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Haege C, Jagiella S, Giesselmann F. Towards Nematic Phases in Ionic Liquid Crystals - A Simulation Study. Chemphyschem 2023; 24:e202200424. [PMID: 36053025 PMCID: PMC10092135 DOI: 10.1002/cphc.202200424] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2022] [Revised: 08/30/2022] [Indexed: 01/04/2023]
Abstract
Ionic liquid crystals (ILCs) are soft matter materials with broad liquid crystalline phases and intrinsic electric conductivity. They typically consist of a rod-shaped mesogenic ion and a smaller spherical counter-ion. Their mesomorphic properties can be easily tuned by exchanging the counter ion. ILCs show a strong tendency to form smectic A phases due to the segregation of ionic and the non-ionic molecular segments. Nematic phases are therefore extremely rare in ILCs and the question of why nematic phases are so exceptional in existing ILCs, and how nematic ILCs might be obtained in the future is of vital interest for both the fundamental understanding and the potential applications of ILCs. Here, we present the result of a simulation study, which highlights the crucial role of the location of the ionic charge on the rod-like mesogenic ions in the phase behaviour of ILCs. We find that shifting the charge from the ends towards the centre of the mesogenic ion destabilizes the liquid crystalline state and induces a change from smectic A to nematic phases.
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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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Makarov GI, Reshetnikova RV, Bartashevich EV. Modeling the Compressibility of a Multicomponent Liquid-Crystalline Phase CHS1 by Means of Molecular Dynamics. RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A 2022. [DOI: 10.1134/s0036024422070202] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Kapernaum N, Lange A, Ebert M, Grunwald MA, Haege C, Marino S, Zens A, Taubert A, Giesselmann F, Laschat S. Current Topics in Ionic Liquid Crystals. Chempluschem 2021; 87:e202100397. [PMID: 34931472 DOI: 10.1002/cplu.202100397] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2021] [Revised: 11/10/2021] [Indexed: 12/20/2022]
Abstract
Ionic liquid crystals (ILCs), that is, ionic liquids exhibiting mesomorphism, liquid crystalline phases, and anisotropic properties, have received intense attention in the past years. Among others, this is due to their special properties arising from the combination of properties stemming from ionic liquids and from liquid crystalline arrangements. Besides interesting fundamental aspects, ILCs have been claimed to have tremendous application potential that again arises from the combination of properties and architectures that are not accessible otherwise, or at least not accessible easily by other strategies. The current review highlights recent developments in ILC research, starting with some key fundamental aspects. Further subjects covered include the synthesis and variations of modern ILCs, including the specific tuning of their mesomorphic behavior. The review concludes with reflections on some applications that may be within reach for ILCs and finally highlights a few key challenges that must be overcome prior and during true commercialization of ILCs.
