908 results match your criteria hard-sphere model


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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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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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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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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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

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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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.

Authors:
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

Dynamical Density Functional Theory for the Drying and Stratification of Binary Colloidal Dispersions.

Langmuir 2021 Feb 20;37(4):1399-1409. Epub 2021 Jan 20.

Department of Mathematical Sciences, Loughborough University, Loughborough LE11 3TU, United Kingdom.

We develop a dynamical density functional theory based model for the drying of colloidal films on planar surfaces. We consider mixtures of two different sizes of hard-sphere colloids. Depending on the solvent evaporation rate and the initial concentrations of the two species, we observe varying degrees of stratification in the final dried films. Read More

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February 2021

Classical density-functional theory applied to the solid state.

Phys Rev E 2020 Dec;102(6-1):062136

Center for Nonlinear Phenomena and Complex Systems CP 231, Université Libre de Bruxelles, 1050 Brussels, Belgium.

The standard model of classical density-functional theory (cDFT) for pair potentials consists of a hard-sphere functional plus a mean-field term accounting for long ranged attraction. However, most implementations using sophisticated fundamental measure hard-sphere functionals suffer from potential numerical instabilities either due to possible instabilities in the functionals themselves or due to implementations that mix real- and Fourier-space components inconsistently. Here we present a new implementation based on a demonstrably stable hard-sphere functional that is implemented in a completely consistent manner. Read More

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December 2020

Time-Resolved Small-Angle X-ray Scattering Studies during Aqueous Emulsion Polymerization.

J Am Chem Soc 2021 Jan 14;143(3):1474-1484. Epub 2021 Jan 14.

Department of Chemistry, University of Sheffield, Dainton Building, Brook Hill, Sheffield S3 7HF, United Kingdom.

The persulfate-initiated aqueous emulsion polymerization of 2,2,2-trifluoroethyl methacrylate (TFEMA) is studied by time-resolved small-angle X-ray scattering (SAXS) at 60 °C using a stirrable reaction cell. TFEMA was preferred to styrene because it offers much greater X-ray scattering contrast relative to water, which is essential for sufficient temporal resolution. The evolution in particle size is monitored by both in situ SAXS and ex situ DLS in the absence or presence of an anionic surfactant (sodium dodecyl sulfate, SDS). Read More

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January 2021

Temperature, Pressure, and Length-Scale Dependence of Solvation in Water-like Solvents. I. Small Solvophobic Solutes.

J Phys Chem B 2021 01 29;125(1):297-306. Epub 2020 Dec 29.

Departamento de Física Aplicada, Universidad de Vigo, Campus del Agua, Ourense 32004, Spain.

We analyze the role of temperature, pressure, and solute's molecular size on the pattern of isochoric and isobaric solvation of small hard-sphere solutes in TIP4P/2005 water and in a water-like "Jagla" solvent exhibiting unusual thermodynamics. To this end, we employ molecular simulation to determine solvation free energies, isochoric solvation energies and entropies, isobaric solvation enthalpies and entropies, partial molecular volumes, and isothermal density derivatives of the solvation free energy along isobaric and isothermal paths covering solvent's stable liquid and supercritical states as well as supercooled and "stretched" liquid states. Results are found to be consistent with the most primitive scaled-particle theory and the Gaussian model of small-length-scale solvation. Read More

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January 2021

Understanding charged vesicle suspensions as Wigner glasses: dynamical aspects.

J Phys Condens Matter 2021 Mar;33(10):104001

Department of Chemical, Materials and Production Engineering, University of Naples Federico II, P.le Tecchio 80, Naples 80125, Italy.

Suspensions of charged vesicles in water with added salt are widespread in nature and industrial production. Here we investigate, via Brownian dynamics simulations, a model that grasps the key features of these systems, with bidisperse colloidal beads interacting via a hard-core and an electrostatic double layer potential. Our goal is to focus on a set of interaction parameters that is not generic but measured in recent experiments, and relevant for a class of consumer products, such as liquid fabric softeners. Read More

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Experimental Determination of H and CO Diffusion Coefficients in a Wax Mixture Confined in a Porous Titania Catalyst Support.

J Phys Chem B 2020 Dec 20;124(48):10971-10982. Epub 2020 Nov 20.

