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Li Z, Raab A, Kolmangadi MA, Busch M, Grunwald M, Demel F, Bertram F, Kityk AV, Schönhals A, Laschat S, Huber P. Self-Assembly of Ionic Superdiscs in Nanopores. ACS NANO 2024; 18:14414-14426. [PMID: 38760015 PMCID: PMC11155240 DOI: 10.1021/acsnano.4c01062] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/23/2024] [Revised: 04/23/2024] [Accepted: 05/01/2024] [Indexed: 05/19/2024]
Abstract
Discotic ionic liquid crystals (DILCs) consist of self-assembled superdiscs of cations and anions that spontaneously stack in linear columns with high one-dimensional ionic and electronic charge mobility, making them prominent model systems for functional soft matter. Compared to classical nonionic discotic liquid crystals, many liquid crystalline structures with a combination of electronic and ionic conductivity have been reported, which are of interest for separation membranes, artificial ion/proton conducting membranes, and optoelectronics. Unfortunately, a homogeneous alignment of the DILCs on the macroscale is often not achievable, which significantly limits the applicability of DILCs. Infiltration into nanoporous solid scaffolds can, in principle, overcome this drawback. However, due to the experimental challenges to scrutinize liquid crystalline order in extreme spatial confinement, little is known about the structures of DILCs in nanopores. Here, we present temperature-dependent high-resolution optical birefringence measurement and 3D reciprocal space mapping based on synchrotron X-ray scattering to investigate the thermotropic phase behavior of dopamine-based ionic liquid crystals confined in cylindrical channels of 180 nm diameter in macroscopic anodic aluminum oxide membranes. As a function of the membranes' hydrophilicity and thus the molecular anchoring to the pore walls (edge-on or face-on) and the variation of the hydrophilic-hydrophobic balance between the aromatic cores and the alkyl side chain motifs of the superdiscs by tailored chemical synthesis, we find a particularly rich phase behavior, which is not present in the bulk state. It is governed by a complex interplay of liquid crystalline elastic energies (bending and splay deformations), polar interactions, and pure geometric confinement and includes textural transitions between radial and axial alignment of the columns with respect to the long nanochannel axis. Furthermore, confinement-induced continuous order formation is observed in contrast to discontinuous first-order phase transitions, which can be quantitatively described by Landau-de Gennes free energy models for liquid crystalline order transitions in confinement. Our observations suggest that the infiltration of DILCs into nanoporous solids allows tailoring their nanoscale texture and ion channel formation and thus their electrical and optical functionalities over an even wider range than in the bulk state in a homogeneous manner on the centimeter scale as controlled by the monolithic nanoporous scaffolds.
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Affiliation(s)
- Zhuoqing Li
- Institute
for Materials and X-ray Physics, Hamburg
University of Technology, Denickestr. 15, 21073 Hamburg, Germany
- Centre
for X-ray and Nano Science CXNS, Deutsches
Elektronen-Synchrotron DESY, Notkestr. 85, 22607 Hamburg, Germany
| | - Aileen Raab
- Institut
für Organische Chemie, Universität
Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany
| | - Mohamed Aejaz Kolmangadi
- Bundesanstalt
für Materialforschung und -prüfung (BAM), Unter den Eichen 87, 12205 Berlin, Germany
| | - Mark Busch
- Institute
for Materials and X-ray Physics, Hamburg
University of Technology, Denickestr. 15, 21073 Hamburg, Germany
- Centre
for X-ray and Nano Science CXNS, Deutsches
Elektronen-Synchrotron DESY, Notkestr. 85, 22607 Hamburg, Germany
| | - Marco Grunwald
- Institut
für Organische Chemie, Universität
Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany
| | - Felix Demel
- Institut
für Organische Chemie, Universität
Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany
| | - Florian Bertram
- Deutsches
Elektronen-Synchrotron DESY, Notkestr. 85, 22607 Hamburg, Germany
| | - Andriy V. Kityk
- Faculty of
Electrical Engineering, Czestochowa University
of Technology, Al. Armii
Krajowej 17, 42-200 Czestochowa, Poland
| | - Andreas Schönhals
- Bundesanstalt
für Materialforschung und -prüfung (BAM), Unter den Eichen 87, 12205 Berlin, Germany
- Institut
für Chemie, Technische Universität
Berlin, Straße des
17. Juni 135, 10623 Berlin, Germany
| | - Sabine Laschat
- Institut
für Organische Chemie, Universität
Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany
| | - Patrick Huber
- Institute
for Materials and X-ray Physics, Hamburg
