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Nakai F, Kröger M, Ishida T, Uneyama T, Doi Y, Masubuchi Y. Increase in rod diffusivity emerges even in Markovian nature. Phys Rev E 2023; 107:044604. [PMID: 37198810 DOI: 10.1103/physreve.107.044604] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2023] [Accepted: 03/22/2023] [Indexed: 05/19/2023]
Abstract
Rod-shaped particles embedded in certain matrices have been reported to exhibit an increase in their center of mass diffusivity upon increasing the matrix density. This increase has been considered to be caused by a kinetic constraint in analogy with tube models. We investigate a mobile rodlike particle in a sea of immobile point obstacles using a kinetic Monte Carlo scheme equipped with a Markovian process, that generates gaslike collision statistics, so that such kinetic constraints do essentially not exist. Even in such a system, provided the particle's aspect ratio exceeds a threshold value of about 24, the unusual increase in the rod diffusivity emerges. This result implies that the kinetic constraint is not a necessary condition for the increase in the diffusivity.
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Affiliation(s)
- Fumiaki Nakai
- Department of Materials Physics, Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa, Nagoya 464-8603, Japan
| | - Martin Kröger
- Polymer Physics, Department of Materials, ETH Zurich, CH-8093 Zurich, Switzerland
- Magnetism and Interface Physics, Department of Materials, ETH Zurich, CH-8093 Zurich, Switzerland
| | - Takato Ishida
- Department of Materials Physics, Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa, Nagoya 464-8603, Japan
| | - Takashi Uneyama
- Department of Materials Physics, Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa, Nagoya 464-8603, Japan
| | - Yuya Doi
- Department of Materials Physics, Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa, Nagoya 464-8603, Japan
| | - Yuichi Masubuchi
- Department of Materials Physics, Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa, Nagoya 464-8603, Japan
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2
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Varma VA, Malhotra I, Babu SB. Enhancement in the diffusivity of Brownian spheroids in the presence of spheres. Phys Rev E 2022; 106:014602. [PMID: 35974557 DOI: 10.1103/physreve.106.014602] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2021] [Accepted: 06/13/2022] [Indexed: 06/15/2023]
Abstract
In the present paper, we have extended the simulation technique Brownian cluster dynamics (BCD) to analyze the dynamics of the binary mixture of hard ellipsoids and spheres. The shape dependent diffusional properties have been incorporated into BCD using Perrin's factor and compared with analytical results of a one-component ellipsoidal system. We have investigated pathways to enhance the diffusivity of spheroids in the binary mixture by manipulating the phase behavior of the system through varying the fraction of spheres in the binary mixture. We show that at low volume fraction the spherical particles have a higher diffusion coefficient than the ellipsoids due to the higher friction coefficient. However, at a higher volume fraction, we show that the diffusion coefficient of the ellipsoids increases irrespective of the aspect ratio due to the anisotropic shape.
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Affiliation(s)
- Vikki Anand Varma
- Out of Equilibrium Group, Department of Physics, Indian Institute of Technology Delhi, New Delhi 110016, India
| | - Isha Malhotra
- Out of Equilibrium Group, Department of Physics, Indian Institute of Technology Delhi, New Delhi 110016, India
| | - Sujin B Babu
- Out of Equilibrium Group, Department of Physics, Indian Institute of Technology Delhi, New Delhi 110016, India
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3
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Schimansky-Geier L, Lindner B, Milster S, Neiman AB. Demixing of two species via reciprocally concentration-dependent diffusivity. Phys Rev E 2021; 103:022113. [PMID: 33736075 DOI: 10.1103/physreve.103.022113] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2020] [Accepted: 01/22/2021] [Indexed: 11/07/2022]
Abstract
We propose a model for demixing of two species by assuming a density-dependent effective diffusion coefficient of the particles. Both sorts of microswimmers diffuse as active overdamped Brownian particles with a noise intensity that is determined by the surrounding density of the respective other species within a sensing radius r_{s}. A higher concentration of the first (second) sort will enlarge the diffusion and, in consequence, the intensity of the noise experienced by the second (first) sort. Numerical and analytical investigations of steady states of the macroscopic equations prove the demixing of particles due to this reciprocally concentration-dependent diffusivity. An ambiguity of the numerical integration scheme for the purely local model (r_{s}→0) is resolved by considering nonvanishing sensing radii in a nonlocal model with r_{s}>0.
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Affiliation(s)
- Lutz Schimansky-Geier
- Institute of Physics, Humboldt University at Berlin, Newtonstrasse 15, D-12489 Berlin, Germany
| | - Benjamin Lindner
- Institute of Physics, Humboldt University at Berlin, Newtonstrasse 15, D-12489 Berlin, Germany.,Bernstein Center for Computational Neuroscience Berlin, Philippstrasse 13, Haus 2, 10115 Berlin, Germany
| | - Sebastian Milster
- Institute of Physics, Humboldt University at Berlin, Newtonstrasse 15, D-12489 Berlin, Germany.,Institute of Physics, Albert Ludwig University of Freiburg Hermann-Herder-Strasse 3, D-79104 Freiburg, Germany
| | - Alexander B Neiman
- Department of Physics and Astronomy, Ohio University, Athens, Ohio 45701, USA.,Neuroscience Program, Ohio University, Athens, Ohio 45701, USA
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Structure and rheology of soft hybrid systems of magnetic nanoparticles in liquid-crystalline matrices: results from particle-resolved computer simulations. PHYSICAL SCIENCES REVIEWS 2020. [DOI: 10.1515/psr-2019-0108] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Abstract
Hybrid mixtures composed of magnetic nanoparticles (MNP) in liquid crystalline (LC) matrices are a fascinating class of soft materials with intriguing physical properties and a wide range of potential applications, e.g., as stimuli-responsive and adaptive materials. Already in the absence of an external stimulus, these systems can display various types of orientationally disordered and ordered phases, which are enriched by self-assembled structures formed by the MNPs. In the presence of external fields, one typically observes highly nonlinear macroscopic behavior. However, an understanding of the structure and dynamics of such systems on the particle level has, so far, remained elusive. In the present paper we review recent computer simulation studies targeting the structure, equilibrium dynamics and rheology of LC-MNP systems, in which the particle sizes of the two components are comparable. As a numerically tractable model system we consider mixtures of soft spherical or elongated particles with a permanent magnetic dipole moment and ellipsoidal non-magnetic particles interacting via a Gay-Berne potential. We address, first, equilibrium aspects such as structural organization and self-assembly (cluster formation) of the MNPs in dependence of the orientational state of the matrix, the role of the size ratio, the impact of an external magnetic field, and the translational and orientational diffusion of the two components. Second, we discuss the non-equilibrium dynamics of LC-MNP mixtures under planar shear flow, considering both, spherical and non-spherical MNPs. Our results contribute to a detailed understanding of these intriguing hybrid materials, and they may serve as a guide for future experiments.
