RECENT DEVELOPMENTS IN NEMATOGENIC BENT-CORE MESOGENS: AN X-RAY DIFFRACTION PERSPECTIVE

2011 ◽  
Vol 20 (04) ◽  
pp. 485-499 ◽  
Author(s):  
FRANCESCO VITA ◽  
IMMACOLATA F. PLACENTINO ◽  
ORIANO FRANCESCANGELI
Keyword(s):  
Small Angle ◽  
Nematic Phase ◽  
Short Range ◽  
X Ray Diffraction ◽  
X Ray ◽  
Recent Developments ◽  
Diffraction Signal

Bent-core mesogens are attracting great attention because of their potentially biaxial and polar nematic phase. In this paper, we review the results of our recent X-ray diffraction studies on the nematic phase of oxadiazole-based mesogens. The evolution of the small-angle diffraction signal with temperature points to the existence of nano-sized cybotactic clusters, characterized by short-range smectic-like fluctuations. However, in contrast to classical cybotaxis of calamitic nematics, these fluctuations do not have a pretransitional nature. They explain most of the extraordinary properties of bent-core mesogens and, in particular, are responsible for the unique ferroelectric response exhibited by one of our compounds.

Small-angle x-ray diffraction study of mixtures showing re-entrant nematic phase and induced smectic Ad phase

1998 ◽  
Author(s):  
S. K. Giri ◽  
N. K. Pradham ◽  
R. Paul ◽  
S. Paul ◽  
P. Mandal ◽  
...  
Keyword(s):  
Diffraction Study ◽  
Small Angle ◽  
Nematic Phase ◽  
X Ray Diffraction ◽  
X Ray ◽  
Smectic A

scholarly journals Comparative 2H NMR and X-Ray Diffraction Investigation of a Bent-Core Liquid Crystal Showing a Nematic Phase

Crystals ◽  
2020 ◽  
Vol 10 (4) ◽  
pp. 284
Author(s):  
Maria Ghilardi ◽  
Fabrizio C. Adamo ◽  
Francesco Vita ◽  
Oriano Francescangeli ◽  
Valentina Domenici
Keyword(s):  
Low Temperatures ◽  
Nematic Phase ◽  
Short Range ◽  
Orientational Order ◽  
Bend Angle ◽  
2H Nmr ◽  
X Ray Diffraction ◽  
Complementary Information ◽  
X Ray ◽  
2H Nmr Spectroscopy

Bent-core liquid crystals showing a nematic phase stable at low temperatures are very attractive for applicative purposes in view of the inherent biaxial nature of the nematic phase. In this work, a typical five-ring bent-core mesogen was investigated by means of 2H NMR spectroscopy and X-ray diffraction (XRD) methods. These techniques provide complementary information on the structural properties of the nematic phase and the average mesogen conformation: small-angle XRD reveals the presence of short-range positional order in the form of skewed cybotaxis, while a comparison of the orientational order parameters measured by wide-angle XRD and NMR provides an estimate of the molecule bend angle. In addition, 2H NMR puts in evidence the occurrence of an unexpected transition to a low-temperature tilted phase, having a crystalline or smectic-like character. The results were compared with those of previous 13C NMR investigations.

Cybotaxis dominates the nematic phase of bent-core mesogens: a small-angle diffuse X-ray diffraction study

Soft Matter ◽  
2011 ◽  
Vol 7 (3) ◽  
pp. 895-901 ◽  
Author(s):  
Oriano Francescangeli ◽  
Francesco Vita ◽  
Claudio Ferrero ◽  
Theo Dingemans ◽  
Edward T. Samulski
Keyword(s):  
Diffraction Study ◽  
Small Angle ◽  
Nematic Phase ◽  
X Ray Diffraction ◽  
X Ray

Nachweis von Inhomogenitäten bzw. Konzentrationsfluktuationen in Schmelzen des Systems Al-In mittels Röntgen-Kleinwinkelstreuung

1975 ◽  
Vol 30 (6-7) ◽  
pp. 775-783
Author(s):  
Jochen Hoehler ◽  
Siegfried Steeb
Keyword(s):  
Correlation Length ◽  
Small Angle ◽  
Short Range ◽  
Short Range Order ◽  
Volume Concentration ◽  
Total Concentration ◽  
Concentration Fluctuations ◽  
The Other ◽  
X Ray Diffraction ◽  
X Ray

