Surface patterning is widely employed to modulate surface properties, given the well-established influence of surface structures on wetting behavior and related interfacial phenomena. In this study, chemical heterogeneity was introduced via stripe-patterned surfaces functionalized with self-assembled monolayers (SAMs) composed of two types of organic molecules differing in water affinity. Three distinct heterogeneous stripe-patterned surfaces were fabricated accordingly. Experimental observations have demonstrated that the macroscopic contact angle on such heterogeneous surfaces can be effectively described by the Cassie equation. However, the applicability of the Cassie model to microscopic droplets remains contentious, particularly when the droplet size approaches the scale of surface heterogeneity, which is commonly observed at the nanoscale. Additionally, surface heterogeneity can induce contact line pinning, resulting in metastable contact angles as droplet size varies. To investigate these effects, molecular dynamics simulations were conducted to examine the wetting behavior of water droplets on nanoscale heterogeneous surfaces. The results indicate that larger differences in wettability between the two components lead to more pronounced spreading of the droplet contact area under equivalent droplet sizes, potentially due to enhanced pinning forces at the contact line.
Zhao et al. (Wed,) studied this question.