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Ferreiro-Córdova C, Royall CP, van Duijneveldt JS. Anisotropic viscoelastic phase separation in polydisperse hard rods leads to nonsticky gelation. Proc Natl Acad Sci U S A 2020; 117:3415-3420. [PMID: 32005711 PMCID: PMC7035602 DOI: 10.1073/pnas.1909357117] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Spinodal demixing into two phases having very different viscosities leads to viscoelastic networks-i.e., gels-usually as a result of attractive particle interactions. Here, however, we demonstrate demixing in a colloidal system of polydisperse, rod-like clay particles that is driven by particle repulsions instead. One of the phases is a nematic liquid crystal with a highly anisotropic viscosity, allowing flow along the director, but suppressing it in other directions. This phase coexists with a dilute isotropic phase. Real-space analysis and molecular-dynamics simulations both reveal a long-lived network structure that is locally anisotropic, yet macroscopically isotropic. We show that our system exhibits the characteristics of colloidal gelation, leading to nonsticky gels.
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Affiliation(s)
- Claudia Ferreiro-Córdova
- School of Chemistry, University of Bristol, Bristol BS8 1TS, United Kingdom
- Centre for Nanoscience and Quantum Information, University of Bristol, Bristol BS8 1FD, United Kingdom
- Université Paris-Saclay, CNRS, Laboratoire de Physique des Solides, 91405 Orsay, France
| | - C Patrick Royall
- School of Chemistry, University of Bristol, Bristol BS8 1TS, United Kingdom;
- Centre for Nanoscience and Quantum Information, University of Bristol, Bristol BS8 1FD, United Kingdom
- H. H. Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL, United Kingdom
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Hoshino T, Nakayama M, Fujinami S, Nakatani T, Kohmura Y, Kato T. Static structure and dynamical behavior of colloidal liquid crystals consisting of hydroxyapatite-based nanorod hybrids. SOFT MATTER 2019; 15:3315-3322. [PMID: 30810584 DOI: 10.1039/c9sm00101h] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Biominerals such as bones and teeth have elaborate nanostructures composed of aligned anisotropic hydroxyapatite (HAp) nanocrystals, which results in excellent mechanical properties. Construction of such ordered structures of HAp nanocrystals in synthetic materials is challenging. Recently, we reported that HAp-nanorod-based colloidal liquid crystals could be obtained. In the present study, the static structure and dynamics of liquid-crystalline (LC) colloidal dispersions of HAp nanorods are investigated by using small-angle X-ray scattering (SAXS) and X-ray photon correlation spectroscopy (XPCS). The SAXS results reveal that the interparticle distance decreases with increasing HAp concentration, φHAp, and the decrease of the interparticle distance for the short-axis direction is significantly smaller in the LC phase than the interparticle distance in the isotropic phase. In the dynamical studies of the LC phase using XPCS, we observe the diffusive motion of the HAp colloids, with the diffusion coefficient being dependent on the wave number. The diffusive motion slows down with increasing φHAp. We observe anisotropic dynamics after long-term storage (160 days after sealing), whereas only isotropic dynamics are observed in the initial XPCS measurements after short-term storage (14 days after sealing). Moreover, we have found that the dynamics slows down with increasing storage time.
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Affiliation(s)
- Taiki Hoshino
- RIKEN SPring-8 Center, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan.
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Shrivastav GP, Klapp SHL. Anomalous transport of magnetic colloids in a liquid crystal-magnetic colloid mixture. SOFT MATTER 2019; 15:973-982. [PMID: 30652721 DOI: 10.1039/c8sm02090f] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
We report an extensive molecular dynamics study on the translational dynamics of a hybrid system composed of dipolar soft spheres (DSS), representing ferromagnetic particles, suspended in a liquid crystal (LC) matrix. We observe that the LC matrix strongly modifies the dynamics of the DSS. In the isotropic regime, the DSS show a crossover from subdiffusive to normal diffusive behavior at long times, with an increase of the subdiffusive regime as the dipolar coupling strength is increased. In the nematic regime, the LC matrix, due to the collective reorientation of LC particles, imposes a cylindrical confinement on the DSS chains. This leads to a diffusive dynamics of DSS along the nematic director and a subdiffusive dynamics (with an exponent of ∼0.5) in the perpendicular direction. The confinement provided by the LC matrix is also reflected by the oscillatory behavior of the components of the velocity autocorrelation function of the DSS in the nematic phase.
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Affiliation(s)
- Gaurav P Shrivastav
- Institut für Theoretische Physik, Technische Universität Berlin, Hardenberg Str. 36, 10623 Berlin, Germany.
