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Comparing Microscopic and Macroscopic Dynamics in a Paradigmatic Model of Glass-Forming Molecular Liquid. Int J Mol Sci 2022; 23:ijms23073556. [PMID: 35408916 PMCID: PMC8998722 DOI: 10.3390/ijms23073556] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2022] [Revised: 03/12/2022] [Accepted: 03/20/2022] [Indexed: 02/04/2023] Open
Abstract
Glass transition is a most intriguing and long-standing open issue in the field of molecular liquids. From a macroscopic perspective, glass-forming systems display a dramatic slowing-down of the dynamics, with the inverse diffusion coefficient and the structural relaxation times increasing by orders of magnitude upon even modest supercooling. At the microscopic level, single-molecule motion becomes strongly intermittent, and can be conveniently described in terms of “cage-jump” events. In this work, we investigate a paradigmatic glass-forming liquid, the Kob–Andersen Lennard–Jones model, by means of Molecular Dynamics simulations, and compare the macroscopic and microscopic descriptions of its dynamics on approaching the glass-transition. We find that clear changes in the relations between macroscopic timescales and cage-jump quantities occur at the crossover temperature where Mode Coupling-like description starts failing. In fact, Continuous Time Random Walk and lattice model predictions based on cage-jump statistics are also violated below the crossover temperature, suggesting the onset of a qualitative change in cage-jump motion. Interestingly, we show that a fully microscopic relation linking cage-jump time- and length-scales instead holds throughout the investigated temperature range.
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2
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Pastore R, Kikutsuji T, Rusciano F, Matubayasi N, Kim K, Greco F. Breakdown of the Stokes-Einstein relation in supercooled liquids: A cage-jump perspective. J Chem Phys 2021; 155:114503. [PMID: 34551555 DOI: 10.1063/5.0059622] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
The breakdown of the Stokes-Einstein relation in supercooled liquids, which is the increase in the ratio τατD between the two macroscopic times for structural relaxation and diffusion on decreasing the temperature, is commonly ascribed to dynamic heterogeneities, but a clear-cut microscopic interpretation is still lacking. Here, we tackle this issue exploiting the single-particle cage-jump framework to analyze molecular dynamics simulations of soft disk assemblies and supercooled water. We find that τατD∝⟨tp⟩⟨tc⟩, where ⟨tp⟩ and ⟨tc⟩ are the cage-jump times characterizing slow and fast particles, respectively. We further clarify that this scaling does not arise from a simple term-by-term proportionality; rather, the relations τα∝⟨tp⟩⟨ΔrJ 2⟩ and τD∝⟨tc⟩⟨ΔrJ 2⟩ effectively connect the macroscopic and microscopic timescales, with the mean square jump length ⟨ΔrJ 2⟩ shrinking on cooling. Our work provides a microscopic perspective on the Stokes-Einstein breakdown and generalizes previous results on lattice models to the case of more realistic glass-formers.
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Affiliation(s)
- Raffaele Pastore
- Department of Chemical, Materials and Production Engineering, University of Naples Federico II, P.le Tecchio 80, Napoli 80125, Italy
| | - Takuma Kikutsuji
- Division of Chemical Engineering, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan
| | - Francesco Rusciano
- Department of Chemical, Materials and Production Engineering, University of Naples Federico II, P.le Tecchio 80, Napoli 80125, Italy
| | - Nobuyuki Matubayasi
- Division of Chemical Engineering, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan
| | - Kang Kim
- Division of Chemical Engineering, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan
| | - Francesco Greco
- Department of Chemical, Materials and Production Engineering, University of Naples Federico II, P.le Tecchio 80, Napoli 80125, Italy
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3
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Casuso I, Redondo-Morata L, Rico F. Biological physics by high-speed atomic force microscopy. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2020; 378:20190604. [PMID: 33100165 PMCID: PMC7661283 DOI: 10.1098/rsta.2019.0604] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
While many fields have contributed to biological physics, nanotechnology offers a new scale of observation. High-speed atomic force microscopy (HS-AFM) provides nanometre structural information and dynamics with subsecond resolution of biological systems. Moreover, HS-AFM allows us to measure piconewton forces within microseconds giving access to unexplored, fast biophysical processes. Thus, HS-AFM provides a tool to nourish biological physics through the observation of emergent physical phenomena in biological systems. In this review, we present an overview of the contribution of HS-AFM, both in imaging and force spectroscopy modes, to the field of biological physics. We focus on examples in which HS-AFM observations on membrane remodelling, molecular motors or the unfolding of proteins have stimulated the development of novel theories or the emergence of new concepts. We finally provide expected applications and developments of HS-AFM that we believe will continue contributing to our understanding of nature, by serving to the dialogue between biology and physics. This article is part of a discussion meeting issue 'Dynamic in situ microscopy relating structure and function'.