Abstract By means of small angle X-ray diffraction work it was revealed that ball-shaped segregated regions with diameters of 8 up to 10 Å exist in molten Al-In alloys. Interpretation of segregated regions as originated by concentration fluctuations shows, according to the method of Ornstein-Zernike, that the correlation length is approximately 3 Å. According to the method of modulation of monotonic Laue scattering, positive values between 0.04 and 0.2 for the coefficient of short range order were obtained. Apparently the melts consist of a matrix with statistical distribution of the atoms of both kinds together with two kinds of ball-shaped segregated regions, one kind containing only Aluminium-, the other only Indium-atoms. A plot showing the variation of volume concentration wAIT of Aluminium regions versus total concentration wT of regions of any kind is given: wT may reach from 0.2 up to 30 vol.-%.

Small-angle X-ray diffraction investigation of twinned opal-like structures

2012 ◽  
Vol 54 (10) ◽  
pp. 2073-2082 ◽  
Author(s):  
A. K. Samusev ◽  
I. S. Sinev ◽  
K. B. Samusev ◽  
M. V. Rybin ◽  
A. A. Mistonov ◽  
...  
Keyword(s):  
Small Angle ◽  
X Ray Diffraction ◽  
X Ray

Time-resolved isothermal crystallization of absorbable PGA-co-PLA copolymer by synchrotron small-angle X-ray scattering and wide-angle X-ray diffraction

Polymer ◽  
2001 ◽  
Vol 42 (21) ◽  
pp. 8965-8973 ◽  
Author(s):  
Zhi-Gang Wang ◽  
Xuehui Wang ◽  
Benjamin S. Hsiao ◽  
Saša Andjelić ◽  
Dennis Jamiolkowski ◽  
...  
Keyword(s):  
Small Angle ◽  
Isothermal Crystallization ◽  
Wide Angle ◽  
X Ray Diffraction ◽  
Time Resolved ◽  
X Ray ◽  
X Ray Scattering ◽  
Ray Scattering

Short-range order in some alloys of the Ge-As-Te semiconducting glassy system by X-ray diffraction

1987 ◽  
Vol 22 (12) ◽  
pp. 4357-4361 ◽  
Author(s):  
R. A. Ligero ◽  
J. Vázquez ◽  
P. Villares ◽  
R. Jimńez-Garay
Keyword(s):  
Short Range ◽  
Short Range Order ◽  
Range Order ◽  
X Ray Diffraction ◽  
Glassy System ◽  
X Ray

A high-throughput assembly of beam-shaping channel-cut monochromators for laboratory high-resolution X-ray diffraction and small-angle X-ray scattering experiments

2021 ◽  
Vol 54 (3) ◽  
Author(s):  
Peter Nadazdy ◽  
Jakub Hagara ◽  
Petr Mikulik ◽  
Zdenko Zaprazny ◽  
Dusan Korytar ◽  
...  
Keyword(s):  
High Resolution ◽  
Small Angle ◽  
Photon Flux ◽  
Photon Flux Density ◽  
X Ray Diffraction ◽  
High Beam ◽  
X Ray ◽  
X Ray Scattering ◽  
Beam Collimation ◽  
Ray Scattering

A four-bounce monochromator assembly composed of Ge(111) and Ge(220) monolithic channel-cut monochromators with V-shaped channels in a quasi-dispersive configuration is presented. The assembly provides an optimal design in terms of the highest transmittance and photon flux density per detector pixel while maintaining high beam collimation. A monochromator assembly optimized for the highest recorded intensity per detector pixel of a linear detector placed 2.5 m behind the assembly was realized and tested by high-resolution X-ray diffraction and small-angle X-ray scattering measurements using a microfocus X-ray source. Conventional symmetric and asymmetric Ge(220) Bartels monochromators were similarly tested and the results were compared. The new assembly provides a transmittance that is an order of magnitude higher and 2.5 times higher than those provided by the symmetric and asymmetric Bartels monochromators, respectively, while the output beam divergence is twice that of the asymmetric Bartels monochromator. These results demonstrate the advantage of the proposed monochromator assembly in cases where the resolution can be partially sacrificed in favour of higher transmittance while still maintaining high beam collimation. Weakly scattering samples such as nanostructures are an example. A general advantage of the new monochromator is a significant reduction in the exposure time required to collect usable experimental data. A comparison of the theoretical and experimental results also reveals the current limitations of the technology of polishing hard-to-reach surfaces in X-ray crystal optics.

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