Special Issue "Ionic 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 December 2018)

Special Issue Editor

Guest Editor
Dr. Giacomo Saielli

CNR Institute on Membrane Technology, Padua Unit and Department of Chemical Sciences, University of Padua. Via Marzolo, 1 - 35131, Padova, Italy
Website | E-Mail
Phone: +39-049-8275279
Fax: +39-049-8275239
Interests: ionic liquid crystals; ionic liquids; liquid crystals; viologens; density fuctional theory; molecular dynamics simulation; Gay-Berne models; nuclear magnetic resonance

Special Issue Information

Dear Colleagues,

Thermotropic Ionic Liquid Crystals (ILCs) are materials able to embed the extraordinary solvation and conductive properties of ionic liquids (ILs) within the partially-ordered phases of liquid crystals (LCs). They can be considered as belonging to a sort of Middle Earth, at the intersection between the realm of LCs and the kingdom of ILs.  ILCs are normally composed of the same type of cation/anion combinations that can be found in ILs; however, often because of the presence of long alkyl chains, microsegregation drives the formation of ordered mesophases at the macroscopic level, usually of smectic type.

Applications of ILCs mostly tend to exploit the organized/anisotropic/partially ordered structure of the ionic fluid phase for enhancing the conduction of matter and or charge; thereofore they have been studied as electrolytes in batteries, dye sensitized solar cells,  electrochemical sensors, electrofluorescence switches, membranes for water desalination, among others. However, because of the relatively large viscosity of ILCs, compared to ILs and LCs, both fundamental as well as application-oriented studies to improve the performace of ILC-based devices are timely and welcome by the scientific community. Moreover, the quest for an ionic nematic phase with a wide thermal range of stability at or around room temperature is still an open challenge and an ideal playground for the joint efforts of chemists, physicists and materials scientists .

Therefore, we invite researchers to submit their papers to this Special Issue of Crystals dedicated to “Ionic Liquid Crystals”. Manuscripts can be related to any aspect of ILCs science, for example (but not limited to):

  • synthesis of novel ILC compounds;
  • structure/property relationships in ILCs;
  • novel types of ionic mesophases;
  • applications of ILCs in devices;
  • biotechnological applications of ILCs;
  • physical properties of ionic mesophases;
  • computer simulations of the phase behaviour of ILCs;
  • theoretical models of ILCs

Dr. Giacomo Saielli
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 1400 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

  • Ionic liquids
  • Liquid crystals
  • Ionic mesophases
  • Quaternary ammonium salts
  • Microphase segregation
  • Electrochemical sensors
  • Ionic electrolytes

Published Papers (7 papers)