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8
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Roy S, Luzhbin DA, Chen YL. Investigation of nematic to smectic phase transition and dynamical properties of strongly confined semiflexible polymers using Langevin dynamics. SOFT MATTER 2018; 14:7382-7389. [PMID: 30203825 DOI: 10.1039/c8sm01100a] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
We investigated the nematic to smectic phase transition for strongly confined semiflexible polymer solutions in slit-like confinements using GPU-accelerated Langevin dynamics. We characterized the phase transitions from the nematic to smectic phases for semi-flexible polymer solutions as the polymer density increased. The dependence for the lyotropic nematic to smectic transition can be collapsed by scaling exponents between 0.2 and 0.3. The smectic C phase is found for all the cases with the polymer orientation director tilted with respect to smectic layer lateral alignment. As the chain rigidity increases, the transition density decreases for systems in which the polymer persistence length (P) to slit height (H) ratios are 1.25, 2.5, 3.75, 5 and 25. We also characterized the polymer dynamics for the isotropic-nematic-smectic transitions. The overall polymer diffusivity decreased steadily as the polymer density increased. We observed anomalous polymer diffusion along the nematic director near the isotropic-nematic transition, similar to previously reported behavior for nematic-forming ellipsoids. Polymer diffusivity decreased sharply by two orders of magnitude upon the nematic-smectic transition.
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Affiliation(s)
- Supriya Roy
- Institute of Physics, Academia Sinica, Taipei, Taiwan, Republic of China.
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9
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Mukherjee B, Peter C, Kremer K. Single molecule translocation in smectics illustrates the challenge for time-mapping in simulations on multiple scales. J Chem Phys 2018; 147:114501. [PMID: 28938812 DOI: 10.1063/1.5001482] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Understanding the connections between the characteristic dynamical time scales associated with a coarse-grained (CG) and a detailed representation is central to the applicability of the coarse-graining methods to understand molecular processes. The process of coarse graining leads to an accelerated dynamics, owing to the smoothening of the underlying free-energy landscapes. Often a single time-mapping factor is used to relate the time scales associated with the two representations. We critically examine this idea using a model system ideally suited for this purpose. Single molecular transport properties are studied via molecular dynamics simulations of the CG and atomistic representations of a liquid crystalline, azobenzene containing mesogen, simulated in the smectic and the isotropic phases. The out-of-plane dynamics in the smectic phase occurs via molecular hops from one smectic layer to the next. Hopping can occur via two mechanisms, with and without significant reorientation. The out-of-plane transport can be understood as a superposition of two (one associated with each mode of transport) independent continuous time random walks for which a single time-mapping factor would be rather inadequate. A comparison of the free-energy surfaces, relevant to the out-of-plane transport, qualitatively supports the above observations. Thus, this work underlines the need for building CG models that exhibit both structural and dynamical consistency to the underlying atomistic model.
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Affiliation(s)
| | - Christine Peter
- Department of Chemistry, University of Konstanz, 78547 Konstanz, Germany
| | - Kurt Kremer
- Max-Planck-Institut für Polymerforschung, Ackermannweg 10, 55128 Mainz, Germany
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10
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Chien FT, Lin PK, Chien W, Hung CH, Yu MH, Chou CF, Chen YL. Crowding-facilitated macromolecular transport in attractive micropost arrays. Sci Rep 2017; 7:1340. [PMID: 28465594 PMCID: PMC5430964 DOI: 10.1038/s41598-017-01248-8] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2017] [Accepted: 03/27/2017] [Indexed: 11/18/2022] Open
Abstract
Our study of DNA dynamics in weakly attractive nanofabricated post arrays revealed crowding enhances polymer transport, contrary to hindered transport in repulsive medium. The coupling of DNA diffusion and adsorption to the microposts results in more frequent cross-post hopping and increased long-term diffusivity with increased crowding density. We performed Langevin dynamics simulations and found maximum long-term diffusivity in post arrays with gap sizes comparable to the polymer radius of gyration. We found that macromolecular transport in weakly attractive post arrays is faster than in non-attractive dense medium. Furthermore, we employed hidden Markov analysis to determine the transition of macromolecular adsorption-desorption on posts and hopping between posts. The apparent free energy barriers are comparable to theoretical estimates determined from polymer conformational fluctuations.
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Affiliation(s)
- Fan-Tso Chien
- Institute of Physics, Academia Sinica, Taipei, Taiwan, ROC.,Department of Life Science, National Dong Hwa University, Hualien, Taiwan, ROC
| | - Po-Keng Lin
- Institute of Physics, Academia Sinica, Taipei, Taiwan, ROC
| | - Wei Chien
- Institute of Physics, Academia Sinica, Taipei, Taiwan, ROC.,Department of Physics, National Taiwan University, Taipei, Taiwan, ROC
| | - Cheng-Hsiang Hung
- Department of Physics, National Taiwan University, Taipei, Taiwan, ROC
| | - Ming-Hung Yu
- Institute of Physics, Academia Sinica, Taipei, Taiwan, ROC
| | - Chia-Fu Chou
- Institute of Physics, Academia Sinica, Taipei, Taiwan, ROC
| | - Yeng-Long Chen
- Institute of Physics, Academia Sinica, Taipei, Taiwan, ROC. .,Department of Physics, National Taiwan University, Taipei, Taiwan, ROC. .,Department of Chemical Engineering, National Tsing-Hua University, Hsinchu, Taiwan, ROC.
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11
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Frechette L, Stratt RM. The inherent dynamics of isotropic- and nematic-phase liquid crystals. J Chem Phys 2017; 144:234505. [PMID: 27334177 DOI: 10.1063/1.4953618] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
The geodesic (shortest) pathways through the potential energy landscape of a liquid can be thought of as defining what its dynamics would be if thermal noise were removed, revealing what we have called the "inherent dynamics" of the liquid. We show how these inherent paths can be located for a model liquid crystal former, showing, in the process, how the molecular mechanisms of translation and reorientation compare in the isotropic and nematic phases of these systems. These mechanisms turn out to favor the preservation of local orientational order even under macroscopically isotropic conditions (a finding consistent with the experimental observation of pseudonematic domains in these cases), but disfavor the maintenance of macroscopic orientational order, even in the nematic phase. While the most efficient nematic pathways that maintain nematic order are indeed shorter than those that do not, it is apparently difficult for the system to locate these paths, suggesting that molecular motion in liquid-crystal formers is dynamically frustrated, and reinforcing the sense that there are strong analogies between liquid crystals and supercooled liquids.
