scholarly journals Mesomorphic and Thermal Behavior of Symmetric Bent-Core Liquid Crystal Compounds Derived from Resorcinol and Isophthalic Acid

Crystals ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 1215
Author(s):  
Catalina Ionica Ciobanu ◽  
Iulian Berladean ◽  
Elena-Luiza Epure ◽  
Aurel Simion ◽  
Gabriela Lisa ◽  
...  
Keyword(s):  
Liquid Crystalline ◽  
Polarized Light ◽  
Isophthalic Acid ◽  
Theoretical Explanation ◽  
The Core ◽  
Disubstituted Benzene ◽  
Molecular Modeling Studies ◽  
Thermogravimetric Studies ◽  
The Difference ◽  
Nematic Phases

Bent-core liquid crystals (BCLC) have been widely studied as a result of their unusual polar and chiral properties. Similar to calamitic and discotic molecules, BCLC molecules also exhibit nematic phases, besides other higher order mesophases. The aim of this work is to comparatively analyze the mesomorphic behavior of some bent-core 1,3-disubstituted benzene core compounds derived from resorcinol and isophthalic acid. Thus, the two classes of compounds differ in the nature of the orientation of the ester bond between the benzene central core and the two branches attached to the core. The mesomorphic behavior was elucidated by polarized light optical microscopy and differential calorimetry. Given the relatively high isotropic points of the compounds, confirmation of the thermal stability in the domains manifesting liquid crystalline properties was performed by thermogravimetric studies. The theoretical explanation of the difference in mesomorphic behavior for the two classes was based on molecular modeling studies.

scholarly journals A Review on Synthesis, Properties, of Liquid Crystal Dendrimers

2021 ◽  
Vol 24 (4) ◽  
pp. 15-25
Author(s):  
Zinah H. Aliand ◽  
◽  
Nasreen R. Jber ◽  
Keyword(s):  
Liquid Crystalline ◽  
Chemical Nature ◽  
Molecular Design ◽  
Supramolecular Organization ◽  
Branching Pattern ◽  
The Core ◽  
Dendritic Core ◽  
Synthesis Properties ◽  
Nematic Phases ◽  
Liquid Crystalline Dendrimers

This review provides brief information concerning with the dendrimer. The supramolecular organization of selected examples of liquid-crystalline dendrimers within lamellar, columnar and nematic phases is reported. It is shown that tuning of the mesomorphic structure can be achieved by an appropriate molecular design depending upon the chemical nature of the terminal mesogenic groups, dendritic core and dendrimer generation. The pseudospherical shape of a dendrimer arises from its structure, which consists of an internal region (the core) which is connected to repeating units constituting a radial branching pattern.

Liquid Crystalline Compounds in the Thiophene Series, Part 11+ Liquid Crystalline Thiophene Carboxylic Esters

1995 ◽  
Vol 50 (8) ◽  
pp. 1265-1274 ◽  
Author(s):  
Gerhard Koßmehl ◽  
Barbara Hirsch
Keyword(s):  
Liquid Crystalline ◽  
Polarized Light ◽  
Scanning Calorimetry ◽  
Crystalline Phases ◽  
H Nmr ◽  
Smectic Phases ◽  
Liquid Crystalline Phases ◽  
Nematic Phases ◽  
Optical Textures ◽  
Carboxylic Esters

The new series of ten 4,4'-bis(5-alkyl-2-thienylcarbonyloxy)azobenzenes (2a -2j) and ten 2,5-bis(5-alkyl-2-thienylcarbonyloxy)toluenes (3a -3j) were prepared. These, as yet unknown esters were characterized in relation to their structures by elemental analyses, IR, UV, 1H NMR spectra and MS. The azobenzene-esters 2a -2j which form liquid crystalline phases were studied by microscopy under polarized light and DSC (differential scanning calorimetry). Through the observation of the optical textures nematic phases were monitored. Only 2j has an additional smectic phase; 2h and 2i form monotropic smectic phases during cooling. The toluene-esters 3a -3j do not form liquid crystalline phases.

