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We propose a polydisperse hard sphere model for numerical calculation of the analytic radial distribution function of multi-component atomic liquids. The vibrational part of atomic thermal motion in liquids is modeled by the effective density profile of polydisperse hard spheres. We applied an orthogonal polynomial technique for the solution of a system of Ornstein-Zernike equations using the hard sphere Percus-Yevick analytic expression for the direct correlation functions. The partial radial distribution functions were calculated for the case of a binary liquid where the size distribution of the components is specified by Schultz distributions. [ABSTRACT FROM AUTHOR]

This work is devoted to the numerical modeling of highly polydisperse granular materials in view of investigating the texture and mechanical behavior in quasi-static shearing. The polydispersity is modeled in terms of size span and curvature of the particle size distributions. A method is proposed to generate representative size distributions both in number and volume of size classes, and the accessible polydispersity parameters are determined for tractable number of particles. A geometrical method is used to construct large samples and to study the resulting texture in a systematic manner as a function of size distribution. These samples are then subjected to simple shear with periodic boundary conditions by means of the contact dynamics method. We show that: 1) The highest level of solid fraction corresponds to uniform distribution by particle volume fractions; 2) The shear strength in the steady state is independent of polydispersity; 3) A detailed analysis of the texture and force transmission indicates that this property results from the mutual compensation between the anisotropies of contact orientations and branch-vector lengths, and also from the fact that the strong force chains are mainly captured by the largest particles; 4) In the presence of adhesion between particles, the Coulomb cohesion increases with size span. [ABSTRACT FROM AUTHOR]

We investigate the water distribution and the link between suction and water content in granular media. Firstly, we examine the effect of suction on the shape and the volume of the liquid bridge for different parameters (grain radius, inter-particle distance, contact angle, surface tension). This local behaviour is then used in a discrete element study of a sample composed of several thousands of grains. We focus our study on the pendular state. The existence of a liquid film around the grains which involves the continuity of the liquid phase is assumed. The water distribution and the water content associated with a given suction are calculated. Then retention curves of the granular media are built. Four different methods are used. The first is based on the local expression of the capillary force coupled with the “gorge method,” the second is based on the Laplace equation, and the third and the fourth are based on the integration of the differential equation that defines the liquid bridge shape. A parametric study is made to bring to light the effect of macroscopic parameters (grain-size distribution, density) and physical parameters (liquid/air surface tension, contact angle) on the water retention curve. Finally, numerical data are compared to experimental results. [ABSTRACT FROM AUTHOR]

We have studied the solid-fluid coexistence for systems of polydisperse soft spheres with near-Gaussian diameter distributions that interact via an inverse power potential, the softness of which is being tuned. The study employs simulation in the isobaric semigrand ensemble. Gibbs-Duhem integration is used to trace the coexistence pressure as a function of the variance of the imposed activity distribution. Both the fluid-solid coexistence densities and volume fractions are monotonically increasing functions of the polydispersity s, which is given in terms of the standard deviation in the particle diameter distribution function. We observe a terminal polydispersity, i.e. a polydispersity above which there can be no fluid-solid coexistence. At the terminus, polydispersity increases from 5.8% to 6.1% to 6.4% and to 6.7% for the solid phase as the softness parameter n, takes on smaller values: from 100 to 50 to 12 and to 10 respectively. [ABSTRACT FROM AUTHOR]

Fluids of particles exhibiting strong short—ranged attraction compared with the thermal energy are largely dominated by clustering, i.e. by the formation of particle aggregates that persist for very long times compared to diffusion times. Dilute liquid metals are a typical example where electron delocalisation induces strong cohesion forces and clustering. However, purely repulsive fluids of hard particles, driven solely by entropy, also exhibit (geometry—induced) clustering, especially in low dimensionality. This is the case in fluids of hard rectangles (e.g. cylindrical molecules adsorbed on a surface), where particle shape promotes a novel phase possessing four—fold symmetry (tetratic phase). Even though two—particle correlations can explain the formation of the tetratic phase, clustering (a multi—particle effect) greatly enhances its stability with respect to the usual uniaxial nematic phase. A simple scaled—particle theory can be used to account for these effects. [ABSTRACT FROM AUTHOR]