Wetting Criteria of Intrinsic Contact Angle To Distinguish between Hydrophilic and Hydrophobic Micro-/Nanotextured Surfaces: Experimental and Theoretical Analysis with Synchrotron X-ray Imaging.
In this study, the existing knowledge on the wetting criterion, that is, the intrinsic contact angle, for distinguishing between hydrophilic and hydrophobic textured surfaces is verified experimentally. A precise apparent contact angle is measured on micro-, nano-, and micro-/nanotextured surfaces to quantitatively define the surface-wetting conditions. In particular, X-ray tomography is introduced to measure precise geometric morphologies of nano- and micro-/nanotextured surfaces, and the wetting state of the textured surfaces is clearly visualized using synchrotron X-ray imaging. By comparing previous theoretical models and experimental results, it is verified that the intrinsic contact angle for distinguishing between hydrophilic and hydrophobic textured surfaces should be corrected from 90° to 43°. In addition, nonwetting phenomena in the region of the intrinsic contact angle between 43° and 90° are discussed.