University of Technology, Denickestr. 15, 21073 Hamburg, Germany
- Centre
for X-ray and Nano Science CXNS, Deutsches
Elektronen-Synchrotron DESY, Notkestr. 85, 22607 Hamburg, Germany
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H. Siboni N, Shrivastav GP, Klapp SHL. Non-monotonic response of a sheared magnetic liquid crystal to a continuously increasing external field. J Chem Phys 2020; 152:024505. [DOI: 10.1063/1.5126398] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Affiliation(s)
- Nima H. Siboni
- Institut für Theoretische Physik, Technische Universität Berlin, Hardenbergstraße 36, 10623 Berlin, Germany
| | - Gaurav P. Shrivastav
- Institute für Theoretical Physics, Technische Universität Wien, Wiedner Hauptstr. 8-10, 1040 Vienna, Austria
| | - Sabine H. L. Klapp
- Institut für Theoretische Physik, Technische Universität Berlin, Hardenbergstraße 36, 10623 Berlin, Germany
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3
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Sentker K, Yildirim A, Lippmann M, Zantop AW, Bertram F, Hofmann T, Seeck OH, Kityk AV, Mazza MG, Schönhals A, Huber P. Self-assembly of liquid crystals in nanoporous solids for adaptive photonic metamaterials. NANOSCALE 2019; 11:23304-23317. [PMID: 31788679 DOI: 10.1039/c9nr07143a] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Nanoporous media exhibit structures significantly smaller than the wavelengths of visible light and can thus act as photonic metamaterials. Their optical functionality is not determined by the properties of the base materials, but rather by tailored, multiscale structures, in terms of precise pore shape, geometry, and orientation. Embedding liquid crystals in pore space provides additional opportunities to control light-matter interactions at the single-pore, meta-atomic scale. Here, we present temperature-dependent 3D reciprocal space mapping using synchrotron-based X-ray diffraction in combination with high-resolution birefringence experiments on disk-like mesogens (HAT6) imbibed in self-ordered arrays of parallel cylindrical pores 17 to 160 nm across in monolithic anodic aluminium oxide (AAO). In agreement with Monte Carlo computer simulations we observe a remarkably rich self-assembly behaviour, unknown from the bulk state. It encompasses transitions between the isotropic liquid state and discotic stacking in linear columns as well as circular concentric ring formation perpendicular and parallel to the pore axis. These textural transitions underpin an optical birefringence functionality, tuneable in magnitude and in sign from positive to negative via pore size, pore surface-grafting and temperature. Our study demonstrates that the advent of large-scale, self-organised nanoporosity in monolithic solids along with confinement-controllable phase behaviour of liquid-crystalline matter at the single-pore scale provides a reliable and accessible tool to design materials with adjustable optical anisotropy, and thus offers versatile pathways to fine-tune polarisation-dependent light propagation speeds in materials. Such a tailorability is at the core of the emerging field of transformative optics, allowing, e.g., adjustable light absorbers and extremely thin metalenses.
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Affiliation(s)
- Kathrin Sentker
- Institute of Materials Physics and Technology, Hamburg University of Technology, 21073 Hamburg, Germany.
| | - Arda Yildirim
- Bundesanstalt für Materialforschung und -prüfung (BAM), Unter den Eichen 87, D-12205 Berlin, Germany
| | - Milena Lippmann
- Deutsches Elektronen-Synchrotron DESY, Notkestrasse 85, D-22607 Hamburg, Germany
| | - Arne W Zantop
- Max-Planck-Institute for Dynamics and Self-Organization, Am Faßberg 17, D-37077 Göttingen, Germany
| | - Florian Bertram
- Deutsches Elektronen-Synchrotron DESY, Notkestrasse 85, D-22607 Hamburg, Germany
| | - Tommy Hofmann
- Helmholtz-Zentrum Berlin für Materialien und Energie, 14109 Berlin, Germany
| | - Oliver H Seeck
- Deutsches Elektronen-Synchrotron DESY, Notkestrasse 85, D-22607 Hamburg, Germany
| | - Andriy V Kityk
- Faculty of Electrical Engineering, Czestochowa University of Technology, 42-200 Czestochowa, Poland.
| | - Marco G Mazza
- Max-Planck-Institute for Dynamics and Self-Organization, Am Faßberg 17, D-37077 Göttingen, Germany and Interdisciplinary Centre for Mathematical Modelling and Department of Mathematical Sciences, Loughborough University, Loughborough, Leicestershire LE11 3TU, UK
| | - Andreas Schönhals
- Bundesanstalt für Materialforschung und -prüfung (BAM), Unter den Eichen 87, D-12205 Berlin, Germany
| | - Patrick Huber
- Institute of Materials Physics and Technology, Hamburg University of Technology, 21073 Hamburg, Germany.