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Research

Open AccessArticle
Decreasing the Residual DC Voltage by Neutralizing the Charged Mobile Ions in Liquid Crystals
Crystals 2019, 9(4), 181; https://doi.org/10.3390/cryst9040181
Received: 14 March 2019 / Revised: 23 March 2019 / Accepted: 25 March 2019 / Published: 27 March 2019
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Abstract
The decrease of the residual direct current (DC) voltage (Vrdc) of the anti-parallel liquid crystal (LC) cell using silver (Ag)-doped Polyimide (Ag-d-PI) alignment layers is presented in this manuscript. A series of Ag/PI composite thin layers are prepared by spurting or [...] Read more.
The decrease of the residual direct current (DC) voltage (Vrdc) of the anti-parallel liquid crystal (LC) cell using silver (Ag)-doped Polyimide (Ag-d-PI) alignment layers is presented in this manuscript. A series of Ag/PI composite thin layers are prepared by spurting or doping PI thin layers with Ag nano-particles, and Ag/PI composite thin layers are highly transparent and resistive. LC are homogeneously aligned between 2.0 mg/mL Ag-d-PI alignment layers, and the Vrdc of the cell that assembled with Ag-d-PI alignment layers decreases about 82%. The decrease of Vrdc is attributed to the trapping and neutralizing of mobile ions by Ag nano-particles. Regardless of the effect of Ag nano-particles on the conductivity of Ag-d-PI alignment layers, the voltage holding ratio (VHR) of the cells is maintained surprisingly. The experiment results reveal a simple design for a low Vrdc LC cell. Full article
(This article belongs to the Special Issue Ionic Liquid Crystals)
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Open AccessArticle
Thermotropic Liquid-Crystalline Properties of Viologens Containing 4-n-alkylbenzenesulfonates
Crystals 2019, 9(2), 77; https://doi.org/10.3390/cryst9020077
Received: 28 December 2018 / Revised: 26 January 2019 / Accepted: 28 January 2019 / Published: 1 February 2019
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Abstract
A series of viologens containing 4-n-alkylbenzenesulfonates were synthesized by the metathesis reaction of 4-n-alkylbenzenesulfonic acids or sodium 4-n-alkylbezenesulfonates with the respective viologen dibromide in alcohols. Their chemical structures were characterized by Fourier Transform Infrared, 1H and 13C Nuclear Magnetic Resonance spectra [...] Read more.
A series of viologens containing 4-n-alkylbenzenesulfonates were synthesized by the metathesis reaction of 4-n-alkylbenzenesulfonic acids or sodium 4-n-alkylbezenesulfonates with the respective viologen dibromide in alcohols. Their chemical structures were characterized by Fourier Transform Infrared, 1H and 13C Nuclear Magnetic Resonance spectra and elemental analysis. Their thermotropic liquid-crystalline (LC) properties were examined by differential scanning calorimetry and polarizing optical microscopy. They formed LC phases above their melting transitions and showed isotropic transitions. As expected, all the viologen salts had excellent stabilities in the temperature range of 278–295 °C as determined by thermogravimetric analysis. Full article
(This article belongs to the Special Issue Ionic Liquid Crystals)
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Open AccessFeature PaperArticle
Improved Electronic Transport in Ion Complexes of Crown Ether Based Columnar Liquid Crystals
Crystals 2019, 9(2), 74; https://doi.org/10.3390/cryst9020074
Received: 21 December 2018 / Revised: 28 January 2019 / Accepted: 29 January 2019 / Published: 31 January 2019
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Abstract
The Li+- and K+-complexes of new discotic mesogens, where two n-alkoxy-substituted triphenylene cores are connected by a central crown ether (12-crown-4 and 18-crown-6), provide interesting structural and electronic properties. The inter- and intra-columnar structure was investigated by small and [...] Read more.
The Li+- and K+-complexes of new discotic mesogens, where two n-alkoxy-substituted triphenylene cores are connected by a central crown ether (12-crown-4 and 18-crown-6), provide interesting structural and electronic properties. The inter- and intra-columnar structure was investigated by small and wide angle X-ray scattering. The electronic and ionic transports were studied by temperature dependent photoconductivity and impedance spectroscopy, respectively. Besides a strong increase of the stability and the width of the columnar phases the presence of soft anions (iodide, thiocyanate, tetrafluoroborate) leads to an improved intra-columnar order. The hereby shortened stacking-distance of the triphenylene cores leads to a significant increase of the photoconductivity in the columnar mesophase. Furthermore, the ionic conductivity of the new materials was investigated on macroscopically aligned thin films. The existence of channels for fast cation transport formed by the stacked crown ether moieties in the centre of each column can be excluded. The cations are coordinated strongly and therefore contributing only little to the conductivity. The ionic conductivity is dominated by the anisotropic migration of the non-coordinated anions through the liquid, like side chains favouring the propagation parallel to the columns. Iodide migrates about 20 times faster than thiocyanate and 100 times faster than tetrafluoroborate. Full article
(This article belongs to the Special Issue Ionic Liquid Crystals)
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Open AccessCommunication
Substituted Azolium Disposition: Examining the Effects of Alkyl Placement on Thermal Properties
Crystals 2019, 9(1), 34; https://doi.org/10.3390/cryst9010034
Received: 23 December 2018 / Revised: 4 January 2019 / Accepted: 6 January 2019 / Published: 11 January 2019
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Abstract
We describe the thermal phase characteristics of a series of 4,5-bis(n-alkyl)azolium salts that were studied using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), polarized-light optical microscopy (POM), and synchrotron-based small- to wide-angle X-ray scattering (SWAXS) measurements. Key results were obtained for [...] Read more.
