2,387 results match your criteria hard-sphere

Interacting hard-sphere fluids in an external field.

Phys Rev E 2021 Mar;103(3-1):032604

Department of Physics, University of Rhode Island, Kingston, Rhode Island 02881, USA.

We present a method for studying equilibrium properties of interacting fluids in an arbitrary external field. The fluid is composed of monodisperse spherical particles with hard-core repulsion and additional interactions of arbitrary shape and limited range. Our method of analysis is exact in one dimension and provides demonstrably good approximations in higher dimensions. Read More

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Testing the Stokes-Einstein relation with the hard-sphere fluid model.

Phys Rev E 2021 Mar;103(3):L030103

Department of Physics, Xiamen University, Xiamen 361005, Fujian, China.

The Stokes-Einstein (SE) relation has been widely applied to quantitatively describe the Brownian motion. Notwithstanding, here we show that even for a simple fluid, the SE relation may fail over a wide range of the Brownian particle's size. Namely, although the SE relation could be a good approximation for a large enough Brownian particle, a significant error may appear when decreasing the Brownian particle's size down to several hundred times the size of the fluid molecules, and the error increases with the decrease of the Brownian particle's size. Read More

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Determining the nonequilibrium criticality of a Gardner transition via a hybrid study of molecular simulations and machine learning.

Proc Natl Acad Sci U S A 2021 Mar;118(11)

Department of Physics and Astronomy, University of Waterloo, Waterloo, ON N2L 3G1, Canada.

Apparent critical phenomena, typically indicated by growing correlation lengths and dynamical slowing down, are ubiquitous in nonequilibrium systems such as supercooled liquids, amorphous solids, active matter, and spin glasses. It is often challenging to determine if such observations are related to a true second-order phase transition as in the equilibrium case or simply a crossover and even more so to measure the associated critical exponents. Here we show that the simulation results of a hard-sphere glass in three dimensions are consistent with the recent theoretical prediction of a Gardner transition, a continuous nonequilibrium phase transition. Read More

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Molecular dynamics simulations vs field-cycling NMR relaxometry: Structural relaxation mechanisms in the glass-former glycerol revisited.

J Chem Phys 2021 Mar;154(12):124503

Institute of Condensed Matter Physics, Technische Universität Darmstadt, Hochschulstraße 6, 64289 Darmstadt, Germany.

We combine field-cycling (FC) relaxometry and molecular dynamics (MD) simulations to study the rotational and translational dynamics associated with the glassy slowdown of glycerol. The H NMR spin-lattice relaxation rates R(ω) probed in the FC measurements for different isotope-labelled compounds are computed from the MD trajectories for broad frequency and temperature ranges. We find high correspondence between experiment and simulation. Read More

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BoltzmaNN: Predicting effective pair potentials and equations of state using neural networks.

J Chem Phys 2021 Mar;154(12):124123

Institute of Physics, Johannes Gutenberg University Mainz, Staudingerweg 7, 55128 Mainz, Germany.

Neural networks (NNs) are employed to predict equations of state from a given isotropic pair potential using the virial expansion of the pressure. The NNs are trained with data from molecular dynamics simulations of monoatomic gases and liquids, sampled in the NVT ensemble at various densities. We find that the NNs provide much more accurate results compared to the analytic low-density limit estimate of the second virial coefficient and the Carnahan-Starling equation of state for hard sphere liquids. Read More

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Self-consistent construction of bridge functional based on the weighted density approximation.

J Chem Phys 2021 Mar;154(12):124113

Department of Molecular Engineering, Graduate School of Engineering, Kyoto University, Kyoto 615-8510, Japan.

A parameter-free bridge functional is presented using a weighted density approximation (WDA). The key point of this scheme is the utilization of Baxter's relation connecting the second-order direct correlation function (DCF) to the higher-order DCF with the density derivative. The free energy density required for the WDA is determined in a self-consistent manner using Baxter's relation and Percus's test particle method. Read More

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Sound Velocities of Generalized Lennard-Jones ( - 6) Fluids Near Freezing.

Sergey Khrapak

Molecules 2021 Mar 16;26(6). Epub 2021 Mar 16.

Reseash and Edicational Centre for Ion, Bauman Moscow State Technical University, 105005 Moscow, Russia.

