Scaling of anisotropic droplet shapes on chemically stripe-patterned surfaces

We present an experimental study of the tunable anisotropic wetting behavior of chemically patterned anisotropic surfaces. Asymmetric glycerol droplet shapes, arising from patterns of alternating hydrophilic (pristine SiO2) and hydrophobic (fluoroalkylsilane self-assembled monolayers) stripes with dimensions in the low-micrometer range, are investigated in relation to stripe widths. Owing to the well-defined small droplet volume, the equilibrium shape as well as the observed contact angles exhibit unique scaling behavior. Only the relative width of hydrophilic and hydrophobic stripes proves to be a relevant parameter. Our results on morphologically flat, chemically patterned surfaces show similarities with those of experiments on topographically corrugated substrates. They are discussed in terms of the energetics at the liquid-solid interface.