Surfaces with nanostructure patterning are broadly encountered in nature, and they play a significant role in regulating various phenomena such as phase transition at the liquid/solid interface. Here, we designed two kinds of template substrates with periodic nanostructure patterns [i.e., nanotrench (NT) and nanopore (NP)]. Surface nanodroplets produced on these nanostructure surfaces were characterized to acquire their morphology and wetting properties. We show that nanostructure patterning could effectively regulate the shape, contact radius, and nucleate site of nanodroplets. While nanodroplets on the NT structure are constrained in one dimension, nanodroplets on the NP structure have enhanced the wetting property with constraints from two dimensions. Further numerical analysis indicates that the morphology and contact angles of nanodroplets on the NT structure depend on the substrate wettability and the droplet volume. These observations demonstrate how physical geometry and chemical heterogeneity of a substrate surface affect the growth and spreading of surface nanodroplets, which deepens our understanding on nanoscale phase separation.
Keywords: atomic force microscopy; nanodroplets; nanoscale wetting; nanostructure patterning; solvent exchange; wetting transition.