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Abstract
The existence of a ferroelectric fluid phase for systems of 1000-2000 dipolar hard or soft spheres is well established by numerical simulations. Theoretical approaches proposed to determine the stability of such a phase are either in qualitative agreement with the simulation results or disagree with them. Experimental results for systems of molecules or particles with large electric or magnetic dipole moments are also inconclusive. As a contribution to the question of existence and stability of a fluid ferroelectric phase this simulation work considers system sizes of the order of 10 000 particles, thus an order of magnitude larger than those used in previous studies. It shows that although ferroelectricity is not affected by an increase of system size, different spatial arrangements of the dipolar hard spheres in such a phase are possible whose free energies seem to differ only marginally.
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Affiliation(s)
- D Levesque
- Université de Paris-Sud, Laboratoire de Physique Théorique, UMR8627, Bâtiment 210, 91405 Orsay Cedex, France
| | - J-J Weis
- Université de Paris-Sud, Laboratoire de Physique Théorique, UMR8627, Bâtiment 210, 91405 Orsay Cedex, France
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Ouyang WZ, Xu SH, Sun ZW. Gas-liquid phase coexistence in quasi-two-dimensional Stockmayer fluids: A molecular dynamics study. J Chem Phys 2011; 134:014901. [DOI: 10.1063/1.3521393] [Citation(s) in RCA: 5] [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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Köfinger J, Wilding NB, Kahl G. Phase behavior of a symmetrical binary fluid mixture. J Chem Phys 2006; 125:234503. [PMID: 17190563 DOI: 10.1063/1.2393241] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We have investigated the phase behavior of a symmetrical binary fluid mixture for the situation where the chemical potentials mu(1) and mu(2) of the two species differ. Attention is focused on the set of interparticle interaction strengths for which, when mu(1)=mu(2), the phase diagram exhibits both a liquid-vapor critical point and a tricritical point. The corresponding phase behavior for the case mu(1) not equalmu(2) is investigated via integral-equation theory calculations within the mean spherical approximation and grand canonical Monte Carlo (GCMC) simulations. We find that two possible subtypes of phase behavior can occur, these being distinguished by the relationship between the triple lines in the full phase diagram in the space of temperature, density, and concentration. We present the detailed form of the phase diagram for both subtypes and compare with the results from GCMC simulations, finding good overall agreement. The scenario via which one subtype evolves into the other is also studied, revealing interesting features.
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Affiliation(s)
- Jürgen Köfinger
- Faculty of Physics, University of Vienna, Boltzmanngasse 5, A-1090 Wien, Austria
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Schöll-Paschinger E, Kahl G. Type-IV phase behavior in fluids with an internal degree of freedom. J Chem Phys 2005; 123:134508. [PMID: 16223315 DOI: 10.1063/1.2042447] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We have identified a fourth archetype of phase diagram in binary symmetrical mixtures, which is encountered when the ratio of the interaction between the unlike and the like particles is sufficiently small. This type of phase diagram is characterized by the fact that the lambda line (i.e., the line of the second-order demixing transition) intersects the first-order liquid-vapor curve at densities smaller than the liquid-vapor critical density.
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Schöll-Paschinger E, Levesque D, Weis JJ, Kahl G. Phase diagram of a binary symmetric hard-core Yukawa mixture. J Chem Phys 2005; 122:024507. [PMID: 15638598 DOI: 10.1063/1.1829632] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We assess the accuracy of the self-consistent Ornstein-Zernike approximation for a binary symmetric hard-core Yukawa mixture by comparison with Monte Carlo simulations of the phase diagrams obtained for different choices of the ratio alpha of the unlike-to-like interactions. In particular, from the results obtained at alpha=0.75 we find evidence for a critical endpoint in contrast to recent studies based on integral equation and hierarchical reference theories. The variation of the phase diagrams with range of the Yukawa potential is investigated.
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McWhirter JL, Patey GN. Orientational ordering and disordering of a simple dipolar fluid under shear flow. J Chem Phys 2002. [DOI: 10.1063/1.1513361] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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Antonevych O, Forstmann F, Diaz-Herrera E. Phase diagram of symmetric binary fluid mixtures: first-order or second-order demixing. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2002; 65:061504. [PMID: 12188729 DOI: 10.1103/physreve.65.061504] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/23/2002] [Indexed: 05/23/2023]
Abstract
Binary fluid mixtures of 1:1 concentration can demix in a phase transition of first order or of second order. We analyze the two scenarios in density-concentration space and relate them to the structure of the line at which the demixing coexistence surface cuts the liquid-vapor coexistence surface. These scenarios help us to decide between first and second order for a model of a symmetric Lennard-Jones mixture. An optimized reference hypernetted chain integral equation method is employed for calculating the correlation functions and from there the pressure and chemical potentials. We conclude that demixing of a 1:1 mixture is of first order in the whole range of parameters that we have investigated. We did not find a critical point in the 1:1 concentration plane.
