Molecular Dynamics Simulations of Water Condensation on Surfaces with Tunable Wettability

Abstract

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.

Molecular-Level Understanding of the Influence of Ions and Water on HMGB1 Adsorption Induced by Surface Hydroxylation of Titanium Implants

“…On the other hand, the hydroxyl groups on the surface are also observed to orient to capture the approaching water molecules, thereby minimizing their energy. 65 Since the hydroxyl groups on the fully hydroxylated surface have similar parameters to the -OH groups of water, a similar gap is obtained between the surface hydroxyl peak and the first water oxygen (OW) peak in the density profile. In contrast to the non-hydroxylated system, less ordering of the second water layer was observed in the hydroxylated system, as evidenced by the peak height in Figure 8.…”

“…The next two hydrogen peaks in Figure 8b A reorientation of the water molecules was observed near the hydrophilic TiO 2 surface as a result of strong electrostatic interactions. 65 Due to the strong network of hydrogen bonds, the first layer of water on the non-hydroxylated surface is very stable and prevents other molecules from directly adsorbing onto the surface. Therefore, essentially no protein residues or ions pass beyond this first layer of water (Figure 7b).…”

Effects and Mechanism of Surface Water Wettability and Operating Frequency on Response Linearity of Flexible IDE Capacitive Humidity Sensor

“…The heterogeneous nucleation was preferred on the hydrophilic region of a patterned hydrophilic–hydrophobic substrate [ 31 , 32 , 33 ]. It was predicted by the molecular dynamics simulation of water condensation that the rate of heterogeneous nucleation was higher on a surface with higher water wettability [ 34 ].…”

“…On the other hand, the number of water droplets increased less from 32 to 320 on the surface with the medium WCA of 67° and remained at 32 without any increase on the surface with the high WCA of 129°. This setting of simulation is plausible considering the higher rate of droplet nucleation on the surface with higher water wettability [ 34 ].…”

Molecular-Level Understanding of the Influence of Ions and Water on HMGB1 Adsorption Induced by Surface Hydroxylation of Titanium Implants

“…A reorientation of the water molecules was observed near the hydrophilic TiO 2 surface as a result of strong electrostatic interactions. 65 Due to the strong network of hydrogen bonds, the first layer of water on the non-hydroxylated surface is very stable and prevents other molecules from directly adsorbing onto the surface. Therefore, essentially no protein residues or ions pass beyond this first layer of water (Figure 7b).…”