1
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Svenšek D, Sočan J, Praprotnik M. Density-Nematic Coupling in Isotropic Solution of DNA: Multiscale Model. Macromol Rapid Commun 2024:e2400382. [PMID: 39122482 DOI: 10.1002/marc.202400382] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2024] [Revised: 07/26/2024] [Indexed: 08/12/2024]
Abstract
Monte Carlo simulations of isotropic solutions of double-stranded DNA (deoxyribonucleic acid) are performed using the well-established oxDNA model. By comparing the fluctuation amplitudes with theoretical predictions, the parameters of a generic macroscopic model of an isotropic linear polymer solution/melt are determined. A multiscale continuum field model is thus obtained, corresponding to the full specificity of the isotropic phase of double-stranded DNA in the usual B-form as perceived at the macroscopic level. Present research is particularly focused on the coupling between spatial concentration/density variations of the polymer and the emerging nematic orientation order of the chains. This rather unfamiliar, only recently described phenomenon, inherent to linear polymers, is outlined and interpreted. Quantitative predictions are provided for the degree of nematic order induced by concentration gradients in isotropic solutions of double-stranded DNA.
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Affiliation(s)
- Daniel Svenšek
- Laboratory for Molecular Modeling, National Institute of Chemistry, Ljubljana, SI-1001, Slovenia
- Department of Physics, Faculty of Mathematics and Physics, University of Ljubljana, Ljubljana, SI-1000, Slovenia
| | - Jaka Sočan
- Laboratory for Molecular Modeling, National Institute of Chemistry, Ljubljana, SI-1001, Slovenia
| | - Matej Praprotnik
- Laboratory for Molecular Modeling, National Institute of Chemistry, Ljubljana, SI-1001, Slovenia
- Department of Physics, Faculty of Mathematics and Physics, University of Ljubljana, Ljubljana, SI-1000, Slovenia
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2
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Revignas D, Ferrarini A. On the elusive saddle-splay and splay-bend elastic constants of nematic liquid crystals. J Chem Phys 2023; 159:034905. [PMID: 37470424 DOI: 10.1063/5.0153831] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2023] [Accepted: 06/27/2023] [Indexed: 07/21/2023] Open
Abstract
The elastic behavior of nematics is commonly described in terms of the three so-called bulk deformation modes, i.e., splay, twist, and bend. However, the elastic free energy contains also other terms, often denoted as saddle-splay and splay-bend, which contribute, for instance, in confined systems. The role of such terms is controversial, partly because of the difficulty of their experimental determination. The saddle-splay (K24) and splay-bend (K13) elastic constants remain elusive also for theories; indeed, even the possibility of obtaining unambiguous microscopic expressions for these quantities has been questioned. Here, within the framework of Onsager theory with Parsons-Lee correction, we obtain microscopic estimates of the deformation free energy density of hard rod nematics in the presence of different director deformations. In the limit of a slowly changing director, these are directly compared with the macroscopic elastic free energy density. Within the same framework, we derive also closed microscopic expressions for all elastic coefficients of rodlike nematics. We find that the saddle-splay constant K24 is larger than both K11 and K22 over a wide range of particle lengths and densities. Moreover, the K13 contribution comes out to be crucial for the consistency of the results obtained from the analysis of the microscopic deformation free energy density calculated for variants of the splay deformation.