In a recent paper [S. Khrapak, Molecules , 3498 (2020)], the longitudinal and transverse sound velocities of a conventional Lennard-Jones system at the liquid-solid coexistence were calculated. It was shown that the sound velocities remain almost invariant along the liquid-solid coexistence boundary lines and that their magnitudes are comparable with those of repulsive soft-sphere and hard-sphere models at the fluid-solid phase transition. Read More

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Effects of Polydispersity on the Phase Behavior of Additive Hard Spheres in Solution.

Molecules 2021 Mar 11;26(6). Epub 2021 Mar 11.

Laboratory of Physics and Physical Chemistry of Foods, Wageningen University, Bornse Weilanden 9, 6708 WG Wageningen, The Netherlands.

The ability to separate enzymes, nucleic acids, cells, and viruses is an important asset in life sciences. This can be realised by using their spontaneous asymmetric partitioning over two macromolecular aqueous phases in equilibrium with one another. Such phases can already form while mixing two different types of macromolecules in water. Read More

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Revisiting the Charged Shell Model: A Density Functional Theory for Electrolytes.

J Chem Theory Comput 2021 Apr 30;17(4):2409-2416. Epub 2021 Mar 30.

Department of Physiology and Biophysics, Rush University Medical Center, Chicago, Illinois 60612, United States.

Classical density functional theory (DFT) has proven to be a sophisticated and efficient approach for investigating charge systems. In DFT, the excess free energy functional for inhomogeneous charged hard-sphere fluids consists of hard-core interactions and charge-charge electrostatic interactions. The former component can be precisely described by well-established fundamental measure theory (FMT). Read More

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Self-assembly behavior and conformation of amphiphilic hemicellulose-graft-fatty acid micelles.

Carbohydr Polym 2021 Jun 3;261:117886. Epub 2021 Mar 3.

State Key Laboratory of Pulp and Paper Engineering, South China University of Technology, Guangzhou, 510640, PR China. Electronic address:

In this work, a series of amphiphilic hemicellulose-based grafting polymers are synthesized by homogeneous esterification with various hydrophobic chain fatty acids. With the flexible chain conformation of hemicelluloses, the hemicellulose-graft-fatty acid is self-assembled into hard sphere micelles in aqueous solution through hydrophobic interactions. The resultant micelles show apparent hydrodynamic radius (R) varying in the range of 34-57 nm and radius of gyration (R varying from 30 to 44 nm. Read More

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Collision of a hard ball with singular points of the boundary.

Chaos 2021 Jan;31(1):013123

School of Mathematics, Georgia Institute of Technology, Atlanta, Georgia 30332, USA.

Recently, physical billiards were introduced where a moving particle is a hard sphere rather than a point as in standard mathematical billiards. It has been shown that in the same billiard tables, the physical billiards may have totally different dynamics than mathematical billiards. This difference appears if the boundary of a billiard table has visible singularities (internal corners if the billiard table is two-dimensional); i. Read More

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January 2021

Vitrification is a spontaneous non-equilibrium transition driven by osmotic pressure.

J Phys Condens Matter 2021 Mar 15. Epub 2021 Mar 15.

Chemical Engineering, Stanford University, 443 Via Ortega, Stanford, California, 94305-6104, UNITED STATES.

Persistent dynamics in colloidal glasses suggest the existence of a non-equilibrium driving force for structural relaxation during glassy aging. But the implicit assumption in the literature that colloidal glasses form within the metastable state bypasses the search for a driving force for vitrification and glassy aging and its connection with a metastable state. The natural relation of osmotic pressure to number-density gradients motivates us to investigate the osmotic pressure as this driving force. Read More

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In situ synchrotron diffraction and modeling of non-equilibrium solidification of a MnFeCoNiCu alloy.

Sci Rep 2021 Mar 15;11(1):5921. Epub 2021 Mar 15.

Colorado School of Mines, Golden, CO, 80401, USA.

