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Zavvou EE, Welch C, Mehl GH, Vanakaras AG, Karahaliou PK. Comparative Study of the Optical and Dielectric Anisotropy of a Difluoroterphenyl Dimer and Trimer Forming Two Nematic Phases. MATERIALS (BASEL, SWITZERLAND) 2024; 17:2555. [PMID: 38893819 PMCID: PMC11173927 DOI: 10.3390/ma17112555] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/26/2024] [Revised: 05/22/2024] [Accepted: 05/23/2024] [Indexed: 06/21/2024]
Abstract
We present a comparative study of the optical and dielectric anisotropy of a laterally fluorinated liquid crystal dimer and its homologous trimer, both exhibiting two nematic phases. In the high-temperature nematic phase, both oligomers exhibit positive optical anisotropy with similar magnitude, which, however, is lower in comparison with the optical anisotropy of the monomer. In the same temperature range, the dielectric permittivity along and perpendicular to the nematic director, measured on magnetically aligned samples, reveals negative dielectric anisotropy for both oligomers, which saturates as the temperature approaches the N-N phase transition temperature. Comparison of the dielectric anisotropies of the oligomers with the corresponding anisotropy of the monomer indicates a systematic variation of its magnitude with the number of the linked mesogenic units. Results are compared with the corresponding anisotropies of the cyanobiphenyl dimers, the archetypal compounds with two nematic phases, and are discussed in terms of the dipolar structure of the mesogens and the dipolar correlations in their nematic phases.
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Affiliation(s)
| | - Chris Welch
- Department of Chemistry, University of Hull, Hull HU6 7RX, UK; (C.W.); (G.H.M.)
| | - Georg H. Mehl
- Department of Chemistry, University of Hull, Hull HU6 7RX, UK; (C.W.); (G.H.M.)
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Brumby PE, Kowaguchi A, Nozawa T, Yasuoka K, Wensink HH. Pre-Smectic Ordering and the Unwinding Helix in Monte Carlo Simulations of Cholesteric Liquid-Crystals. J Phys Chem B 2023; 127:7194-7204. [PMID: 37540189 DOI: 10.1021/acs.jpcb.3c02018] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/05/2023]
Abstract
In this paper, molecular chirality is studied for liquid-crystal fluids represented by hard rods with the addition of an attractive chiral dispersion term. Chiral forces between molecular pairs are assumed to be long-ranged and are described in terms of the pseudotensor of Goossens [W. J. A. Goossens, Mol. Cryst. Liq. Cryst. 1971, 12, 237-244]. Following Varga and Jackson [S. Varga and G. Jackson, Chem. Phys. Lett. 2003, 377, 6-12], this is combined with a hard-spherocylinder core. We investigate the relationship between molecular chirality and the helical pitch of the system, which occurs in the absence of full three-dimensional periodic boundary conditions. The dependence of the wavenumber of this pitch on the thermodynamic variables, temperature, and density is measured. We also explore the use of a novel surface boundary interaction model. As a result of this approach, we are able to lower the temperature of the system without the occurrence of nematic droplets, which would interfere with the formation of a uniaxial pitch. Regarding the theoretical predictions of Wensink and Jackson [H. H. Wensink and G. Jackson, J. Chem. Phys. 2009, 130, 234911], on the one hand, we have qualitative agreement with the observed non-monotonic density dependence of the wavenumber. Initially increasing with density, the wavenumber reaches a maximum, before falling as the density moves toward the point of phase transition from cholesteric to smectic. However, further analysis for shorter rods, in the presence of novel boundary conditions, reveals some disagreement with the theory, at least in this case; the unwinding of the cholesteric helix in the cholesteric phase occurs simultaneously with subtle increases in smectic ordering. These pre-smectic fluctuations have not been accounted for so far in theories on cholesterics but turn out to play a key role in controlling the pitch of cholesteric phases of rod-shaped mesogens with a small to moderate aspect ratio.
