Aggregation kinetics in a model colloidal suspension

We present molecular dynamics simulations of aggregation kinetics in a colloidal suspension modeled as a highly asymmetric binary mixture. Starting from a configuration with largely uncorrelated colloidal particles the system relaxes by coagulation-fragmentation dynamics to a structured state of low-dimensionality clusters with an exponential size distribution. The results show that short-range repulsive interactions alone can give rise to so-called cluster phases. For the present model and probably other, more common colloids, the observed clusters appear to be equilibrium phase fluctuations induced by the entropic inter-colloidal attractions

Comment on "Model for Heat Conduction in Nanofluids"

A Comment on the Letter by D. Hemanth Kumar et al., Phys. Rev. Lett. 93, 144301 (2004)Comment: 2 page

Entropy scaling laws for diffusion

Comment to the letter of Samanta et al., Phys. Rev. Lett. 92, 145901 (2004).Comment: 2 pages, 1 figur

Surface-Directed Spinodal Decomposition in Binary Fluid Mixtures

We consider the phase separation of binary fluids in contact with a surface which is preferentially wetted by one of the components of the mixture. We review the results available for this problem and present new numerical results obtained using a mesoscopic-level simulation technique for the 3-dimensional problem.Comment: RevTeX, 7 figure

Freezing Kinetics in Overcompressed Water

We report high pressure dynamic compression experiments of liquid water along a quasi-adiabatic path leading to the formation of ice VII. We observe dynamic features resembling Van der Waals loops and find that liquid water is compacted to a metastable state close to the ice density before the onset of crystallization. By analyzing the characteristic kinetic time scale involved we estimate the nucleation barrier and conclude that liquid water has been compressed to a high pressure state close to its thermodynamic stability limit

Transport in a highly asymmetric binary fluid mixture

We present molecular dynamics calculations of the thermal conductivity and viscosities of a model colloidal suspension with colloidal particles roughly one order of magnitude larger than the suspending liquid molecules. The results are compared with estimates based on the Enskog transport theory and effective medium theories (EMT) for thermal and viscous transport. We find, in particular, that EMT remains well applicable for predicting both the shear viscosity and thermal conductivity of such suspensions when the colloidal particles have a ``typical'' mass, i.e. much larger than the liquid molecules. Very light colloidal particles on the other hand yield higher thermal conductivities, in disagreement with EMT. We also discuss the consequences of these results to some proposed mechanisms for thermal conduction in nanocolloidal suspensions.Comment: 13 pages, 6 figures, to appear in Physical Review E (2007

A study of tantalum pentoxide Ta2O5 structures up to 28 GPa

Tantalum pentoxide Ta2O5 with the orthorhombic L-Ta2O5 structure has been experimentally studied up to 28.3 GPa (at ambient temperature) using synchrotron angle-dispersive powder X-ray diffraction (XRD). The ambient pressure phase remains stable up to 25 GPa where with increased pressure a crystalline to amorphous phase transition occurs. A detailed equation of state (EOS), including pressure dependent lattice parameters, is reported. The results of this study were compared with a previous high-pressure XRD study by Li et al. A clear discrepancy between the ambient-pressure crystal structures and, consequently, the reported EOSs between the two studies was revealed. The origin of this discrepancy is attributed to two different crystal structures used to index the XRD patterns

Diffusion and conduction in a salt-free colloidal suspension via molecular dynamics simulations

Molecular dynamics (MD) simulations are used to determine the diffusion coefficients, electrophoretic mobilities and electrical conductivity of a charged colloidal suspension in the salt-free regime as a function of the colloid charge. The behavior of the colloidal particles' diffusion constant can be well understood in terms of two coupled effects: counterion 'condensation' and slowdown due to the relaxation effect. We find that the conductivity exhibits a maximum which approximately separates the regimes of counterion-dominated and colloid-dominated conduction. We analyze the electrophoretic mobilities and the conductivity in terms of commonly employed assumptions about the role of "free" and "condensed" counterions, and discuss different interpretations of this approach.Comment: 10 pages, 4 figure