Phase coexistence in the hard-sphere Yukawa chain fluid with chain length polydispersity: High temperature approximation

High temperature approximation (HTA) is used to describe the phase behavior of polydisperse multi-Yukawa hard-sphere chain fluid mixtures with chain length polydispersity. It is demonstrated that in the frames of the HTA the model belongs to the class of ``truncatable free energy models'', i.e. the models with thermodynamical properties (Helmholtz free energy, chemical potential and pressure) defined by the finite number of generalized moments. Using this property we were able to calculate the complete phase diagram (i.e., cloud and shadow curves as well as binodals) and chain length distribution functions of the coexisting phases.Comment: 18 pages, 13 figure

Phase coexistance in polydisperse mixture of hard-sphere colloidal and flexible chain particles

A theoretical scheme for the calculation of the full phase diagram (including cloud and shadow curves, binodals and distribution functions of the coexisting phases) for colloid-polymer mixtures with polymer chain length polydispersity and hard-sphere colloidal and polymeric monomer sizes polydispersity is proposed. The scheme combines thermodynamic perturbation theory for associating fluids and recently developed method used to determine the phase diagram of polydisperse spherical shape colloidal fluids (L.Bellier-Castella {\it et al.}, {\it J.Chem.Phys.} {\bf 113}, 8337(2000)). By way of illustration we present and discuss the full phase diagram for the mixture with polydispersity in the size of the hard-sphere colloidal particles.Comment: 6 pages, 4 figure

Colloidal brazil nut effect in sediments of binary charged suspensions

Equilibrium sedimentation density profiles of charged binary colloidal suspensions are calculated by computer simulations and density functional theory. For deionized samples, we predict a colloidal ``brazil nut'' effect: heavy colloidal particles sediment on top of the lighter ones provided that their mass per charge is smaller than that of the lighter ones. This effect is verifiable in settling experiments.Comment: 4 pages, 4 figure

Aging and memory properties of topologically frustrated magnets

The model 2d kagome system (H3O)Fe3(SO4)2(OH)6 and the 3d pyrochlore Y2Mo2O7 are two well characterized examples of low-disordered frustrated antiferromagnets which rather then condensing into spin liquid have been found to undergo a freezing transition with spin glass-like properties. We explore more deeply the comparison of their properties with those of spin glasses, by the study of characteristic rejuvenation and memory effects in the non-stationary susceptibility. While the pyrochlore shows clear evidence for these non-trivial effects, implying temperature selective aging, that is characteristic of a wide hierarchical distribution of equilibration processes, the kagome system does n not show clearly these effects. Rather, it seems to evolve towards the same final state independently of temperature.Comment: submitted for the proceedings of the 46th MMM conference (Seattle, 2001

Polydisperse hard spheres at a hard wall

The structural properties of polydisperse hard spheres in the presence of a hard wall are investigated via Monte Carlo simulation and density functional theory (DFT). Attention is focussed on the local density distribution $\rho(\sigma,z)$, measuring the number density of particles of diameter $\sigma$ at a distance $z$ from the wall. The form of $\rho(\sigma,z)$ is obtained for bulk volume fractions $\eta_b=0.2$ and $\eta_b=0.4$ for two choices of the bulk parent distribution: a top-hat form, which we study for degrees of polydispersity $\delta=11.5$ and $\delta=40.4$, and a truncated Schulz form having $\delta=40.7$. Excellent overall agreement is found between the DFT and simulation results, particularly at $\eta_b=0.2$. A detailed analysis of $\rho(\sigma,z)$ confirms the presence of oscillatory size segregation effects observed in a previous DFT study (Pagonabarraga {\em et al.}, Phys. Rev. Lett. {\bf 84}, 911 (2000)). For large $\delta$, the character of these oscillation is observed to depend strongly on the shape of the parent distribution. In the vicinity of the wall, attractive $\sigma$-dependent depletion interactions are found to greatly enhance the density of the largest particles. The local degree of polydispersity $\delta(z)$ is suppressed in this region, while further from the wall it exhibits oscillations.Comment: 12 pages revte

