Beyond Microstructures: Surface Polarity as the Key To Reversible Hydrophobicity in Natural Plant Leaves

The superhydrophobic of plant leaves, such as those of rice and lotus, has long been attributed to surface micro-nano structures and wax layers. Here, we reveal a previously overlooked determinant─surface polarity─as the principal factor governing leaf wettability. Through controlled oxygen plasma exposure, we demonstrate reversible switching between hydrophobic and hydrophilic states on multiple plant species without altering their intrinsic surface topography, as confirmed by scanning electron microscopy. Surface charge characterization indicates that plasma treatment introduces uniform positive charges, which dictates the transition toward hydrophilicity. Subsequent charge removal via electrical grounding restores the original hydrophobic state, a reversible process that remains stable over hundreds of cycles. These findings challenge the classical structural model and establish surface polarity as the central mechanism for dynamic wettability control on biological surfaces. This approach offers promising utility in agriculture by enabling precise modulation of droplet-leaf interactions, thereby enhancing pesticide adhesion and utilization efficiency. Our work not only advances fundamental understanding of biointerfacial phenomena but also provides a scalable strategy for sustainable agrochemical management.