CNRS Physics of Liquids and Complex Matter

Creteil, France

CNRS Physics of Liquids and Complex Matter

Creteil, France

Time filter

Source Type

Chung S.,CNRS Physics of Liquids and Complex Matter | Samin S.,University Utrecht | Holm C.,University of Stuttgart | Malherbe J.G.,CNRS Physics of Liquids and Complex Matter | Amokrane S.,CNRS Physics of Liquids and Complex Matter
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2017

We study, using Langevin dynamics simulations, the change in composition of a binary colloidal mixture confined in a finite-length channel, induced by an external field. The field-induced transition from a near-bulk composition to an inverted population is studied as a function of time, for different field strengths and system parameters. For state points corresponding to reversible field cycles, the cyclic filling and emptying of the channel by the minority species are compared. Extrapolation of the physical relaxation times to the colloidal regime is performed through a series of simulations at increasing value of the damping parameter. For state points at which the mixture is unstable at zero field, reproducible irreversible cycles are illustrated. For reversible field cycles, the scaling with the particles size of the characteristic cycling time is discussed. © 2017 American Physical Society.


Chung S.,CNRS Physics of Liquids and Complex Matter | Malherbe J.G.,CNRS Physics of Liquids and Complex Matter | Amokrane S.,CNRS Physics of Liquids and Complex Matter
Molecular Physics | Year: 2015

We study by Monte Carlo simulation the model of a binary mixture of neutral and dipolar hard spheres confined between two widely separated planar walls and subjected to a uniform external field. The goal is to investigate the structural response and the phase transitions of a fluid of hard-sphere-like colloids dispersed in a low-permittivity solvent under the combined effect of geometrical confinement and applied field. In a wide slab, the direction of the field, either normal or perpendicular to the walls, remains one of the most important factors that govern the response of the mixture: in normal field, a wide variety of structural effects are evidenced, including partial wetting or drying of the wall; in parallel field, phase separation is favoured with a specific population of the region close to the wall and a clear separation of the two species. These results suggest possible means to modulate the response of the confined fluid for specific needs. © 2015 Taylor & Francis.


Brunet C.,CNRS Physics of Liquids and Complex Matter | Malherbe J.G.,CNRS Physics of Liquids and Complex Matter | Amokrane S.,CNRS Physics of Liquids and Complex Matter
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2010

The recently proposed method for modulating through an external field the composition of a binary fluid mixture adsorbed in a slit pore is discussed. The population inversion near the bulk (demixing) instability is first analyzed in the case of a symmetric mixture of nonadditive hard spheres, without field. It is next investigated for a mixture comprising dipolar particles subject to an external field. The influence of several factors on the adsorption curves including bulk composition, pore width, field direction, polarizability versus permanent dipoles, and temperature on this field induced population inversion is shown by Monte Carlo simulation. © 2010 The American Physical Society.


Germain P.,CNRS Physics of Liquids and Complex Matter | Amokrane S.,CNRS Physics of Liquids and Complex Matter
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2010

The interplay between physical gelation and equilibrium phase transitions in asymmetric binary mixtures is analyzed from the effective fluid approach, in which the big particles interact via a short-range effective attraction beyond the core due to the depletion mechanism. The question of the universality of the scenario for dynamical arrest is then addressed. The comparison of the phase diagrams of the hard-sphere mixture and the Asakura-Oosawa models at various size ratios shows that strong specificity is observed for nonideal depletants. In particular, equilibrium gelation, without the competition with fluid-fluid transition is possible in mixtures of hard-sphere colloids. This is interpreted from the specificities of the effective potential, such as its oscillatory behavior and its complex variation with the physical parameters. The consequences on the dynamical arrest and the fluid-fluid transition are then investigated by considering in particular the role of the well at contact and the first repulsive barrier. This is done for the actual effective potential in the hard-sphere mixture and for a square well and shoulder model, which allows a separate discussion of the role of the different parameters, in particular on the localization length and the escape time. This study is next extended to mixtures of "hard-sphere-like" colloids with residual interactions. It confirms the trends relative to equilibrium gelation and illustrates a diversity of the phase behavior well beyond the scenarios expected from simple models. © 2010 The American Physical Society.


Germain P.,CNRS Physics of Liquids and Complex Matter
Journal of Chemical Physics | Year: 2010

We analyze the influence of residual attractions on the static and some dynamic properties of size asymmetric mixtures of "hard-sphere-like" colloids. These attractions, usually neglected in the theoretical analysis, are characterized by a very short range and a moderate strength reflecting the underlying microscopic structure of the colloidal particles. Their effect on the potentials of mean force is analyzed from analytical expressions obtained from low density expansions. The effective potential of the big particle fluid is next considered. An analytical expression is proposed for estimating the deviation with respect to the hard sphere depletion potential. This case is compared to that of mixtures with noninteracting depletants. The important consequences on the binodals and the glass transition lines of the effective fluid are discussed in both cases. This study is next extended to other properties-the specific heat and the low shear viscosity-which incorporate contributions from the two components of the binary mixture. © 2010 American Institute of Physics.