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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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Pin JM, Mija A, Sbirrazzuoli N. Stereodynamic control of star-epoxy/anhydride crosslinking actuated by liquid-crystalline phase transitions. SOFT MATTER 2017; 13:1956-1965. [PMID: 28170018 DOI: 10.1039/c6sm02624a] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
The epoxy/anhydride copolymerization kinetics of an original star-epoxy monomer (TriaEP) was explored in dynamic heating mode using a series of isoconversional methods. Negative values of the apparent activation energy (Eα) related to an anti-Arrhenius behavior were observed. The transition from Arrhenius to anti-Arrhenius behavior and vice versa depending on the Eα of polymerization was correlated with the dynamics of mesophasic fall-in/fall-out events, physically induced transition (PIT) and chemically induced transition (CIT). This self-assembly phenomenon induces the generation of an anisotropic crosslinked architecture exhibiting both nematic discotic (ND) and nematic columnar (NC) organization. Particular emphasis was placed on evaluating the juxtaposition/contribution of the liquid-crystalline transitions to crosslinking, considering both the reaction dynamics and the macromolecular vision.
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Affiliation(s)
- Jean-Mathieu Pin
- Université Côte d'Azur, Institut de Chimie de Nice, UMR CNRS 7272, 06108 Nice cedex 02, France.
| | - Alice Mija
- Université Côte d'Azur, Institut de Chimie de Nice, UMR CNRS 7272, 06108 Nice cedex 02, France.
| | - Nicolas Sbirrazzuoli
- Université Côte d'Azur, Institut de Chimie de Nice, UMR CNRS 7272, 06108 Nice cedex 02, France.
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6
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Całus S, Borowik L, Kityk AV, Eich M, Busch M, Huber P. Thermotropic interface and core relaxation dynamics of liquid crystals in silica glass nanochannels: a dielectric spectroscopy study. Phys Chem Chem Phys 2015; 17:22115-24. [PMID: 26255586 DOI: 10.1039/c5cp03039k] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We report dielectric relaxation spectroscopy experiments on two rod-like liquid crystals of the cyanobiphenyl family (5CB and 6CB) confined in tubular nanochannels with 7 nm radius and 340 micrometer length in a monolithic, mesoporous silica membrane. The measurements were performed on composites for two distinct regimes of fractional filling: monolayer coverage at the pore walls and complete filling of the pores. For the layer coverage a slow surface relaxation dominates the dielectric properties. For the entirely filled channels the dielectric spectra are governed by two thermally-activated relaxation processes with considerably different relaxation rates: a slow relaxation in the interface layer next to the channel walls and a fast relaxation in the core region of the channel filling. The strengths and characteristic frequencies of both relaxation processes have been extracted and analysed as a function of temperature. Whereas the temperature dependence of the static capacitance reflects the effective (average) molecular ordering over the pore volume and is well described within a Landau-de Gennes theory, the extracted relaxation strengths of the slow and fast relaxation processes provide an access to distinct local molecular ordering mechanisms. The order parameter in the core region exhibits a bulk-like behaviour with a strong increase in the nematic ordering just below the paranematic-to-nematic transition temperature TPN and subsequent saturation during cooling. By contrast, the surface ordering evolves continuously with a kink near TPN. A comparison of the thermotropic behaviour of the monolayer with the complete filling reveals that the molecular order in the core region of the pore filling affects the order of the peripheral molecular layers at the wall.
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Affiliation(s)
- Sylwia Całus
- Faculty of Electrical Engineering, Czestochowa University of Technology, 42-200 Czestochowa, Poland.
