ABSTRACT
It is well known that the lotus leaf has attracted immense scientific interest due to its superior self-cleaning property (Fig. 1.2), exhibiting a high water contact angle (CA) above 160° and a small sliding angle (SA) ~2°.6 Barthlott and Nienhuis first revealed that the large CA is attributed to the epicuticula wax and the micrometer-scale papillae structure of the lotus leaf surface.7 Jiang et al. later found that there are the micro-/nanoscale hierarchical structures on the lotus leaf.8 After considering the contribution of the nanostructures, the theoretical model calculation indicates the CA can be over 160°, which is well consistent with the observed experimental results. It is obvious that the upper side of lotus leaf with a typical micro-/nanoscale hierarchical papillae and the epicuticular wax makes raindrops easily roll across the upper side of lotus leaf carrying away dirt and debris. On the other hand, we found that there are many microfolds around the margin of lotus leaf in the form of ring-bands, introducing high-energy barrier against water to block the water underneath preventing overflow onto its upper surface.9 Thus, the upper side of lotus leaf can keep itself clean from the dirt particles that are brought away when the water droplets roll off. This self-cleaning effect is usually called “lotus effect,” which shows great importance in fundamental research and potential in industrial applications.