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Affiliation(s)
- Nadia Kapernaum
- Institut für Physikalische Chemie, Universität Stuttgart, Pfaffenwaldring 55, 70569, Stuttgart, Germany
| | - Alyna Lange
- Institut für Chemie, Universität Potsdam, Karl-Liebknecht-Str. 24-25, 14476, Golm, Germany
| | - Max Ebert
- Institut für Organische Chemie, Universität Stuttgart, Pfaffenwaldring 55, 70569, Stuttgart, Germany
| | - Marco A Grunwald
- Institut für Organische Chemie, Universität Stuttgart, Pfaffenwaldring 55, 70569, Stuttgart, Germany
| | - Christian Haege
- Institut für Physikalische Chemie, Universität Stuttgart, Pfaffenwaldring 55, 70569, Stuttgart, Germany
| | - Sebastian Marino
- Institut für Physikalische Chemie, Universität Stuttgart, Pfaffenwaldring 55, 70569, Stuttgart, Germany
| | - Anna Zens
- Institut für Organische Chemie, Universität Stuttgart, Pfaffenwaldring 55, 70569, Stuttgart, Germany
| | - Andreas Taubert
- Institut für Chemie, Universität Potsdam, Karl-Liebknecht-Str. 24-25, 14476, Golm, Germany
| | - Frank Giesselmann
- Institut für Physikalische Chemie, Universität Stuttgart, Pfaffenwaldring 55, 70569, Stuttgart, Germany
| | - Sabine Laschat
- Institut für Organische Chemie, Universität Stuttgart, Pfaffenwaldring 55, 70569, Stuttgart, Germany
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Saielli G, Castiglione F, Mauri M, Simonutti R, Mele A. Xenon Diffusion in Ionic Liquids with Blurred Nanodomain Separation. Chemphyschem 2021; 22:1880-1890. [PMID: 34251740 DOI: 10.1002/cphc.202100423] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2021] [Revised: 07/11/2021] [Indexed: 11/09/2022]
Abstract
The dynamics of xenon gas, loaded in a series of 1-alkyl-3-methylimidazolium based ionic liquids, probes the formation of increasingly blurred polar/apolar nanodomains as a function of the anion type and the cation chain length. Exploiting 129 Xe NMR spectroscopy techniques, like Pulse Gradient Spin Echo (PGSE) and inversion recovery (IR), the diffusion motion and relaxation times are determined for 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [Cn C1 im][TFSI]. A correlation between the ILs nano-structure and both xenon diffusivity and relaxation times, as well as chemical shifts, is outlined. Interestingly, comparison with previous results of the same properties in the homologous imidazolium chlorides and hexafluorophospate shows an opposite trend with the alkyl chain length. Classical molecular dynamics (MD) simulations are used to calculate the xenon and cation and anion diffusion coefficients in the same systems, including imidazolium cations with longer chains (n=4, 6, 8 … 20). An almost quantitative agreement with the experiments validates the MD simulations and, at the same time, provides the necessary structural and dynamic microscopic insights on the nano-segregation and diffusion of xenon in bistriflimide, chloride and hexafluorphosphate salts allowing to observe and rationalize the shaping effect of the cation in the nanostructure.
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Affiliation(s)
- Giacomo Saielli
- CNR - ITM Institute on Membrane Technology, Padova Unit, Via Marzolo, 1, 35131, Padova, Italy.,Department of Chemical Sciences, University of Padova, Via Marzolo, 1, 35131, Padova, Italy
| | - Franca Castiglione
- Department of Chemistry, Materials and Chemical Engineering "G. Natta", Politecnico di Milano, Piazza L. Da Vinci, 32, 20133, Milano, Italy
| | - Michele Mauri
- Dipartimento di Scienza dei Materiali, Università degli Studi di Milano Bicocca, Via Roberto Cozzi, 53, 20125, Milano, Italy
| | - Roberto Simonutti
- Dipartimento di Scienza dei Materiali, Università degli Studi di Milano Bicocca, Via Roberto Cozzi, 53, 20125, Milano, Italy
| | - Andrea Mele
- Department of Chemistry, Materials and Chemical Engineering "G. Natta", Politecnico di Milano, Piazza L. Da Vinci, 32, 20133, Milano, Italy.,CNR - SCITEC Istituto di Scienze e Tecnologie Chimiche, Via A. Corti 12, 20133, Milano, Italy
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Saielli G, Satoh K. A coarse-grained model of ionic liquid crystals: the effect of stoichiometry on the stability of the ionic nematic phase. Phys Chem Chem Phys 2019; 21:20327-20337. [PMID: 31495845 DOI: 10.1039/c9cp03296g] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
We have investigated, by means of molecular dynamics simulations, the phase behaviour of mixtures of charged ellipsoidal Gay-Berne (GB) particles and spherical Lennard-Jones (LJ) particles, as a coarse-grained model of ionic liquid crystals (ILCs). The anisotropic GB particles represent cations usually found in ILCs, for example, pyridinium or bipyridinium salts, while the spherical LJ particles are taken as a model of anions like common halides, hexafluorophosphate and tetrafluoroborate. Here we have focused our attention on the effect of the stoichiometry of the system (that is, the GB : LJ ratio n : m in the salt formula [GB]n[LJ]m) on the stability and thermal range of the ionic liquid crystal phases formed, with special attention to the ionic nematic phase. To isolate the stoichiometry effect, a comparison of four different systems with GB : LJ ratios of 1 : 3, 1 : 2, 1 : 1 and 2 : 1 is made by keeping the packing fraction and the charge of the minor component fixed. Our results suggest a way to improve the stability of the ionic nematic phase by enhancing the anisotropic van der Waals interaction compared to the Coulomb interaction, and by increasing the proportion of anisotropic particles in the mixture.