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Affiliation(s)
- Ignacio Casuso
- Aix-Marseile University, Inserm, CNRS, LAI, 163 Av. de Luminy, 13009 Marseille, France
| | - Lorena Redondo-Morata
- Center for Infection and Immunity of Lille, INSERM U1019, CNRS UMR 8204, 59000 Lille, France
| | - Felix Rico
- Aix-Marseile University, Inserm, CNRS, LAI, 163 Av. de Luminy, 13009 Marseille, France
- e-mail:
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4
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Hoffmann MM, Too MD, Vogel M, Gutmann T, Buntkowsky G. Breakdown of the Stokes-Einstein Equation for Solutions of Water in Oil Reverse Micelles. J Phys Chem B 2020; 124:9115-9125. [PMID: 32924487 DOI: 10.1021/acs.jpcb.0c06124] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
An experimental study is presented for the reverse micellar system of 15% by mass polydisperse hexaethylene glycol monodecylether (C10E6) in cyclohexane with varying amounts of added water up to 4% by mass. Measurements of viscosity and self-diffusion coefficients were taken as a function of temperature between 10 and 45 °C at varying sample water loads but fixed C10E6/cyclohexane composition. The results were used to inspect the validity of the Stokes-Einstein equation for this system. Unreasonably small reverse average micelle radii and aggregation numbers were obtained with the Stokes-Einstein equation, but reasonable values for these quantities were obtained using the ratio of surfactant-to-cyclohexane self-diffusion coefficients. While bulk viscosity increased with increasing water load, a concurrent expected decrease of self-diffusion coefficient was only observed for the surfactant and water but not for cyclohexane, which showed independence of water load. Moreover, a spread of self-diffusion coefficients was observed for the protons associated with the ethylene oxide repeat unit in samples with polydisperse C10E6 but not in a sample with monodisperse C10E6. These findings were interpreted by the presence of reverse micelle to reverse micelle hopping motions that with higher water load become increasingly selective toward C10E6 molecules with short ethylene oxide repeat units, while those with long ethylene oxide repeat units remain trapped within the reverse micelle because of the increased hydrogen bonding interactions with the water inside the growing core of the reverse micelle. Despite the observed breakdown of the Stokes-Einstein equation, the temperature dependence of the viscosities and self-diffusion coefficients was found to follow Arrhenius behavior over the investigated range of temperatures.
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Affiliation(s)
- Markus M Hoffmann
- Department of Chemistry and Biochemistry, State University of New York College at Brockport, Brockport, New York 14420, United States
| | - Matthew D Too
- Department of Chemistry and Biochemistry, State University of New York College at Brockport, Brockport, New York 14420, United States
| | - Michael Vogel
- Institute of Condensed Matter Physics, Technical University Darmstadt, Hochschulstraße 6, Darmstadt 64289, Germany
| | - Torsten Gutmann
- Institute of Physical Chemistry, Technical University Darmstadt, Alarich-Weiss-Straße 8, Darmstadt D-64287, Germany
| | - Gerd Buntkowsky
- Institute of Physical Chemistry, Technical University Darmstadt, Alarich-Weiss-Straße 8, Darmstadt D-64287, Germany
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5
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Das Mahanta D, Mitra RK. Connection of large amplitude angular jump motions with temporal heterogeneity in aqueous solutions. Phys Chem Chem Phys 2020; 22:9339-9348. [PMID: 32309843 DOI: 10.1039/d0cp00491j] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
It has now been established that large angular jumps do take place when a rotating water molecule exchanges its hydrogen bond (H-bond) identity. This motion differs from the small angular diffusional steps occurring within short time intervals which define the 'Debye diffusion model' of water dynamics. We intend to investigate whether these two processes do eventually complement each other. In this present investigation the orientational dynamics of water in its mixture with a small hydrophobic molecule 1,2-dimethoxy ethane (DME) is studied microscopically using the all-atom classical molecular dynamics (MD) simulation technique. We found that the reorientational motions of water molecules are governed by continuous making and breaking of intermolecular H-bonds with their partners. We characterise these H-bond reorientation motions with the description of the "large amplitude angular jump model" and explore the coupling between the rotational and translational motions. By following the trajectories of each molecule in the solutions we describe the orientational dynamics of liquid water with a 'continuous time random walk' (CTRW) approach. Finally, we explore the diffusivity distribution through the jump properties of the water molecules, which successfully leads to the inherent transient heterogeneity of the solutions. We observe that the heterogeneity increases with increasing DME content in the mixtures. Our study correlates the coupling between rotational and translational motions of water molecules in the mixtures.
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Affiliation(s)
- Debasish Das Mahanta
- Chemical, Biological and Macromolecular Sciences, S. N. Bose National Centre for Basic Sciences, Block-JD, Sector-III, Salt Lake, Kolkata, 700106, India.
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Camisasca G, Schlesinger D, Zhovtobriukh I, Pitsevich G, Pettersson LGM. A proposal for the structure of high- and low-density fluctuations in liquid water. J Chem Phys 2019; 151:034508. [PMID: 31325915 DOI: 10.1063/1.5100875] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Based on recent experimental data that can be interpreted as indicating the presence of specific structures in liquid water, we build and optimize two structural models which we compare with the available experimental data. To represent the proposed high-density liquid structures, we use a model consisting of chains of water molecules, and for low-density liquid, we investigate fused dodecahedra as templates for tetrahedral fluctuations. The computed infrared spectra of the models are in very good agreement with the extracted experimental spectra for the two components, while the extracted structures from molecular dynamics (MD) simulations give spectra that are intermediate between the experimentally derived spectra. Computed x-ray absorption and emission spectra as well as the O-O radial distribution functions of the proposed structures are not contradicted by experiment. The stability of the proposed dodecahedral template structures is investigated in MD simulations by seeding the starting structure, and remnants found to persist on an ∼30 ps time scale. We discuss the possible significance of such seeds in simulations and whether they can be viable candidates as templates for structural fluctuations below the compressibility minimum of liquid water.
