Effect of particle and substrate wettability on evaporation-driven assembly of colloidal monolayers

Assembled monolayers of colloidal particles are crucial for various applications, including opto-electronics, surface engineering, as well as light harvesting, and catalysis. A common approach for self-assembly is the drying of a colloidal suspension film on a solid substrate using technologies such as printing and coating. However, this approach often presents challenges such as low surface coverage, stacking faults, and the formation of multiple layers. We numerically investigate the influence of substrate and particle wettability on the deposited pattern. Higher substrate wettability results in a monolayer with a hexagonal arrangement of deposited particles on the substrate. Conversely, lower substrate wettability leads to droplet formation after the film ruptures, leading to the formation of particle clusters. Furthermore, we reveal that higher particle wettability can mitigate the impact of the substrate wettability and facilitate the formation of highly ordered monolayers. We propose theoretical models predicting the surface coverage fraction dependent on particle volume fraction, initial film thickness, particle radius, as well as substrate and particle wettability, and validate these models with simulations. Our findings provide valuable insights for optimizing the deposition process in the creation of assembled monolayers of colloidal particles.