What happened to the gas-liquid transition in the system of dipolar hard spheres?

We explore the equilibrium properties of a system composed of dipolar hard spheres. A new theory based on the ideas derived from the work of Debye and H\"uckel, Bjerrum, and Onsager is proposed to explain the absence of the anticipated critical point in this system

Renormalized Jellium model for charge-stabilized colloidal suspensions

We introduce a renormalized Jellium model to calculate the equation of state for charged colloidal suspensions. An almost perfect agreement with Monte Carlo simulations is found. Our self-consistent approach naturally allows to define the effective charge of particles {\em at finite colloidal density}. Although this quantity may differ significantly from its counterpart obtained from the standard Poisson-Boltzmann cell approach, the osmotic pressures for both models are in good agreement. We argue that by construction, the effective charge obtained using the Jellium approximation is more appropriate to the study of colloidal interactions. We also discuss a possibility of a fluid-fluid critical point and show how the new equation of state can be used to shed light on the surprising results found in recent sedimentation experiments.Comment: 4 pages, 3 figure

Comment on: Thermostatistics of Overdamped Motion of Interacting Particles [arXiv:1008.1421]

In a recent paper, Phys. Rev. Lett. 105 260601 (2010) [arXiv:1008.1421], Andrade et al., argued that classical particles confined in a parabolic trap at T=0 distribute themselves in accordance with the Tsallis statistics. To prove their point the authors performed molecular dynamics simulations. Here we show that the model of Andrade et al. can be solved exactly. The distribution of particles at T=0 has nothing to do with the Tsallis entropy and is determined simply by the force balance

Colloidal charge reversal: Dependence on the ionic size and the electrolyte concentration

Extensive Monte Carlo simulations and scaling arguments are used to study the colloidal charge reversal. The critical colloidal surface charge density $\sigma_c$ at which the reversal first appears is found to depend strongly on the ionic size. We find that $\sigma_c$ has an inflection point as a function of the electrolyte concentration. The width of the plateau region in the vicinity of the inflection point depends on the temperature and the ionic radius $a$. In agreement with the theoretical predictions it is found that the critical colloidal charge above which the electrophoretic mobility becomes reversed diverges as $Z_c \sim 1/a^2$ in the limit $a \to 0$.Comment: 5 pages, 4 figure

Non-equilibrium Statistical Mechanics of Two-dimensional Vortices

It has been observed empirically that two dimensional vortices tend to cluster forming a giant vortex. To account for this observation Onsager introduced a concept of negative absolute temperature in equilibrium statistical mechanics. In this Letter we will show that in the thermodynamic limit a system of interacting vortices does not relax to the thermodynamic equilibrium, but becomes trapped in a non-equilibrium stationary state. We will show that the vortex distribution in this non-equilibrium stationary state has a characteristic core-halo structure, which can be predicted {\it a priori}. All the theoretical results are compared with explicit molecular dynamics simulations