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. Since 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 more realistic surfaces of alkanethiol self-assembled monolayers with different head group chemistries. We show that decreasing the 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 coworkers. By connecting the results obtained from different surface characterization techniques, here we provide molecular-level explanations of water condensation on surfaces of different wettability. We anticipate that this fundamental knowledge gained can be applied to various water harvesting applications.

Molecular dynamics simulation of water condensation on surfaces with tunable wettability

ACS Fall 2020 Virtual Meeting

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