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Affiliation(s)
- Paul E Brumby
- Department of Mechanical Engineering, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan
| | - Akie Kowaguchi
- Department of Mechanical Engineering, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan
| | - Takuma Nozawa
- Department of Mechanical Engineering, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan
| | - Kenji Yasuoka
- Department of Mechanical Engineering, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan
| | - Henricus H Wensink
- Laboratoire de Physique des Solides─UMR 8502, Université Paris-Saclay & CNRS, Orsay 91405, France
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3
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Yamanouchi T, Cuadra R, Satoh A. Feasibility of multi-particle collision dynamics for rod-like particles and its application to a change in the orientational regime of a hematite particle suspension. Mol Phys 2021. [DOI: 10.1080/00268976.2021.1955987] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Affiliation(s)
- Takeru Yamanouchi
- Department of Mechanical Engineering, Akita Prefectural University, Yurihonjo, Japan
| | - Rafael Cuadra
- Department of Mechanical Engineering, Akita Prefectural University, Yurihonjo, Japan
| | - Akira Satoh
- Department of Mechanical Engineering, Akita Prefectural University, Yurihonjo, Japan
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Campos-Villalobos G, Dijkstra M, Patti A. Nonconventional Phases of Colloidal Nanorods with a Soft Corona. PHYSICAL REVIEW LETTERS 2021; 126:158001. [PMID: 33929217 DOI: 10.1103/physrevlett.126.158001] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/26/2020] [Accepted: 03/11/2021] [Indexed: 06/12/2023]
Abstract
Using computer simulations, we investigate the phase behavior of hard-core spherocylinders with a length-to-diameter ratio L/σ=5 and coated by a soft deformable corona of length λ/σ=1.35. When quasi-two-dimensional layers are formed in smectic and solid phases at low temperatures, the competition between the two intrinsic length scales of the parallel aligned particles leads to the stabilization of different in-plane lattices of nonconventional symmetry, including low-density hexagonal, square, and high-density hexagonal crystals, as well as an intriguing dodecagonal quasicrystal. Our Letter opens up the opportunity to control the assembly of anisotropic nanoparticles into structures with preengineered symmetry-dependent physical properties.
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Affiliation(s)
- Gerardo Campos-Villalobos
- Department of Chemical Engineering and Analytical Science, University of Manchester, Sackville Street, Manchester M13 9PL, United Kingdom
- Soft Condensed Matter, Debye Institute for Nanomaterials Science, Department of Physics, Utrecht University, Princetonplein 1, 3584 CC Utrecht, The Netherlands
| | - Marjolein Dijkstra
- Soft Condensed Matter, Debye Institute for Nanomaterials Science, Department of Physics, Utrecht University, Princetonplein 1, 3584 CC Utrecht, The Netherlands
| | - Alessandro Patti
- Department of Chemical Engineering and Analytical Science, University of Manchester, Sackville Street, Manchester M13 9PL, United Kingdom
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5
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Bedolla E, Padierna LC, Castañeda-Priego R. Machine learning for condensed matter physics. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2020; 33:053001. [PMID: 32932243 DOI: 10.1088/1361-648x/abb895] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/30/2020] [Accepted: 09/15/2020] [Indexed: 06/11/2023]
Abstract
Condensed matter physics (CMP) seeks to understand the microscopic interactions of matter at the quantum and atomistic levels, and describes how these interactions result in both mesoscopic and macroscopic properties. CMP overlaps with many other important branches of science, such as chemistry, materials science, statistical physics, and high-performance computing. With the advancements in modern machine learning (ML) technology, a keen interest in applying these algorithms to further CMP research has created a compelling new area of research at the intersection of both fields. In this review, we aim to explore the main areas within CMP, which have successfully applied ML techniques to further research, such as the description and use of ML schemes for potential energy surfaces, the characterization of topological phases of matter in lattice systems, the prediction of phase transitions in off-lattice and atomistic simulations, the interpretation of ML theories with physics-inspired frameworks and the enhancement of simulation methods with ML algorithms. We also discuss in detail the main challenges and drawbacks of using ML methods on CMP problems, as well as some perspectives for future developments.
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Affiliation(s)
- Edwin Bedolla
- División de Ciencias e Ingenierías, Universidad de Guanajuato, Loma del Bosque 103, 37150 León, Mexico
| | - Luis Carlos Padierna
- División de Ciencias e Ingenierías, Universidad de Guanajuato, Loma del Bosque 103, 37150 León, Mexico
| | - Ramón Castañeda-Priego
- División de Ciencias e Ingenierías, Universidad de Guanajuato, Loma del Bosque 103, 37150 León, Mexico
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Rosenberg M, Gregorin Ž, Boštjančič PH, Sebastián N, Lisjak D, Kantorovich SS, Mertelj A, Sánchez PA. The influence of polydispersity on the structural properties of the isotropic phase of magnetic nanoplatelets. J Mol Liq 2020. [DOI: 10.1016/j.molliq.2020.113293] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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7
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Satoh A, Okada K, Futamura M. Attachment characteristics of charged magnetic cubic particles to two parallel electrodes (3D Monte Carlo simulations). MOLECULAR SIMULATION 2020. [DOI: 10.1080/08927022.2020.1780230] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Affiliation(s)
- Akira Satoh
- Department of Mechanical Engineering, Akita Prefectural University, Yurihonjo, Japan
| | - Kazuya Okada
- Graduate School of Akita Prefectural University, Yurihonjo, Japan
| | - Muneo Futamura
- Department of Mechanical Engineering, Akita Prefectural University, Yurihonjo, Japan
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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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9
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Suzuki S, Satoh A, Wada S. Monte Carlo simulations of magnetic particle suspensions with a simple assessment method for the particle overlap between magnetic spheroids. Mol Phys 2019. [DOI: 10.1080/00268976.2019.1607915] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Affiliation(s)
- Seiya Suzuki
- Department of Mechanical Engineering, Graduate School of Akita Prefectural University, Yurihonjo, Japan
