A thermodynamic model developed by Carey and Wemhoff[1] to predict pressure and spinodal temperature as a function of position in a fluid near a mean field solid wall was applied and extended to atomic surfaces with pyramid shaped indentations. The model was extended to indentations from 1.1 to 4.2 nm in depth using the Lennard-Jones (LJ) fluid as well as water on magnesium oxide. The location of critical sized nuclei seen in constant temperature and pressure molecular dynamics (MD) simulations of argon on a LJ solid are found in regions predicted by the model to have a relatively low pressure and spinodal temperature. Nucleation occurs outside the region where pressure is greater that ten percent of the bulk value in cases where the model predicts high pressure near the surface. Nucleation occurs at the surface when the model predicts a region of tension near the surface. Making the solid-fluid potential more attractive decreased the depth of the high pressure region. A confinement effect was also seen. The width to depth ratio of the affected region decreased with increasing indentation depth and approached a constant value. In the argon case with ε_solid-fluid = ε_fluid-fluid/2, the model predicts a region of tension near the surface. As the indentation depth increases, the region of minimum pressure goes from being above the flat part of the surface, to being above the indentation, and finally to being in the indentation. This is consistent with MD simulations which showed that nucleation rates with 1.1 nm indentations were the same as on a flat surface, but larger for 3.2 nm indentations with enhanced probability of void formation in the indentation relative to the flat part of the surface. This model can predict both the location of nucleation and the approximate size of geometric defects that will significantly affect that location in a computationally efficient manner.

[1] Carey, V. P., and Wemhoff, A. P., 2005, “Thermodynamic analysis of near-wall effects on phase stability and homogeneous nucleation during rapid surface heating,” Int. J. Heat Mass Transfer, 48, pp. 5431–5445.