Investigation on the mechanisms of cluster formation and transition from adsorption to condensation

Abstract

In order to understand the mechanism of cluster formation and transition from adsorption to condensation, a series of theoretical analysis based on the Zeta adsorption model and molecular dynamics simulations are hybrid to study the transition process of argon atoms adsorption on a solid surface. The influence of solid-fluid interaction strength and temperature difference are discussed. Results show that the interfacial adsorption dominates the density profiles in the near wall region. With the increase of temperature difference, the enlarged chemical potential difference drives the transition from adsorption to condensation. The critical temperature differences for the transition are determined. The smaller value of solid-fluid interaction induces a larger condensation resistance, which results in a bigger value of critical temperature difference. Meanwhile, the cluster formation and transition process are theoretically described based on the Zeta adsorption model, without singularity at saturation pressure. The predicted adsorption sites show a good agreement with the molecular dynamics simulations. Once the pressure ratio exceeds a certain value, the adsorption sites are occupied by homogeneous clusters, which initiates the liquid phase to wet the surface. The wetting condition is determined. Also, in terms of Gibbs equation, the surface tension is lowered from the solid surface tension without adsorption to the value at wetting. The critical temperature difference for the transition obtained by theoretical prediction coincides well with the molecular dynamics simulation.