| | - Akira Satoh
- Department of Mechanical Engineering, Akita Prefectural University, Yurihonjo, Japan
| | - Shouhei Wada
- Department of Mechanical Engineering, Graduate School of Akita Prefectural University, Yurihonjo, Japan
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10
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Zákutná D, Falke Y, Dresen D, Prévost S, Bender P, Honecker D, Disch S. Morphological and crystallographic orientation of hematite spindles in an applied magnetic field. NANOSCALE 2019; 11:7149-7156. [PMID: 30778464 DOI: 10.1039/c8nr09583c] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
The magnetic response of spindle-shaped hematite (α-Fe2O3) nanoparticles was investigated by simultaneous small-angle and wide-angle X-ray scattering (SAXS/WAXS) experiments. The field-dependent magnetic and nematic order parameters of the magnetic single-domain nanospindles in a static magnetic field are fully described by SAXS simulations of an oriented ellipsoid with the implemented Langevin function. The experimental scattering intensities of the spindle-like particles can be modeled simply by using the geometrical (length, radius, size distribution) and magnetic parameters (strength of magnetic field, magnetic moment) obtained from isotropic SAXS and macroscopic magnetization measurements, respectively. Whereas SAXS gives information on the morphological particle orientation in the applied field, WAXS texture analysis elucidates the atomic scale orientation of the magnetic easy direction in the hematite crystal structure. Our results strongly suggest the tendency for uniaxial anisotropy but indicate significant thermal fluctuations of the particle moments within the hematite basal plane.
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Affiliation(s)
- Dominika Zákutná
- Large Scale Structures group, Institut Laue-Langevin, 71 avenue des Martyrs, F-38042 Grenoble, France
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11
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Nozawa T, Brumby PE, Yasuoka K. Effect of Central Longitudinal Dipole Interactions on Chiral Liquid-Crystal Phases. Int J Mol Sci 2018; 19:ijms19092715. [PMID: 30208651 PMCID: PMC6164681 DOI: 10.3390/ijms19092715] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2018] [Revised: 09/05/2018] [Accepted: 09/06/2018] [Indexed: 12/03/2022] Open
Abstract
Monte Carlo simulations of chiral liquid-crystals, represented by a simple coarse-grained chiral Gay–Berne model, were performed to investigate the effect of central longitudinal dipole interactions on phase behavior. A systematic analysis of the structural properties and phase behavior of both achiral and chiral systems, with dipole interactions, reveals differing effects; strong dipole interactions enhance the formation of layered structures; however, chiral interactions may prevent the formation of such phases under certain conditions. We also observed a short-ranged smectic structure within the cholesteric phases with strong dipole interactions. This constitutes possible evidence of presmectic ordering and/or the existence of chiral line liquid phases, which have previously been observed in X-ray experiments to occur between the smectic twisted grain boundary and cholesteric phases. These results provide a systematic understanding of how the phase behavior of chiral liquid-crystals changes when alterations are made to the strength of dipole interactions.
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Affiliation(s)
- Takuma Nozawa
- Department of Mechanical Engineering, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan.
| | - Paul E Brumby
- Department of Mechanical Engineering, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan.
| | - Kenji Yasuoka
- Department of Mechanical Engineering, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan.
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12
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Okada K, Satoh A. Quasi-2D Monte Carlo simulations of the regime change in the aggregates of magnetic cubic particles on a material surface. Mol Phys 2017. [DOI: 10.1080/00268976.2016.1278477] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Affiliation(s)
- Kazuya Okada
- Graduate School of Akita Prefectural University, Yurihonjo, Japan
| | - Akira Satoh
- Department of Machine Intelligence and System Engineering, Akita Prefectural University, Yurihonjo, Japan
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13
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Chung S, Malherbe J, Amokrane S. Effect of an external field on the structure and the phase transitions of a confined mixture of neutral and dipolar hard spheres. Mol Phys 2015. [DOI: 10.1080/00268976.2015.1014003] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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14
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Viveros-Méndez PX, Gil-Villegas A, Aranda-Espinoza S. Monte Carlo computer simulation of sedimentation of charged hard spherocylinders. J Chem Phys 2014; 141:044905. [PMID: 25084954 DOI: 10.1063/1.4890819] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
In this article we present a NVT Monte Carlo computer simulation study of sedimentation of an electroneutral mixture of oppositely charged hard spherocylinders (CHSC) with aspect ratio L/σ = 5, where L and σ are the length and diameter of the cylinder and hemispherical caps, respectively, for each particle. This system is an extension of the restricted primitive model for spherical particles, where L/σ = 0, and it is assumed that the ions are immersed in an structureless solvent, i.e., a continuum with dielectric constant D. The system consisted of N = 2000 particles and the Wolf method was implemented to handle the coulombic interactions of the inhomogeneous system. Results are presented for different values of the strength ratio between the gravitational and electrostatic interactions, Γ = (mgσ)/(e(2)/Dσ), where m is the mass per particle, e is the electron's charge and g is the gravitational acceleration value. A semi-infinite simulation cell was used with dimensions Lx ≈ Ly and Lz = 5Lx, where Lx, Ly, and Lz are the box dimensions in Cartesian coordinates, and the gravitational force acts along the z-direction. Sedimentation effects were studied by looking at every layer formed by the CHSC along the gravitational field. By increasing Γ, particles tend to get more packed at each layer and to arrange in local domains with an orientational ordering along two perpendicular axis, a feature not observed in the uncharged system with the same hard-body geometry. This type of arrangement, known as tetratic phase, has been observed in two-dimensional systems of hard-rectangles and rounded hard-squares. In this way, the coupling of gravitational and electric interactions in the CHSC system induces the arrangement of particles in layers, with the formation of quasi-two dimensional tetratic phases near the surface.