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Affiliation(s)
- Gaia Camisasca
- Department of Physics, AlbaNova University Center, Stockholm University, S-106 91 Stockholm, Sweden
| | - Daniel Schlesinger
- Department of Environmental Science and Analytical Chemistry & Bolin Centre for Climate Research, Stockholm University, 114 18 Stockholm, Sweden
| | - Iurii Zhovtobriukh
- Department of Physics, AlbaNova University Center, Stockholm University, S-106 91 Stockholm, Sweden
| | - George Pitsevich
- Belarusian State University, Nezavisimosti Ave., 4, 220030 Minsk, Belarus
| | - Lars G M Pettersson
- Department of Physics, AlbaNova University Center, Stockholm University, S-106 91 Stockholm, Sweden
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Kipnusu WK, Elsayed M, Iacob C, Pawlus S, Krause-Rehberg R, Paluch M. Glassy dynamics predicted by mutual role of free and activation volumes. SOFT MATTER 2019; 15:4656-4661. [PMID: 31149697 DOI: 10.1039/c9sm00363k] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Broadband Dielectric Spectroscopy (BDS) at elevated pressures and Positron Annihilation Lifetime Spectroscopy (PALS) are employed to elucidate the importance of the ratio of activation and free volumes during vitrification. We show that this ratio has a linear correlation with the structural relaxation of glass forming liquids in a wide temperature range hence engendering it as a vital input in the description of the dynamic glass transition.
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Affiliation(s)
- Wycliffe K Kipnusu
- GROC UJI, Institute of New Imaging Technologies, Department of Physics, Universitat Jaume I, Avda. Sos Baynat s/n, 12071 Castellón, Spain.
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8
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Kikutsuji T, Kim K, Matubayasi N. Diffusion dynamics of supercooled water modeled with the cage-jump motion and hydrogen-bond rearrangement. J Chem Phys 2019; 150:204502. [DOI: 10.1063/1.5095978] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Takuma Kikutsuji
- Division of Chemical Engineering, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan
| | - Kang Kim
- Division of Chemical Engineering, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan
- Institute for Molecular Science, Okazaki, Aichi 444-8585, Japan
| | - Nobuyuki Matubayasi
- Division of Chemical Engineering, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan
- Elements Strategy Initiative for Catalysts and Batteries, Kyoto University, Katsura, Kyoto 615-8520, Japan
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9
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Pedersen UR. Statistics of small length scale density fluctuations in supercooled viscous liquids. J Chem Phys 2019; 150:094505. [PMID: 30849876 DOI: 10.1063/1.5080277] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Many successful theories of liquids near the melting temperature assume that small length scale density fluctuations follow Gaussian statistics. This paper presents a numerical investigation of density fluctuations in the supercooled viscous regime using an enhanced sampling method. Five model systems are investigated: the single component Lennard-Jones liquid, the Kob-Andersen binary mixture, the Wahnström binary mixture, the Lewis-Wahnström model of ortho-terphenyl, and the TIP4P/Ice model of water. The results show that the Gaussian approximation persists to a good degree into the supercooled viscous regime; however, it is less accurate at low temperatures. The analysis suggests that non-Gaussian fluctuations are related to crystalline configurations. Implications for theories of the glass transition are discussed.
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Affiliation(s)
- Ulf R Pedersen
- Glass and Time, IMFUFA, Department of Science and Environment, Roskilde University, P.O. Box 260, DK-4000 Roskilde, Denmark
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10
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Ma X, Davidson ZS, Still T, Ivancic RJS, Schoenholz SS, Liu AJ, Yodh AG. Heterogeneous Activation, Local Structure, and Softness in Supercooled Colloidal Liquids. PHYSICAL REVIEW LETTERS 2019; 122:028001. [PMID: 30720295 DOI: 10.1103/physrevlett.122.028001] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/04/2018] [Revised: 08/08/2018] [Indexed: 06/09/2023]
Abstract
We experimentally characterize heterogeneous nonexponential relaxation in bidisperse supercooled colloidal liquids utilizing a recent concept called "softness" [Phys. Rev. Lett. 114, 108001 (2015)PRLTAO0031-900710.1103/PhysRevLett.114.108001]. Particle trajectory and structure data enable classification of particles into subgroups with different local environments and propensities to hop. We determine residence times t_{R} between particle hops and show that t_{R} derived from particles in the same softness subgroup are exponentially distributed. Using the mean residence time t[over ¯]_{R} for each softness subgroup, and a Kramers' reaction rate model, we estimate the activation energy barriers E_{b} for particle hops, and show that both t[over ¯]_{R} and E_{b} are monotonic functions of softness. Finally, we derive information about the combinations of large and small particle neighbors that determine particle softness, and we explicitly show that multiple exponential relaxation channels in the supercooled liquid give rise to its nonexponential behavior.
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Affiliation(s)
- Xiaoguang Ma
- Department of Physics & Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
- Complex Assemblies of Soft Matter, CNRS-Solvay-UPenn UMI 3254, Bristol, Pennsylvania 19007-3624, USA
| | - Zoey S Davidson
- Department of Physics & Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Tim Still
- Department of Physics & Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Robert J S Ivancic
- Department of Physics & Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - S S Schoenholz
- Google Brain, 1600 Amphitheatre Parkway, Mountain View, California 94043, USA
| | - A J Liu
- Department of Physics & Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - A G Yodh
- Department of Physics & Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
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11
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Bhowmik BP, Tah I, Karmakar S. Non-Gaussianity of the van Hove function and dynamic-heterogeneity length scale. Phys Rev E 2018; 98:022122. [PMID: 30253524 DOI: 10.1103/physreve.98.022122] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2018] [Indexed: 11/07/2022]
Abstract
Non-Gaussian nature of the probability distribution of particles' displacements in the supercooled temperature regime in glass-forming liquids are believed to be one of the major hallmarks of glass transition. It has already been established that this probability distribution, which is also known as the van Hove function, shows universal exponential tail. The origin of such an exponential tail in the distribution function is attributed to the hopping motion of particles observed in the supercooled regime. The non-Gaussian nature can also be explained if one assumes that the system has heterogeneous dynamics in space and time. Thus exponential tail is the manifestation of dynamic heterogeneity. In this work we directly show that non-Gaussianity of the distribution of particles' displacements occur over the dynamic heterogeneity length scale and the dynamical behavior course grained over this length scale becomes homogeneous. We study the non-Gaussianity of the van Hove function by systematically coarse graining at different length scales and extract the length scale of dynamic heterogeneity at which the shape of the van Hove function crosses over from non-Gaussian to Gaussian. The obtained dynamic heterogeneity scale is found to be in very good agreement with the scale obtained from other conventional methods.