Department of Chemical Engineering and Biotechnology, University of Cambridge, West Cambridge Site, Philippa Fawcett Drive, Cambridge CB3 0AS, U.K.

The ability to measure and predict molecular diffusion coefficients in multicomponent mixtures is not only of fundamental scientific interest but also of significant relevance in understanding how catalytic processes proceed. In the present work, the direct measurement of the molecular diffusion of H and CO gas-phase species diffusing in -alkane mixtures using pulsed-field gradient (PFG) nuclear magnetic resonance (NMR) methods is reported. The work is of direct relevance to Fischer-Tropsch (FT) catalysis, with the measurements being made of the gas-wax system with the wax in both the bulk liquid state and when confined within a titania catalyst support, at temperatures and pressures typical of low-temperature FT synthesis. Read More

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December 2020

Computation of the solid-liquid interfacial free energy in hard spheres by means of thermodynamic integration.

Phys Rev E 2020 Oct;102(4-1):042123

Physikalisches Institut, Albert-Ludwigs-Universitt, 79104 Freiburg, Germany.

We used a thermodynamic integration scheme, which is specifically designed for disordered systems, to compute the interfacial free energy of the solid-liquid interface in the hard-sphere model. We separated the bulk contribution to the total free energy from the interface contribution, performed a finite-size scaling analysis, and obtained for the (100)-interface γ=0.591(11)k_{B}Tσ^{-2}. Read More

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October 2020

Complex Formation of Silica Nanoparticles with Collagen: Effects of the Conformation of Collagen.

Langmuir 2020 12 16;36(47):14425-14431. Epub 2020 Nov 16.

Department of Macromolecular Science, Graduate School of Science, Osaka University, 1-1, Machikaneyama-cho, Toyonaka, Osaka 560-0043, Japan.

Negatively charged Ludox silica nanoparticles (SiNPs) form a complex with atelocollagen (AC) in acidic buffers (pH = 4 or 3). AC is a low-immunogenic derivative of collagen obtained by the removal of N- and C-terminal telopeptide components. Mixed solutions of negatively charged SiNPs and AC were turbid, while positively charged SiNPs (Ludox CL) did not form a complex with AC in pH 4 buffer, indicating that electrostatic attraction is the dominant force to form the complex. Read More

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December 2020

Polarized radiative transfer in dense dispersed media containing optically soft sticky particles.

Opt Express 2020 Sep;28(19):28252-28268

This paper focuses on polarized radiative transfer in dispersed layers composed of densely packed optically soft particles while considering the effects of dependent scattering and particle agglomeration. The radiative properties of the particles for different agglomeration degrees are calculated using the Lorenz-Mie theory combined with the Percus-Yevick sticky hard sphere model, and the vector radiative transfer equation is solved by using the spectral method. The normalized Stokes reflection matrix elements of the layers for different particle sizes, particle volume fractions and layer thicknesses are discussed. Read More

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September 2020

Dynamics of ionic flows via Poisson-Nernst-Planck systems with local hard-sphere potentials: Competition between cations.

Math Biosci Eng 2020 05;17(4):3736-3766

Department of Mathematics, New Mexico Institute of Mining and Technology, Socorro, NM 87801, USA.

We study a quasi-one-dimensional steady-state Poisson-Nernst-Planck type model for ionic flows through a membrane channel with three ion species, two positively charged with the same valence and one negatively charged. Bikerman's local hard-sphere potential is included in the model to account for ion sizes. The problem is treated as a boundary value problem of a singularly perturbed differential system. Read More

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Ion-specific clustering of metal-amphiphile complexes in rare earth separations.

Nanoscale 2020 Oct;12(39):20202-20210

Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, IL 60439, USA.

The nanoscale structure of a complex fluid can play a major role in the selective adsorption of ions at the nanometric interfaces, which is crucial in industrial and technological applications. Here we study the effect of anions and lanthanide ions on the nanoscale structure of a complex fluid formed by metal-amphiphile complexes, using small angle X-ray scattering. The nano- and mesoscale structures we observed can be directly connected to the preferential transfer of light (La and Nd) or heavy (Er and Lu) lanthanides into the complex fluid from an aqueous solution. Read More

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October 2020

Extension of the hard-sphere model for particle-flow simulations.

Phys Rev E 2020 Aug;102(2-1):022909

Western Norway University of Applied Sciences, Department of Mechanical and Marine Engineering, Bergen, Norway.

