Molecular Dynamics Simulations of Water Condensation on Surfaces with Tunable Wettability.

Water condensation plays a major role in a wide range of industrial applications. Over the past few years, many studies have shown interest in designing surfaces with enhanced water condensation and removal properties. It is well known that heterogeneous nucleation outperforms homogeneous nucleation in the condensation process. Because heterogeneous nucleation initiates on a surface at a small scale, it is highly desirable to characterize water-surface interactions at the molecular level. Molecular dynamics (MD) simulations can provide direct insight into heterogeneous nucleation and advance surface designs. Existing MD simulations of water condensation on surfaces were conducted by tuning the solid-water van der Waals interaction energy as a substitute for modeling surfaces with different wettabilities. However, this approach cannot reflect the real intermolecular interactions between the surface and water molecules. Here, we report MD simulations of water condensation on realistic surfaces of alkanethiol self-assembled monolayers with different head group chemistries. We show that decreasing surface hydrophobicity significantly increases the electrostatic forces between water molecules and the surface, thus increasing the water condensation rate. We observe a strong correlation between our rate of condensation results and the results from other surface characterization metrics, such as the interfacial thermal conductance, contact angle, and the molecular-scale wettability metric of Garde and co-workers. This work provides insight into the water condensation process at the molecular scale on surfaces with tunable wettability.