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Affiliation(s)
- Bhanu Prasad Bhowmik
- Tata Institute of Fundamental Research, 36/P, Gopanpally Village, Serilingampally Mandal, Ranga Reddy District, Hyderabad, 500107 Telangana, India
| | - Indrajit Tah
- Tata Institute of Fundamental Research, 36/P, Gopanpally Village, Serilingampally Mandal, Ranga Reddy District, Hyderabad, 500107 Telangana, India
| | - Smarajit Karmakar
- Tata Institute of Fundamental Research, 36/P, Gopanpally Village, Serilingampally Mandal, Ranga Reddy District, Hyderabad, 500107 Telangana, India
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12
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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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Turci F, Speck T, Royall CP. Structural-dynamical transition in the Wahnström mixture. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2018; 41:54. [PMID: 29700690 DOI: 10.1140/epje/i2018-11662-3] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/26/2018] [Accepted: 04/12/2018] [Indexed: 06/08/2023]
Abstract
In trajectory space, dynamical heterogeneities in glass-forming liquids correspond to the emergence of a dynamical phase transition between an active phase poor in local structure and an inactive phase which is rich in local structure. We support this scenario with the study of a model additive mixture of Lennard-Jones particles, quantifying how the choice of the relevant structural and dynamical observable affects the transition in trajectory space. We find that the low mobility, structure-rich phase is dominated by icosahedral order. Applying a non-equilibrium rheological protocol, we connect local order to the emergence of mechanical rigidity.
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Affiliation(s)
- Francesco Turci
- H.H. Wills Physics Laboratory, University of Bristol, BS8 1TL, Bristol, UK.
- Centre for Nanoscience and Quantum Information, BS8 1FD, Bristol, UK.
| | - Thomas Speck
- Institut für Physik, Johannes Gutenberg-Universität Mainz, Staudingerweg 7-9, 55128, Mainz, Germany
| | - C Patrick Royall
- H.H. Wills Physics Laboratory, University of Bristol, BS8 1TL, Bristol, UK
- Centre for Nanoscience and Quantum Information, BS8 1FD, Bristol, UK
- School of Chemistry, University of Bristol, BS8 1TS, Bristol, UK
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14
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Using a Time-Based Weighting Criterion to Enhance Link Prediction in Social Networks. ENTERP INF SYST-UK 2018. [DOI: 10.1007/978-3-319-93375-7_2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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15
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Caballero NB, Zuriaga M, Tamarit JL, Serra P. Dynamic heterogeneity in an orientational glass. J Chem Phys 2017; 147:184501. [DOI: 10.1063/1.5004671] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Nirvana B. Caballero
- CNEA, CONICET, Centro Atomico Bariloche, 8400 San Carlos de Bariloche, Rio Negro, Argentina
| | - Mariano Zuriaga
- Facultad de Matemática, Astronomía, Física y Computación, Universidad Nacional de Córdoba, Córdoba, Argentina and IFEG-CONICET, Ciudad Universitaria, X5016LAE Córdoba, Argentina
| | - Josep Lluís Tamarit
- Grup de Caracterització de Materials, Departament de Física, EEBE and Barcelona Research Center in Multiscale Science and Engineering, Eduard Maristany, 10-14, 08019 Barcelona, Catalonia, Spain
| | - Pablo Serra
- Facultad de Matemática, Astronomía, Física y Computación, Universidad Nacional de Córdoba, Córdoba, Argentina and IFEG-CONICET, Ciudad Universitaria, X5016LAE Córdoba, Argentina
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16
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Pastore R, Pesce G, Sasso A, Ciamarra MP. Many facets of intermittent dynamics in colloidal and molecular glasses. Colloids Surf A Physicochem Eng Asp 2017. [DOI: 10.1016/j.colsurfa.2017.06.019] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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17
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Casalegno M, Raos G, Appetecchi GB, Passerini S, Castiglione F, Mele A. From Nanoscale to Microscale: Crossover in the Diffusion Dynamics within Two Pyrrolidinium-Based Ionic Liquids. J Phys Chem Lett 2017; 8:5196-5202. [PMID: 28976762 DOI: 10.1021/acs.jpclett.7b02431] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Knowledge of the ion motion in room temperature ionic liquids (RTILs) is critical for their applications in a number of fields, from lithium batteries to dye-sensitized solar cells. Experiments on a limited number of RTILs have shown that on macroscopic time scales the ions typically undergo conventional, Gaussian diffusion. On shorter time scales, however, non-Gaussian behavior has been observed, similar to supercooled fluids, concentrated colloidal suspensions, and more complex systems. Here we characterize the diffusive motion of ionic liquids based on the N-butyl-N-methylpyrrolidinium (PYR14) cation and bis(trifluoro methanesulfonyl)imide (TFSI) or bis(fluorosulfonyl)imide (FSI) anions. A combination of pulsed gradient spin-echo (PGSE) NMR experiments and molecular dynamics (MD) simulations demonstrates a crossover from subdiffusive behavior to conventional Gaussian diffusion at ∼10 ns. The deconvolution of molecular displacements into a continuous spectrum of diffusivities shows that the short-time behavior is related to the effects of molecular caging. For PYR14FSI, we identify the change of short-range ion-counterion associations as one possible mechanism triggering long-range displacements.