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Affiliation(s)
- P X Viveros-Méndez
- Unidad Académica de Física, Universidad Autónoma de Zacatecas, Calzada Solidaridad esq. Paseo, La Bufa s/n, 98060 Zacatecas, Zacatecas, México
| | - Alejandro Gil-Villegas
- Departamento de Ingeniería Física, División de Ciencias e Ingenierías, Campus León, Universidad de Guanajuato, Loma del Bosque 103, Lomas del Campestre, 37150 León, Guanajuato, México
| | - S Aranda-Espinoza
- Unidad Académica de Física, Universidad Autónoma de Zacatecas, Calzada Solidaridad esq. Paseo, La Bufa s/n, 98060 Zacatecas, Zacatecas, México
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15
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Bose TK, Saha J. Ferroelectric order in liquid crystal phases of polar disk-shaped ellipsoids. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2014; 89:052509. [PMID: 25353817 DOI: 10.1103/physreve.89.052509] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/21/2014] [Indexed: 06/04/2023]
Abstract
The demonstration of a spontaneous macroscopic ferroelectric order in liquid phases in the absence of any long range positional order is considered an outstanding problem of both fundamental and technological interest. Recently, we reported that a system of polar achiral disklike ellipsoids can spontaneously exhibit a long searched ferroelectric nematic phase and a ferroelectric columnar phase with strong axial polarization. The major role is played by the dipolar interactions. The model system of interest consists of attractive-repulsive Gay-Berne oblate ellipsoids embedded with two parallel point dipoles positioned symmetrically on the equatorial plane of the ellipsoids. In the present work, we investigate in detail the profound effects of changing the separation between the two symmetrically placed dipoles and the strength of the dipoles upon the existence of different ferroelectric discotic liquid crystal phases via extensive off-lattice N-P-T Monte Carlo simulations. Ferroelectric biaxial phases are exhibited in addition to the uniaxial ferroelectric fluids where the phase biaxiality results from the dipolar interactions. The structures of all the ferroelectric configurations of interest are presented in detail. Simple phase diagrams are determined which include different polar and apolar discotic fluids generated by the system.
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Affiliation(s)
- Tushar Kanti Bose
- Department of Physics, University of Calcutta, 92 Acharya Prafulla Chandra Road, Kolkata-700009, India
| | - Jayashree Saha
- Department of Physics, University of Calcutta, 92 Acharya Prafulla Chandra Road, Kolkata-700009, India
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16
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Wu L, Müller EA, Jackson G. Understanding and Describing the Liquid-Crystalline States of Polypeptide Solutions: A Coarse-Grained Model of PBLG in DMF. Macromolecules 2014. [DOI: 10.1021/ma401230x] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Liang Wu
- Department of Chemical Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom
| | - Erich A. Müller
- Department of Chemical Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom
| | - George Jackson
- Department of Chemical Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom
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17
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Wu L, Jackson G, Müller EA. Liquid crystal phase behaviour of attractive disc-like particles. Int J Mol Sci 2013; 14:16414-42. [PMID: 23965962 PMCID: PMC3759919 DOI: 10.3390/ijms140816414] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2013] [Revised: 07/24/2013] [Accepted: 07/25/2013] [Indexed: 11/17/2022] Open
Abstract
We employ a generalized van der Waals-Onsager perturbation theory to construct a free energy functional capable of describing the thermodynamic properties and orientational order of the isotropic and nematic phases of attractive disc particles. The model mesogen is a hard (purely repulsive) cylindrical disc particle decorated with an anisotropic square-well attractive potential placed at the centre of mass. Even for isotropic attractive interactions, the resulting overall inter-particle potential is anisotropic, due to the orientation-dependent excluded volume of the underlying hard core. An algebraic equation of state for attractive disc particles is developed by adopting the Onsager trial function to characterize the orientational order in the nematic phase. The theory is then used to represent the fluid-phase behaviour (vapour-liquid, isotropic-nematic, and nematic-nematic) of the oblate attractive particles for varying values of the molecular aspect ratio and parameters of the attractive potential. When compared to the phase diagram of their athermal analogues, it is seen that the addition of an attractive interaction facilitates the formation of orientationally-ordered phases. Most interestingly, for certain aspect ratios, a coexistence between two anisotropic nematic phases is exhibited by the attractive disc-like fluids.
