Tracer diffusion in colloidal suspensions under dilute and crowded conditions with hydrodynamic interactions

We consider tracer diffusion in colloidalsuspensions under solid loading conditions, where hydrodynamic interactions play an important role. To this end, we carry out computer simulations based on the hybrid stochastic rotation dynamics-molecular dynamics (SRD-MD) technique. Many details of the simulation method are discussed in detail. In particular, our choices for the SRD-MD parameters and for the different scales are adapted to simulating colloidalsuspensions under realistic conditions. Our simulation data are compared with published theoretical, experimental and numerical results and compared to Brownian dynamics simulation data. We demonstrate that our SRD-MD simulations reproduce many features of the hydrodynamics in colloidal fluids under finite loading. In particular, finite-size effects and the diffusive behavior of colloids for a range of volume fractions of the suspension show that hydrodynamic interactions are correctly included within the SRD-MD technique.Peer reviewe

Two-steps versus one-step solidification pathways of binary metallic nanodroplet

The solidification of AgCo, AgNi, and AgCu nanodroplets is studied by molecular dynamics simulations in the size range of 2-8 nm. All these systems tend to phase separate in the bulk solid with surface segregation of Ag. Despite these similarities, the simulations reveal clear differences in the solidification pathways. AgCo and AgNi already separate in the liquid phase, and they solidify in configurations close to equilibrium. They can show a two-step solidification process in which Co-/Ni-rich parts solidify at higher temperatures than the Ag-rich part. AgCu does not separate in the liquid and solidifies in one step, thereby remaining in a kinetically trapped state down to room temperature. The solidification mechanisms and the size dependence of the solidification temperatures are analyzed, finding qualitatively different behaviors in AgCo/AgNi compared to AgCu. These differences are rationalized by an analytical model

Simulations of heteroaggregation in a suspension of alumina and silica particles: Effect of dilution

International audienceThe influence of dilution on the aggregation process of suspensions composed of two kinds of oxide particles alumina positively charged particles d1=400 nm and silica negatively charged particles d2=250 nm has been studied by computer simulations. Two kinds of simulations have been performed: Brownian dynamics simulations to study the aggregation process and its kinetics and global minimization searches to find the most stable configurations of aggregates. We show that the rate of dilution has a strong influence on the structure and on the shape of aggregates in Brownian dynamics simulations. By confronting these aggregates with the stable aggregates found by global minimization, we demonstrate that they are metastable and their shape is explained by the competition between the kinetics of aggregate coalescence and the kinetics of aggregate reorganization into more stable configurations

Growth of isolated Co clusters in the gas phase: experiment and molecular dynamics simulation

International audienceThe structures of cobalt clusters are investigated by simulations and experiments. The growth process of isolated clusters in gas phase is simulated by molecular dynamics, growing clusters atom by atom from a small seed up to the size of 600 atoms. Experimentally, clusters are generated by a laser ablation cluster generator using low energy clusters beam deposition. Then, the deposited aggregates are characterized with high resolution transmission electronic microscope. Simulation results are compared with the experiment, and with previous density functional theory and semiempirical calculations, obtaining a good agreement both for the geometric structures and for the behavior of lattice contraction. Finally, aggregation simulations are performed to determine the nucleation rate of cobalt monomers

Hydrodynamics in simulations of colloidal suspensions : hybrid stochastic rotation dynamics - molecular dynamics technique

International audienc

Heteroaggregation between Al2O3 submicron particles and SiO2 nanoparticles: experiment and simulation

International audienceThe aggregation process of a two-component dilute system (3 vol %), made of alumina submicrometer particles and silica nanoparticles, is studied by Brownian dynamics simulations. Alumina and silica particles have very different sizes (diameters of 400 and 25 nm, respectively). The particle-particle interaction potential is of the DLVO form. The parameters of the potential are extracted from the experiments. The simulations show that the experimentally observed aggregation phenomena between alumina particles are due to the silica-alumina attraction that induces an effective driving force for alumina-alumina aggregation. The experimental data for silica adsorption on alumina are very well reproduced

Self-assembly of oppositely charged particles in dilute ceramic suspensions: predictive role of simulations

International audienceCeramics suspensions composed of oppositely charged alumina and silica particles are studied experimentally and by means of Brownian dynamics simulations. Alumina and silica particles have quite similar sizes, the former having an average diameter larger by a factor 1.6. The suspension behavior is studied as a function of composition