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Affiliation(s)
- Layne Frechette
- Department of Chemistry, Brown University, Providence, Rhode Island 02912, USA
| | - Richard M Stratt
- Department of Chemistry, Brown University, Providence, Rhode Island 02912, USA
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12
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Cinacchi G, Pintus AM, Tani A. Diffusion of helical particles in the screw-like nematic phase. J Chem Phys 2016; 145:134903. [DOI: 10.1063/1.4963016] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
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13
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Chien W, Chen YL. Abnormal polymer transport in crowded attractive micropost arrays. SOFT MATTER 2016; 12:7969-7976. [PMID: 27714308 DOI: 10.1039/c6sm01488g] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
We investigate polymer diffusion in a quasi-two-dimensional environment decorated with attractive cylindrical posts using Langevin dynamics simulation. We find that the polymer diffusivity has non-monotonic dependence on the post array density. This diffusive behavior strongly depends on the adsorption-desorption transition and the critical adsorption strength εc. For ε < εc, the polymer undergoes normal diffusion and the diffusivity decreases as the post density increases due to the reduction of the void volume. For ε > εc, polymer dynamics is strongly mediated by post adsorption, and we observe a regime where the polymer diffusivity increases as the post density increases. The polymer diffusivity reaches a maximum, which can be attributed to cross-post translation enabled by large polymer conformation fluctuations. We find both cross-post transport and polymer conformation fluctuations strongly depend on the post absorption strength and the chain length.
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Affiliation(s)
- Wei Chien
- Department of Physics, National Taiwan University, Taipei, Taiwan and Institute of Physics, Academia Sinica, Taipei, Taiwan
| | - Yeng-Long Chen
- Department of Physics, National Taiwan University, Taipei, Taiwan and Institute of Physics, Academia Sinica, Taipei, Taiwan and Department of Chemical Engineering, National Tsing-Hua University, Hsinchu, Taiwan.
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14
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Kasimov D, Admon T, Roichman Y. Diffusion of a nanowire rod through an obstacle field. Phys Rev E 2016; 93:050602. [PMID: 27300819 DOI: 10.1103/physreve.93.050602] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2015] [Indexed: 06/06/2023]
Abstract
We report the experimental realization of a rod diffusing in a two-dimensional obstacle field following the single rod dynamics. We use a silver nanowire as our rod and two types of obstacles: repelling light beams and polymer pillars. We study the effect of hydrodynamic interactions on the transport of the rod, comparing both experimental realizations and recent simulations. We propose a framework for analyzing the transport through such systems, and we predict a new superdiffusive regime of rod transport at high obstacle concentration and short times.
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Affiliation(s)
- Dror Kasimov
- Raymond & Beverly Sackler School of Physics and Astronomy, Tel Aviv University, Tel Aviv 6997801, Israel
| | - Tamir Admon
- Raymond & Beverly Sackler School of Chemistry, Tel Aviv University, Tel Aviv 6997801, Israel
| | - Yael Roichman
- Raymond & Beverly Sackler School of Chemistry, Tel Aviv University, Tel Aviv 6997801, Israel
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15
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Mederos L, Velasco E, Martínez-Ratón Y. Hard-body models of bulk liquid crystals. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2014; 26:463101. [PMID: 25335432 DOI: 10.1088/0953-8984/26/46/463101] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Hard models for particle interactions have played a crucial role in the understanding of the structure of condensed matter. In particular, they help to explain the formation of oriented phases in liquids made of anisotropic molecules or colloidal particles and continue to be of great interest in the formulation of theories for liquids in bulk, near interfaces and in biophysical environments. Hard models of anisotropic particles give rise to complex phase diagrams, including uniaxial and biaxial nematic phases, discotic phases and spatially ordered phases such as smectic, columnar or crystal. Also, their mixtures exhibit additional interesting behaviours where demixing competes with orientational order. Here we review the different models of hard particles used in the theory of bulk anisotropic liquids, leaving aside interfacial properties and discuss the associated theoretical approaches and computer simulations, focusing on applications in equilibrium situations. The latter include one-component bulk fluids, mixtures and polydisperse fluids, both in two and three dimensions, and emphasis is put on liquid-crystal phase transitions and complex phase behaviour in general.
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Affiliation(s)
- Luis Mederos
- Instituto de Ciencia de Materiales de Madrid, CSIC, Sor Juana Inés de la Cruz, 3, E-28049 Madrid, Spain
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16
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Naderi S, van der Schoot P. Effect of bending flexibility on the phase behavior and dynamics of rods. J Chem Phys 2014; 141:124901. [DOI: 10.1063/1.4895730] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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17
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Foulaadvand ME, Yarifard M. Two-dimensional system of hard ellipses: a molecular dynamics study. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2013; 88:052504. [PMID: 24329285 DOI: 10.1103/physreve.88.052504] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/21/2013] [Indexed: 06/03/2023]
Abstract
We have simulated the dynamics of a two-dimensional system of hard ellipses by event-oriented molecular dynamics in microcanonical NVE ensemble. Various quantities, namely longitudinal and transverse velocity auto-correlation functions, translational and rotational diffusion mean-squared displacements, pressure, intermediate self-scattering function, radial distribution function, and angular spatial correlation, have been obtained and their dependence on packing fraction is characterized. Despite absence of prominent positional ordering, the orientational degree of freedom behaves nontrivially and exhibits interesting features. Slowing down is observed in the angular part of the motion near isotropic-nematic phase transition. It is shown that above a certain packing fraction the rotational mean-squared displacement exhibits a three-stage temporal regime including a plateau. Comparison to 2D system of hard needles is made and it is shown that from positional viewpoint, the ellipse system is more ordered.