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Affiliation(s)
- Davide Revignas
- Department of Chemical Sciences, University of Padova, Via Marzolo 1, 35131 Padova, Italy
| | - Alberta Ferrarini
- Department of Chemical Sciences, University of Padova, Via Marzolo 1, 35131 Padova, Italy
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3
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Wood EL, Greco C, Ivanov DA, Kremer K, Daoulas KC. Mesoscopic Modeling of a Highly-Ordered Sanidic Polymer Mesophase and Comparison With Experimental Data. J Phys Chem B 2022; 126:2285-2298. [PMID: 35290739 PMCID: PMC8958507 DOI: 10.1021/acs.jpcb.1c10599] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
![]()
Board-shaped polymers
form sanidic mesophases: assemblies of parallel
lamellae of stacked polymer backbones separated by disordered side
chains. Sanidics vary significantly with respect to polymer order
inside their lamellae, making them “stepping stones”
toward the crystalline state. Therefore, they are potentially interesting
for studying crystallization and technological applications. Building
on earlier mesoscopic models of the most disordered sanidics Σd, we focus on the other extreme, near-crystalline order, and
develop a generic model that captures a highly ordered Σr mesophase. Polymers are described by generic hindered-rotation
chains. Anisotropic nonbonded potentials, with strengths comparable
to the thermal energy, mimic board-like monomer shapes. Lamellae equilibrated
with Monte Carlo simulations, for a broad range of model parameters,
have intralamellar order typical for Σr mesophases:
periodically stacked polymers that are mutually registered along their
backbones. Our mesophase shows registration on both monomer and chain
levels. We calculate scattering patterns and compare with data published
for highly ordered sanidic mesophases of two different polymers: polyesters
and polypeptoids. Most of the generic structural features that were
identified in these experiments are present in our model. However,
our mesophase has correlations between chains located in different
lamellae and is therefore closer to the crystalline state than the
experimental samples.
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Affiliation(s)
- Emma L Wood
- Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany
| | - Cristina Greco
- Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany
| | - Dimitri A Ivanov
- Institute for Problems of Chemical Physics, Russian Academy of Sciences, Semenov Prospect 1, 142432 Chernogolovka, Russia.,Lomonosov Moscow State University, Leninskie Gory 1, 119991 Moscow, Russia.,Institut de Sciences des Matériaux de Mulhouse, CNRS UMR 7361, 15 Jean Starcky, F-68057 Mulhouse, France.,Sirius University of Science and Technology, 1 Olympic Ave, 354340, Sochi, Russia
| | - Kurt Kremer
- Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany
| | - Kostas Ch Daoulas
- Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany
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4
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Nikoubashman A. Ordering, phase behavior, and correlations of semiflexible polymers in confinement. J Chem Phys 2021; 154:090901. [DOI: 10.1063/5.0038052] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Affiliation(s)
- Arash Nikoubashman
- Institute of Physics, Johannes Gutenberg University Mainz, Staudingerweg 7, 55128 Mainz, Germany
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5
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Wensink HH. Polymeric Nematics of Associating Rods: Phase Behavior, Chiral Propagation, and Elasticity. Macromolecules 2019. [DOI: 10.1021/acs.macromol.9b01421] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Henricus H. Wensink
- Laboratoire de Physique des Solides—UMR 8502, CNRS, Université Paris-Sud, Université Paris-Saclay, 91405 Orsay, France
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6
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Midya J, Egorov SA, Binder K, Nikoubashman A. Phase behavior of flexible and semiflexible polymers in solvents of varying quality. J Chem Phys 2019; 151:034902. [DOI: 10.1063/1.5110393] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Affiliation(s)
- Jiarul Midya
- Institute of Physics, Johannes Gutenberg University Mainz, Staudingerweg 7, 55128 Mainz,
Germany
| | - Sergei A. Egorov
- Department of Chemistry, University of Virginia, McCormick Road, Charlottesville, Virginia 22904-4319,
USA
| | - Kurt Binder
- Institute of Physics, Johannes Gutenberg University Mainz, Staudingerweg 7, 55128 Mainz,
Germany
| | - Arash Nikoubashman
- Institute of Physics, Johannes Gutenberg University Mainz, Staudingerweg 7, 55128 Mainz,
Germany
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7
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Popadić A, Svenšek D, Podgornik R, Praprotnik M. Density–Nematic Coupling in Isotropic Linear Polymers: Acoustic and Osmotic Birefringence. ADVANCED THEORY AND SIMULATIONS 2019. [DOI: 10.1002/adts.201900019] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Affiliation(s)
- Aleksandar Popadić
