Symmetric mixtures in slit-like pores with selective walls

Abstract

Symmetric mixtures characterized by high negative geometric and energetic non-additivity do not exhibit phase separation in the bulk. However, the phase separation occurs when such mixtures are confined in slit pores with selective walls. It is demonstrated that the wall selectivity affects the pore filling. When the difference of the interaction energies between the mixture components and pore walls is lower than a certain threshold value, condensation occurs between a dilute phase and the mixed liquid. When this difference exceeds the threshold value, the pore filling may occur in two steps. The first is the condensation of a dilute phase into the demixed liquid, and the second step leads to the formation of the mixed liquid. We have elucidated the changes in the phase behavior caused by non-additivity of symmetric mixtures, and by the difference in the interaction energies of the components with pore walls.

Figures (12)

• Figure 1: The schematic representations of the bulk phase diagram for the mixtures with high negative energetic and geometric non-uniformity. Panels a, c, and e (b, d, and f) show the $\mu-T$ ($\rho-T$) projections of the phase diagrams for $s<s_o(e)$, $s\in (s_o(e),s_1(e))$, and $s>s_1(e)$, respectively.
• Figure 2: (Colour online) (Panel a) Changes of the bulk critical temperature, $T_{c,b}$, with $s$. (Panel b) Changes of the capillary condensation critical temperature, $T_c(H)$, with pore width, obtained for two different values of $s$, are given in the figure. (Panel c) The log-log plots of $\Delta T_c =T_{c,b}-T_c(H)$ against $1/H$ for the same systems as shown in panel b. Dashed lines are the fits to the scaling relation (\ref{['eq-scala']}). (Panel d) Changes of the capillary condensation critical temperature with $s$, for the pore of $H=10$, and different values of $\bar{\varepsilon}_{gs}$ equal to 5 (filled circles), 10 (filled squares), and 15 (filled diamonds). All results correspond to the systems with $e=0.6$.
• Figure 3: (Colour online) Panel a--c show the density profiles recorded for the systems with $e=0.6$ and $s=0.68$, for $\bar{\varepsilon}_{gs}=5$, $T=1.10$ and $\mu=-3.73$ (panel a), $\bar{\varepsilon}_{gs}=10$, $T=1.05$ and $\mu=-4.12$ (panel b), and $\bar{\varepsilon}_{gs}=15$, $T=1.02$ and $\mu=-4.38$ (panel c). Panels d-f show the adsorption-desorption isotherms for the same systems as in panels a--c.
• Figure 4: (Colour online) The $\rho-T$ projections of phase diagrams for the systems characterized by $e=0.6$, $s=0.62$, $\bar{\varepsilon}_{gs}=5$, and $H=10$, for $\Delta V =2.0$ (panel a), and $2.4$ (panel b). In panel a, we have shown the densities of the components A (filled squares), and B (filled diamonds), and the total density (filled circles). The inset to panel b shows the estimated $\mu-T$ projection of the phase diagram for $\Delta V =2.4$.
• Figure 5: (Colour online) The examples of adsorption-desorption isotherms at different temperatures (given in the figure) for the systems with $e=0.6$, $s=0.62$, $\bar{\varepsilon}_{gs}=5$, and $H=10$. Panels a, b, and c correspond to $\Delta V =2.0$, while panels d and e to $\Delta V =2.4$. Circles correspond to the total density, while squares and diamonds correspond to the densities of components A and B, respectively.