Special Issue "Nuclear Magnetic Resonance of Liquid Crystals"

A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Liquid Crystals".

Deadline for manuscript submissions: closed (31 May 2020).

Special Issue Editor

Prof. Dr. Valentina Domenici
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Guest Editor
Soft Matter Spectroscopy Laboratory, Department of Chemistry and Industrial Chemistry, University of Pisa, Via Giuseppe Moruzzi, 13 - 56124, Pisa, Italy
Interests: liquid crystals; liquid crystal elastomers; 2H NMR; orientational order; supramolecular organization; self assembling; conformational properties; dynamics

Special Issue Information

Dear Colleagues,

Liquid crystals represent a class of soft materials with very peculiar properties, mostly related to the rich variety of structures having different degrees of 1D, 2D or 3D order. These partially ordered systems have been the object of NMR investigations since the 1960s, but they are still considered a challenging topic for the development of new NMR methods. Moreover, NMR spectroscopy was often a crucial technique in order to clarify the relationship between the macroscopic and molecular-level properties of liquid crystals.

In recent years, increasing interests about new liquid crystalline materials, the discovery of novel mesophases and their supramolecular structures, have offered the opportunity to apply NMR spectroscopy to investigate several fundamental aspects of liquid crystals, such as the conformational behavior, the orientational ordering, the alignment and director distribution properties, as well as molecular and collective dynamics.

This Special Issue, entitled “Nuclear Magnetic Resonance of Liquid Crystals”, aims to collect original research papers and review articles concerning the most recent research in this field, taking into account both theoretical and experimental works.

The potential topics of this Special Issue include, but are not limited to:

  • NMR characterization of new mesophases
  • Development of new NMR methods to study liquid crystals
  • Multinuclear NMR approach to study liquid crystals
  • Study of the orientational order of liquid crystals by NMR
  • Study of the molecular dynamics of liquid crystals by NMR
  • NMR relaxometry applied to liquid crystals
  • NMR diffusometry applied to liquid crystals
  • NMR study of biaxial phases
  • NMR study of lyotropic liquid crystals
  • NMR study of ionic liquid crystals
  • NMR study of thermotropic liquid crystals
  • NMR methods to study conformational properties in partially oriented media
  • NMR study of liquid crystalline polymers, elastomers and gels.
  • NMR investigations of nanostructured composites based on liquid crystals
  • NMR investigations of self-assembled biological systems

It is my pleasure to invite you and your colleagues to submit a manuscript to this Special Issue.

Prof. Dr. Valentina Domenici
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Crystals is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • NMR methods
  • Order and dynamics of Liquid Crystals
  • Structural and self-assembling properties
  • Partially Ordered Systems.

Published Papers (4 papers)