- Laboratory for Molecular ModelingNational Institute of ChemistrySI‐1001 Ljubljana Slovenia
| | - Daniel Svenšek
- Department of Physics, Faculty of Mathematics and PhysicsUniversity of LjubljanaSI‐1000 Ljubljana Slovenia
| | - Rudolf Podgornik
- Department of Physics, Faculty of Mathematics and PhysicsUniversity of LjubljanaSI‐1000 Ljubljana Slovenia
- Department of Theoretical PhysicsJ. Stefan InstituteSI‐1000 Ljubljana Slovenia
- School of Physical Sciences and Kavli Institute for Theoretical SciencesUniversity of Chinese Academy of SciencesBeijing 100049 China
- CAS Key Laboratory of Soft Matter Physics, Institute of PhysicsChinese Academy of SciencesBeijing 100190 China
| | - Matej Praprotnik
- Laboratory for Molecular ModelingNational Institute of ChemistrySI‐1001 Ljubljana Slovenia
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8
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Milchev A, Egorov SA, Binder K, Nikoubashman A. Nematic order in solutions of semiflexible polymers: Hairpins, elastic constants, and the nematic-smectic transition. J Chem Phys 2018; 149:174909. [PMID: 30408984 DOI: 10.1063/1.5049630] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Coarse-grained models of lyotropic solutions of semiflexible polymers are studied by both molecular dynamics simulations and density functional theory calculations, using an implicit solvent bead-spring model with a bond-angle potential. We systematically vary the monomer density, persistence length, and contour length over a wide range and explore the full range from the isotropic-nematic transition to the nematic-smectic transition. In the nematic regime, we span the entire regime from rigid-rod like polymers to thin wormlike chains, confined in effective straight tubes caused by the collective nematic effective ordering field. We show that the distribution of bond angles relative to the director is well described by a Gaussian, irrespective of whether the chains are rod-like or rather flexible. However, the related concept of "deflection length" is shown to make sense only in the latter case for rather dilute solutions since otherwise the deflection length is of the order of about two bond lengths only. When the solution is semi-dilute, a substantial renormalization of the persistence length occurs, while this effect is absent in the isotropic phase even at rather high monomer densities. The effective radii of the "tubes" confining the chains in the related description of orientational ordering are significantly larger than the distances between neighboring chains, providing evidence for a pronounced collective character of orientational fluctuations. Hairpins can be identified close to the isotropic-nematic transition, and their probability of occurrence agrees qualitatively with the Vroege-Odijk theory. The corresponding theoretical predictions for the elastic constants, however, are not in good agreement with the simulations. We attribute the shortcomings of the theories to their neglect of the coupling between local density and orientational fluctuations. Finally, we detected for this model a transition to a smectic phase for reduced monomer densities near 0.7.
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Affiliation(s)
- Andrey Milchev
- Institute for Physical Chemistry, Bulgarian Academia of Sciences, 1113 Sofia, Bulgaria
| | - Sergei A Egorov
- Institute of Physics, Johannes Gutenberg University Mainz, Staudingerweg 7, 55128 Mainz, Germany
| | - Kurt Binder
- Institute of Physics, Johannes Gutenberg University Mainz, Staudingerweg 7, 55128 Mainz, Germany
| | - Arash Nikoubashman
- Institute of Physics, Johannes Gutenberg University Mainz, Staudingerweg 7, 55128 Mainz, Germany
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9
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Popadić A, Svenšek D, Podgornik R, Daoulas KC, Praprotnik M. Splay-density coupling in semiflexible main-chain nematic polymers with hairpins. SOFT MATTER 2018; 14:5898-5905. [PMID: 29972386 DOI: 10.1039/c8sm00835c] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
A main-chain nematic polymer melt/solution exhibits macroscopic orientational order of main polymer chains, i.e., a preferred (nematic) direction. It has long been known that in such polymeric liquid crystals spatial density/concentration variations and distortions of the nematic direction are coupled, obeying a vectorial continuity constraint whose rigidity increases with chain length. Its vectorial nature precludes the application to flexible chains, where backfolds (hairpins) are present and apolar nematic symmetry is manifest, which has been its puzzling feature from the beginning. We now establish a description of the splay-density coupling in the case of arbitrary backfolding, devising a continuity constraint for the "recovered" polar order of the chain tangents and introducing hairpins as its new type of sources. Performing detailed Monte Carlo simulations of nematic monodomain melts of "soft" worm-like chains with variable length and flexibility, we show via their structure factors that the weakening of the coupling due to the backfolding can be consistently quantified on the macroscopic level.