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Affiliation(s)
- Ostap Antonevych
- Institut für Theoretische Physik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany
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Allahyarov E, Löwen H. Influence of solvent granularity on the effective interaction between charged colloidal suspensions. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2001; 63:041403. [PMID: 11308839 DOI: 10.1103/physreve.63.041403] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/26/2000] [Indexed: 05/23/2023]
Abstract
We study the effect of solvent granularity on the effective force between two charged colloidal particles by computer simulations of the primitive model of strongly asymmetric electrolytes with an explicitly added hard-sphere solvent. Apart from molecular oscillating forces for nearly touching colloids that arise from solvent and counterion layering, the counterions are attracted towards the colloidal surfaces by solvent depletion providing a simple statistical description of hydration. This, in turn, has an important influence on the effective forces for larger distances which are considerably reduced as compared to the prediction based on the primitive model. When these forces are repulsive, the long-distance behavior can be described by an effective Yukawa pair potential with a solvent-renormalized charge. As a function of colloidal volume fraction and added salt concentration, this solvent-renormalized charge behaves qualitatively similar to that obtained via the Poisson-Boltzmann cell model, but there are quantitative differences. For divalent counterions and nanosized colloids, on the other hand, the hydration may lead to overscreened colloids with mutual attraction while the primitive model yields repulsive forces. All these new effects can be accounted for through a solvent-averaged primitive model (SPM) which is obtained from the full model by integrating out the solvent degrees of freedom. The SPM was used to access larger colloidal particles without simulating the solvent explicitly.
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Affiliation(s)
- E Allahyarov
- Institut für Theoretische Physik II, Heinrich-Heine-Universität Düsseldorf, D-40225 Düsseldorf, Germany
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Huke B, Lucke M. Magnetization of ferrofluids with dipolar interactions: A born-mayer expansion. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 2000; 62:6875-6890. [PMID: 11102042 DOI: 10.1103/physreve.62.6875] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/11/2000] [Indexed: 05/23/2023]
Abstract
For ferrofluids that are described by a system of hard spheres interacting via dipolar forces we evaluate the magnetization as a function of the internal magnetic field with a Born-Mayer technique and an expansion in the dipolar coupling strength. Two different approximations are presented for the magnetization, considering different contributions to a series expansion in terms of the volume fraction of the particles and the dipolar coupling strength.
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Affiliation(s)
- B Huke
- Institut fur Theoretische Physik, Universitat des Saarlandes, D-66041 Saarbrucken, Germany
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Banerjee S, Widom M. Ferromagnetic liquid thin films under applied field. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 2000; 61:4171-4176. [PMID: 11088212 DOI: 10.1103/physreve.61.4171] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/10/1999] [Indexed: 05/23/2023]
Abstract
Theoretical calculations, computer simulations, and experiments indicate the possible existence of a ferromagnetic liquid state, although definitive experimental evidence is lacking. Should such a state exist, demagnetization effects would force a nontrivial magnetization texture. Since liquid droplets are deformable, the droplet shape is coupled with the magnetization texture. In a thin-film geometry in zero applied field, the droplet has a circular shape and a rotating magnetization texture with a point vortex at the center. We calculate the elongation and magnetization texture of such a ferromagnetic thin-film liquid droplet confined between two parallel plates under a weak applied magnetic field. The vortex stretches into a domain wall and exchange forces break the reflection symmetry. This behavior contrasts qualitatively and quantitatively with the elongation of paramagnetic thin films.
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Affiliation(s)
- S Banerjee
- Department of Physics, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA
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Camp PJ, Patey GN. Orientational order in model dipolar fluids. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 1999; 60:4280-4. [PMID: 11970281 DOI: 10.1103/physreve.60.4280] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/12/1999] [Indexed: 04/18/2023]
Abstract
Fluids of hard spheres each carrying two parallel point dipoles have been investigated using constant-volume Monte Carlo computer simulations. The results show that both ferroelectric and antiferroelectric fluid phases can be stabilized at high density and low temperature by dipolar interactions alone, if the separation between the dipoles on each sphere is sufficiently large. A simple lattice calculation provides some insight into the balance between dipole energy and orientational entropy which governs the polarization state.
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Affiliation(s)
- P J Camp
- Department of Chemistry, University of British Columbia, Vancouver, Canada V6T 1Z1
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Osipov MA, Teixeira PI. Structure of strongly dipolar fluids at low densities. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 1996; 54:2597-2609. [PMID: 9965371 DOI: 10.1103/physreve.54.2597] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
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Groh B, Dietrich S. Density-functional theory for the freezing of Stockmayer fluids. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 1996; 54:1687-1697. [PMID: 9965245 DOI: 10.1103/physreve.54.1687] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
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Groh B, Dietrich S. Structural and thermal properties of orientationally ordered dipolar fluids. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 1996; 53:2509-2530. [PMID: 9964537 DOI: 10.1103/physreve.53.2509] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
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