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Affiliation(s)
- Giacomo Saielli
- CNR Institute on Membrane Technology, Unit of Padova, Via Marzolo, 1, 35131 Padova, Italy.
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Di Pietro ME, Margola T, Celebre G, De Luca G, Saielli G. A combined LX-NMR and molecular dynamics investigation of the bulk and local structure of ionic liquid crystals. SOFT MATTER 2019; 15:4486-4497. [PMID: 31093625 DOI: 10.1039/c9sm00612e] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
The unique power of NMR spectroscopy in anisotropic media (LX-NMR) as a tool to obtain local and bulk structural information, combined with the effectiveness of molecular dynamics simulations at the atomistic level, shows very attractive potentialities for the study of interesting, even though still poorly understood, materials such as Ionic Liquid Crystals (ILCs). In this work, we focused our attention, in particular, on the orientational ordering of two mesophases: 1-dodecyl-3-methylimidazolium chloride, [C12C1im]Cl, and 1-dodecyl-3-methylimidazolium tetrafluoroborate, [C12C1im][BF4]. Both ILCs were studied by a 2H NMR direct investigation of the molecules forming the phases, suitably deuterated, and by 1H NMR spectroscopy, using the small rigid probe-solutes 1,4-dichlorobenzene (DCB), dissolved in [C12C1im][BF4] and [C12C1im]Cl, and 1,4-dibromobenzene (DBB) dissolved in [C12C1im][BF4], to probe the local, internal structure and organization of the mesophases. The experimental results were then compared with the predictions, by atomistic MD simulations, of the structure of the smectic phase of the two salts, at two selected temperatures, containing a single DCB molecule as a probe. The MD simulations show that the DCB solute is distributed only within the hydrophobic layers of the ILC. Orientational order parameters of the imidazolium cations and of the DCB molecule were obtained and compared with the experiments, showing a general good agreement and allowing a deeper understanding of the microscopic structure of the systems.
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Affiliation(s)
- Maria Enrica Di Pietro
- Dipartimento di Chimica e Tecnologie Chimiche, Università della Calabria, Via P. Bucci, cubo 14C, 87036 Rende, CS, Italy.
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Makarov GI, Bartashevich EV, Khnykina KA, Podgornov FV. Molecular dynamics simulation and experimental investigation of material and structural parameters of multicomponent ferroelectric liquid crystal mixture. J Mol Liq 2019. [DOI: 10.1016/j.molliq.2019.03.096] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
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Affiliation(s)
- Michael P. Allen
- Department of Physics, University of Warwick, Coventry, UK
- H. H. Wills Physics Laboratory, Royal Fort, Bristol, UK
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Weber CC, Brooks NJ, Castiglione F, Mauri M, Simonutti R, Mele A, Welton T. On the structural origin of free volume in 1-alkyl-3-methylimidazolium ionic liquid mixtures: a SAXS and 129Xe NMR study. Phys Chem Chem Phys 2019; 21:5999-6010. [PMID: 30809621 DOI: 10.1039/c9cp00587k] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Ionic liquid (IL) mixtures enable the design of fluids with finely tuned structural and physicochemical properties for myriad applications. In order to rationally develop and design IL mixtures with the desired properties, a thorough understanding of the structural origins of their physicochemical properties and the thermodynamics of mixing needs to be developed. To elucidate the structural origins of the excess molar volume within IL mixtures containing ions with different alkyl chain lengths, 3 IL mixtures containing 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ILs have been explored in a joint small angle X-ray scattering (SAXS) and 129Xe NMR study. The apolar domains of the IL mixtures were shown to possess similar dimensions to the largest alkyl chain of the mixture with the size evolution determined by whether the shorter alkyl chain was able to interact with the apolar domain. 129Xe NMR results illustrated that the origin of excess molar volume in these mixtures was due to fluctuations within these apolar domains arising from alkyl chain mismatch, with the formation of a greater number of smaller voids within the IL structure. These results indicate that free volume effects for these types of mixtures can be predicted from simple considerations of IL structure and that the structural basis for the formation of excess molar volume in these mixtures is substantially different to IL mixtures formed of different types of ions.