The solidification mechanism and segregation behavior of laser-melted MnFeCoNiCu was firstly investigated via in situ synchrotron x-ray diffraction at millisecond temporal resolution. The transient composition evolution of the random solid solution during sequential solidification of dendritic and interdendritic regions complicates the analysis of synchrotron diffraction data via any single conventional tool, such as Rietveld refinement. Therefore, a novel approach combining a hard-sphere approximation model, thermodynamic simulation, thermal expansion measurement and microstructural characterization was developed to assist in a fundamental understanding of the evolution of local composition, lattice parameter, and dendrite volume fraction corresponding to the diffraction data. Read More

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Memory Formation in Jammed Hard Spheres.

Phys Rev Lett 2021 Feb;126(8):088001

Department of Chemistry, Duke University, Durham, North Carolina 27708, USA.

Liquids equilibrated below an onset condition share similar inherent states, while those above that onset have inherent states that markedly differ. Although this type of materials memory was first reported in simulations over 20 years ago, its physical origin remains controversial. Its absence from mean-field descriptions, in particular, has long cast doubt on its thermodynamic relevance. Read More

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February 2021

Self-assembly and thermoreversible rheology of perfluorocarbon nanoemulsion-based gels with amphiphilic copolymers.

Colloids Surf B Biointerfaces 2021 Feb 18;202:111641. Epub 2021 Feb 18.

Department of Chemistry, Stony Brook University, Stony Brook, NY 11794-3400, USA. Electronic address:

Perfluorocarbon (PFC) nanoemulsions have great potential in biomedical applications due to their unique chemical stability, biocompatibility, and possibilities for enhanced oxygen supply. The addition of amphiphilic block copolymers promotes the formation and long-term stability of emulsion-based gels. In this work, we report the systematic study of the impact of adding amphiphilic triblock copolymers to water-in-perfluorocarbon nanoemulsions on their structure and viscoelasticity, utilizing small-angle neutron and X-ray scattering (SANS and SAXS) and rheology. Read More

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February 2021

An entropy scaling demarcation of gas- and liquid-like fluid behaviors.

J Chem Phys 2020 May;152(19):191102

Department of Science and Environment, Roskilde University, Postbox 260, DK-4000 Roskilde, Denmark.

In this work, we propose a generic and simple definition of a line separating gas-like and liquid-like fluid behaviors from the standpoint of shear viscosity. This definition is valid even for fluids such as the hard sphere and the inverse power law that exhibit a unique fluid phase. We argue that this line is defined by the location of the minimum of the macroscopically scaled viscosity when plotted as a function of the excess entropy, which differs from the popular Widom lines. Read More

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Comparison of Huggins Coefficients and Osmotic Second Virial Coefficients of Buffered Solutions of Monoclonal Antibodies.

Polymers (Basel) 2021 Feb 17;13(4). Epub 2021 Feb 17.

Material Science and Engineering Laboratory, National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, MD 20899, USA.

The Huggins coefficient is a well-known metric for quantifying the increase in solution viscosity arising from intermolecular interactions in relatively dilute macromolecular solutions, and there has been much interest in this solution property in connection with developing improved antibody therapeutics. While numerous measurements have been reported for select monoclonal antibodies (mAbs) solutions, there has been limited study of in terms of the fundamental molecular interactions that determine this property. In this paper, we compare measurements of the osmotic second virial coefficient , a common metric of intermolecular and interparticle interaction strength, to measurements of for model antibody solutions. Read More

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February 2021

Solvation effects on diffusion processes of a macromolecule: Accuracy required for radial distribution function to calculate diffusion coefficient.

J Chem Phys 2021 Feb;154(8):084501

Department of Chemistry, Kyushu University, Fukuoka 819-0395, Japan.

We investigate the dependence of the diffusion coefficient of a large solute particle on the solvation structure around a solute. The diffusion coefficient of a hard-sphere system is calculated by using a perturbation theory of large-particle diffusion with radial distribution functions around the solute. To obtain the radial distribution function, some integral equation theories are examined, such as the Percus-Yevick (PY), hypernetted-chain (HNC), and modified HNC theories using a bridge function proposed by Kinoshita (MHNC) closures. Read More

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February 2021

An Artificial Neural Network Reveals the Nucleation Mechanism of a Binary Colloidal AB Crystal.

ACS Nano 2021 Mar 23;15(3):4335-4346. Epub 2021 Feb 23.

Soft Condensed Matter, Debye Institute for Nanomaterials Science, Department of Physics, Utrecht University, Princetonplein 1, 3584 CC Utrecht, The Netherlands.