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Affiliation(s)
- Aleksandar Popadić
- Laboratory for Molecular Modeling, National Institute of Chemistry, SI-1001 Ljubljana, Slovenia
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10
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Affiliation(s)
- Emanuele Romani
- Dipartimento di Fisica, “Sapienza” Università di Roma, P.le A. Moro 2, 00185 Roma, Italy
| | - Alberta Ferrarini
- Dipartimento di Scienze Chimiche, Università di Padova, via Marzolo 1, I-35131 Padova, Italy
| | - Cristiano De Michele
- Dipartimento di Fisica, “Sapienza” Università di Roma, P.le A. Moro 2, 00185 Roma, Italy
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11
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Ramírez-Hernández A, Hur SM, Armas-Pérez JC, de la Cruz MO, de Pablo JJ. Demixing by a Nematic Mean Field: Coarse-Grained Simulations of Liquid Crystalline Polymers. Polymers (Basel) 2017; 9:E88. [PMID: 30970766 PMCID: PMC6431948 DOI: 10.3390/polym9030088] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2016] [Accepted: 02/24/2017] [Indexed: 11/17/2022] Open
Abstract
Liquid crystalline polymers exhibit a particular richness of behaviors that stems from their rigidity and their macromolecular nature. On the one hand, the orientational interaction between liquid-crystalline motifs promotes their alignment, thereby leading to the emergence of nematic phases. On the other hand, the large number of configurations associated with polymer chains favors formation of isotropic phases, with chain stiffness becoming the factor that tips the balance. In this work, a soft coarse-grained model is introduced to explore the interplay of chain stiffness, molecular weight and orientational coupling, and their role on the isotropic-nematic transition in homopolymer melts. We also study the structure of polymer mixtures composed of stiff and flexible polymeric molecules. We consider the effects of blend composition, persistence length, molecular weight and orientational coupling strength on the melt structure at the nano- and mesoscopic levels. Conditions are found where the systems separate into two phases, one isotropic and the other nematic. We confirm the existence of non-equilibrium states that exhibit sought-after percolating nematic domains, which are of interest for applications in organic photovoltaic and electronic devices.
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Affiliation(s)
- Abelardo Ramírez-Hernández
- Materials Science Division, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439, USA
- Institute for Molecular Engineering, The University of Chicago, Chicago, IL 60637, USA; (S.-M.H.); (J.C.A.-P.)
| | - Su-Mi Hur
- Institute for Molecular Engineering, The University of Chicago, Chicago, IL 60637, USA; (S.-M.H.); (J.C.A.-P.)
- School of Polymer Science and Engineering, Chonnam National University, Gwangju 500-757, Korea
| | - Julio C. Armas-Pérez
- Institute for Molecular Engineering, The University of Chicago, Chicago, IL 60637, USA; (S.-M.H.); (J.C.A.-P.)
- División de Ciencias e Ingenierías, Campus León, Universidad de Guanajuato, Loma del Bosque 103, León, Guanajuato 37150, Mexico
| | - Monica Olvera de la Cruz
- Department of Materials Science and Engineering, Northwestern University, Evanston, IL 60208, USA;
| | - Juan J. de Pablo
- Materials Science Division, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439, USA
- Institute for Molecular Engineering, The University of Chicago, Chicago, IL 60637, USA; (S.-M.H.); (J.C.A.-P.)
