Figure 1

(a) Illustration of the asymmetric NAHS model with positive nonadditivity. The solid boundaries represent the hard cores of the small and big species. The dotted line represents the nonadditive hard core between unlike species, which here is attributed only to smaller particles. (b) Three examples of general planar hard walls. The additive wall treats the two species equally, while the $b$-type and $s$-type walls have properties similar to the big and small particles, respectively.Reuse & Permissions

Figure 2

(a) Pairs of density profiles ${\rho }_s(z)$ (left panel) and ${\rho }_b(z)$ (right panel) of the NAHS fluid with $q=0.5$ and $\Delta =0.2$ at a $b$-type wall and at bulk coexistence on the $s$-rich side of the phase diagram. The shaded regions represent the range of profiles possessing $n=0$ or $1,\hspace{0.5em}2,\hspace{0.5em}3,\hspace{0.5em}4$, or $5$ adsorbed $b$-rich layers, and the region where the adsorbed film becomes infinitely thick. The solid lines represent specific examples from the middle of each range. The inset shows the adsorption of each species ${\Gamma }_i$ as a function of ${\eta }_s$. (b) The corresponding phase diagram in the (${\eta }_s,{\eta }_b$) plane. There is a series of layering transitions that intersect the bulk binodal ($*$) and descend into the $s$-rich one-phase region, ending in a surface critical point ($ˆ$). For clarity only the first two transitions are shown in full, while the remaining transitions are represented only by their intersection with the bulk binodal. The inset shows the location of the first layering and the “wetting” transitions in relation to the bulk critical point ($•$).Reuse & Permissions

Figure 3

Same as Fig. 2a, but for the $s$-type wall. The coexistence curve is traced on the $b$-rich side of the phase diagram. As the wetting critical point is approached the smaller particles strongly adsorb at the wall, replacing the bigger particles and growing a thick film. Below the wetting critical point the film is infinitely thick. The inset shows the adsorptions ${\Gamma }_i$ against the difference in the packing fraction of the small species from its value at the wetting critical point, ${\eta }_s^{*}-{\eta }_s$, on a logarithmic scale, where ${\eta }_s^{*}=0.0043$.Reuse & Permissions

Figure 4

Value of ${\eta }_s$ at (i) the intercept of the layering transitions with the bulk binodal (solid lines) and (ii) the location of the critical wetting transition critical point (dashed line), as a function of the scaled wall offset $\delta l/{\sigma }_{\mathit{ss}}$. As $\delta l/{\sigma }_{\mathit{ss}}$ is increased from 0.2 ($b$-type wall) the layering transitions move along the binodal toward the bulk critical point, located at ${\eta }_s^{\mathrm{crit}}\simeq 0.05$. At $\delta l/{\sigma }_{\mathit{ss}}\simeq 0.27$ the layering transitions coalesce and the surface transition becomes critical wetting. As $\delta l$ increases toward the additive case, the critical wetting transition approaches the bulk critical point. Increasing $\delta l$ further, the wetting critical point moves to the other side of the binodal. The inset shows the $s$-type wall wetting critical point ($▴$) in relation to the bulk critical point ($•$).Reuse & Permissions