Origin of the Difference in Phase Transition Behavior between TwoType of All-Organic Radical Liquid Crystals

2008 ◽  
Vol 55 ◽  
pp. 42-45
Author(s):  
Yoshiaki Uchida ◽  
Rui Tamura ◽  
Naohiko Ikuma ◽  
Satoshi Shimono ◽  
Hiroki Takahashi ◽  
...  
Keyword(s):  
Molecular Structure ◽  
Phase Transition ◽  
Liquid Crystalline ◽  
Crystallographic Analysis ◽  
Side Chain ◽  
Organic Radical ◽  
Phase Transition Behavior ◽  
X Ray ◽  
The Core ◽  
The Difference

We have synthesized two types of all-organic radical liquid crystalline (LC) compounds, trans-2-alkoxyphenyl-5-[4-(4-alkoxybenzenecarbonyloxy)phenyl]-2,5-dimethylpyrrolidine-1-oxy (1) and 4-alkoxyphenyl trans-4-[5-(4-alkoxyphenyl)-2,5-dimethylpyrrolidine-1-oxy-2-yl]benzoate (2) and have fully characterized their LC properties. Although the only difference in the molecular structure between 1 and 2 is the orientation of a binding group connecting the core portion and one side-chain (-OCO- and -COO- for 1 and 2), the racemic or enantiomerically enriched 2 showed an SmA phase, or SmA* and TGBA* phases, which were not observed for 1, besides N and SmC, or N* and SmC* phases, respectively. Here we discuss the origin of these differences on the basis of their crystal structures determined by X-ray crystallographic analysis.

On resolving fine periodic microstructures in the optical microscope

1989 ◽  
Vol 47 ◽  
pp. 364-365
Author(s):  
W.S. Putnam ◽  
C. Viney
Keyword(s):  
Liquid Crystalline ◽  
Numerical Aperture ◽  
Polarized Light ◽  
Normal Incidence ◽  
Optical Microscope ◽  
Angle Of Incidence ◽  
Resolution Limit ◽  
Crystalline Materials ◽  
Periodic Microstructures ◽  
Liquid Crystalline Materials

Many sheared liquid crystalline materials (fibers, films and moldings) exhibit a fine banded microstructure when observed in the polarized light microscope. In some cases, for example Kevlar® fiber, the periodicity is close to the resolution limit of even the highest numerical aperture objectives. The periodic microstructure reflects a non-uniform alignment of the constituent molecules, and consequently is an indication that the mechanical properties will be less than optimal. Thus it is necessary to obtain quality micrographs for characterization, which in turn requires that fine detail should contribute significantly to image formation.It is textbook knowledge that the resolution achievable with a given microscope objective (numerical aperture NA) and a given wavelength of light (λ) increases as the angle of incidence of light at the specimen surface is increased. Stated in terms of the Abbe resolution criterion, resolution improves from λ/NA to λ/2NA with increasing departure from normal incidence.

Liquid Crystal Trimers Incorporating Saturated Isosteres of Benzene and Exhibiting Modulated Nematic Phases

2019 ◽  
Author(s):  
Adam Al-Janabi ◽  
Richard Mandle
Keyword(s):  
Liquid Crystal ◽  
Helical Structure ◽  
Molecular Shape ◽  
Saturated Hydrocarbons ◽  
Fluid System ◽  
Structural Requirement ◽  
Disubstituted Benzene ◽  
Bona Fide ◽  
Nematic Phases ◽  
Bend Angles

<p>The nematic twist-bend (N<sub>TB</sub>) liquid crystal phase possesses a local helical structure with a pitch length of a few nanometres and is the first example of spontaneous symmetry breaking in a fluid system. All known examples of the N­<sub>TB­</sub> phase occur in materials whose constituent mesogenic units are aromatic hydrocarbons. It is not clear if this is due to synthetic convenience or a <i>bona fide</i> structural requirement for a material to exhibit this phase of matter. In this work we demonstrate that materials consisting largely of saturated hydrocarbons could also give rise to this mesophase. Furthermore, replacement of 1,4-disubstituted benzene with <i>trans</i> 1,4-cyclohexane or even 1,4-cubane does not especially alter the transition temperatures of the resulting material nor does it appear to impact upon the heliconical tilt angle, suggesting the local structure of the phase is unperturbed. Calculating the probability distribution of bend angles reveals that the choice of isosteric group has little impact on the overall molecular shape, demonstrating the shape-driven nature of the N<sub>TB</sub> phase. </p>

scholarly journals Hexakis(terthiophenylthio)benzene as a Mew Class Liquid Crystalline Molecule

1999 ◽  
Vol 23 (10) ◽  
pp. 596-597
Author(s):  
Shinobu Inoue ◽  
Shoji Nishiguchi ◽  
Satoshi Murakami ◽  
Yoshio Aso ◽  
Tetsuo Otsubo ◽  
...  
Keyword(s):  
Liquid Crystalline ◽  
Smectic A ◽  
Smectic C ◽  
Nematic Phases

A disk-like molecule, in which six α-linked terthiophenes are connected to a central benzene core via a thioether linkage, shows a sequence of calamitic liquid crystalline mesomorphism involving smectic C, smectic A and nematic phases.

