Wetting behaviors of individual nanostructures.

Pinning of a liquid contact line by micro/nanoscale defects is attributed as the physical origin of macroscopic contact angle hysteresis. However, direct experimental quantification of the pinning effect at the nanoscale has yet to be fully explored to establish this link. Here we present an experimental technique to systematically investigate the wetting behaviors of individual hydrophilic nanostructures with diameters from 2000 nm down to 75 nm. Our results show that the macroscopic pinning behavior is preserved for nanostructures with dimensions down to approximately 200 nm. In addition, the estimated depinning liquid contact angle at the nanoscale is in agreement with the macroscopic receding contact angle, which indicates a physical link between nanoscopic pinning to the macroscopic liquid receding phenomenon.