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Affiliation(s)
- M Ebrahim Foulaadvand
- Department of Physics, University of Zanjan, P.O. Box 45196-311, Zanjan, Iran and Computational Physical Sciences Research Laboratory, Department of Nano-Sciences, Institute for Research in Fundamental Sciences (IPM), P.O. Box 19395-5531, Tehran, Iran
| | - Mohsen Yarifard
- Department of Physics, University of Zanjan, P.O. Box 45196-311, Zanjan, Iran
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18
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Zhao T, Wang X. Dissipative particle dynamics study of translational diffusion of rigid-chain rodlike polymer in nematic phase. J Chem Phys 2013; 139:104902. [DOI: 10.1063/1.4820134] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
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19
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Dobrindt J, Rodrigo Teixeira da Silva E, Alves C, Oliveira CLP, Nallet F, Andreoli de Oliveira E, Navailles L. Anisotropic Brownian motion in ordered phases of DNA fragments. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2012; 35:3. [PMID: 22270455 DOI: 10.1140/epje/i2012-12003-4] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/17/2011] [Accepted: 12/20/2011] [Indexed: 05/31/2023]
Abstract
Using Fluorescence Recovery After Photobleaching, we investigate the Brownian motion of DNA rod-like fragments in two distinct anisotropic phases with a local nematic symmetry. The height of the measurement volume ensures the averaging of the anisotropy of the in-plane diffusive motion parallel or perpendicular to the local nematic director in aligned domains. Still, as shown in using a model specifically designed to handle such a situation and predicting a non-Gaussian shape for the bleached spot as fluorescence recovery proceeds, the two distinct diffusion coefficients of the DNA particles can be retrieved from data analysis. In the first system investigated (a ternary DNA-lipid lamellar complex), the magnitude and anisotropy of the diffusion coefficient of the DNA fragments confined by the lipid bilayers are obtained for the first time. In the second, binary DNA-solvent system, the magnitude of the diffusion coefficient is found to decrease markedly as DNA concentration is increased from isotropic to cholesteric phase. In addition, the diffusion coefficient anisotropy measured within cholesteric domains in the phase coexistence region increases with concentration, and eventually reaches a high value in the cholesteric phase.
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Affiliation(s)
- J Dobrindt
- Université de Bordeaux, Centre de recherche Paul-Pascal - CNRS, 115 avenue du Docteur-Schweitzer, F-33600, Pessac, France
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Yamaguchi D, Miyamoto N, Fujita T, Nakato T, Koizumi S, Ohta N, Yagi N, Hashimoto T. Aspect-ratio-dependent phase transitions and concentration fluctuations in aqueous colloidal dispersions of charged platelike particles. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2012; 85:011403. [PMID: 22400569 DOI: 10.1103/physreve.85.011403] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/19/2011] [Revised: 09/14/2011] [Indexed: 05/22/2023]
Abstract
Phase transitions of aqueous colloidal dispersions of charged platelike particles of niobate nanosheets were investigated as a function of the aspect ratio (r(asp)) and particle volume concentration (φ(p)) by means of small-angle neutron scattering and small-angle x-ray scattering. The results elucidated the following three pieces of evidence: (1) the macroscopic phase separation of the dispersions into an isotropic phase and a liquid crystalline (LC) phase under the conditions of (a) varying r(asp) (1.3×10(-4) ≤ r(asp) ≤ 2.5×10(-3)) at a constant φ(p) = 0.01 and (b) varying φ(p) (0.01 ≤ φ(p) ≤ 0.025) at a constant r(asp) = 2.5×10(-3), a mechanism of which is proposed in the text, where r(asp) ≡ d/ ̅L, with d and ̅L being thickness and the average lateral size of the plates, respectively; (2) the r(asp)-induced phase transition of the LC phase from a nematic phase to a highly periodic layered phase, the line shapes of the scattering peaks of which were examined by Caillé's analysis, upon increasing r(asp) under the condition (a); (3) the LC phase having remarkable concentration fluctuations of the particles which are totally unexpected for the conventional lyotropic molecular LC but which are anticipated to be general for the platelike colloidal particles.
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Affiliation(s)
- Daisuke Yamaguchi
- Quantum Beam Science Directorate, Japan Atomic Energy Agency, Tokai, Naka, Ibaraki 319-1195, Japan
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21
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Mazza MG, Greschek M, Valiullin R, Kärger J, Schoen M. Entropy-driven enhanced self-diffusion in confined reentrant supernematics. PHYSICAL REVIEW LETTERS 2010; 105:227802. [PMID: 21231424 DOI: 10.1103/physrevlett.105.227802] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/10/2010] [Indexed: 05/30/2023]
Abstract
We present a molecular dynamics study of reentrant nematic phases using the Gay-Berne-Kihara model of a liquid crystal in nanoconfinement. At densities above those characteristic of smectic A phases, reentrant nematic phases form that are characterized by a large value of the nematic order parameter S≃1. Along the nematic director these "supernematic" phases exhibit a remarkably high self-diffusivity, which exceeds that for ordinary, lower-density nematic phases by an order of magnitude. Enhancement of self-diffusivity is attributed to a decrease of rotational configurational entropy in confinement. Recent developments in the pulsed field gradient NMR technique are shown to provide favorable conditions for an experimental confirmation of our simulations.
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Affiliation(s)
- Marco G Mazza
- Stranski-Laboratorium für Physikalische und Theoretische Chemie, Technische Universität Berlin, Straße des 17. Juni 135, 10623 Berlin, Germany
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22
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Alarcón-Waess O. The role played by self-orientational properties in nematics of colloids with molecules axially symmetric. J Chem Phys 2010; 132:144902. [PMID: 20406010 DOI: 10.1063/1.3383242] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The self-orientational structure factor as well as the short-time self-orientational diffusion coefficient is computed for colloids composed by nonspherical molecules. To compute the short-time dynamics the hydrodynamic interactions are not taken into account. The hard molecules with at least one symmetry axis considered are: rods, spherocylinders, and tetragonal parallelepipeds. Because both orientational properties in study are written in terms of the second and fourth order parameters, these automatically hold the features of the order parameters. That is, they present a discontinuity for first order transitions, determining in this way the spinodal line. In order to analyze the nematic phase only, we choose the appropriate values for the representative quantities that characterize the molecules. Different formalisms are used to compute the structural properties: de Gennes-Landau approach, Smoluchowski equation and computer simulations. Some of the necessary inputs are taken from literature. Our results show that the self-orientational properties play an important role in the characterization and the localization of axially symmetric phases. While the self-structure decreases throughout the nematics, the short-time self-diffusion does not decrease but rather increases. We study the evolution of the second and fourth order parameters; we find different responses for axial and biaxial nematics, predicting the possibility of a biaxial nematics in tetragonal parallelepiped molecules. By considering the second order in the axial-biaxial phase transition, with the support of the self-orientational structure factor, we are able to propose the density at which this occurs. The short-time dynamics is able to predict a different value in the axial and the biaxial phases. Because the different behavior of the fourth order parameter, the diffusion coefficient is lower for a biaxial phase than for an axial one. Therefore the self-structure factor is able to localize continuous phase transitions involving axially symmetric phases and the short-time self-orientational diffusion is able to distinguish the ordered phase by considering the degree of alignment, that is, axial or biaxial.