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Affiliation(s)
- Liang Wu
- Department of Chemical Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ, UK; E-Mails: (L.W.); (G.J.)
| | - George Jackson
- Department of Chemical Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ, UK; E-Mails: (L.W.); (G.J.)
| | - Erich A. Müller
- Department of Chemical Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ, UK; E-Mails: (L.W.); (G.J.)
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18
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Bose TK, Saha J. Monte Carlo simulations of spontaneous ferroelectric order in discotic liquid crystals. PHYSICAL REVIEW LETTERS 2013; 110:265701. [PMID: 23848900 DOI: 10.1103/physrevlett.110.265701] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/18/2012] [Revised: 03/29/2013] [Indexed: 06/02/2023]
Abstract
The demonstration of a spontaneous macroscopic ferroelectric order in liquid phases in the absence of any long-range positional order is considered as an outstanding problem of great fundamental and technological interest. We report here off-lattice Monte Carlo simulations of a system of polar achiral disklike ellipsoids which spontaneously exhibit a novel ferroelectric nematic phase which is a liquid in three dimensions, considering attractive-repulsive pair interaction suitable for the anisotropic particles. At lower temperature, the ferroelectric nematic phase condenses to a ferroelectric hexagonal columnar fluid with an axial macroscopic polarization. A spontaneous ferroelectric order of dipolar origin is established here for the first time in columnar liquid crystals. Our study demonstrates that simple dipolar interactions are indeed sufficient to produce a class of novel ferroelectric fluids of essential interest. The present work reveals the structure-property relationship of achieving long searched ferroelectric liquid crystal phases and transitions between them, and we hope these findings will help in future development of technologically important fluid ferroelectric materials.
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Affiliation(s)
- Tushar Kanti Bose
- Department of Physics, University of Calcutta, 92 Acharya Prafulla Chandra Road, Kolkata 700 009, India.
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19
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Di Pietro ME, Celebre G, De Luca G, Zimmermann H, Cinacchi G. Smectic order parameters via liquid crystal NMR spectroscopy: Application to a partial bilayer smectic A phase. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2012; 35:112. [PMID: 23099532 DOI: 10.1140/epje/i2012-12112-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/13/2012] [Revised: 07/05/2012] [Accepted: 10/05/2012] [Indexed: 06/01/2023]
Abstract
Solute molecules were dissolved in the liquid crystal 4-cyano-4'-n-octyloxybiphenyl (8OCB), known to form a partial bilayer smectic-A phase. Through measurement of solutes' and solvent's orientational order parameters via nuclear magnetic resonance spectroscopy, and their analysis via a statistical thermodynamic density functional theory, values of the solvent's positional order parameters and solutes' positional-orientational distribution functions were obtained. Near to the transition to the nematic phase, the main positional order parameter of the smectic liquid crystal turned out to be comprised in the interval 0.4-0.6, though the quality of the fittings assuming the phase as nematic all across the temperature range investigated was only slightly worse. This may be ascribed to the looseness of the partial bilayer smectic structure. Solutes were found to preferentially lie in those regions where liquid crystal molecule terminal chains are located.
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Affiliation(s)
- Maria Enrica Di Pietro
- Dipartimento di Chimica, Università della Calabria, Campus di Arcavacata, Via Pietro Bucci Cubo 12C, I-87036, Rende (Cosenza), Italy
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20
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Wu L, Wensink H, Jackson G, Müller E. A generic equation of state for liquid crystalline phases of hard-oblate particles. Mol Phys 2012. [DOI: 10.1080/00268976.2011.649794] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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21
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Morales-Anda L, Wensink HH, Galindo A, Gil-Villegas A. Anomalous columnar order of charged colloidal platelets. J Chem Phys 2012; 136:034901. [PMID: 22280777 DOI: 10.1063/1.3673877] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Monte Carlo computer simulations are carried out for a model system of like-charged colloidal platelets in the isothermal-isobaric ensemble (NpT). The aim is to elucidate the role of electrostatic interactions on the structure of synthetic clay systems at high particle densities. Short-range repulsions between particles are described by a suitable hard-core model representing a discotic particle. This potential is supplemented with an electrostatic potential based on a Yukawa model for the screened Coulombic potential between infinitely thin disklike macro-ions. The particle aspect-ratio and electrostatic parameters were chosen to mimic an aqueous dispersion of thin, like-charged, rigid colloidal platelets at finite salt concentration. An examination of the fluid phase diagram reveals a marked shift in the isotropic-nematic transition compared to the hard cut-sphere reference system. Several statistical functions, such as the pair correlation function for the center-of-mass coordinates and structure factor, are obtained to characterize the structural organization of the platelets phases. At low salinity and high osmotic pressure we observe anomalous hexagonal columnar structures characterized by interpenetrating columns with a typical intercolumnar distance corresponding to about half of that of a regular columnar phase. Increasing the ionic strength leads to the formation of glassy, disordered structures consisting of compact clusters of platelets stacked into finite-sized columns. These so-called "nematic columnar" structures have been recently observed in systems of charge-stabilized gibbsite platelets. Our findings are corroborated by an analysis of the static structure factor from a simple density functional theory.