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Affiliation(s)
- Mosè Casalegno
- Department of Chemistry, Materials and Chemical Engineering "G. Natta", Politecnico di Milano , Piazza L. Da Vinci, 32, 20133 Milano, Italy
| | - Guido Raos
- Department of Chemistry, Materials and Chemical Engineering "G. Natta", Politecnico di Milano , Piazza L. Da Vinci, 32, 20133 Milano, Italy
| | - Giovanni Battista Appetecchi
- ENEA, Italian National Agency for New Technology, Energy and Sustainable Economic Development, Materials and Physicochemical Processes Laboratory , Via Anguillarese 301, 00196 Rome, Italy
| | - Stefano Passerini
- Helmholtz Institute Ulm, Karlsruhe Institute of Technology , Helmholtzstrasse 11, 89081 Ulm, Germany
- Karlsruhe Institute of Technology , P.O. Box 3640, 76131 Karlsruhe, Germany
| | - Franca Castiglione
- Department of Chemistry, Materials and Chemical Engineering "G. Natta", Politecnico di Milano , Piazza L. Da Vinci, 32, 20133 Milano, Italy
| | - Andrea Mele
- Department of Chemistry, Materials and Chemical Engineering "G. Natta", Politecnico di Milano , Piazza L. Da Vinci, 32, 20133 Milano, Italy
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Parmar ADS, Sengupta S, Sastry S. Length-Scale Dependence of the Stokes-Einstein and Adam-Gibbs Relations in Model Glass Formers. PHYSICAL REVIEW LETTERS 2017; 119:056001. [PMID: 28949755 DOI: 10.1103/physrevlett.119.056001] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/06/2016] [Indexed: 05/23/2023]
Abstract
The Adam-Gibbs (AG) relation connects the dynamics of a glass-forming liquid to its thermodynamics via the configurational entropy and is of fundamental importance in descriptions of glassy behavior. The breakdown of the Stokes-Einstein relation (SEB) between the diffusion coefficient and the viscosity (or structural relaxation times) in glass formers raises the question as to which dynamical quantity the AG relation describes. By performing molecular dynamics simulations, we show that the AG relation is valid over the widest temperature range for the diffusion coefficient and not for the viscosity or relaxation times. Studying relaxation times defined at a given wavelength, we find that SEB and the deviation from the AG relation occur below a temperature at which the correlation length of dynamical heterogeneity equals the wavelength probed.
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Affiliation(s)
- Anshul D S Parmar
- Theoretical Sciences Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Bengaluru 560064, India
- TIFR Center for Interdisciplinary Sciences, 21 Brundavan Colony, Narsingi, Hyderabad 500075, India
| | - Shiladitya Sengupta
- Theoretical Sciences Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Bengaluru 560064, India
- Department of Fundamental Engineering, Institute of Industrial Science, The University of Tokyo, Komaba 4-6-1, Meguro-ku, Tokyo 153-8505, Japan
| | - Srikanth Sastry
- Theoretical Sciences Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Bengaluru 560064, India
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19
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Accelerated crystallization of colloidal glass by mechanical oscillation. Sci Rep 2017; 7:1369. [PMID: 28465535 PMCID: PMC5430959 DOI: 10.1038/s41598-017-01484-y] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2017] [Accepted: 03/28/2017] [Indexed: 11/09/2022] Open
Abstract
Crystallization of a hard-sphere colloidal glass by mechanical oscillation is investigated, and accelerated crystallization is found at a specific frequency. The crystallization frequency increases as attractive force between particles increases, indicating that interparticle interaction affects the crystallization frequency. Time scale of the mechanical oscillation is different from that of the slow relaxation, and notable relationship with the low-frequency mode is not observed. The experimental results are not explained by the previously proposed model for crystallization by oscillatory shear. Conversely, we speculate that activations of the fast relaxation and particle motion in crystal-like clusters are possible causes of the observations.
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20
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Pastore R, Pesce G, Sasso A, Pica Ciamarra M. Cage Size and Jump Precursors in Glass-Forming Liquids: Experiment and Simulations. J Phys Chem Lett 2017; 8:1562-1568. [PMID: 28301929 DOI: 10.1021/acs.jpclett.7b00187] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Glassy dynamics is intermittent, as particles suddenly jump out of the cage formed by their neighbors, and heterogeneous, as these jumps are not uniformly distributed across the system. Relating these features of the dynamics to the diverse local environments explored by the particles is essential to rationalize the relaxation process. Here we investigate this issue characterizing the local environment of a particle with the amplitude of its short time vibrational motion, as determined by segmenting in cages and jumps the particle trajectories. Both simulations of supercooled liquids and experiments on colloidal suspensions show that particles in large cages are likely to jump after a small time-lag, and that, on average, the cage enlarges shortly before the particle jumps. At large time-lags, the cage has essentially a constant size, which is smaller for longer-lasting cages. Finally, we clarify how this coupling between cage size and duration controls the average behavior and opens the way to a better understanding of the relaxation process in glass-forming liquids.
