Investigation of the behavior of water and oil droplets on nanostructured surfaces: a molecular dynamics simulation study

This study conducted molecular dynamics simulations to estimate the behavior of water and oil droplets on the same surface and to investigate how oil droplets respond to varying surface conditions. The surfaces were considered from a flat plate to pillared surfaces with varying heights. Additionally, three surface conditions were examined by altering the solid-surface characteristic energy: lipophobic (weakly hydrophobic), weak lipophobic, and lipophilic conditions. The results showed that as the pillar height increased, the contact angle of the water droplet on the weak hydrophobic surfaces increased, while that of the 1, 2-dichloroethane (DCE) droplet remained relatively constant. In the case of weak lipophobic conditions, the top and bottom parts of the DCE droplet exhibited distinct behaviors as the pillar height increased. Furthermore, under lipophilic conditions, the oil droplets displayed varying patterns in their shape changes with increasing pillar height. These findings imply that droplet behavior on surfaces can be manipulated by engineering structures without necessitating additional external forces or energy inputs. This research provides valuable insights into the potential for separating and merging different types of liquids.