Water vapor condensation behavior on different wetting surfaces via molecular dynamics simulation

Understanding water vapor condensation behavior at molecular level provides critical insights and useful guidance towards applications such as atmospheric water harvesting. In this work, condensation behavior of water vapor with a range of concentrations is investigated by molecular dynamics simulation on surfaces with different wetting states, viz. hydrophilic, hydrophobic, superhydrophilic, and superhydrophobic under five levels of water vapor content. The effect of water vapor content on condensation morphology, condensation beginning time, number of water molecules condensed over time, and accumulation rate are quantitatively examined. The results demonstrate that water condensation mass increases linearly with time on hydrophilic and superhydrophilic surfaces, while displaying a two-stage behavior on hydrophobic and superhydrophobic surfaces. The increase at the first stage is slower than the second stage. Higher water vapor content enables earlier nucleation and shortens the duration of the slow increase stage for hydrophobic and superhydrophobic surfaces. Quantitatively, water condensation mass increases linearly with the relative humidity of the vapor, and the coefficient with relative humidity on the hydrophilic, hydrophobic, superhydrophilic and superhydrophobic surfaces is 25.74 x 10-19, 8.31 x 10-19, 27.63 x 10-19, and 1.34 x 10-19, respectively. Our results show that increasing water vapor content has more significant impact on hydrophilic and superhydrophilic surfaces than hydrophobic and superhydrophobic surfaces. In addition, increasing water vapor content has minor effect on condensation rate in the slow increase stage on hydrophobic and superhydrophobic surfaces, but significantly increase the condensation rate on the rapid increase stage.