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7
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Całus S, Kityk AV, Borowik L, Lefort R, Morineau D, Krause C, Schönhals A, Busch M, Huber P. High-resolution dielectric study reveals pore-size-dependent orientational order of a discotic liquid crystal confined in tubular nanopores. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2015; 92:012503. [PMID: 26274191 DOI: 10.1103/physreve.92.012503] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/19/2015] [Indexed: 05/16/2023]
Abstract
We report a high-resolution dielectric study on a pyrene-based discotic liquid crystal (DLC) in the bulk state and confined in parallel tubular nanopores of monolithic silica and alumina membranes. The positive dielectric anisotropy of the DLC molecule at low frequencies (in the quasistatic case) allows us to explore the thermotropic collective orientational order. A face-on arrangement of the molecular discs on the pore walls and a corresponding radial arrangement of the molecules is found. In contrast to the bulk, the isotropic-to-columnar transition of the confined DLC is continuous, shifts with decreasing pore diameter to lower temperatures, and exhibits a pronounced hysteresis between cooling and heating. These findings corroborate conclusions from previous neutron and x-ray-scattering experiments as well as optical birefringence measurements. Our study also indicates that the relative simple dielectric technique presented here is a quite efficient method in order to study the thermotropic orientational order of DLC-based nanocomposites.
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Affiliation(s)
- Sylwia Całus
- Faculty of Electrical Engineering, Czestochowa University of Technology, 42-200 Czestochowa, Poland
| | - Andriy V Kityk
- Faculty of Electrical Engineering, Czestochowa University of Technology, 42-200 Czestochowa, Poland
| | - Lech Borowik
- Faculty of Electrical Engineering, Czestochowa University of Technology, 42-200 Czestochowa, Poland
| | - Ronan Lefort
- Institut de Physique de Rennes, UMR 6251, Université de Rennes 1, 35042 Rennes, France
| | - Denis Morineau
- Institut de Physique de Rennes, UMR 6251, Université de Rennes 1, 35042 Rennes, France
| | - Christina Krause
- BAM Federal Institute for Materials Research and Testing, D-12203 Berlin, Germany
| | - Andreas Schönhals
- BAM Federal Institute for Materials Research and Testing, D-12203 Berlin, Germany
| | - Mark Busch
- Institute of Materials Physics and Technology, Hamburg University of Technology (TUHH), D-21073 Hamburg-Harburg, Germany
| | - Patrick Huber
- Institute of Materials Physics and Technology, Hamburg University of Technology (TUHH), D-21073 Hamburg-Harburg, Germany
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8
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Całus S, Jabłońska B, Busch M, Rau D, Huber P, Kityk AV. Paranematic-to-nematic ordering of a binary mixture of rodlike liquid crystals confined in cylindrical nanochannels. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2014; 89:062501. [PMID: 25019799 DOI: 10.1103/physreve.89.062501] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/04/2014] [Indexed: 06/03/2023]
Abstract
We explore the optical birefringence of the nematic binary mixtures 6CB_{1-x}7CB_{x} (0 ≤ x ≤ 1) embedded into parallel-aligned nanochannels of mesoporous alumina and silica membranes for channel radii of 3.4 ≤ R ≤ 21.0 nm. The results are compared with the bulk behavior and analyzed with a Landau-de Gennes model. Depending on the channel radius the nematic ordering in the cylindrical nanochannels evolves either discontinuously (subcritical regime, nematic ordering field σ<1/2) or continuously (overcritical regime, σ>1/2), but in both cases with a characteristic paranematic precursor behavior. The strength of the ordering field, imposed by the channel walls, and the magnitude of quenched disorder varies linearly with the mole fraction x and scales inversely proportionally with R for channel radii larger than 4 nm. The critical pore radius, R_{c}, separating a continuous from a discontinuous paranematic-to-nematic evolution varies linearly with x and differs negligibly between the silica and alumina membranes. We find no hints of preferred adsorption of one species at the channels walls. By contrast, a linear variation of the nematic-to-paranematic transition point T_{PN} and of the nematic ordering field σ versus x suggests that the binary mixtures of cyanobiphenyls 6CB and 7CB keep their homogeneous bulk stoichiometry also in nanoconfinement, at least for channel diameters larger than ∼7 nm.