Colloidal suspensions of two species have the ability to form binary crystals under certain conditions. The hunt for these functional materials and the countless investigations on their formation process are justified by the plethora of synergetic and collective properties these binary superlattices show. Among the many crystal structures observed over the past decades, the highly exotic colloidal AB crystal was predicted to be stable in binary hard-sphere mixtures nearly 30 years ago, yet the kinetic pathway of how homogeneous nucleation occurs in this system is still unknown. Read More

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Phase behavior of binary hard-sphere mixtures: Free volume theory including reservoir hard-core interactions.

J Chem Phys 2021 Feb;154(7):074902

Laboratory of Physical Chemistry, Department of Chemical Engineering and Chemistry, and Institute for Complex Molecular Systems (ICMS), Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands.

Comprehensive calculations were performed to predict the phase behavior of large spherical colloids mixed with small spherical colloids that act as a depletant. To this end, the free volume theory (FVT) of Lekkerkerker et al. [Europhys. Read More

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February 2021

Universality in Driven and Equilibrium Hard Sphere Liquid Dynamics.

Phys Rev Lett 2021 Feb;126(5):058002

Theoretische Physik II, Physikalisches Institut, Universität Bayreuth, D-95447 Bayreuth, Germany.

We demonstrate that the time evolution of the van Hove dynamical pair correlation function is governed by adiabatic forces that arise from the free energy and by superadiabatic forces that are induced by the flow of the van Hove function. The superadiabatic forces consist of drag, viscous, and structural contributions, as occur in active Brownian particles, in liquids under shear and in lane forming mixtures. For hard sphere liquids, we present a power functional theory that predicts these universal force fields in quantitative agreement with our Brownian dynamics simulation results. Read More

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February 2021

Free energy and segregation dynamics of two channel-confined polymers of different lengths.

Phys Rev E 2021 Jan;103(1-1):012501

Department of Physics, University of Prince Edward Island, 550 University Avenue, Charlottetown, Prince Edward Island C1A 4P3, Canada.

Polymers confined to a narrow channel are subject to strong entropic forces that tend to drive the molecules apart. In this study, we use Monte Carlo computer simulations to study the segregation behavior of two flexible hard-sphere polymers under confinement in a cylindrical channel. We focus on the effects of using polymers of different lengths. Read More

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January 2021

Structural characterization and statistical properties of jammed soft ellipsoid packing.

Soft Matter 2021 Mar;17(10):2963-2972

Shanghai Key Laboratory of Magnetic Resonance, Institute of Materials, School of Physics and Electronic Science, East China Normal University, Shanghai 200241, P. R. China.

The jamming transition and jammed packing structures of hydrogel soft ellipsoids are studied using magnetic resonance imaging techniques. As the packing fraction increases, the fluctuation of local free volume decreases and the fluctuation of particle deformation increases. Effective thermodynamic quantities are obtained by characterizing these fluctuations using k-gamma distributions based on an underlying statistical model for granular materials. Read More

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Prandtl Number in Classical Hard-Sphere and One-Component Plasma Fluids.

Molecules 2021 Feb 5;26(4). Epub 2021 Feb 5.

Joint Institute for High Temperatures, Russian Academy of Sciences, 125412 Moscow, Russia.

The Prandtl number is evaluated for the three-dimensional hard-sphere and one-component plasma fluids, from the dilute weakly coupled regime up to a dense strongly coupled regime near the fluid-solid phase transition. In both cases, numerical values of order unity are obtained. The Prandtl number increases on approaching the freezing point, where it reaches a quasi-universal value for simple dielectric fluids of about ≃1. Read More

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February 2021

Probing sedimentation non-ideality of particulate systems using analytical centrifugation.

Soft Matter 2021 Mar;17(10):2803-2814

Institute of Particle Technology (LFG), Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Cauerstraße 4, 91058 Erlangen, Germany. and Interdisciplinary Center for Functional Particle Systems (FPS), Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Haberstraße 9a, 91058 Erlangen, Germany.