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Affiliation(s)
- O Alarcón-Waess
- Departamento de Actuaria, Física y Matemáticas, UDLA, Puebla, Cholula, 72820 Puebla, Mexico.
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23
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Martínez-Haya B, Cuetos A. Columnar phases of discotics with orientation-dependent interactions. J Chem Phys 2009; 131:074901. [DOI: 10.1063/1.3207284] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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24
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Cinacchi G, De Gaetani L. Diffusivity of wormlike particles in isotropic melts and the influence of local nematization. J Chem Phys 2009; 130:144905. [DOI: 10.1063/1.3110605] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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25
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Dynamics of Thermotropic Liquid Crystals Across the Isotropic-Nematic Transition and Their Similarity with Glassy Relaxation in Supercooled Liquids. ADVANCES IN CHEMICAL PHYSICS 2009. [DOI: 10.1002/9780470431917.ch6] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register]
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26
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Cinacchi G, De Gaetani L. Mechanism of diffusion in the smectic- A phase of wormlike rods studied by computer simulation. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2009; 79:011706. [PMID: 19257051 DOI: 10.1103/physreve.79.011706] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/25/2008] [Revised: 10/14/2008] [Indexed: 05/27/2023]
Abstract
Molecular dynamics computer simulations have been carried out in the smectic- A phase of stiff wormlike rods. The analysis of the long trajectories generated has allowed for a detailed insight into that diffusion mechanism which is operative in the above-mentioned liquid-crystalline phase, as recently visualized in a system of colloidal virus rods. Fast particles, i.e., those able to move abruptly out from one into an adjacent layer, have been identified. Their properties, such as the velocity autocorrelation function and the orientational distribution function, have been determined and compared to the corresponding quantities valid for a generic rod.
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Affiliation(s)
- Giorgio Cinacchi
- Centro di Ricerca Ercole De Castro, Università di Bologna, Via Vincenzo Toffano 2, I-40125 Bologna, Italy.
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27
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Cuetos A, Martínez-Haya B. Columnar phases of discotic spherocylinders. J Chem Phys 2008; 129:214706. [DOI: 10.1063/1.3028539] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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28
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Mima T, Yasuoka K. Interfacial anisotropy in the transport of liquid crystals confined between flat, structureless walls: a molecular dynamics simulation approach. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2008; 77:011705. [PMID: 18351864 DOI: 10.1103/physreve.77.011705] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/29/2007] [Revised: 11/13/2007] [Indexed: 05/26/2023]
Abstract
Molecular dynamics simulations of uniaxial Gay-Berne ellipsoids as prolate liquid crystal molecules confined between two flat, structureless walls have been carried out in order to investigate anisotropy in their dynamic properties. Several physical quantities are profiled as a function of distance from a wall. The walls stimulate ellipsoids into different behaviors from those of the bulk system. The profiles of self-diffusion coefficients, which are distinguished in each direction of a director-based coordinate system, show that the ellipsoids are more diffusive parallel to the walls and less diffusive perpendicular to the walls with decreasing distance from the walls. According to the self-rotation coefficient and rotational viscosity profiles, ellipsoids are easy to rotate parallel to the walls and hard to rotate in the plane perpendicular to the walls. The analyses of velocity autocorrelation functions, angular velocity autocorrelation functions, director angular velocity autocorrelation functions, and their spectra are useful for the investigation of anisotropy near the walls. We conclude that the flat, structureless wall not only prevents ellipsoids from diffusing and rotating in the plane perpendicular to the walls, but also stimulates them to diffuse and rotate in the plane parallel to the walls.
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Affiliation(s)
- Toshiki Mima
- Department of Mechanical Engineering, Keio University, Yokohama 223-8522, Japan.
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29
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Application and New Developments in Polymer-Dispersed Liquid Crystal Simulation Studies. MACROMOL THEOR SIMUL 2007. [DOI: 10.1002/mats.200700008] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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30
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Chakrabarti D, Jana B, Bagchi B. Orientational relaxation in a discotic liquid crystal. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2007; 75:061703. [PMID: 17677279 DOI: 10.1103/physreve.75.061703] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/13/2006] [Indexed: 05/16/2023]
Abstract
We investigate orientational relaxation of a model discotic liquid crystal, consisting of disclike molecules, by molecular dynamics simulations along two isobars starting from the high temperature isotropic phase. The two isobars have been so chosen that (a) the phase sequence isotropic- (I-) nematic- (N-) columnar (C) appears upon cooling along one of them and (b) the sequence isotropic- (I-) columnar- (C) along the other. While the orientational relaxation in the isotropic phase near the I-N phase transition in system (a) shows a power law decay at short to intermediate times, such power law relaxation is not observed in the isotropic phase near the I-C phase boundary in system (b). In order to understand this difference (the existence or the absence of the power law decay), we calculated the growth of the orientational pair distribution functions (OPDFs) near the I-N phase boundary and also near the I-C phase boundary. We find that the OPDF shows a marked growth in long range correlation as the I-N phase boundary is approached in the I-N-C system (a), but such a growth is absent in the I-C system, which appears to be consistent with the result that I-N phase transition in the former is weakly first order while the I-C phase transition in the latter is not weak. As the system settles into the nematic phase, the decay of the single-particle second-rank orientational time correlation function follows a pattern that is similar to what is observed with calamitic liquid crystals and supercooled molecular liquids.
