How does ethane wet different substrates?

Abstract

Computer simulations are employed to investigate the adsorption mechanisms of ethane on both homogeneous and inhomogeneous substrates. For homogeneous surfaces, the full range of surface phase transitions - from incomplete to complete wetting - can be accessed by tuning the strength of the surface potential. The resulting layering transition temperatures show excellent agreement with experimental measurements of ethane on graphite. By contrast, although all inhomogeneous substrates exhibit a prewetting transition, the adsorption mechanisms are strongly influenced by the stripe width.

Figures (7)

• Figure 1: Part (a): Schematic representation of the ethane molecule modelled using the TraPPe force field. Part (b): Sketches of the homogeneous and inhomogeneous substrates.
• Figure 2: (Colour online) Part (a): Bulk phase diagram in the temperature-density plane, with critical points indicated by an asterisk for experiments and a filled circle for simulations. Part (b): Examples of probability distributions $P(\rho)$ obtained from the hyper-parallel tempering method. Part (c): Temperature dependence of the Binder's cumulant for three system sizes.
• Figure 3: (Colour online) Part (a): Bulk (black and green points) and surface (red and blue points) phase diagrams in the $\mu-T$ plane. Green square points are estimated using equation \ref{['eq:luis']} while the remaining ones are obtained from the equal area rule as described in section \ref{['sec:coex']}. Red circles are the results for the substrate with $\varepsilon_{fw}=5\varepsilon$ where the prewetting transition is observed, starting at $T_W$ marked as a pink asterisk, and terminating in the critical prewetting point, T$_{C,PW}$. Blue triangles correspond to the layering transitions occurring in the system with $\varepsilon_{fw}=6\varepsilon$. Magnified region emphasizing the layering transitions is shown in part (b). Part (c): Phase diagram of the thin-thick film transition for $\varepsilon_{fw}=5\varepsilon$. Part (d): Temperature dependence of the Binder's cumulant for four system sizes for the first layering transition. Part (e): Probability distributions of excess adsorption per unit area for systems with different number of layers. Part (f): Phase diagram of the layering transitions for $\varepsilon_{fw}=6\varepsilon$. Critical point for the first layering is marked as a filled triangle.
• Figure 4: (Colour online) Part (a): Bulk (black solid line) and surface (red, green and blue points) phase diagrams in the $\mu-T$ plane. Part (b): Phase diagram of the thin-thick film transition for different stripe widths and homogeneous substrate $\varepsilon_{fw}=5.0$ (magenta circles).
• Figure 5: (Colour online) Part (a): Excess adsorption isotherms $N^{\text{ex}}/A$ as a function of chemical potential $\mu$ calculated for a homogeneous substrate with $\varepsilon_{fw}=5.0\varepsilon$ and (b-d) three different stripes width $L_S$. Dash-dotted lines indicate the bulk coexistence chemical potential $\mu_C$ at the corresponding temperature.