Mariana Barcenas

Vapor–liquid surface tension of strong short-range Yukawa fluid

The thermodynamic properties of strong short-range attractive Yukawa fluids, κ = 10, 9, 8, and 7, are determined by combining the slab technique with the standard and the replica exchange Monte Carlo (REMC) methods. A good agreement was found among the coexistence curves of these systems calculated by REMC and those previously reported in the literature. However, REMC allows exploring the coexistence at lower temperatures, where dynamics turns glassy. To obtain the surface tension we employed, for both methods, a procedure that yields the pressure tensor components for discontinuous potentials. The surface tension results obtained by the standard MC and REMC techniques are in good agreement.

Coexistence and interfacial properties of triangle-well fluids

Coexistence and interfacial properties of triangle-well fluids are determined by combining the slab technique and the replica exchange algorithm for different interaction ranges (λ = 1.5, 1.75, 2.0, 2.5, and 3). This is implemented using both Monte Carlo and molecular dynamics methods. We make use of a recently proposed substitution of the hard-core repulsion by a linear function with a large negative slope. This makes possible to gain access through the virial route to thermodynamical properties and to employ widely spread packages such as Gromacs. Coexistence curves of these systems were calculated with both implementations and compared to those previously reported in the literature. A good agreement was found among them. Surface tension data obtained from Monte Carlo and molecular dynamics techniques also show a good agreement.

Structural properties of fluids interacting via piece-wise constant potentials with a hard core.

The structural properties of fluids whose molecules interact via potentials with a hard core plus two piece-wise constant sections of different widths and heights are presented. These follow from the more general development previously introduced for potentials with a hard core plus n piece-wise constant sections [A. Santos, S. B. Yuste, and M. Lopez de Haro, Condens. Matter Phys. 15, 23602 (2012)] in which use was made of a semi-analytic rational-function approximation method. The results of illustrative cases comprising eight different combinations of wells and shoulders are compared both with simulation data and with those that follow from the numerical solution of the Percus-Yevick and hypernetted-chain integral equations. It is found that the rational-function approximation generally predicts a more accurate radial distribution function than the Percus-Yevick theory and is comparable or even superior to the hypernetted-chain theory. This superiority over both integral equation theories is lost, however, at high densities, especially as the widths of the wells and/or the barriers increase.

Temperature dependence of the colloidal agglomeration inhibition: Computer simulation study

There exist experimental evidences that the structure and extension of colloidal aggregates in suspensions change dramatically with temperature. This results in an associated change in the suspension rheology. Experimental studies of the inhibitor applications to control the particle clustering have revealed some unexpected tendencies. Namely, the heating of colloidal suspensions has provoked either extension or reduction of the colloidal aggregates. To elucidate the origin of this behavior, we investigate the influence of temperature on the stabilizing effect of the inhibitor, applying an associative two-component fluid model. Our results of the canonical Monte Carlo simulations indicate that the anomalous effect of the temperature may not be necessarily explained by the temperature dependent changes in the inhibitor tail conformation, as has been suggested recently by Won et al. [Langmuir 21, 924 (2005)]. We show that the competition between colloid-colloid and colloid-inhibitor associations, which, in turn, depends on the temperature and the relative concentrations, may be one of the main reasons for the unexpected temperature dependence of inhibitor efficacy.

Coexistence and interfacial properties of a triangle-well mimicking the Lennard-Jones fluid and a comparison with noble gases

Coexistence and interfacial properties of a triangle-well (TW) fluid are obtained with the aim of mimicking the Lennard-Jones (LJ) potential and approach the properties of noble gases. For this purpose, the scope of the TW is varied to match vapor-liquid densities and surface tension. Surface tension and coexistence curves of TW systems with different ranges were calculated with replica exchange Monte Carlo and compared to those data previously reported in the literature for truncated and shifted (STS), truncated (ST), and full Lennard-Jones (full-LJ) potentials. We observed that the scope of the TW potential must be increased to approach the STS, ST, and full-LJ properties. In spite of the simplicity of TW expression, a remarkable agreement is found. Furthermore, the variable scope of the TW allows for a good match of the experimental data of argon and xenon.

Thermodynamic properties of triangle-well fluids in two dimensions: MC and MD simulations.

With the aim of providing complementary data of the thermodynamics properties of the triangular well potential, the vapor/liquid phase diagrams for such potential with different interaction ranges were calculated in two dimensions by Monte Carlo and molecular dynamics simulations; also, the vapor/liquid interfacial tension was calculated. As reported for other interaction potentials, it was observed that the reduction of the dimensionality makes the phase diagram to shrink. Finally, with the aid of reported data for the same potential in three dimensions, it was observed that this potential does not follow the principle of corresponding states.

Modeling of colloid agglomeration inhibition inside a slitlike pore

An extended particle agglomeration control model and Monte Carlo simulation methodology were used to describe the behavior of the colloidal aggregation process in presence of inhibitor as a confined fluid. In this work results about the mean cluster size, Z, with respect to different variables, temperature, inhibitor concentration and pore size, are presented and showed that Z strongly depends on the slitlike pore size. In addition, a temperature interval where the heating of the system leads to the particle clustering was found.