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Affiliation(s)
- Raffaele Pastore
- CNR-SPIN, sezione di Napoli, Dipartimento di Fisica, Campus universitario di Monte S. Angelo, Via Cintia, 80126 Napoli, Italy
| | - Giuseppe Pesce
- Dipartimento di Fisica, Universitá di Napoli Federico II, Campus universitario di Monte S. Angelo, Via Cintia, 80126 Napoli, Italy
| | - Antonio Sasso
- Dipartimento di Fisica, Universitá di Napoli Federico II, Campus universitario di Monte S. Angelo, Via Cintia, 80126 Napoli, Italy
| | - Massimo Pica Ciamarra
- CNR-SPIN, sezione di Napoli, Dipartimento di Fisica, Campus universitario di Monte S. Angelo, Via Cintia, 80126 Napoli, Italy
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University , Singapore , 639798
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21
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Pastore R, Pesce G, Caggioni M. Differential Variance Analysis: a direct method to quantify and visualize dynamic heterogeneities. Sci Rep 2017; 7:43496. [PMID: 28290540 PMCID: PMC5349610 DOI: 10.1038/srep43496] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2016] [Accepted: 01/24/2017] [Indexed: 11/10/2022] Open
Abstract
Many amorphous materials show spatially heterogenous dynamics, as different regions of the same system relax at different rates. Such a signature, known as Dynamic Heterogeneity, has been crucial to understand the nature of the jamming transition in simple model systems and is currently considered very promising to characterize more complex fluids of industrial and biological relevance. Unfortunately, measurements of dynamic heterogeneities typically require sophisticated experimental set-ups and are performed by few specialized groups. It is now possible to quantitatively characterize the relaxation process and the emergence of dynamic heterogeneities using a straightforward method, here validated on video microscopy data of hard-sphere colloidal glasses. We call this method Differential Variance Analysis (DVA), since it focuses on the variance of the differential frames, obtained subtracting images at different time-lags. Moreover, direct visualization of dynamic heterogeneities naturally appears in the differential frames, when the time-lag is set to the one corresponding to the maximum dynamic susceptibility. This approach opens the way to effectively characterize and tailor a wide variety of soft materials, from complex formulated products to biological tissues.
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Affiliation(s)
- Raffaele Pastore
- CNR-SPIN, sezione di Napoli, Via Cintia, 80126 Napoli, Italy.,University of Cincinnati, UC Simulation Center, 2728 Vine Street, Cincinnati, OH 45219, USA.,Corporate Engineering, The Procter &Gamble Company, Cincinnati, 8256 Union Centre Blvd., West Chester, OH 45069, USA
| | - Giuseppe Pesce
- Università di Napoli "Federico II", Dipartimento di Fisica, Via Cintia, 80126 Napoli, Italy
| | - Marco Caggioni
- Corporate Engineering, The Procter &Gamble Company, Cincinnati, 8256 Union Centre Blvd., West Chester, OH 45069, USA
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22
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Teomy E, Shokef Y. Hydrodynamics in kinetically constrained lattice-gas models. Phys Rev E 2017; 95:022124. [PMID: 28297932 DOI: 10.1103/physreve.95.022124] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2016] [Indexed: 06/06/2023]
Abstract
Kinetically constrained models are lattice-gas models that are used for describing glassy systems. By construction, their equilibrium state is trivial and there are no equal-time correlations between the occupancy of different sites. We drive such models out of equilibrium by connecting them to two reservoirs of different densities, and we measure the response of the system to this perturbation. We find that under the proper coarse-graining, the behavior of these models may be expressed by a nonlinear diffusion equation, with a model- and density-dependent diffusion coefficient. We find a simple approximation for the diffusion coefficient, and we show that the relatively mild discrepancy between the approximation and our numerical results arises due to non-negligible correlations that appear as the system is driven out of equilibrium, even when the density gradient is infinitesimally small. Similar correlations appear when such kinetically constrained models are driven out of equilibrium by applying a uniform external force. We suggest that these correlations are the reason for the same discrepancy between the approximate diffusion coefficient and the numerical results for a broader group of models-nongradient lattice-gas models-for which kinetically constrained models are arguably the simplest example thereof.
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Affiliation(s)
- Eial Teomy
- School of Mechanical Engineering and Sackler Center for Computational Molecular and Materials Science, Tel Aviv University, Tel Aviv 69978, Israel
- Department of Physics, Bar Ilan University, Ramat Gan 52900, Israel
| | - Yair Shokef
- School of Mechanical Engineering and Sackler Center for Computational Molecular and Materials Science, Tel Aviv University, Tel Aviv 69978, Israel
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23
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Piscitelli A, Pica Ciamarra M. Escape rate and diffusion of a Stochastically Driven particle. Sci Rep 2017; 7:41442. [PMID: 28120904 PMCID: PMC5264591 DOI: 10.1038/srep41442] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2016] [Accepted: 12/19/2016] [Indexed: 02/03/2023] Open
Abstract
The dynamical properties of a tracer repeatedly colliding with heat bath particles can be described within a Langevin framework provided that the tracer is more massive than the bath particles, and that the collisions are frequent. Here we consider the escape of a particle from a potential well, and the diffusion coefficient in a periodic potential, without making these assumptions. We have thus investigated the dynamical properties of a Stochastically Driven particle that moves under the influence of the confining potential in between successive collisions with the heat bath. In the overdamped limit, both the escape rate and the diffusion coefficient coincide with those of a Langevin particle. Conversely, in the underdamped limit the two dynamics have a different temperature dependence. In particular, at low temperature the Stochastically Driven particle has a smaller escape rate, but a larger diffusion coefficient.