We describe the thermal phase characteristics of a series of 4,5-bis(n-alkyl)azolium salts that were studied using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), polarized-light optical microscopy (POM), and synchrotron-based small- to wide-angle X-ray scattering (SWAXS) measurements. Key results were obtained for 1,3-dimethyl-4,5-bis(n-undecyl)imidazolium iodide (1-11), 1,3-dimethyl-4,5-bis(n-pentadecyl)imidazolium iodide (1-15), and 1,2,3-trimethyl-4,5-bis(n-pentadecyl)imidazolium iodide (2), which were found to adopt enantiotropic smectic A mesophases. Liquid-crystalline mesophases were not observed for 1,3-dimethyl-4,5-bis(n-heptyl)imidazolium iodide (1-7), 3-methyl-4,5-bis(n-pentadecyl)thiazolium iodide (3), and 2-amino-4,5-bis(n-pentadecyl)imidazolium chloride (4). Installing substituents in the 4- and 5-positions of the imidazolium salts appears to increase melting points while lowering clearing points when compared to data reported for 1,3-disubstituted analogues. Full article
(This article belongs to the Special Issue Ionic Liquid Crystals)
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Open AccessArticle
Phase Behaviors of Ionic Liquids Heating from Different Crystal Polymorphs toward the Same Smectic-A Ionic Liquid Crystal by Molecular Dynamics Simulation
Crystals 2019, 9(1), 26; https://doi.org/10.3390/cryst9010026
Received: 11 December 2018 / Revised: 28 December 2018 / Accepted: 29 December 2018 / Published: 3 January 2019
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Abstract
Five distinct crystal structures, based on experimental data or constructed manually, of ionic liquid [C14Mim][NO3] were heated in NPT molecular dynamics simulations under the same pressure such that they melted into the liquid crystal (LC) phase and then into [...] Read more.
Five distinct crystal structures, based on experimental data or constructed manually, of ionic liquid [C14Mim][NO3] were heated in NPT molecular dynamics simulations under the same pressure such that they melted into the liquid crystal (LC) phase and then into the liquid phase. It was found that the more entropy-favored structure had a higher solid-LC transition temperature: Before the transition into the LC, all systems had to go through a metastable state with the side chains almost perpendicular to the polar layers. All those crystals finally melted into the same smectic-A LC structure irrelevant of the initial crystal structure. Full article
(This article belongs to the Special Issue Ionic Liquid Crystals)
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Open AccessArticle
Molecular and Segmental Orientational Order in a Smectic Mesophase of a Thermotropic Ionic Liquid Crystal
Crystals 2019, 9(1), 18; https://doi.org/10.3390/cryst9010018
Received: 30 November 2018 / Revised: 20 December 2018 / Accepted: 24 December 2018 / Published: 28 December 2018
Cited by 1 | PDF Full-text (1100 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
We investigate conformational dynamics in the smectic A phase formed by the mesogenic ionic liquid 1-tetradecyl-3-methylimidazolium nitrate. Solid-state high-resolution 13C nuclear magnetic resonance (NMR) spectra are recorded in the sample with the mesophase director aligned in the magnetic field of the NMR [...] Read more.
We investigate conformational dynamics in the smectic A phase formed by the mesogenic ionic liquid 1-tetradecyl-3-methylimidazolium nitrate. Solid-state high-resolution 13C nuclear magnetic resonance (NMR) spectra are recorded in the sample with the mesophase director aligned in the magnetic field of the NMR spectrometer. The applied NMR method, proton encoded local field spectroscopy, delivers heteronuclear dipolar couplings of each 13C spin to its 1H neighbours. From the analysis of the dipolar couplings, orientational order parameters of the C–H bonds along the hydrocarbon chain were determined. The estimated value of the molecular order parameter S is significantly lower compared to that in smectic phases of conventional non-ionic liquid crystals. Full article
(This article belongs to the Special Issue Ionic Liquid Crystals)
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Open AccessArticle
Comparison of the Mesomorphic Behaviour of 1:1 and 1:2 Mixtures of Charged Gay-Berne GB(4.4,20.0,1,1) and Lennard-Jones Particles
Crystals 2018, 8(10), 371; https://doi.org/10.3390/cryst8100371
Received: 1 September 2018 / Revised: 18 September 2018 / Accepted: 19 September 2018 / Published: 20 September 2018
Cited by 2 | PDF Full-text (7133 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
We present a Molecular Dynamics study of mixtures of charged Gay-Berne (GB) ellipsoids and spherical Lennard-Jones (LJ) particles as models of ionic liquids and ionic liquid crystals. The GB system is highly anisotropic (GB(4.4,20.0,1,1)) and we observe a rich mesomorphism, with ionic nematic [...] Read more.
We present a Molecular Dynamics study of mixtures of charged Gay-Berne (GB) ellipsoids and spherical Lennard-Jones (LJ) particles as models of ionic liquids and ionic liquid crystals. The GB system is highly anisotropic (GB(4.4,20.0,1,1)) and we observe a rich mesomorphism, with ionic nematic and smectic phases in addition to the isotropic mixed phase and crystalline phases with honeycomb structure. The systems have been investigated by analyzing the orientational and translational order parameters, as well as radial distribution functions. We have directly compared 1:1 mixtures, where the GB and LJ particles have a charge equal in magnitude and opposite in sign, and 1:2 mixtures where the number of LJ particles is twice as large compared to the GB and their charge half in magnitude. The results highlight the role of the long-range isotropic electrostatic interaction compared to the short-range van der Waals anisotropic contribution, and the effect of the stoichiometry on the stability of ionic mesophases. Full article
(This article belongs to the Special Issue Ionic Liquid Crystals)
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