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Research

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Open AccessArticle
Comparative 2H NMR and X-Ray Diffraction Investigation of a Bent-Core Liquid Crystal Showing a Nematic Phase
Crystals 2020, 10(4), 284; https://doi.org/10.3390/cryst10040284 - 09 Apr 2020
Abstract
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 [...] Read more.
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. Full article
(This article belongs to the Special Issue Nuclear Magnetic Resonance of Liquid Crystals)
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Open AccessArticle
NMR Spectroscopic Study of Orientational Order in Imidazolium-Based Ionic Liquid Crystals
Crystals 2019, 9(10), 495; https://doi.org/10.3390/cryst9100495 - 25 Sep 2019
Cited by 4
Abstract
We report on molecular and local orientational order of a series of imidazolium-based ionic liquid crystals exhibiting layered smectic A mesophase. Materials constituting of 1-dodecyl-3-methylimidazolium cation, and different counter-ions, were investigated. We apply two-dimensional 13C-1H dipolar NMR spectroscopy to quantify [...] Read more.
We report on molecular and local orientational order of a series of imidazolium-based ionic liquid crystals exhibiting layered smectic A mesophase. Materials constituting of 1-dodecyl-3-methylimidazolium cation, and different counter-ions, were investigated. We apply two-dimensional 13C-1H dipolar NMR spectroscopy to quantify orientational order of C-H bonds of the organic cation. The experimental data supported the structural model of the interdigitated chains aligned with the smectic layer normal. Molecular order parameter S was found to increase in the anion sequence BF4 < I < Br < Cl. This trend correlates well with ionic radius, negative charge delocalization, and hydrogen-bonding properties of the anions. Full article
(This article belongs to the Special Issue Nuclear Magnetic Resonance of Liquid Crystals)
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Open AccessArticle
Study of Liquid Crystals Showing Two Isotropic Phases by 1H NMR Diffusometry and 1H NMR Relaxometry
Crystals 2019, 9(3), 178; https://doi.org/10.3390/cryst9030178 - 26 Mar 2019
Cited by 1
Abstract
In this work, we report a study of two thermotropic liquid crystalline samples showing a not common mesophase behavior. The samples, namely a di-benzyloxy biphenyl derivative labelled 9/2 RS/RS, and a bimesogenic liquid crystal labelled L1, show a direct transition between [...] Read more.
In this work, we report a study of two thermotropic liquid crystalline samples showing a not common mesophase behavior. The samples, namely a di-benzyloxy biphenyl derivative labelled 9/2 RS/RS, and a bimesogenic liquid crystal labelled L1, show a direct transition between two isotropic phases followed, at lower temperatures, by the optically isotropic, 3D structured, cubic phase. These systems have been investigated by means of 1H NMR diffusometry and 1H NMR relaxometry in order to characterize their isotropic–isotropic’–cubic mesophase behavior, mainly on the dynamic point of view. In particular, the temperature trend of the self-diffusion coefficients measured for both samples allowed us to significantly distinguish between the two isotropic phases, while the temperature dependence of the 1H spin-lattice relaxation time (T1) did not show significant discontinuities at the isotropic–isotropic’ phase transition. A preliminary analysis of the frequency-dependence of 1H T1 at different temperatures gives information about the main motional processes active in the isotropic mesophases. Full article
(This article belongs to the Special Issue Nuclear Magnetic Resonance of Liquid Crystals)
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Review

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Open AccessReview
Peculiarities in the Director Reorientation and the NMR Spectra Evolution in a Nematic Liquid Crystals under the Effect of Crossed Electric and Magnetic Fields
Crystals 2019, 9(5), 262; https://doi.org/10.3390/cryst9050262 - 20 May 2019
Cited by 1
Abstract
The illustrative description of the field-induced peculiarities of the director reorientation in the microsized nematic volumes under the effect of crossed magnetic B and electric E fields have been proposed. The most interesting feature of such configuration is that the nematic phase becomes [...] Read more.
The illustrative description of the field-induced peculiarities of the director reorientation in the microsized nematic volumes under the effect of crossed magnetic B and electric E fields have been proposed. The most interesting feature of such configuration is that the nematic phase becomes unstable after applying the strong E . The theoretical analysis of the reorientational dynamics of the director field provides an evidence for the appearance of the spatially periodic patterns in response to applied large E directed at an angle α to B . The feature of this approach is that the periodic distortions arise spontaneously from a homogeneously aligned nematic sample that ultimately induces a faster response than in the uniform mode. The nonuniform rotational modes involve additional internal elastic distortions of the conservative nematic system and, as a result, these deformations decrease of the viscous contribution U vis to the total energy U of the nematic phase. In turn, that decreasing of U vis leads to decrease of the effective rotational viscosity coefficient γ eff ( α ) . That is, a lower value of γ eff ( α ) , which is less than one in the bulk nematic phase, gives the less relaxation time τ on ( α ) γ eff ( α ) , when α is bigger than the threshold value α th . The results obtained by Deuterium NMR spectroscopy confirm theoretically obtained dependencies of τ on ( α ) on α . Full article
(This article belongs to the Special Issue Nuclear Magnetic Resonance of Liquid Crystals)
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