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Haege C, Jagiella S, Giesselmann F. Molecular Electron Density Distribution and X-Ray Diffraction Patterns of Smectic A Liquid Crystals - A Simulation Study. Chemphyschem 2019; 20:2466-2472. [PMID: 31361389 DOI: 10.1002/cphc.201900538] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2019] [Indexed: 11/07/2022]
Abstract
X-ray diffraction (XRD) is one of the most important methods to assess the long-range translational order in smectic A (SmA) liquid crystals. Nevertheless, the knowledge about the influence of the molecular electron density distribution (MEDD) on the XRD pattern is rather limited because it is not possible to vary the orientational order, the translational order and the MEDD independently in an experiment. We here present a systematic simulation study in which we examine this effect and show that the MEDD indeed has a major impact on the general appearance of the XRD pattern. More specifically, we find that the smectic layer peaks and the intensity ratios thereof strongly depend on the width of the MEDD. The classic approach by Leadbetter et al. to determine the smectic translational order parameter ∑ from XRD intensities works if the MEDD is quite narrow. In all other cases the influence of the MEDD has to be taken into account.
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Affiliation(s)
- Christian Haege
- Institute of Physical Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70569, Stuttgart, Germany
| | - Stefan Jagiella
- Institute of Physical Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70569, Stuttgart, Germany
| | - Frank Giesselmann
- Institute of Physical Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70569, Stuttgart, Germany
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Kapernaum N, Wuckert E, Frey W, Marino S, Wahl M, Giesselmann F, Laschat S. Hunting for smectic C in calamitic azobenzene ionic liquid crystals with different cationic head groups. J PHYS ORG CHEM 2017. [DOI: 10.1002/poc.3779] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Nadia Kapernaum
- Institut für Physikalische Chemie; Universität Stuttgart; Stuttgart Germany
| | - Eugen Wuckert
- Institut für Organische Chemie; Universität Stuttgart; Stuttgart Germany
| | - Wolfgang Frey
- Institut für Organische Chemie; Universität Stuttgart; Stuttgart Germany
| | - Sebastian Marino
- Institut für Physikalische Chemie; Universität Stuttgart; Stuttgart Germany
| | - Manuel Wahl
- Institut für Physikalische Chemie; Universität Stuttgart; Stuttgart Germany
| | - Frank Giesselmann
- Institut für Physikalische Chemie; Universität Stuttgart; Stuttgart Germany
| | - Sabine Laschat
- Institut für Organische Chemie; Universität Stuttgart; Stuttgart Germany
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Singh G, Fu J, Agra-Kooijman DM, Song JK, Vengatesan MR, Srinivasarao M, Fisch MR, Kumar S. X-ray and Raman scattering study of orientational order in nematic and heliconical nematic liquid crystals. Phys Rev E 2016; 94:060701. [PMID: 28085478 DOI: 10.1103/physreve.94.060701] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2016] [Indexed: 05/16/2023]
Abstract
The temperature dependence of the orientational order parameters 〈P_{2}(cosβ)〉 and 〈P_{4}(cosβ)〉 in the nematic (N) and twist-bend nematic (N_{tb}) phases of the liquid crystal dimer CB7CB have been measured using x-ray and polarized Raman scattering. The 〈P_{2}(cosβ)〉 obtained from both techniques are the same, while 〈P_{4}(cosβ)〉, determined by Raman scattering is, as expected, systematically larger than its x-ray value. Both order parameters increase in the N phase with decreasing temperature, drop across the N-N_{tb} transition, and continue to decrease. In the N_{tb} phase, the x-ray value of 〈P_{4}(cosβ)〉 eventually becomes negative, providing a direct and independent confirmation of a conical molecular orientational distribution. The heliconical tilt angle α, determined from orientational distribution functions in the N_{tb} phase, increases to ∼24^{∘} at ∼15 K below the transition. In the N_{tb} phase, α(T)∝(T^{*}-T)^{λ}, with λ=0.19±0.03. The transition supercools by 1.7 K, consistent with its weakly first-order nature. The value of λ is close to 0.25 indicating close proximity to a tricritical point.
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Affiliation(s)
- Gautam Singh
- Department of Physics, Kent State University, Kent, Ohio 44242, USA
- Department of Applied Physics, Amity Institute of Applied Sciences, Amity University, Noida, UP 201313, India
| | - Jinxin Fu
- School of Materials Science and Engineering, School of Chemistry and Biochemistry, and Center for Advanced Research on Optical Microscopy, Georgia Institute of Technology, Atlanta, Georgia 30332-0295, USA
| | | | - Jang-Kun Song
- School of Electronic and Electrical Engineering, Sungkyunkwan University, Suwon, Republic of Korea
| | - M R Vengatesan
- School of Electronic and Electrical Engineering, Sungkyunkwan University, Suwon, Republic of Korea
| | - Mohan Srinivasarao
- School of Materials Science and Engineering, School of Chemistry and Biochemistry, and Center for Advanced Research on Optical Microscopy, Georgia Institute of Technology, Atlanta, Georgia 30332-0295, USA
| | - Michael R Fisch
- College of Applied Engineering Sustainability and Technology, Kent State University, Kent, Ohio 44242, USA
| | - Satyendra Kumar
- Department of Physics, Kent State University, Kent, Ohio 44242, USA
- Division of Research and Department of Physics, University at Albany, Albany, New York 12222, USA
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Jenz F, Osipov MA, Jagiella S, Giesselmann F. Orientational distribution functions and order parameters in "de Vries"-type smectics: A simulation study. J Chem Phys 2016; 145:134901. [PMID: 27782446 DOI: 10.1063/1.4963660] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Simple smectic A liquid crystal phases with different types of prescribed orientational distribution functions have been simulated and compared in order to study the possibility to distinguish between the Maier-Saupe type and cone-like orientational distributions using the popular method of Davidson et al. [J. Phys. II 5, 113 (1995)]. This method has been used to extract the orientational distribution functions from simulated diffraction patterns, and the results have been compared with actual distribution functions which have been prescribed during simulations. It has been shown that it is indeed possible to distinguish between these two qualitatively different types of orientational distribution already from the shape of the 2D diffraction pattern. Moreover, typical experimental diffraction patterns for "de Vries"-type smectic liquid crystals appear to be close to the ones which have been simulated using the prescribed Maier-Saupe orientational distribution function.
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Affiliation(s)
- Frank Jenz
- Institute of Physical Chemistry, Pfaffenwaldring 55, University of Stuttgart, Stuttgart, Germany
| | - Mikhail A Osipov
- Department of Mathematics and Statistics, G1 1XH, University of Strathclyde, Glasgow, United Kingdom
| | - Stefan Jagiella
- Institute of Physical Chemistry, Pfaffenwaldring 55, University of Stuttgart, Stuttgart, Germany
| | - Frank Giesselmann
- Institute of Physical Chemistry, Pfaffenwaldring 55, University of Stuttgart, Stuttgart, Germany
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