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Affiliation(s)
- Dwaipayan Chakrabarti
- Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore 560012, India
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31
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32
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Allen MP, Evans GT, Frenkel D, Mulder BM. Hard Convex Body Fluids. ADVANCES IN CHEMICAL PHYSICS 2007. [DOI: 10.1002/9780470141458.ch1] [Citation(s) in RCA: 174] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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33
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Idrissi A, Longelin S, Damay P, Krishtal S, Kiselev M. Analysis of the transverse and the longitudinal pseudodiffusion of CO2 in sub- and supercritical states: a molecular-dynamics analysis. J Chem Phys 2006; 125:224501. [PMID: 17176143 DOI: 10.1063/1.2400855] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
We have performed molecular-dynamics simulations of CO(2) system along the gas-liquid coexistence curve and on the isochore 94.22 cm(3) mol(-1) (which corresponds to the critical isochore). The calculation has been carried out in order to analyze the diffusion of CO(2) and particularly to figure out how the diffusion coefficient may be decomposed along the molecular axes. This makes it possible to analyze the anisotropy of the diffusion along these axes and to shed light on the microscopic changes which accompany such behavior. This anisotropy is traced back to the effect of the translation-rotation coupling (TRC) along the molecular axes. Along the liquid-gas coexistence curve, the pseudolongitudinal diffusion is found to be more rapid than the transverse one. The opposite trend is found along the isochore 94.22 cm(3) mol(-1). The role of the local structure was explored by calculating intermediate scattering function and the autocorrelation functions for the forces acting along the molecular axes. It is shown that the strength of the TRC effect is correlated to the difference between the relaxation times of the local structure, that of the reorientation along the molecular axes, and that of the translational motion. The analysis of the correlation time and the average mean square force along the longitudinal and transverse directions confirms the anisotropy of the local environment that determines the translational dynamics of a molecule.
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Affiliation(s)
- A Idrissi
- Laboratoire de Spectrochimie Infrarouge et Raman (UMR CNRS A8516), Centre d'Etudes et de Recherches Lasers et Applications, Université des Sciences et Technologies de Lille, 59655 Villeneuve d'Ascq Cedex, France.
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34
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Idrissi A, Damay P, Krishtal S, Kiselev M. Analysis of the Effect of Translation−Rotation Coupling on Diffusion along the Molecular Axes. J Phys Chem B 2006; 110:18560-5. [PMID: 16970484 DOI: 10.1021/jp061194t] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The analysis of the microscopic diffusion processes of CO(2) and H(2)O in the coordinate system defined by the molecular orientation allows a new criterion to be introduced which provides information on the short and long time behavior of the rotation-translation coupling as well as to quantify the strength of this coupling. We discuss the general conditions under which this affects the translation diffusion "seen" by the molecule along its molecular axes. The results show that the translation-rotation coupling is correlated to the local environment in shaping the longitudinal and transversal translation dynamics of a molecule at a microscopic level.
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Affiliation(s)
- A Idrissi
- Laboratoire de Spectrochimie Infrarouge et Raman (UMR CNRS A8516), Centre d'Etudes et de Recherches Lasers et Applications, Université des Sciences et Technologies de Lille, 59655 Villeneuve d'Ascq Cedex, France
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35
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Affiliation(s)
- Shuang Tang
- a Department of Chemistry , Oregon State University , Corvallis , Oregon , 97331 , USA
| | - Glenn T. Evans
- a Department of Chemistry , Oregon State University , Corvallis , Oregon , 97331 , USA
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36
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37
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Cinacchi G, De Gaetani L, Tani A. Diffusion and viscosity of a calamitic liquid crystal model studied by computer simulation. J Chem Phys 2005; 122:184513. [PMID: 15918735 DOI: 10.1063/1.1895718] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
We report a molecular dynamics simulation study on an ensemble of rod-like particles, each composed of nine soft spheres held rigidly along a line. We have calculated translational mean square displacements and velocity autocorrelation functions in the fluid phases exhibited by the model, i.e., smectic A, nematic and isotropic. These quantities have then been used to compute diffusion coefficients. In addition, we have calculated viscosities in the nematic and isotropic phases. Despite its crude nature, the model is capable of providing a faithful reproduction of many features of the transport behavior observed in real liquid-crystalline materials. The simulation results have been compared with the predictions of the modified affine transformation theory, finding only a fair agreement.
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Affiliation(s)
- Giorgio Cinacchi
- Dipartimento di Chimica e Chimica Industriale, Università di Pisa, Via Risorgimento 35, I-56126 Pisa, Italy
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38
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Ilg P. Anisotropic diffusion in nematic liquid crystals and in ferrofluids. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2005; 71:051407. [PMID: 16089535 DOI: 10.1103/physreve.71.051407] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/19/2005] [Revised: 02/15/2005] [Indexed: 05/03/2023]
Abstract
A unified, mean-field kinetic theory approach to the anisotropic translational diffusion observed in liquid crystals and in ferrofluids is proposed. In the dilute regime, unified expressions for the parallel as well as for the perpendicular diffusion coefficient in terms of orientational order parameters are found that apply for liquid crystals as well as for ferrofluids. This result explains the common origin of the anisotropic diffusion found in liquid crystals and in ferrofluids. Differences between the two liquids appear in the semi-dilute regime, where the diffusion coefficients depend on the specific interaction potentials. Explicit expressions for the diffusion coefficients are worked out also in this regime within a mean-field approximation. Comparisons with previous theoretical and experimental results are performed, showing satisfactory agreement to the present results.
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Affiliation(s)
- Patrick Ilg
- Institut für Theoretische Physik, Technische Universität Berlin, Hardenbergstrasse 36, D-10623 Berlin, Germany.
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39
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Chrzanowska A. The Enskog-type theory of the velocity autocorrelations in the two-dimensional nematic of hard needles. J Chem Phys 2004; 120:2857-71. [PMID: 15268433 DOI: 10.1063/1.1640350] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
As it was shown from molecular dynamics of two-dimensional hard needles, the uniaxial velocity autocorrelation function (VACF) of this system exhibits a two time scale character. This corresponds to the symmetry of the particles. In this paper we provide a theory of the Enskog type that corroborates the idea that the VACF can be successfully described as a sum of two single decays. From the comparison between molecular dynamics and theoretical results, we show that the Enskog approach is a satisfactory kinetic theory, which functions as well in the nematic as in the isotropic phase. Different properties of VACFs have been investigated, in particular, the dependence on the orientational order, temperature, and particles' inertness.
