Nature’s design for superhydrophobicity in tropical leaves

Water repellency, exemplified in nature, has fascinated the materials community. This behaviour is utilised to biomimic self-cleaning effects for technological applications. Tropical leaves of three species, namely Moringa oleifera, Euphorbia milii and Caesalpinia ferrea, are investigated in this study. Wettability measurements show that C. ferrea leaf was superhydrophobic with a contact angle greater than 150°, while the other two leaves were hydrophobic with contact angles greater than 140° but less than 150°. Surface morphological studies reveal a structure with irregular wax structures on all the three leaves, unlike the regular wax structures such as tubules or platelets typically observed in most of the superhydrophobic leaves. The surface features were quantified on C. ferrea leaf surface due to its reduced wettability among the three leaves. The parameters such as height, mid-width, and radius of curvature of the cell and thickness of the wax film were determined. This study will possibly provide a new insight into developing self-cleaning surfaces with irregular nanostructures as opposed to conventional regular nanostructure patterns.