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12
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Milchev A, Egorov SA, Binder K. Semiflexible polymers confined in a slit pore with attractive walls: two-dimensional liquid crystalline order versus capillary nematization. SOFT MATTER 2017; 13:1888-1903. [PMID: 28180230 DOI: 10.1039/c7sm00105c] [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
Semiflexible polymers under good solvent conditions interacting with attractive planar surfaces are investigated by Molecular Dynamics (MD) simulations and classical Density Functional Theory (DFT). A bead-spring type potential complemented by a bending potential is used, allowing variation of chain stiffness from completely flexible coils to rod-like polymers whose persistence length by far exceeds their contour length. Solvent is only implicitly included, monomer-monomer interactions being purely repulsive, while two types of attractive wall-monomer interactions are considered: (i) a strongly attractive Mie-type potential, appropriate for a strictly structureless wall, and (ii) a corrugated wall formed by Lennard-Jones particles arranged on a square lattice. It is found that in dilute solutions the former case leads to the formation of a strongly adsorbed surface layer, and the profile of density and orientational order in the z-direction perpendicular to the wall is predicted by DFT in nice agreement with MD. While for very low bulk densities a Kosterlitz-Thouless type transition from the isotropic phase to a phase with power-law decay of nematic correlations is suggested to occur in the strongly adsorbed layer, for larger densities a smectic-C phase in the surface layer is detected. No "capillary nematization" effect at higher bulk densities is found in this system, unlike systems with repulsive walls. This finding is attributed to the reduction of the bulk density (in the center of the slit pore) due to polymer adsorption on the attractive wall, for a system studied in the canonical ensemble. Consequently in a system with two attractive walls nematic order in the slit pore can occur only at a higher density than for a bulk system.
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Affiliation(s)
- Andrey Milchev
- Institute for Physical Chemistry, Bulgarian Academia of Sciences, 1113 Sofia, Bulgaria. and Institut für Physik, Johannes Gutenberg Universität Mainz, 55099 Mainz, Germany
| | - Sergei A Egorov
- Institut für Physik, Johannes Gutenberg Universität Mainz, 55099 Mainz, Germany and Department of Chemistry, University of Virginia, Charlottesville, VA 22901, USA
| | - Kurt Binder
- Institut für Physik, Johannes Gutenberg Universität Mainz, 55099 Mainz, Germany
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13
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Thermodynamics of a Compressible Maier-Saupe Model Based on the Self-Consistent Field Theory of Wormlike Polymer. Polymers (Basel) 2017; 9:polym9020048. [PMID: 30970727 PMCID: PMC6431982 DOI: 10.3390/polym9020048] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2016] [Revised: 01/27/2017] [Accepted: 01/30/2017] [Indexed: 11/17/2022] Open
Abstract
This paper presents a theoretical formalism for describing systems of semiflexible polymers, which can have density variations due to finite compressibility and exhibit an isotropic-nematic transition. The molecular architecture of the semiflexible polymers is described by a continuum wormlike-chain model. The non-bonded interactions are described through a functional of two collective variables, the local density and local segmental orientation tensor. In particular, the functional depends quadratically on local density-variations and includes a Maier–Saupe-type term to deal with the orientational ordering. The specified density-dependence stems from a free energy expansion, where the free energy of an isotropic and homogeneous homopolymer melt at some fixed density serves as a reference state. Using this framework, a self-consistent field theory is developed, which produces a Helmholtz free energy that can be used for the calculation of the thermodynamics of the system. The thermodynamic properties are analysed as functions of the compressibility of the model, for values of the compressibility realizable in mesoscopic simulations with soft interactions and in actual polymeric materials.
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14
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Greco C, Jiang Y, Chen JZY, Kremer K, Daoulas KC. Maier-Saupe model of polymer nematics: Comparing free energies calculated with Self Consistent Field theory and Monte Carlo simulations. J Chem Phys 2016; 145:184901. [PMID: 27846703 DOI: 10.1063/1.4966919] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Self Consistent Field (SCF) theory serves as an efficient tool for studying mesoscale structure and thermodynamics of polymeric liquid crystals (LC). We investigate how some of the intrinsic approximations of SCF affect the description of the thermodynamics of polymeric LC, using a coarse-grained model. Polymer nematics are represented as discrete worm-like chains (WLC) where non-bonded interactions are defined combining an isotropic repulsive and an anisotropic attractive Maier-Saupe (MS) potential. The range of the potentials, σ, controls the strength of correlations due to non-bonded interactions. Increasing σ (which can be seen as an increase of coarse-graining) while preserving the integrated strength of the potentials reduces correlations. The model is studied with particle-based Monte Carlo (MC) simulations and SCF theory which uses partial enumeration to describe discrete WLC. In MC simulations the Helmholtz free energy is calculated as a function of strength of MS interactions to obtain reference thermodynamic data. To calculate the free energy of the nematic branch with respect to the disordered melt, we employ a special thermodynamic integration (TI) scheme invoking an external field to bypass the first-order isotropic-nematic transition. Methodological aspects which have not been discussed in earlier implementations of the TI to LC are considered. Special attention is given to the rotational Goldstone mode. The free-energy landscape in MC and SCF is directly compared. For moderate σ the differences highlight the importance of local non-bonded orientation correlations between segments, which SCF neglects. Simple renormalization of parameters in SCF cannot compensate the missing correlations. Increasing σ reduces correlations and SCF reproduces well the free energy in MC simulations.