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Affiliation(s)
- L Morales-Anda
- Departamento de Ingeniería Física, División de Ciencias e Ingenierías Campus León, Universidad de Guanajuato, Colonia Lomas del Campestre, León 37150, México
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Wensink HH, Jackson G. Cholesteric order in systems of helical Yukawa rods. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2011; 23:194107. [PMID: 21525561 DOI: 10.1088/0953-8984/23/19/194107] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
We consider the interaction potential between two chiral rod-like colloids which consist of a thin cylindrical backbone decorated with a helical charge distribution on the cylinder surface. For sufficiently slender helical rods a simple scaling expression is derived which relates the chiral 'twisting' potential to the microscopic properties of the particles, such as the internal helical pitch, charge density and electrostatic screening parameter. To predict the behaviour of the macroscopic cholesteric pitch of the fluid bulk phase we invoke a simple second-virial theory generalized to treat anisotropic states with weakly twisted director fields. It is shown that, while particles with weakly coiled helices always form a cholesteric phase whose helical sense is commensurate with that of the internal helix, more strongly coiled rods lead to the formation of a cholesteric state of opposite sense. The correlation between the helical symmetry at the microscopic and macroscopic scale is found to be very sensitive to the pitch of the Yukawa helix. Mixing helical particles of sufficiently disparate length and internal pitch may give rise to a demixing of the uniform cholesteric phase into two fractions with a different macroscopic pitch. Our findings could be relevant to the interpretation of experimental observations in systems of cellulose and chitin microfibres, DNA and fd virus rods.
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Affiliation(s)
- H H Wensink
- Department of Chemical Engineering, Imperial College London, London, UK.
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Varga S, Jackson G. A study of steric chirality: the chiral nematic phase of a system of chiral two-site HGO molecules. Mol Phys 2011. [DOI: 10.1080/00268976.2011.556577] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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Brumby PE, Haslam AJ, de Miguel E, Jackson G. Subtleties in the calculation of the pressure and pressure tensor of anisotropic particles from volume-perturbation methods and the apparent asymmetry of the compressive and expansive contributions. Mol Phys 2011. [DOI: 10.1080/00268976.2010.530301] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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Jiménez-Serratos G, Avendaño C, Gil-Villegas A, González-Tovar E. Computer simulation of charged hard spherocylinders at low temperatures. Mol Phys 2011. [DOI: 10.1080/00268976.2010.524171] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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Martín-Betancourt M, Romero-Enrique JM, Rull LF. Finite-size scaling study of the liquid–vapour critical point of dipolar square-well fluids. Mol Phys 2010. [DOI: 10.1080/00268970902889659] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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GIL-VILLEGAS BALEJANDRO, McGROTHER and GEORGE JACKSON SIMONC. Reaction-field and Ewald summation methods in Monte Carlo simulations of dipolar liquid crystals. Mol Phys 2010. [DOI: 10.1080/002689797170004] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
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WEIS JJ. PRELIMINARY COMMUNICATION Orientational structure of quasi-two-dimensional dipolar hard spheres. Mol Phys 2010. [DOI: 10.1080/002689798169023] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
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Das P, De J. Crystal structure and microstructure of cholesteryl oleyl carbonate. Chem Phys Lipids 2010; 164:33-41. [PMID: 20951687 DOI: 10.1016/j.chemphyslip.2010.10.001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2009] [Revised: 10/05/2010] [Accepted: 10/05/2010] [Indexed: 10/18/2022]
Abstract
The crystal structure as well as the microstructure, i.e., size and strain, of crystallites of cholesteryl oleyl carbonate was determined from X-ray powder diffraction data. The X-ray line broadening was analyzed through the refinement of TCH-pseudo-Voigt function parameters (isotropic effects) and the refinement of multipolar functions, i.e., symmetrized cubic harmonics (anisotropic effects). The crystal structure turns out to be primitive monoclinic, space group Pc, type I monolayer having two molecules per unit cell with parameters: a=18.921±0.006Å, b=12.952±0.003Å, c=9.276±0.002Å and β=91.32±0.03°. The average size of a well ground specimen of crystallites was 60nm. The average micro-strain, e.g., 45×10(-4) has been tentatively attributed to fatty chain conformational disorder. The unit cell parameters, including the lamellar thickness, of COC crystal is very closely similar to those of another, structurally similar cholesterol ester, e.g., cholesteryl oleate (CO) crystal, space group P2(1), type II monolayer. Type I monolayer structure has been established for COC on the basis of the intensity calculations of the XRD profiles of both CO and COC. The dipolar and structural disorder in a 4:1 molar, binary mixture of CO and COC can be accommodated in an induced smectic phase with a lamellar thickness, which is nearly equal to that of pure CO or pure COC.