Analytical centrifugation is a versatile technique for the quantitative characterization of colloidal systems including colloidal stability. The recent developments in data acquisition and evaluation allow the accurate determination of particle size, shape anisotropy and particle density. High precision analytical centrifugation is in particular suited for the study of particle interactions and concentration-dependent sedimentation coefficients. Read More

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Reevaluating the Role of Polarizability in Ion Mobility Spectrometry.

J Am Soc Mass Spectrom 2021 Mar 3;32(3):618-627. Epub 2021 Feb 3.

Department of Chemistry, Washington State University, Pullman, Washington 99164, United States.

With the expanding commercial availability of gas-phase separation systems that incorporate gas-phase mobility, there is a concurrent rise in efforts to cast the gas-phase mobility coefficient in terms of an ion-neutral collision cross-section (CCS). The motivating factors for this trend are varied, but many aim to complement experimental results with computationally generated CCS values from structural approximations. Unfortunately, the current paradigm for relating experimental mobility results to computationally derived structures relies upon empirical approaches, including a myriad of variables that do not realistically bound the comparison. Read More

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Activated penetrant dynamics in glass forming liquids: size effects, decoupling, slaving, collective elasticity and correlation with matrix compressibility.

Soft Matter 2021 Mar;17(9):2624-2639

Department of Materials Science, University of Illinois, Urbana, IL 61801, USA. and Materials Research Laboratory, University of Illinois, Urbana, IL 61801, USA and Department of Chemistry, University of Illinois, Urbana, IL 61801, USA and Department of Chemical & Biomolecular Engineering, University of Illinois, Urbana, IL 61801, USA.

We employ the microscopic self-consistent cooperative hopping theory of penetrant activated dynamics in glass forming viscous liquids and colloidal suspensions to address new questions over a wide range of high matrix packing fractions and penetrant-to-matrix particle size ratios. The focus is on the mean activated relaxation time of smaller tracers in a hard sphere fluid of larger particle matrices. This quantity also determines the penetrant diffusion constant and connects directly with the structural relaxation time probed in an incoherent dynamic structure factor measurement. Read More

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Theoretical Estimate of the Glass Transition Line of Yukawa One-Component Plasmas.

Molecules 2021 Jan 28;26(3). Epub 2021 Jan 28.

Space and Plasma Physics, Royal Institute of Technology, SE-100 44 Stockholm, Sweden.

The mode coupling theory of supercooled liquids is combined with advanced closures to the integral equation theory of liquids in order to estimate the glass transition line of Yukawa one-component plasmas from the unscreened Coulomb limit up to the strong screening regime. The present predictions constitute a major improvement over the current literature predictions. The calculations confirm the validity of an existing analytical parameterization of the glass transition line. Read More

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January 2021

Diameter Dependence of Water Filling in Lithographically Segmented Isolated Carbon Nanotubes.

ACS Nano 2021 Feb 29;15(2):2778-2790. Epub 2021 Jan 29.

Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States.

Although the structure and properties of water under conditions of extreme confinement are fundamentally important for a variety of applications, they remain poorly understood, especially for dimensions less than 2 nm. This problem is confounded by the difficulty in controlling surface roughness and dimensionality in fabricated nanochannels, contributing to a dearth of experimental platforms capable of carrying out the necessary precision measurements. In this work, we utilize an experimental platform based on the interior of lithographically segmented, isolated single-walled carbon nanotubes to study water under extreme nanoscale confinement. Read More

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February 2021

Phase Behavior of Lyotropic Liquid-Crystalline Polymers under Varying Solvent Conditions: Effect of External Fields on the Phase Diagram.

Sergei A Egorov

J Phys Chem B 2021 Feb 28;125(5):1513-1528. Epub 2021 Jan 28.

Department of Chemistry, University of Virginia, Charlottesville, Virginia 22901, United States.

In this work, we report a Density Functional Theory based study of phase behavior of lyotropic liquid-crystalline polymers under both good and varying solvent conditions in the presence of external electric or magnetic field. Our microscopic model for the good solvent case is based on the tangent hard-sphere chain with bond-bending potential to account for the chain stiffness; the variable solvent quality is modeled by adding attractive monomer-monomer interactions. The phase diagrams are constructed in three intensive variables (temperature, pressure, and field strength), and are characterized by the presence of critical and triple lines, which originate from the critical and triple points of the corresponding zero-field case. Read More

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February 2021