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Affiliation(s)
- Cristina Greco
- Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany
| | - Ying Jiang
- School of Chemistry and Environment, Center of Soft Matter Physics and its Applications, Beihang University, Beijing 100191, China
| | - Jeff Z Y Chen
- Department of Physics and Astronomy, University of Waterloo, Waterloo, Ontario N2L4K1, Canada
| | - Kurt Kremer
- Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany
| | - Kostas Ch Daoulas
- Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany
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15
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Egorov SA, Milchev A, Binder K. Semiflexible Polymers in the Bulk and Confined by Planar Walls. Polymers (Basel) 2016; 8:E296. [PMID: 30974573 PMCID: PMC6432127 DOI: 10.3390/polym8080296] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2016] [Revised: 07/27/2016] [Accepted: 07/29/2016] [Indexed: 11/21/2022] Open
Abstract
Semiflexible polymers in solution under good solvent conditions can undergo an isotropic-nematic transition. This transition is reminiscent of the well-known entropically-driven transition of hard rods described by Onsager's theory, but the flexibility of the macromolecules causes specific differences in behavior, such as anomalous long wavelength fluctuations in the ordered phase, which can be understood by the concept of the deflection length. A brief review of the recent progress in the understanding of these problems is given, summarizing results obtained by large-scale molecular dynamics simulations and density functional theory. These results include also the interaction of semiflexible polymers with hard walls and the wall-induced nematic order, which can give rise to capillary nematization in thin film geometry. Various earlier theoretical approaches to these problems are briefly mentioned, and an outlook on the status of experiments is given. It is argued that in many cases of interest, it is not possible to describe the scaled densities at the isotropic-nematic transition as functions of the ratio of the contour length and the persistence length alone, but the dependence on the ratio of chain diameter and persistence length also needs to be considered.
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Affiliation(s)
- Sergei A Egorov
- Department of Chemistry, University of Virginia, Charlottesville, VA 22901, USA.
- Institut für Physik, Johannes Gutenberg Universität Mainz, 55099 Mainz, Germany.
| | - Andrey Milchev
- Institute for Physical Chemistry, Bulgarian Academia of Sciences, 1113 Sofia, Bulgaria.
| | - Kurt Binder
- Institut für Physik, Johannes Gutenberg Universität Mainz, 55099 Mainz, Germany.
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16
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Chen W, Zhu Y, Cui F, Liu L, Sun Z, Chen J, Li Y. GPU-Accelerated Molecular Dynamics Simulation to Study Liquid Crystal Phase Transition Using Coarse-Grained Gay-Berne Anisotropic Potential. PLoS One 2016; 11:e0151704. [PMID: 26986851 PMCID: PMC4795799 DOI: 10.1371/journal.pone.0151704] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2015] [Accepted: 03/02/2016] [Indexed: 12/26/2022] Open
Abstract
Gay-Berne (GB) potential is regarded as an accurate model in the simulation of anisotropic particles, especially for liquid crystal (LC) mesogens. However, its computational complexity leads to an extremely time-consuming process for large systems. Here, we developed a GPU-accelerated molecular dynamics (MD) simulation with coarse-grained GB potential implemented in GALAMOST package to investigate the LC phase transitions for mesogens in small molecules, main-chain or side-chain polymers. For identical mesogens in three different molecules, on cooling from fully isotropic melts, the small molecules form a single-domain smectic-B phase, while the main-chain LC polymers prefer a single-domain nematic phase as a result of connective restraints in neighboring mesogens. The phase transition of side-chain LC polymers undergoes a two-step process: nucleation of nematic islands and formation of multi-domain nematic texture. The particular behavior originates in the fact that the rotational orientation of the mesogenes is hindered by the polymer backbones. Both the global distribution and the local orientation of mesogens are critical for the phase transition of anisotropic particles. Furthermore, compared with the MD simulation in LAMMPS, our GPU-accelerated code is about 4 times faster than the GPU version of LAMMPS and at least 200 times faster than the CPU version of LAMMPS. This study clearly shows that GPU-accelerated MD simulation with GB potential in GALAMOST can efficiently handle systems with anisotropic particles and interactions, and accurately explore phase differences originated from molecular structures.