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Affiliation(s)
- Antonio Piscitelli
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore, Singapore
| | - Massimo Pica Ciamarra
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore, Singapore.,CNR-SPIN, Dipartimento di Scienze Fisiche, Università di Napoli Federico II, I-80126, Napoli, Italy
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24
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Lü YJ, Wang WH. Single-particle dynamics near the glass transition of a metallic glass. Phys Rev E 2017; 94:062611. [PMID: 28085459 DOI: 10.1103/physreve.94.062611] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2016] [Indexed: 11/07/2022]
Abstract
The single-particle dynamics of the glass-forming Cu_{50}Zr_{50} alloy, from the supercooled liquid well above the glass-transition temperature, T_{g} to the glassy state, is studied by using the molecular dynamics simulations. When the liquid is cooled below 1.2T_{g}, the dynamics heterogeneity characterized by the cage-jump motion becomes increasingly pronounced. The analyses based on the continuous time random walk method indicate that the liquid falls out of equilibrium in the present simulation time scale when it is cooled into the regime below 1.02T_{g}. However, we find that the jump length and the jump rate do not display the non-equilibrium behaviors even in the glassy state below T_{g}, which allows us to study the intrinsic dynamic characteristics through T_{g}. The mean waiting time between two successive jumps has a rapid growth following the Vogel-Fulcher-Tammann law as the non-equilibrium regime is approached, in analogy with the temperature behaviors of transport properties for fragile supercooled liquids. In contrast, the jump rate maintains the Arrhenius decay and the jump length has even a weaker temperature dependence when the liquid is cooled into glassy state. We find that a pronounced enhancement of the spatial correlation of jumps occurs accompanied by the glass transition: the string-like cooperative jumps dominate the fast motion instead of the uncorrelated and individual jumps. Our work offers an insight into the equilibrium effect of the single-particle dynamics in glass transition.
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Affiliation(s)
- Y J Lü
- School of Physics, Beijing Institute of Technology, Beijing 100081, People's Republic of China
| | - W H Wang
- Institute of Physics, Chinese Academy of Sciences, Beijing 100190, People's Republic of China
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25
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Guillaud E, Merabia S, de Ligny D, Joly L. Decoupling of viscosity and relaxation processes in supercooled water: a molecular dynamics study with the TIP4P/2005f model. Phys Chem Chem Phys 2017; 19:2124-2130. [DOI: 10.1039/c6cp07863j] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
We show that the TIP4P/2005f water model describes accurately the experimental viscosity and self-diffusion over a large temperature range. We then show the decoupling of viscosity and structural relaxation time in supercooled water.
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Affiliation(s)
- Emmanuel Guillaud
- Univ Lyon
- Université Claude Bernard Lyon 1
- CNRS
- Institut Lumière Matière
- LYON
| | - Samy Merabia
- Univ Lyon
- Université Claude Bernard Lyon 1
- CNRS
- Institut Lumière Matière
- LYON
| | - Dominique de Ligny
- Institute of Glass and Ceramics
- Department of Material Science
- University of Erlangen-Nürnberg
- 91058 Erlangen
- Germany
| | - Laurent Joly
- Univ Lyon
- Université Claude Bernard Lyon 1
- CNRS
- Institut Lumière Matière
- LYON
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26
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Fodor É, Hayakawa H, Visco P, van Wijland F. Active cage model of glassy dynamics. Phys Rev E 2016; 94:012610. [PMID: 27575182 DOI: 10.1103/physreve.94.012610] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2016] [Indexed: 06/06/2023]
Abstract
We build up a phenomenological picture in terms of the effective dynamics of a tracer confined in a cage experiencing random hops to capture some characteristics of glassy systems. This minimal description exhibits scale invariance properties for the small-displacement distribution that echo experimental observations. We predict the existence of exponential tails as a crossover between two Gaussian regimes. Moreover, we demonstrate that the onset of glassy behavior is controlled only by two dimensionless numbers: the number of hops occurring during the relaxation of the particle within a local cage and the ratio of the hopping length to the cage size.
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Affiliation(s)
- Étienne Fodor
- Laboratoire Matière et Systèmes Complexes, UMR 7057 CNRS/P7, Université Paris Diderot, 10 rue Alice Domon et Léonie Duquet, 75205 Paris cedex 13, France
| | - Hisao Hayakawa
- Yukawa Institute for Theoretical Physics, Kyoto University, Kitashirakawa-oiwake cho, Sakyo-ku, Kyoto 606-8502, Japan
| | - Paolo Visco
- Laboratoire Matière et Systèmes Complexes, UMR 7057 CNRS/P7, Université Paris Diderot, 10 rue Alice Domon et Léonie Duquet, 75205 Paris cedex 13, France
| | - Frédéric van Wijland
- Laboratoire Matière et Systèmes Complexes, UMR 7057 CNRS/P7, Université Paris Diderot, 10 rue Alice Domon et Léonie Duquet, 75205 Paris cedex 13, France
- Yukawa Institute for Theoretical Physics, Kyoto University, Kitashirakawa-oiwake cho, Sakyo-ku, Kyoto 606-8502, Japan
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27
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Gradenigo G, Bertin E, Biroli G. Field-induced superdiffusion and dynamical heterogeneity. Phys Rev E 2016; 93:060105. [PMID: 27415189 DOI: 10.1103/physreve.93.060105] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2016] [Indexed: 06/06/2023]
Abstract
By analyzing two kinetically constrained models of supercooled liquids we show that the anomalous transport of a driven tracer observed in supercooled liquids is another facet of the phenomenon of dynamical heterogeneity. We focus on the Fredrickson-Andersen and the Bertin-Bouchaud-Lequeux models. By numerical simulations and analytical arguments we demonstrate that the violation of the Stokes-Einstein relation and the field-induced superdiffusion observed during a long preasymptotic regime have the same physical origin: while a fraction of probes do not move, others jump repeatedly because they are close to local mobile regions. The anomalous fluctuations observed out of equilibrium in the presence of a pulling force ε,σ_{x}^{2}(t)=〈x_{ε}^{2}(t)〉-〈x_{ε}(t)〉^{2}∼t^{3/2}, which are accompanied by the asymptotic decay α_{ε}(t)∼t^{-1/2} of the non-Gaussian parameter from nontrivial values to zero, are due to the splitting of the probes population in the two (mobile and immobile) groups and to dynamical correlations, a mechanism expected to happen generically in supercooled liquids.
