Interplay between demixing and freezing in two-dimensional symmetrical mixtures

The interplay between demixing and freezing in two-dimensional symmetrical binary mixtures of Lennard-Jones particles is studied using Monte Carlo simulation. It is demonstrated that different scenarios are possible. For example, the line of continuous liquid demixing transition can start at the liquid side of the vapor-liquid coexistence at the lower critical end point and then it can terminate at the liquid side of the liquid–demixed solid coexistence at the upper critical end point. Other situations are also possible. We distinguish four different scenarios depending on the interactions between unlike particles.

Figure 1

The phase diagrams (in the $T-\rho$ plane) for the system (a) with $e=0.7$ and $s=1.24$ and (b) with $e=0.7$ and $s=1.0$. In (a), the symbols V, L, and S denote vapor, liquid, and solid phases, respectively, while the subscripts m and dm refer to mixed and demixed phases, respectively.

Figure 2

(Color online) Histograms of density (left panels) and of the order parameter $m$ (right panels) for the systems just below the $T_{l,cep}$ (upper panel), at $T_{l,cep}<T<T_{u,cep}$ (middle panels), and just above $T_{u,cep}$ (lower panels). The temperatures are given in right panels, while the numbers in the left panels give the values of the chemical potential, $\mu$ (in the units of $\epsilon$).

Figure 3

(Color online) The changes of critical, triple-point, and critical end point temperatures with the parameter $e$ for the systems characterized by (a) $s=1.0$ and (b) 1.24.