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Affiliation(s)
- Sylwia Całus
- Faculty of Electrical Engineering, Czestochowa University of Technology, 42-200 Czestochowa, Poland
| | - Beata Jabłońska
- Faculty of Environmental Engineering and Biotechnology, Czestochowa University of Technology, 42-200 Czestochowa, Poland
| | - Mark Busch
- Materials Physics and Technology, Hamburg University of Technology (TUHH), D-21073 Hamburg-Harburg, Germany
| | - Daniel Rau
- FR 7.2 Experimental Physics, Saarland University, D-66123 Saarbrücken, Germany
| | - Patrick Huber
- Materials Physics and Technology, Hamburg University of Technology (TUHH), D-21073 Hamburg-Harburg, Germany and FR 7.2 Experimental Physics, Saarland University, D-66123 Saarbrücken, Germany
| | - Andriy V Kityk
- Faculty of Electrical Engineering, Czestochowa University of Technology, 42-200 Czestochowa, Poland
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9
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Cifelli M, Domenici V, Veracini CA. Recent advancements in understanding thermotropic liquid crystal structure and dynamics by means of NMR spectroscopy. Curr Opin Colloid Interface Sci 2013. [DOI: 10.1016/j.cocis.2013.03.003] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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10
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Dvinskikh SV, Furó I. Anisotropic self-diffusion in nematic, smectic-A, and reentrant nematic phases. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2012; 86:031704. [PMID: 23030930 DOI: 10.1103/physreve.86.031704] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/31/2012] [Indexed: 06/01/2023]
Abstract
The nature of the reentrant nematic phase has been actively investigated both experimentally and theoretically during the past few decades. Most studies concluded that, as concerning molecular dynamics, a reentrant nematic phase is essentially analogous to a conventional nematic one. Recent computer simulations [Mazza et al., Phys. Rev. Lett. 105, 227802 (2010)], however, predicted molecular translational self-diffusion along the phase director that was dominated by a collective transport mode and was, relative to that observed in a conventional nematic phase, enhanced by an order of magnitude. In the present work, the principal components of the diffusion tensor in a reentrant nematic phase are determined experimentally and compared to those in conventional nematic and smectic-A phases. We find that the temperature dependence of the translational diffusion in the two nematic phases, within experimental error, follows a uniform trend and can be adequately described in terms of available diffusion models in nematics. Hence, we find no evidence for enhanced diffusion but confirm instead the similarity of conventional and reentrant nematic phases with respect to molecular translational dynamics.
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Affiliation(s)
- Sergey V Dvinskikh
- KTH Royal Institute of Technology, Department of Chemistry, Division of Applied Physical Chemistry, Teknikringen 36, SE-10044 Stockholm, Sweden.
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11
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Diffusivity maximum in a reentrant nematic phase. Int J Mol Sci 2012; 13:7854-7871. [PMID: 22837730 PMCID: PMC3397562 DOI: 10.3390/ijms13067854] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2012] [Revised: 06/11/2012] [Accepted: 06/13/2012] [Indexed: 12/04/2022] Open
Abstract
We report molecular dynamics simulations of confined liquid crystals using the Gay–Berne–Kihara model. Upon isobaric cooling, the standard sequence of isotropic–nematic–smectic A phase transitions is found. Upon further cooling a reentrant nematic phase occurs. We investigate the temperature dependence of the self-diffusion coefficient of the fluid in the nematic, smectic and reentrant nematic phases. We find a maximum in diffusivity upon isobaric cooling. Diffusion increases dramatically in the reentrant phase due to the high orientational molecular order. As the temperature is lowered, the diffusion coefficient follows an Arrhenius behavior. The activation energy of the reentrant phase is found in reasonable agreement with the reported experimental data. We discuss how repulsive interactions may be the underlying mechanism that could explain the occurrence of reentrant nematic behavior for polar and non-polar molecules.
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12
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Io CW, I L. Microdiffusion in (2 + 1)-dimensional chain-bundle dusty-plasma liquids. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2012; 85:026407. [PMID: 22463337 DOI: 10.1103/physreve.85.026407] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/31/2011] [Indexed: 05/31/2023]
Abstract
Microdiffusion in a (2 + 1)-dimensional liquid with flexible long longitudinal chain bundles, formed by negatively charged dusts suspended in a low-pressure Ar gaseous discharge, is investigated. With increasing time scale τ, the transverse hopping dominated displacement induces the transition from the sub- to the superdiffusion of the single dust, and the growth of spatial displacement correlation of two dusts, which suppresses their relative diffusion. The rise time of displacement correlation increases with dust separation. The bond breaking around the hopping cluster boundary is the main source for long time relative diffusion and causes the presence of the multiple shoulders in the fat tails of the non-Gaussian relative displacement histograms. The stronger longitudinal coupling than the transverse coupling strongly enhances the motion correlation over much larger separation, and suppresses the bond-breaking rate and the relative diffusion of the longitudinal dust pairs.