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Affiliation(s)
- Pradip Das
- Department of Chemistry, Bose Institute, 93/1 A. P. C. Road, Kolkata 700009, India.
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Franco-Melgar M, Haslam AJ, Jackson G. Advances in generalised van der Waals approaches for the isotropic–nematic fluid phase equilibria of thermotropic liquid crystals–an algebraic equation of state for attractive anisotropic particles with the Onsager trial function. Mol Phys 2009. [DOI: 10.1080/00268970903352335] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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Wensink HH, Jackson G. Generalized van der Waals theory for the twist elastic modulus and helical pitch of cholesterics. J Chem Phys 2009; 130:234911. [DOI: 10.1063/1.3153348] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Houssa M, Rull LF, Romero-Enrique JM. Bilayered smectic phase polymorphism in the dipolar Gay–Berne liquid crystal model. J Chem Phys 2009; 130:154504. [DOI: 10.1063/1.3111953] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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Avendaño C, Gil-Villegas A, González-Tovar E. A Monte Carlo simulation study of binary mixtures of charged hard spherocylinders and charged hard spheres. Chem Phys Lett 2009. [DOI: 10.1016/j.cplett.2009.01.017] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Franco-Melgar M, Haslam AJ, Jackson G. A generalisation of the Onsager trial-function approach: describing nematic liquid crystals with an algebraic equation of state. Mol Phys 2008. [DOI: 10.1080/00268970801926958] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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Avendaño C, Gil-Villegas A, González-Tovar E. Computer simulation of charged hard spherocylinders. J Chem Phys 2008; 128:044506. [DOI: 10.1063/1.2823736] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Varga S, Jackson G. Study of the pitch of fluids of electrostatically chiral anisotropic molecules: mean-field theory and simulation. Mol Phys 2006. [DOI: 10.1080/00268970601058556] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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Neal MP, Parker AJ, Grayson M. Computer Simulation of Liquid Crystalline Molecular Asymmetry and its Link to Molecular Design. ACTA ACUST UNITED AC 2006. [DOI: 10.1080/10587250108025000] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Affiliation(s)
- Maureen P. Neal
- a School of Mathematical and Information Sciences, Coventry University , Coventry , CV1 5FB , UK
| | - Andrew J. Parker
- b School of Mathematics and Computing, University of Derby , DE22 1GB , UK
| | - Martin Grayson
- c Department of Chemistry , Sheffield University , S3 7HF , UK
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Mejía-Rosales SJ, Gil-Villegas A, Ivlev BI, Ruiz-García J. Predicting the Phase Diagram of Two-Dimensional Colloidal Systems with Long-Range Interactions. J Phys Chem B 2006; 110:22230-6. [PMID: 17078663 DOI: 10.1021/jp0562328] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The phase diagram of a two-dimensional model system for colloidal particles at the air-water interface was determined using Monte Carlo computer simulations in the isothermic-isobaric ensemble. The micrometer-range binary colloidal interaction has been modeled by hard disklike particles interacting via a secondary minimum followed by a weaker longer-range repulsive maximum, both of the order of kBT. The repulsive part of the potential drives the clustering of particles at low densities and low temperatures. Pinned voids are formed at higher densities and intermediate values of the surface pressure. The analysis of isotherms, translational and orientational correlation functions as well as structure factor gives clear evidence of the presence of a melting first-order transition. However, the melting process can be also followed by a metastable route through a hexatic phase at low surface pressures and low temperatures, before crystalization occurs at higher surface pressure.
