Liquid-gas separation in colloidal electrolytes

Caballero, José B.; Puertas, Antonio M.; Fernández-Barbero, A.; Nieves, F. J. de las; Romero-Enrique, J. M.; Rull, Luis F.

doi:10.1063/1.2159481

Cited by 10 publications

(16 citation statements)

References 32 publications

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“…As observed in simulations 13,14 and in confocal microscopy experiments, 9 the liquid is locally highly structured due to the interplay of attractions and repulsions. Every particle is surrounded of shells of particles with an opposite sign of charge, minimizing the energy of the system.…”

Section: A Liquid-gas Coexistencementioning

confidence: 75%

“…13,14 The critical temperature depends nonmonotonically on the interaction range due to the interplay of attractions and repulsions; as the range is decreased, the critical point first increases and then decreases. The critical density, on the other hand, continuously increases as the range is decreased.…”

Section: Introductionmentioning

confidence: 99%

“…The phase 14 The actual location of the boundary depends on the temperature of the system. diagram is therefore constructed using the colloid volume fraction and the salt concentration as control parameters.…”

Section: Introductionmentioning

confidence: 99%

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Experimental Phase Diagram of Symmetric Binary Colloidal Mixtures with Opposite Charges

2006

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The phase behavior of equimolar mixtures of oppositely charged colloidal systems with similar absolute charges is studied experimentally as a function of the salt concentration in the system and the colloid volume fraction. As the salt concentration increases, fluids of irreversible clusters, gels, liquid-gas coexistence, and finally, homogeneous fluids, are observed. Previous simulations of similar mixtures of Derjaguin-Landau-Verwey-Overbeek (DLVO) particles indeed showed the transition from homogeneous fluids to liquid-gas separation, but also predicted a reentrant fluid phase at low salt concentrations, which is not found in the experiments. Possibly, the fluid of clusters could be caused by a nonergodicity transition responsible for the gel phase in the reentrant fluid phase. Liquid-gas separation takes a delay time after the sample is prepared, whereas gels collapse from the beginning. The density of the liquid in coexistence with a vapor phase depends linearly on the overall colloid density of the system. The vapor, on the other hand, is comprised of equilibrium clusters, as expected from the simulations.

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Section: A Liquid-gas Coexistencementioning

confidence: 75%

Section: Introductionmentioning

confidence: 99%

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Experimental Phase Diagram of Symmetric Binary Colloidal Mixtures with Opposite Charges

2006

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“…3 The phase behavior of the RPM has been extensively studied by means of computer simulations. [4][5][6][7][8][9][10] In the same way, computer simulations have been used to calculate the phase diagram of colloidal electrolytes [10][11][12][13] ͑also recently extended to nonequilibrium situations 14 ͒. In these studies, two different models have been used, both consisting of an effective interaction that considers repulsions at short distances and long-ranged electrostatic interactions modeled via the lineal electrostatic screening theory, mediated by the presence of salt in the medium.…”

Section: Introductionmentioning

confidence: 99%

Complete phase behavior of the symmetrical colloidal electrolyte

Caballero

Noya

Vega

2007

The Journal of Chemical Physics

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We computed the complete phase diagram of the symmetrical colloidal electrolyte by means of Monte Carlo simulations. Thermodynamic integration, together with the Einstein-crystal method, and Gibbs-Duhem integration were used to calculate the equilibrium phase behavior. The system was modeled via the linear screening theory, where the electrostatic interactions are screened by the presence of salt in the medium, characterized by the inverse Debye length, kappa (in this work kappasigma=6). Our results show that at high temperature, the hard-sphere picture is recovered, i.e., the liquid crystallizes into a fcc crystal that does not exhibit charge ordering. In the low temperature region, the liquid freezes into a CsCl structure because charge correlations enhance the pairing between oppositely charged colloids, making the liquid-gas transition metastable with respect to crystallization. Upon increasing density, the CsCl solid transforms into a CuAu-like crystal and this one, in turn, transforms into a tetragonal ordered crystal near close packing. Finally, we have studied the ordered-disordered transitions finding three triple points where the phases in coexistence are liquid-CsCl-disordered fcc, CsCl-CuAu-disordered fcc, and CuAu-tetragonal-disordered fcc.

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“…To check the accuracy of the results few simulations were repeated using 15 × 10 5 Monte Carlo moves per particle for equilibration and 15 × 10 5 Monte Carlo moves per particle for production. To trace the metastable binodal while avoiding crystallization [37,38,39] we use a smaller system with N c =120 particles. To get good statistics 5 to 10 independent Monte Carlo runs are necessary for each value of the density.…”

Section: Model and Methodsmentioning

confidence: 99%

Crystallization and gelation in colloidal systems with short-ranged attractive interactions

2008

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We systematically study the relationship between equilibrium and non-equilibrium phase diagrams of a system of short-ranged attractive colloids. Using Monte Carlo and Brownian dynamics simulations we find a window of enhanced crystallization that is limited at high interaction strength by a slowing down of the dynamics and at low interaction strength by the high nucleation barrier. We find that the crystallization is enhanced by the metastable gas-liquid binodal by means of a two-stage crystallization process. First, the formation of a dense liquid is observed and second the crystal nucleates within the dense fluid. In addition, we find at low colloid packing fractions a fluid of clusters, and at higher colloid packing fractions a percolating network due to an arrested gas-liquid phase separation that we identify with gelation. We find that this arrest is due to crystallization at low interaction energy and it is caused by a slowing down of the dynamics at high interaction strength. Likewise, we observe that the clusters which are formed at low colloid packing fractions are crystalline at low interaction energy, but glassy at high interaction energy. The clusters coalesce upon encounter.

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Liquid-gas separation in colloidal electrolytes

Cited by 10 publications

References 32 publications

Experimental Phase Diagram of Symmetric Binary Colloidal Mixtures with Opposite Charges

Experimental Phase Diagram of Symmetric Binary Colloidal Mixtures with Opposite Charges

Complete phase behavior of the symmetrical colloidal electrolyte

Crystallization and gelation in colloidal systems with short-ranged attractive interactions

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