Unraveling the Interplay of Leaf Structure and Wettability: A Comparative Study on Superhydrophobic Leaves of Cassia tora, Adiantum capillus-veneris, and Bauhinia variegata

TL;DR

This study compares the micro and nanoscale surface structures of superhydrophobic leaves from three plant species, revealing how their unique morphologies influence wettability and droplet behavior, with implications for biomimetic surface design.

Contribution

First detailed correlation of leaf surface micro/nanostructures with wettability across three species, using FESEM imaging and droplet impact analysis.

Findings

Cassia tora exhibits high contact angle hysteresis and roll-off angle due to nano petals.

ACV leaves have hierarchical re-entrant structures with high contact angles.

Bauhinia variegata shows similar superhydrophobicity with distinct micro-ridge features.

Abstract

In this article, superhydrophobic leaves of Cassia tora, Adiantum capillus-veneris (ACV), and Bauhinia Variegate are reported for the first time, and the wettability of these leaf's surfaces was correlated with their surface morphology at micro and nanoscale. Field Emission Scanning Electron Microscopy (FESEM) images of the surfaces were used to get surface morphological information at the micro-nanoscale structures. A special drying method was implemented to ensure the minimal structural collapse of these surfaces under the high vacuum of FESEM. FESEM images of Cassia tora leaves showed widely spaced, low aspect ratio nano petals distributed on bumpy blunt micro features, responsible for high contact angle hysteresis and high roll angle measured on the Cassia tora leaves. ACV leaves showed the presence of micron-scale spherical morphology made of nanoscale hair-like features. These hierarchical re-entrant surface features generated a very high contact angle and low roll-off angle. Leaves of Bauhinia variegate showed similar superhydrophobic and self-cleaning properties. However, surface features were different, which consisted of a higher aspect ratio and closely spaced nano petals uniformly distributed over flat surfaces consisting of micro-scale ridges. Droplet impact studies on these surfaces at different Weber numbers showed different behaviour due to these different micro-nano features.