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Affiliation(s)
- Cameron C Weber
- School of Science, Auckland University of Technology, Auckland, New Zealand
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Saielli G, Margola T, Satoh K. Tuning Coulombic interactions to stabilize nematic and smectic ionic liquid crystal phases in mixtures of charged soft ellipsoids and spheres. SOFT MATTER 2017; 13:5204-5213. [PMID: 28671229 DOI: 10.1039/c7sm00612h] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
We have investigated the effect of electrostatic interactions in mixtures of soft ellipsoids and spheres based on the well-known Gay-Berne (GB) and Lennard-Jones (LJ) potential, respectively. These model systems, in their original version, that is without any electrostatic charge, have been thoroughly investigated in the literature both as pure components and mixtures. In particular, mixtures of particles of different shapes, such as spheres and ellipsoids, tend to phase separate because of the excluded volume effects. Common ionic liquid crystals, based on imidazolium or other quaternary ammonium salts, are usually composed of roughly elongated (although flexible) cations and roughly spherical anions, that is, particles with a similar shape such as the GB and LJ models. Therefore, in this work, we present the results of molecular dynamics simulations of mixtures of positively charged GB and negatively charged LJ particles as models of ionic liquid crystals. Interestingly, by modulating the charge of the particles it is possible to stabilize isotropic, nematic, smectic and crystalline ionic phases. The relative weight of Coulomb (a radial, therefore isotropic interaction) and van der Waals (an anisotropic interaction) contributions is a key parameter to tune the stability of various mesophases.
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Affiliation(s)
- Giacomo Saielli
- Istituto per la Tecnologia delle Membrane del CNR (ITM-CNR), Sede Secondaria di Padova, Via Marzolo, 1-35131, Padova, Italy.
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Saielli G, Wang Y. Role of the Electrostatic Interactions in the Stabilization of Ionic Liquid Crystals: Insights from Coarse-Grained MD Simulations of an Imidazolium Model. J Phys Chem B 2016; 120:9152-60. [DOI: 10.1021/acs.jpcb.6b04717] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Giacomo Saielli
- CNR
Institute on Membrane Technology, Unit of Padova and Department of
Chemical Sciences, University of Padova, Via Marzolo, 1-35131 Padova, Italy
| | - Yanting Wang
- CAS
Key Laboratory of Theoretical Physics, Institute of Theoretical Physics, Chinese Academy of Sciences, 55 East Zhongguancun Road, P.O.
Box 2735, Beijing, 100190, China
- School
of Physical Sciences, University of Chinese Academy of Sciences, 19A Yuquan Road, Beijing 100049, China
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Saielli G. Fully Atomistic Simulations of the Ionic Liquid Crystal [C16mim][NO3]: Orientational Order Parameters and Voids Distribution. J Phys Chem B 2016; 120:2569-77. [DOI: 10.1021/acs.jpcb.5b12469] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Giacomo Saielli
- CNR Institute
on Membrane
Technology and Department of Chemical Sciences, University of Padova, Via Marzolo, 1, 35131 Padova, Italy
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