Initiation of wetting, filmwise condensation and condensate drainage from a surface in a gravity field

Molecular insight into the formation of adsorption clusters based on the zeta isotherm

This work presents a series of molecular dynamics simulations of argon adsorption on a silicon substrate with different lattice orientations. From the simulation results, the density profiles are discussed and the amount of adsorbed particles is obtained at different pressures. It is found that the solid surface orientation has a great influence on the density distributions and atomic arrangements near the surface. With the collected data, the thermal constants derived from the expression of zeta adsorption isotherms are determined. The calculated isotherms agree well with the simulation results. Also, from a microscopic point of view, the molecular insights show that the structures of the adsorbates are present as clusters with different numbers of particles. The size of the clusters changes with pressure. At a relatively small pressure ratio, most of the clusters consist of a single molecule. As the pressure ratio increases, larger sized clusters appear, forming various cluster-types. The molecular cluster distributions are closely consistent with the basic approximation of the zeta adsorption isotherm. Furthermore, the surface adsorption sites determined from molecular dynamics simulation show good agreement with that predicted by the zeta isotherm model, which reaffirms the effectiveness of the theoretical model. When the isotherm is extended to a pressure ratio greater than unity, a finite amount of adsorption is predicted and the wetting conditions are obtained. Affected by the solid surface orientations, the pressure ratio at wetting for the silicon substrate with the (111) surface plane is larger than those of the (100) and (110) surfaces, indicating that a higher subcooling is required for the wetting transition.

Initiation of condensation of toluene and octane vapours on a Si surface

The adsorption of toluene and octane vapours on a homogenous silicon surface was measured under steady, thermal disequilibrium conditions where a vapour at a temperature T ^V is exposed to a solid surface at a lower temperature, T ^S. Zeta adsorption isotherm theory was used along with Gibbsian thermodynamics to examine the adsorption results analytically and to investigate the wetting conditions for these vapours. Further, from the prediction of the cluster distribution in the adsorbate, the conditions for the initiation of a liquid phase are predicted. Finally, the mechanism that determines the condensation mode of hydrocarbons on a silicon surface is investigated.