Gas-liquid phase separation in oppositely charged colloids: Stability and interfacial tension

Abstract

We study the phase behavior and the interfacial tension of the screened Coulomb (Yukawa) restricted primitive model (YRPM) of oppositely charged hard spheres with diameter sigma using Monte Carlo simulations. We determine the gas-liquid and gas-solid phase transitions using free energy calculations and grand-canonical Monte Carlo simulations for varying inverse Debye screening length kappa. We find that the gas-liquid phase separation is stable for kappasigma<or=4, and that the critical temperature decreases upon increasing the screening of the interaction (decreasing the range of the interaction). In addition, we determine the gas-liquid interfacial tension using grand-canonical Monte Carlo simulations. The interfacial tension decreases upon increasing the range of the interaction. In particular, we find that simple scaling can be used to relate the interfacial tension of the YRPM to that of the restricted primitive model, where particles interact with bare Coulomb interactions.

Complete phase behavior of the symmetrical colloidal electrolyte

“…One of us used an exponential law to describe the electrostatic interaction, [12][13][14][15] while Hynninen and co-workers employed a Yukawa potential. 10,11 The gas-liquid transition has been studied for these two models and, indeed, both produce similar results. [11][12][13] However, the equilibrium crystal phases have been studied only for the Yukawa model, 10 showing an exciting phase diagram.…”

“…10,11 The gas-liquid transition has been studied for these two models and, indeed, both produce similar results. [11][12][13] However, the equilibrium crystal phases have been studied only for the Yukawa model, 10 showing an exciting phase diagram. As expected, the complete phase behavior is qualitatively similar to that one of the RPM.…”

“…This selection was motivated because previous calculations using the Yukawa model showed that the gas-liquid transition becomes metastable with respect to solidification from beyond around = 4.5-6. 11 Moreover, the complete phase diagram of the Yukawa model has been computed for this same value = 6. Therefore, our results would serve to see if the gas-liquid transition becomes metastable at this value of and to study the possible effect of the potential model ͑exponential or Yukawa͒ in the phase behavior.…”

“…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.…”

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

“…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.…”