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Affiliation(s)
- Wenduo Chen
- Key Laboratory of Synthetic Rubber & Laboratory of Advanced Power Sources, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, 5625 Renmin Street, Changchun, PR China
| | - Youliang Zhu
- State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, 5625 Renmin Street, Changchun, PR China
| | - Fengchao Cui
- Key Laboratory of Synthetic Rubber & Laboratory of Advanced Power Sources, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, 5625 Renmin Street, Changchun, PR China
| | - Lunyang Liu
- Key Laboratory of Synthetic Rubber & Laboratory of Advanced Power Sources, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, 5625 Renmin Street, Changchun, PR China
| | - Zhaoyan Sun
- State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, 5625 Renmin Street, Changchun, PR China
| | - Jizhong Chen
- State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, 5625 Renmin Street, Changchun, PR China
| | - Yunqi Li
- Key Laboratory of Synthetic Rubber & Laboratory of Advanced Power Sources, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, 5625 Renmin Street, Changchun, PR China
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Svenšek D, Podgornik R. Correlation functions of main-chain polymer nematics constrained by tensorial and vectorial conservation laws. J Chem Phys 2015; 143:114902. [DOI: 10.1063/1.4930920] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Shendruk TN, Yeomans JM. Multi-particle collision dynamics algorithm for nematic fluids. SOFT MATTER 2015; 11:5101-5110. [PMID: 26035731 DOI: 10.1039/c5sm00839e] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Research on transport, self-assembly and defect dynamics within confined, flowing liquid crystals requires versatile and computationally efficient mesoscopic algorithms to account for fluctuating nematohydrodynamic interactions. We present a multi-particle collision dynamics (MPCD) based algorithm to simulate liquid-crystal hydrodynamic and director fields in two and three dimensions. The nematic-MPCD method is shown to successfully reproduce the features of a nematic liquid crystal, including a nematic-isotropic phase transition with hysteresis in 3D, defect dynamics, isotropic Frank elastic coefficients, tumbling and shear alignment regimes and boundary condition-dependent order parameter fields.
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Affiliation(s)
- Tyler N Shendruk
- The Rudolf Peierls Centre for Theoretical Physics, Department of Physics, Theoretical Physics, University of Oxford, 1 Keble Road, Oxford, OX1 3NP, UK.
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Liao Y, Miao B. Structure factor of a Gaussian chain confined between two parallel plates. J Chem Phys 2015; 142:164903. [DOI: 10.1063/1.4919305] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Yi Liao
- College of Materials Science and Opto-Electronic Technology, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Bing Miao
- College of Materials Science and Opto-Electronic Technology, University of Chinese Academy of Sciences, Beijing 100049, China
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Jiang Y, Zhang X, Miao B, Yan D. The study of the structure factor of a wormlike chain in an orientational external field. J Chem Phys 2015; 142:154901. [PMID: 25903904 DOI: 10.1063/1.4917520] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Ying Jiang
- School of Chemistry and Environment, Center of Soft Matter Physics and its Applications, Beihang University, Beijing 100191, China
| | - Xinghua Zhang
- School of Science, Beijing Jiaotong University, Beijing 100044, China
| | - Bing Miao
- College of Materials Science and Opto-Electronic Technology, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Dadong Yan
- Department of Physics, Beijing Normal University, Beijing 100875, China
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