Dynamic transitions in a two dimensional associating lattice gas model

Abstract

Monte Carlo simulation strategies for computing the wetting properties of fluids at geometrically rough surfaces J. Chem. Phys. 135, 184702 (2011) Semi-bottom-up coarse graining of water based on microscopic simulations J. Chem. Phys. 135, 184101 (2011) Hydrophobic interactions in presence of osmolytes urea and trimethylamine-N-oxide J. Chem. Phys. 135, 174501 (2011) Potential of mean force between identical charged nanoparticles immersed in a size-asymmetric monovalent electrolyte J. Chem. Phys. 135, 164705 (2011) Additional information on J. Chem. Phys. Using Monte Carlo simulations we investigate some new aspects of the phase diagram and the behavior of the diffusion coefficient in an associating lattice gas ͑ALG͒ model on different regions of the phase diagram. The ALG model combines a two dimensional lattice gas where particles interact through a soft core potential and orientational degrees of freedom. The competition between soft core potential and directional attractive forces results in a high density liquid phase, a low density liquid phase, and a gas phase. Besides anomalies in the behavior of the density with the temperature at constant pressure and of the diffusion coefficient with density at constant temperature are also found. The two liquid phases are separated by a coexistence line that ends in a bicritical point. The low density liquid phase is separated from the gas phase by a coexistence line that ends in tricritical point. The bicritical and tricritical points are linked by a critical -line. The high density liquid phase and the fluid phases are separated by a second critical -line. We then investigate how the diffusion coefficient behaves on different regions of the chemical potential-temperature phase diagram. We find that diffusivity undergoes two types of dynamic transitions: a fragile-to-strong transition when the critical -line is crossed by decreasing the temperature at a constant chemical potential; and a strong-to-strong transition when the critical -line is crossed by decreasing the temperature at a constant chemical potential.

Diffusion anomaly and dynamic transitions in the Bell–Lavis water model

“…The critical line separating the fluid from the low density liquid phase, at lower pressures, could be associated to a fragile-to-strong transition, whereas the critical line separating the high density fluid from the HDL phase, at higher pressures, was associated to a strong-to-strong dynamic transition. 15 In both cases, the dynamic transition is of the same kind along the whole critical line. Thus, the dynamic transition upon traversing the critical line has been understood to be a result of the change of the structure of the liquid, similarly to the interpretation given to the dynamic transition seen in the case of the crossing of the Widom line.…”

“…15,27 Second, we looked for dynamic transitions by analyzing the behavior of diffusivity with temperature across the critical line, at fixed chemical potentials. Our results showed that two different regimes may be found: If the critical line is crossed at low chemical potential, near the minimum in diffusivity, a fragile-to-strong transition is observed; for higher chemical potentials, near the diffusivity maximum, no dynamic transition is seen.…”

“…This is different from the behavior presented by liquid water, but is common to other lattice models. 15,16,27 A possible reason for this discrepancy is the fact that bonding is more rigid in the lattice model, thus reducing the mobility of particles as compared to continuous models, in which rotations allow for slightly distorted bonds.…”

“…In order to address this question, a number of models which display criticality were investigated as to the presence of fragile-to-strong transitions. [14][15][16] These studies have shown that on crossing the critical line, fragile-to-strong, strong-to-strong, or even fragile-to-fragile transitions could be observed, depending on the specific structure of the phases separated by the critical line. In the particular case of the associated lattice gas model ͑ALG͒, which presents two critical lines, two kinds of dynamic transitions are also present.…”

Structure and anomalous solubility for hard spheres in an associating lattice gas model

“…[7][8][9] Even though there are a number of two and three dimensional lattice models that would in principle exhibit the anomalies present in water, 6,16,[19][20][21] here water is represented by the associating lattice gas (ALG) (Refs. [22][23][24][25][26][27][28]) that has already shown the density and diffusion anomalies described above. The ALG does not have the full complexity of the molecular liquid, however it leads to a network-forming fluid in which directionality plays an important role.…”