The relative influences of disorder and of frustration on the glassy dynamics in magnetic systems

The magnetisation relaxations of three different types of geometrically frustrated magnetic systems have been studied with the same experimental procedures as previously used in spin glasses. The materials investigated are Y$_2$Mo$_2$O$_7$ (pyrochlore system), SrCr$_{8.6}$Ga$_{3.4}$O$_{19}$ (piled pairs of Kagom\'e layers) and (H$_3$O)Fe$_3$(SO$_4$)$_2$(OH)$_6$ (jarosite compound). Despite a very small amount of disorder, all the samples exhibit many characteristic features of spin glass dynamics below a freezing temperature $T_g$, much smaller than their Curie-Weiss temperature $\theta$. The ageing properties of their thermoremanent magnetization can be well accounted for by the same scaling law as in spin glasses, and the values of the scaling exponents are very close. The effects of temperature variations during ageing have been specifically investigated. In the pyrochlore and the bi-Kagom\'e compounds, a decrease of temperature after some waiting period at a certain temperature $T_p$ re-initializes ageing and the evolution at the new temperature is the same as if the system were just quenched from above $T_g$. However, as the temperature is raised back to $T_p$, the sample recovers the state it had previously reached at that temperature. These features are known in spin glasses as rejuvenation and memory effects. They are clear signatures of the spin glass dynamics. In the Kagom\'e compound, there is also some rejuvenation and memory, but much larger temperature changes are needed to observe the effects. In that sense, the behaviour of this compound is quantitatively different from that of spin glasses.Comment: latex VersionCorrigee4.tex, 4 files, 3 figures, 5 pages (Proceedings of the International Conference on Highly Frustrated Magnetism (HFM2003), August 26-30, 2003, Institut Laue Langevin (ILL), Grenoble, France

Density functional theory of polydisperse fluid interfaces

info:eu-repo/semantics/publishe

Density functional theory of soft matter

info:eu-repo/semantics/publishe

Équilibre de phases dans les systèmes de colloïdes polydisperses et de molécules discotiques

Nous présentons une étude sur les équilibres de phases de fluides complexes tels que les colloïdes polydisperses et les molécules discotiques. L'étude théorique sur les colloïdes polydisperses a trait à l'influence de la polydispersité sur les comportements de phases fluides, dans le cadre d'une approximation de fluides de Van der Waals et grâce à la théorie de la fonctionnelle de densité. Elle met en évidence l'existence de caractéristiques originales comme la présence de plusieurs points critiques, la possibilité d'avoir des coexistences à plus de deux phases ainsi que d'autres modifications importantes du diagramme de phases. Nous nous intéressons également aux interfaces entre deux phases fluides polydisperses et plus particulièrement à l'influence de la polydispersité sur la tension de surface et les propriétés d'adsorption. Enfin, nous abordons un autre exemple de luides polydisperses inhomogènes : celui de fluides soumis au champ de pesanteur. Cette étude de la sédimentaiton met en évidence des phénomènes de ségrégation provenant d'une compétition entre les effets de volume exclu, ceux dus à l'attraction et l'influence du champ de psesanteur. D'autre part, une étude par simulations Monte-Carlo de molécules discotiques permet de s'intéresser non plus à l'influence de la polydispersité mais à celle du carctère anisotrope des molécules, à l'originie des phase nématiques et colonnaires. Plus précisément, nous étdions l'nluence du confinement sur la structuration en colonnes et le déplacement à plus haute ou plus basse température de la transition nématique-colonnaire en fonction du type de parois considéréLYON1-BU.Sciences (692662101) / SudocSudocFranceF

Phase diagrams of polydisperse van der Waals fluids

The phase diagrams for fluids composed of spherical particles with a monomodal size distribution is presented. These phase diagrams are obtained on the basis of the van der Waals approximation for the free-energy of a polydisperse fluid. It is found that the largest modifications to the phase diagram of the polydisperse fluid, as compared to its monodisperse counterpart, result from the amplitude polydispersity of the interaction potential.SCOPUS: ar.jinfo:eu-repo/semantics/publishe