Discrete element methods require appropriate models for particle-particle collisions. Usually, researchers use soft-sphere types of models where the collision dynamics is solved numerically. This makes the simulation computationally expensive. Read More

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Numerical Investigation into the Flow Characteristics of Gas Mixtures in Knudsen Pump with Variable Soft Sphere Model.

Micromachines (Basel) 2020 Aug 19;11(9). Epub 2020 Aug 19.

School of Mechanical Engineering and Automation, Northeastern University, Shenyang 110819, Liaoning, China.

In Knudsen pumps with geometric configuration of rectangle, gas flows are induced by temperature gradients along channel walls. In this paper, the direct simulation Monte Carlo (DSMC) method is used to investigate numerically the flow characteristics of H-N mixtures in the Knudsen pump. The variable soft sphere (VSS) model is applied to depict molecular diffusion in the gas mixtures, and the results obtained are compared with those calculated from a variable hard sphere (VHS) model. Read More

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Aggregation, liquid-liquid phase separation, and percolation behaviour of a model antibody fluid constrained by hard-sphere obstacles.

Soft Matter 2020 Sep;16(36):8432-8443

Faculty of Chemistry and Chemical Technology, University of Ljubljana, Večna pot 113, SI-1000 Ljubljana, Slovenia.

This study is concerned with the behaviour of proteins within confinement created by hard-sphere obstacles. An individual antibody molecule is depicted as an assembly of seven hard spheres, organized to resemble a Y-shaped (on average) antibody (7-bead model) protein. For comparison with other studies we, in one case, model the protein as a hard sphere decorated by three short-range attractive sites. Read More

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September 2020

Mpemba effect in driven granular Maxwell gases.

Phys Rev E 2020 Jul;102(1-1):012906

The Institute of Mathematical Sciences, C.I.T. Campus, Taramani, Chennai 600113, India.

A Mpemba effect refers to the counterintuitive result that, when quenched to a low temperature, a system at higher temperature may equilibrate faster than one at intermediate temperatures. This effect has recently been demonstrated in driven granular gases, both for smooth as well as rough hard-sphere systems based on a perturbative analysis. In this paper, we consider the inelastic driven Maxwell gas, a simplified model for a granular gas, where the rate of collision is assumed to be independent of the relative velocity. Read More

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Analytical modeling of micelle growth. 3. Electrostatic free energy of ionic wormlike micelles - Effects of activity coefficients and spatially confined electric double layers.

J Colloid Interface Sci 2021 Jan 25;581(Pt A):262-275. Epub 2020 Jul 25.

Unilever Research & Development Port Sunlight, Bebington CH63 3JW, UK.

Hypotheses: To correctly predict the aggregation number and size of wormlike micelles from ionic surfactants, the molecular-thermodynamic theory has to calculate the free energy per molecule in the micelle with accuracy better than 0.01 kT, which is a serious challenge. The problem could be solved if the effects of mutual confinement of micelle counterion atmospheres, as well as the effects of counterion binding, surface curvature and ionic interactions in the electric double layer (EDL), are accurately described. Read More

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January 2021

A long side chain imidazolium-based graft-type anion-exchange membrane: novel electrolyte and alkaline-durable properties and structural elucidation using SANS contrast variation.

Soft Matter 2020 Sep;16(35):8128-8143

Department of Advanced Functional Materials Research, Takasaki Advanced Radiation Research Institute, National Institutes for Quantum and Radiological Science and Technology (QST), Watanuki-machi 1233, Takasaki, Gunma, 370-1292, Japan.

Newly designed styrylimidazolium-based grafted anion-exchange membranes (StIm-AEMs), in which imidazolium ionic groups are attached to styrene at the far side from the graft chains, were prepared by radiation-induced graft polymerization of p-(2-imidazoliumyl) styrene onto poly(ethylene-co-tetrafluoloethylene) (ETFE) films, followed by N-alkylation and ion-exchange reactions. StIm-AEM having an ion exchange capacity (IEC) of 0.54 mmol g-1 with a grafting degree (GD) of ∼18%, possesses practical conductivity (>50 mS cm-1) even with a very low water uptake (∼10%) and high stability over 600 h in a 1 M KOH solution at 80 °C. Read More

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September 2020