779
Abstract
We review the theoretical research on the influence of disorder on structure and phase behavior of condensed matter system exhibiting continuous symmetry breaking focusing on liquid crystal phase transitions. We discuss the main properties of liquid crystals as adequate systems in which several [...] Read more.
We review the theoretical research on the influence of disorder on structure and phase behavior of condensed matter system exhibiting continuous symmetry breaking focusing on liquid crystal phase transitions. We discuss the main properties of liquid crystals as adequate systems in which several open questions with respect to the impact of disorder on universal phase and structural behavior could be explored. Main advantages of liquid crystalline materials and different experimental realizations of random field-type disorder imposed on liquid crystal phases are described. Full article
(This article belongs to the Special Issue Liquid Crystals)
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