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Affiliation(s)
- Chong-Wai Io
- Department of Physics and Center for Complex Systems, National Central University, Jhongli, Taiwan 32001, Republic of China
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13
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Wittkowski R, Löwen H. Dynamical density functional theory for colloidal particles with arbitrary shape. Mol Phys 2011. [DOI: 10.1080/00268976.2011.609145] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
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14
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Structure and dynamics of reentrant nematics: any open questions after almost 40 years? Int J Mol Sci 2011; 12:5352-72. [PMID: 21954364 PMCID: PMC3179171 DOI: 10.3390/ijms12085352] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2011] [Revised: 08/09/2011] [Accepted: 08/11/2011] [Indexed: 11/17/2022] Open
Abstract
Liquid crystals have attracted enormous interest because of the variety of their phases and richness of their application. The interplay of general physical symmetries and specific molecular features generates a myriad of different phenomena. A surprising behavior of liquid crystals is the reentrancy of phases as temperature, pressure, or concentration are varied. Here, we review the main experimental facts and the different theoretical scenarios that have guided the understanding of bulk reentrant nematics. Recently, some computer simulations of a system confined to nanoscopic scales have found new dynamical features of the reentrant nematic phase. We discuss this prediction in relation with the available experimental evidence on reentrant nematics and with the dynamics of liquids in strongly confined environments.
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15
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Mazza MG, Greschek M, Valiullin R, Schoen M. Role of stringlike, supramolecular assemblies in reentrant supernematic liquid crystals. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2011; 83:051704. [PMID: 21728553 DOI: 10.1103/physreve.83.051704] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/07/2011] [Indexed: 05/31/2023]
Abstract
Using a combination of isothermal-isobaric Monte Carlo and microcanonical molecular dynamics we investigate the relation between structure and self-diffusion in various phases of a model liquid crystal using the Gay-Berne-Kihara potential. These molecules are confined to a mesoscopic slit pore with atomically smooth substrate surfaces. As reported recently [seeM. G. Mazza et al., Phys. Rev. Lett. 105, 227802 (2010)], a reentrant nematic (RN) phase may form at sufficiently high pressures and densities. This phase is characterized by a high degree of nematic order and a substantially enhanced self-diffusivity in the direction of the director n that exceeds that of the lower-density nematic and an intermittent smectic-A phase by about an order of magnitude. Here we demonstrate that the unique transport behavior in the RN phase may be linked to a confinement-induced packing effect that causes the formation of supramolecular, stringlike conformations. The strings consist of several molecules traveling in the direction of n as individual "trains" consisting of chains of molecular "cars."
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Affiliation(s)
- Marco G Mazza
- Stranski-Laboratorium für Physikalische und Theoretische Chemie, Technische Universität Berlin, Berlin, Germany
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16
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Greschek M, Schoen M. Finite-size scaling analysis of isotropic-nematic phase transitions in an anisometric Lennard-Jones fluid. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2011; 83:011704. [PMID: 21405702 DOI: 10.1103/physreve.83.011704] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/15/2010] [Revised: 12/04/2010] [Indexed: 05/30/2023]
Abstract
By means of Monte Carlo simulations in the isothermal-isobaric ensemble, we perform a finite-size scaling analysis of the isotropic-nematic (IN) phase transition. Our model consists of egg-shaped anisometric Lennard-Jones molecules. We employ the cumulant intersection method to locate the pressure P* at which the IN phase transition occurs at a given temperature T. In particular, we focus on second-order cumulants of the largest and middle eigenvalues of the alignment tensor. At fixed T, cumulants for various system sizes intersect at a unique pressure P*. Various known scaling relations for these cumulants are verified numerically. At P*, the isobaric heat capacity passes through a maximum value c(P)(m), which depends on the number of molecules N. This dependency can accurately be described by a power law such that lim(N→∞)c(P)(m)(N)→∞. For sufficiently large N, the pressure at which c(P)(m) is located shifts only very slightly in agreement with the apparent insensitivity of the cumulant intersection to N. In addition, we analyze our data in terms of Landau's theory of phase transitions. Our results are consistent with a weakly discontinuous entropy-driven phase transition.
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Affiliation(s)
- Manuel Greschek
- Fakultät für Mathematik und Naturwissenschaften, Technische Universität Berlin, Berlin, Germany
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