Anisotropic Wettability on One-Dimensional Nanopatterned Surfaces: The Effects of Intrinsic Surface Wettability and Morphology

Large-scale molecular dynamic simulations were conducted to study anisotropic wettability on one-dimensional (1D) nanopatterned surfaces. Hexadecane (C16H34) and decane (C10H22) nanodroplets were used as wetting liquids. Initially, surfaces with various intrinsic wettability (oleophobic and oleophilic) were produced using surface lattice size as a control parameter. These surfaces were subsequently patterned with 1D grooves of different sizes, and their anisotropic wettability was examined. The results show that anisotropic wettability strongly depends on intrinsic surface wettability and surface morphology. The results also demonstrate that the anisotropy in the contact angle is negligible for oleophobic surfaces. However, the anisotropy becomes more evident for oleophilic surfaces and increases with the degree of oleophilicity. Results suggest that anisotropy also depends on the surface morphology, including the patterns' width and height. Monitoring the droplet shape showed that more significant droplet distortion was associated with higher anisotropy. A clear association was lacking between the roughness ratio, r, and the degree of anisotropy. The observed average contact angle for 1D patterned oleophilic surfaces disagreed with the predicted values from the Wenzel theory. However, the theory could correctly predict the state of the droplet being Cassie-Baxter or Wenzel.