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Affiliation(s)
- Agnieszka Chrzanowska
- Institute of Physics, Kraków University of Technology, ul. Podchorazych 1, 30-084 Kraków, Poland.
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40
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Saphiannikova M, Radtchenko I, Sukhorukov G, Shchukin D, Yakimansky A, Ilnytskyi J. Molecular-dynamics simulations and x-ray analysis of dye precipitates in the polyelectrolyte microcapsules. J Chem Phys 2003. [DOI: 10.1063/1.1566732] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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41
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Caprion D, Bellier-Castella L, Ryckaert JP. Influence of shape and energy anisotropies on the phase diagram of discotic molecules. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2003; 67:041703. [PMID: 12786373 DOI: 10.1103/physreve.67.041703] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/22/2003] [Indexed: 05/24/2023]
Abstract
We present Monte Carlo simulations of discotic molecules using the Gay-Berne potential with shape (kappa) and energy (kappa(')) anisotropies. Following the previous work of Bates and Luckhurst [J. Chem. Phys. 104, 6696 (1996)] at kappa=0.345, kappa(')=0.2 when we determine the sequence of different phases at the same reduced pressure P(*)=50, we find an additional phase at low temperatures corresponding to an orthorhombic crystalline phase and we characterize it. Keeping the shape anisotropy fixed at kappa=0.2, we determine the evolution of the phase diagram with varying energy anisotropy. At high kappa('), low anisotropy, the system is not able to build columns while at low kappa('), the system exhibits both orthorhombic crystal as well as hexagonal liquid crystal phases over a wide range of pressures and temperatures. The domain of stability of the nematic phase is found to systematically shift towards higher pressures as kappa(') decreases.
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Affiliation(s)
- D Caprion
- Physique des Polymères, Université Libre de Bruxelles, Campus Plaine, Case Postale 223, Belgium
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42
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Dvinskikh SV, Furó I, Zimmermann H, Maliniak A. Anisotropic self-diffusion in thermotropic liquid crystals studied by 1H and 2H pulse-field-gradient spin-echo NMR. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2002; 65:061701. [PMID: 12188745 DOI: 10.1103/physreve.65.061701] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/25/2002] [Indexed: 05/23/2023]
Abstract
The molecular self-diffusion coefficients in nematic and smectic-A thermotropic liquid crystals are measured using stimulated-echo-type 2H and 1H pulse-field-gradient spin-echo nuclear magnetic resonance (PGSE NMR) combined with multiple-pulse dipolar decoupling and slice selection. The temperature dependence of the principal components of the diffusion tensor in the nematic phase follows a simple Arrhenius relationship except in the region of nematic-isotropic phase transition where it reflects, merely, the decrease of the molecular orientational order. The average of the principal diffusion coefficients in the isotropic-nematic phase transition region is close to the diffusion coefficient in the isotropic phase. At the nematic-smectic-A phase transition the diffusion coefficients change continuously. The results in nematic phase are best described in terms of the affine transformation model for diffusion in nematics formed by hard ellipsoids. In the smectic-A phase the data are interpreted using a modified model for diffusion in presence of a periodic potential along the director.
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Affiliation(s)
- S V Dvinskikh
- Division of Physical Chemistry, Arrhenius Laboratory, Stockholm University, SE-10691 Stockholm, Sweden.
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Singh GS, Kumar B. Transport tensors in perfectly aligned low-density fluids: self-diffusion and thermal conductivity. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2001; 63:061707. [PMID: 11415123 DOI: 10.1103/physreve.63.061707] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/29/2000] [Indexed: 05/23/2023]
Abstract
The modified Taxman equation for the kinetic theory of low-density fluids composed of rigid aspherical molecules possessing internal degrees of freedom is generalized to obtain the transport tensors in a fluid of aligned molecules. The theory takes care of the shape of the particles exactly but the solution has been obtained only for the case of perfectly aligned hard spheroids within the framework of the first Sonine polynomial approximation. The expressions for the thermal-conductivity components have been obtained for the first time whereas the self-diffusion components obtained here turn out to be exactly the same as those derived by Kumar and Masters [Mol. Phys. 81, 491 (1994)] through the solution of the Lorentz-Boltzmann equation. All our expressions yield correct results in the hard-sphere limit.
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Affiliation(s)
- G S Singh
- Department of Physics, University of Roorkee, Roorkee 247 667, India
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44
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Ravichandran S, Bagchi B. Anisotropic diffusion of nonspherical molecules in dense liquids: A molecular dynamics simulation of isolated ellipsoids in the sea of spheres. J Chem Phys 1999. [DOI: 10.1063/1.480076] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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45
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46
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Russo PS, Baylis M, Bu Z, Stryjewski W, Doucet G, Temyanko E, Tipton D. Self-diffusion of a semiflexible polymer measured across the lyotropic liquid-crystalline-phase boundary. J Chem Phys 1999. [DOI: 10.1063/1.479435] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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47
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48
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49
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MacDowell LG, Garzón B, Calero S, Lago S. Dynamical properties and transport coefficients of Kihara linear fluids. J Chem Phys 1997. [DOI: 10.1063/1.473473] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Abstract
A short review is given of recent progress in the computer simulation of liquid crystal phases using hard particles. Emphasis is placed on the richness of phase behaviour that may result from the effects of molecular size and shape alone, and on the role of simulations in testing modern theories of liquid crystal phase transitions, structure and dynamics. Two specific examples are treated in detail: the simulation of twisted nematic liquid crystals, allowing a direct calculation of the twist elastic constant and the helical twisting power of chiral dopant molecules; and the recent quantitative explanation of diffusive behaviour in isotropic and nematic liquids using kinetic theory.
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