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Affiliation(s)
- Sergio J Mejía-Rosales
- Facultad de Ciencias Físico-Matematicas, Universidad Autónoma de Nuevo León, Ciudad Universitaria, San Nicolas de los Garza, NL 66450, Mexico
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Dewar A, Camp PJ. Dipolar interactions, molecular flexibility, and flexoelectricity in bent-core liquid crystals. J Chem Phys 2005; 123:174907. [PMID: 16375569 DOI: 10.1063/1.2062007] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The effects of dipolar interactions and molecular flexibility on the structure and phase behavior of bent-core molecular fluids are studied using Monte Carlo computer simulations. Some calculations of flexoelectric coefficients are also reported. The rigid cores of the model molecules consist of either five or seven soft spheres arranged in a "V" shape with external bend angle gamma. With purely repulsive sphere-sphere interactions and gamma = 0 degrees (linear molecules) the seven-sphere model exhibits isotropic, uniaxial nematic, and untilted and tilted smectic phases. With gamma > or = 20 degrees the untilted smectic phases disappear, while the system with gamma > or = 40 degrees shows a direct tilted smectic-isotropic fluid transition. The addition of electrostatic interactions between transverse dipole moments on the apical spheres is generally seen to reduce the degree of molecular inclination in tilted phases, and destabilizes the nematic and untilted smectic phases of linear molecules. The effects of adding three-segment flexible tails to the ends of five-sphere bent-core molecules are examined using configurational-bias Monte Carlo simulations. Only isotropic and smectic phases are observed. On the one hand, molecular flexibility gives rise to pronounced fluctuations in the smectic-layer structure, bringing the simulated system in better correspondence with real materials; on the other hand, the smectic phase shows almost no tilt. Lastly, the flexoelectric coefficients of various nematic phases--with and without attractive sphere-sphere interactions--are presented. The results are encouraging, but a large computational effort is required to evaluate the appropriate fluctuation relations reliably.
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Affiliation(s)
- Alastair Dewar
- School of Chemistry, The University of Edinburgh, West Mains Road, Edinburgh EH9 3JJ, United Kingdom
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Stambaugh J, Lathrop DP, Ott E, Losert W. Pattern formation in a monolayer of magnetic spheres. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2003; 68:026207. [PMID: 14525084 DOI: 10.1103/physreve.68.026207] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/17/2002] [Indexed: 05/24/2023]
Abstract
Pattern formation is investigated for a vertically vibrated monolayer of magnetic spheres. The spheres of diameter D encase cylindrical magnetic cores of length l. For large D/l, we find that the particles form a hexagonal-close-packed pattern in which the particles' dipole vectors assume a macroscopic circulating vortical pattern. For smaller D/l, the particles form concentric rings. The static configurational magnetic energy (which depends on D/l) appears to be a determining factor in pattern selection even though the experimental system is driven and dissipative.
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Affiliation(s)
- Justin Stambaugh
- Institute for Research in Electronics and Applied Physics, Department of Physics, University of Maryland, College Park, Maryland 20742, USA
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Johnston SJ, Low RJ, Neal MP. Computer simulation of polar bent-core molecules. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2002; 66:061702. [PMID: 12513300 DOI: 10.1103/physreve.66.061702] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/15/2002] [Indexed: 05/24/2023]
Abstract
Results are presented from molecular dynamics simulations in the NPT ensemble of novel bent-core liquid crystal systems. Following on from a previous study of bent-core steric shape, this study examines the effect the addition of a transverse electric dipole has on the phase diagram of a bent-core liquid crystal model. A simple model of the interaction employed a two-site Gay-Berne potential with the sites separated by +/-0.5 reduced units with a central transverse point dipole, for all models investigated. The angle between the sites 180 degrees -gamma was varied in a range gamma=10 degrees to gamma=70 degrees suggested by real molecules. The addition of the dipole to the model tended to stabilize smectic phases and increase the angle of tilted phases. As the angle gamma increased, the transition temperature to the first ordered phase decreased markedly. Smectic A, tilted smectic B, and a spontaneously polarized smectic B phases were observed in the gamma=10 degrees bent-core model. The gamma=20 degrees model showed smectic A and tilted antiferroelectric smectic B phases. The gamma=40 degrees model showed an antiferroelectric phase that exhibited unusual packing behavior. Both the gamma=20 degrees and gamma=40 degrees models demonstrated a significant phase biaxiality in the smectic B phases.
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Affiliation(s)
- Stephen J Johnston
- School of Mathematical and Information Sciences, Coventry University, Coventry, CV1 5FB, United Kingdom
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Varga S, Szalai I, Liszi J, Jackson G. A study of orientational ordering in a fluid of dipolar Gay–Berne molecules using density-functional theory. J Chem Phys 2002. [DOI: 10.1063/1.1469607] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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46
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Berardi R, Ricci M, Zannoni C. Ferroelectric Nematic and Smectic Liquid Crystals from Tapered Molecules. Chemphyschem 2001; 2:443-7. [DOI: 10.1002/1439-7641(20010716)2:7<443::aid-cphc443>3.0.co;2-j] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2001] [Indexed: 11/08/2022]
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van Duijneveldt JS, Gil-Villegas A, Jackson G, Allen MP. Simulation study of the phase behavior of a primitive model for thermotropic liquid crystals: Rodlike molecules with terminal dipoles and flexible tails. J Chem Phys 2000. [DOI: 10.1063/1.481520] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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Houssa M, Rull LF, McGrother SC. Effect of dipolar interactions on the phase behavior of the Gay–Berne liquid crystal model. J Chem Phys 1998. [DOI: 10.1063/1.477615] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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