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Affiliation(s)
- Giacomo Gradenigo
- Université Grenoble Alpes, LIPHY, F-38000 Grenoble, France
- CNRS, LIPHY, F-38000 Grenoble, France
| | - Eric Bertin
- Université Grenoble Alpes, LIPHY, F-38000 Grenoble, France
- CNRS, LIPHY, F-38000 Grenoble, France
| | - Giulio Biroli
- IPhT, Université Paris Saclay, CEA, CNRS, F-91191 Gif-sur-Yvette Cedex, France
- Laboratoire de Physique Statistique, Ecole Normale Supérieure, PSL Research University, Université Paris Diderot Sorbonne Paris-Cité, Sorbonne Universités UPMC Université Paris 06, CNRS, 24 rue Lhomond, 75005 Paris, France
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28
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Wu JH, Jia Q. The heterogeneous energy landscape expression of KWW relaxation. Sci Rep 2016; 6:20506. [PMID: 26879824 PMCID: PMC4754662 DOI: 10.1038/srep20506] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2015] [Accepted: 01/05/2016] [Indexed: 11/09/2022] Open
Abstract
Here we show a heterogeneous energy landscape approach to describing the Kohlrausch-Williams-Watts (KWW) relaxation function. For a homogeneous dynamic process, the distribution of free energy landscape is first proposed, revealing the significance of rugged fluctuations. In view of the heterogeneous relaxation given in two dynamic phases and the transmission coefficient in a rate process, we obtain a general characteristic relaxation time distribution equation for the KWW function in a closed, analytic form. Analyses of numerical computation show excellent accuracy, both in time and frequency domains, in the convergent performance of the heterogeneous energy landscape expression and shunning the catastrophic truncations reported in the previous work. The stretched exponential β, closely associated to temperature and apparent correlation with one dynamic phase, reveals a threshold value of 1/2 defining different behavior of the probability density functions. Our work may contribute, for example, to in-depth comprehension of the dynamic mechanism of glass transition, which cannot be provided by existing approaches.
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Affiliation(s)
- J H Wu
- Peter Grünberg Research Center, Nanjing University of Posts and Telecommunications, Nanjing 210003, China.,Research Institute of Engineering and Technology, Korea University, Seoul 136-713, South Korea.,School of Life Sciences, Shandong University, Jinan 250100, China
| | - Q Jia
- Department of Management, Hohai University, Nanjing 211100, China
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29
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Ciamarra MP, Pastore R, Coniglio A. Particle jumps in structural glasses. SOFT MATTER 2016; 12:358-366. [PMID: 26481331 DOI: 10.1039/c5sm01568e] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Particles in structural glasses rattle around temporary equilibrium positions, that seldom change through a process which is much faster than the relaxation time, known as particle jump. Since the relaxation of the system is due to the accumulation of many such jumps, it could be possible to connect the single particle short time motion to the macroscopic relaxation by understanding the features of the jump dynamics. Here we review recent results in this research direction, clarifying the features of particle jumps that have been understood and those that are still under investigation, and examining the role of particle jumps in different theories of the glass transition.
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Affiliation(s)
- Massimo Pica Ciamarra
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore and CNR-SPIN, Dipartimento di Scienze Fisiche, University of Napoli Federico II, Italy.
| | - Raffaele Pastore
- CNR-SPIN, Dipartimento di Scienze Fisiche, University of Napoli Federico II, Italy.
| | - Antonio Coniglio
- CNR-SPIN, Dipartimento di Scienze Fisiche, University of Napoli Federico II, Italy.
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30
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Pastore R, Raos G. Glassy dynamics of a polymer monolayer on a heterogeneous disordered substrate. SOFT MATTER 2015; 11:8083-8091. [PMID: 26337758 DOI: 10.1039/c5sm01440a] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
We present molecular dynamics simulations of a polymer monolayer on randomly functionalized surfaces that are characterized by different fractions of weakly and strongly attractive sites. We show that the dynamics slow-down upon cooling resembles that of a strong glass-forming liquid. Indeed, the mean-square displacements show an increasingly lasting subdiffusive behaviour before the diffusive regime, with signs of Fickian yet not Gaussian diffusion, and the dynamic correlation functions exhibit a stretched exponential decay. The glassy dynamics of this relatively dilute system is dominated by the interaction of the polymer with the substrate and becomes more marked when the substrate composition is heterogeneous. Accordingly, the estimated glass transition temperature shows a non-monotic dependence on surface composition, in agreement with previous results for the activation energy and with an analysis of the potential energy landscape experienced by the polymer beads. Our findings are relevant to the description of polymer-surface adhesion and friction and the development of polymer nanocomposites with tailored structural and mechanical properties.
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Affiliation(s)
- Raffaele Pastore
- CNR-SPIN, Dipartimento di Scienze Fisiche, University of Napoli Federico II, Italy.
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31
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Pastore R, Coniglio A, Ciamarra MP. Spatial correlations of elementary relaxation events in glass-forming liquids. SOFT MATTER 2015; 11:7214-7218. [PMID: 26264078 DOI: 10.1039/c5sm01510c] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The dynamical facilitation scenario, by which localized relaxation events promote nearby relaxation events in an avalanche process, has been suggested as the key mechanism connecting the microscopic and the macroscopic dynamics of structural glasses. Here we investigate the statistical features of this process via numerical simulations of a model structural glass. First we show that the relaxation dynamics of the system occurs through particle jumps that are irreversible, and that cannot be decomposed in smaller irreversible events. Then we show that each jump does actually trigger an avalanche. The characteristics of this avalanche change upon cooling, suggesting that the relaxation dynamics crossovers from a noise dominated regime, where jumps do not trigger other relaxation events, to a regime dominated by the facilitation process, where a jump triggers more relaxation events.
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