Water vapor condensation on binary mixed substrates: A molecular dynamics study

Abstract

Sophisticated and expensive surface texture design and manufacturing are commonly needed to achieve efficient surfaces with enhanced condensation performances. The high nucleation rate and high droplet removal capacity of a substrate surface acquire trade-off, whose mechanisms have not explicitly been comprehended. Based on the assumption that hydrophilic spots would improve nucleation while a hydrophobic surface can facilitate droplet removal rate, this work studied the nucleation and departure processes on a binary mixed substrate with randomly distributed hydrophilic atoms, with homogeneous substrates being as comparison references. The molecular dynamics simulation results showed that the wettability of the binary mixed substrate could be estimated by the form of the Cassie equation. Unlike the randomly nucleated clusters on a homogeneous substrate, the surface energy analysis verifies that the clusters tend to form on the areas with enriched hydrophilic atoms on a binary mixed substrate. Conversely, the droplets also tend to stick on the hydrophilic areas to deteriorate droplet removal efficiency. Combined with a probability analysis by the Monte Carlo method and MD simulation, a moderated ratio(rm = 25% in this work) was shown to furnish better nucleation properties with minimal deterioration in departure properties than the mono-wettability substrate with the same contact angle.