Spatial Convergence in Height in Central Europe, 1890-1910

2009 ◽  
pp. 90
Author(s):  
Marek Brabec ◽  
John Komlos
Keyword(s):  
Global Economy ◽  
Well Being ◽  
Habsburg Monarchy ◽  
The Core ◽  
Military Recruits ◽  
Convergence Clubs ◽  
Spatial Convergence ◽  
Physical Stature ◽  
The Difference ◽  
Peripheral Areas

We examine spatial convergence in biological well-being in the Habsburg Monarchy, circa 1890-1910, on the basis of evidence of the physical stature of 21-year-old military recruits, disaggregated into 15 Districts. We find that the shorter the population in 1890, the faster its height grew thereafter. Hence, there was convergence in physical stature between the peripheral areas of the monarchy (located in today’s Poland/Ukraine, Romania, and Slovakia) and its core (located in today’s Austria, Czech Republic, and Hungary). The difference in trends between the trend in height in the Polish District of Przemysl and in Vienna was about 0.9 cm per decade, in favor of the former. Convergence among the core Districts themselves was minimal or non-existent, whereas the convergence among the peripheral Districts was more pronounced. Spatial convergence also took place between the peripheral regions and the more developed ones. The pattern is somewhat reminiscent of modern findings on convergence clubs in the global economy.

Gebruiksaspecten van het uitroeppartikel wat in het Nederlands en Fries

2020 ◽  
Vol 136 (4) ◽  
pp. 189-209
Author(s):  
Henk Wolf
Keyword(s):  
The Core ◽  
The Difference ◽  
Lexical Phrase ◽  
High Degree ◽  
Lexical Phrases

Abstract Both Dutch and (West) Frisian make use of the exclamative particle wat (‘how’), that adds an element of surprise about a high degree of something to the semantics of the sentence. In this paper I will first show the similarities between the use of the particle in the two languages. I will demonstrate that, in Dutch, its use is largely confined to constructions that are semantically scalable, whereas in Frisian this restriction is far less strict. I will explain the difference by showing that Dutch wat is a syntactic amplifier of lexical phrases, whereas Frisian wat has developed into a pragmatic amplifier of the core predicate. I will try to account for that difference by showing how homophonous words absent in Dutch are likely to have influenced the use of Frisian wat, and how Dutch prosody strengthens the connection between wat and the amplified lexical phrase, whereas Frisian prosody weakens it. Finally, I will show that the system described as ‘Frisian’ is occasionally found in varieties of Dutch too

scholarly journals Synthesis and mesomorphic properties of calamitic malonates and cyanoacetates tethered to 4-cyanobiphenyls

2012 ◽  
Vol 8 ◽  
pp. 371-378 ◽  
Author(s):  
Katharina C Kress ◽  
Martin Kaller ◽  
Kirill V Axenov ◽  
Stefan Tussetschläger ◽  
Sabine Laschat
Keyword(s):  
Differential Scanning Calorimetry ◽  
Ambient Temperature ◽  
Liquid Crystalline ◽  
X Ray Diffraction ◽  
Cyanoacetic Acid ◽  
Scanning Calorimetry ◽  
Isotropic Liquid ◽  
X Ray ◽  
Nematic Phases ◽  
Mesomorphic Properties

4-Cyano-1,1'-biphenyl derivatives bearing ω-hydroxyalkyl substituents were reacted with methyl 3-chloro-3-oxopropionate or cyanoacetic acid, giving liquid-crystalline linear malonates and cyanoacetates. These compounds formed monotropic nematic phases at 62 °C down to ambient temperature upon cooling from the isotropic liquid. The mesomorphic properties were investigated by differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction (WAXS).

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