Brunet C.,CNRS Physics of Liquids and Complex Matter | Malherbe J.G.,CNRS Physics of Liquids and Complex Matter | Amokrane S.,CNRS Physics of Liquids and Complex Matter
Molecular Physics | Year: 2012

We study the influence of an external field on demixing and its interplay with the field-induced population inversion for a binary mixture of neutral and dipolar non-additive hard-spheres confined in a slit pore. Demixing lines are determined by Gibbs Ensemble Monte Carlo simulations and population inversion paths by grand-canonical/canonical simulations of the pore/bulk equilibrium. Besides the demixing line in the bulk, results are given for two different pore widths and in parallel and normal fields. Similar to the effect of geometrical confinement, a normal field is found to favour the mixed state so that the population inversion does not interfere with demixing. A parallel field leads to more complex scenarios. © 2012 Taylor & Francis.


Tchangnwa Nya F.,CNRS Physics of Liquids and Complex Matter | Tchangnwa Nya F.,University of Maroua | Ayadim A.,CNRS Physics of Liquids and Complex Matter | Germain P.,CNRS Physics of Liquids and Complex Matter | Amokrane S.,CNRS Physics of Liquids and Complex Matter
Journal of Physics Condensed Matter | Year: 2012

We examine the question of the accuracy of the static correlation functions used as input in the mode coupling theory (MCT) of non-ergodic states in binary mixtures. We first consider hard-sphere mixtures and compute the static pair structure from the Ornstein-Zernike equations with the Percus-Yevick closure and more accurate ones that use bridge functions deduced from Rosenfelds fundamental measures functional. The corresponding MCT predictions for the non-ergodicity lines and the transitions between multiple glassy states are determined from the long-time limit of the density autocorrelation functions. We find that while the non-ergodicity transition line is not very sensitive to the input static structure, up to diameter ratios D 2/D 1=10, quantitative differences exist for the transitions between different glasses. The discrepancies with the more accurate closures become even qualitative for sufficiently asymmetric mixtures. They are correlated with the incorrect behavior of the PY structure at high size asymmetry. From the example of ultra-soft potential it is argued that this issue is of general relevance beyond the hard-sphere model. © 2012 IOP Publishing Ltd.


Ayadim A.,CNRS Physics of Liquids and Complex Matter | Germain P.,CNRS Physics of Liquids and Complex Matter | Amokrane S.,CNRS Physics of Liquids and Complex Matter
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2011

We reexamine the convolution approximation commonly used in the mode-coupling theory (MCT) of nonergodic states of classical fluids. This approximation concerns the static correlation functions used as input in the MCT treatment of the dynamics. Besides the hard-sphere model, we consider interaction potentials that present a short-range tail, either attractive or repulsive, beyond the hard core. By using accurate static correlation functions obtained from the fundamental measures functional for hard spheres, we show that the role of three-body direct correlations can be more significant than what is inferred from previous simple ansatzs for pure hard spheres. This may in particular impact the location of the glass transition line and the nonergodicity parameter. © 2011 American Physical Society.


Ndong Mintsa E.,CNRS Physics of Liquids and Complex Matter | Germain P.,CNRS Physics of Liquids and Complex Matter | Amokrane S.,CNRS Physics of Liquids and Complex Matter
European Physical Journal E | Year: 2015

Abstract: We use molecular dynamics simulations to study the influence of short-range structures in the interaction potential between hard-sphere-like colloidal particles. Starting from model potentials and effective potentials in binary mixtures computed from the Ornstein-Zernike equations, we investigate the influence of the range and strength of a possible tail beyond the usual core repulsion or the presence of repulsive barriers. The diffusion coefficient and mean “bond” lifetimes are used as indicators of the effect of this structure on the dynamics. The existence of correlations between the variations of these quantities with the physical parameters is discussed to assess the interpretation of dynamics slowing down in terms of long-lived bonds. We also discuss the question of a universal behaviour determined by the second virial coefficient B(2) and the interplay of attraction and repulsion. While the diffusion coefficient follows the B(2) law for purely attractive tails, this is no longer true in the presence of repulsive barriers. Furthermore, the bond lifetime shows a dependence on the physical parameters that differs from that of the diffusion coefficient. This raises the question of the precise role of bonds on the dynamics slowing down in colloidal gels. Graphical abstract: [Figure not available: see fulltext.] © 2015, EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg.


Ayadim A.,CNRS Physics of Liquids and Complex Matter | Amokrane S.,CNRS Physics of Liquids and Complex Matter
Journal of Physical Chemistry B | Year: 2010

The structure of a binary mixture of nonadditive hard spheres confined in a slit pore is studied by the integral equations method in which the confining medium acts as a giant particle at infinite dilution. The adsorption/desorption curves are studied as a function of the composition and density, when the homogeneous bulk mixture is near the demixing instability. The Ornstein-Zernike integral equations are solved with the reference functional approximation closure in which the bridge functions are derived from Rosenfelds hard sphere functional for additive hard sphere. To study the high composition asymmetry regime in which a population inversion occurs, we developed an approximate closure that overcomes the no solution problem of the integral equation. By comparison with simulation data, this method is shown to be sufficiently accurate for predicting the threshold density for the population inversion. The predictions of simpler closure relations are briefly examined. © 2010 American Chemical Society.

Loading CNRS Physics of Liquids and Complex Matter collaborators
Loading CNRS Physics of Liquids and Complex Matter collaborators