Microscale mechanism of microstructure, micromorphology and Janus wettability of the banana leaf surface

As a result of natural selection, the adaxial and abaxial sides of banana leaves show different wetting states and anisotropy. Janus wettability between the adaxial and abaxial sides of the banana leaf surface is revealed for the first time in this work. This has relevance for the preparation of bionic materials and an important role in the efficient and high-quality production management of pesticide spraying in banana orchards. The main purpose of this research is to analyze and study the microscale mechanism and coupling relationship between the Janus wettability of banana leaf surface and the microstructure and micromorphology. We adopt advanced modern instrument analysis technology, such as contact angle (CA) measurements, field emission scanning electron microscopy (FESEM), X-ray spectrometric analysis (EDS), and Fourier transform infrared spectroscopy (FTIR), and performed tests on the adaxial and abaxial sides of banana leaves to investigate the cause of Janus wettability. The results show that banana leaves exhibit different degrees of anisotropy, mainly due to the surface micromorphology. Banana leaves exhibit a hydrophilic Wenzel state on the adaxial side and a weakly hydrophobic Cassie-Baxter state on the abaxial side. We focused on studying the coupling effect and found that the main coupling element impacting the Janus wettability of the banana leaf surface is the nanopillars microstructure, and the secondary coupling element is the content of hydrophilic functional groups on the surface. This work may lead to the design and fabrication of Janus wetting surfaces by mimicking the nanopillar structure on banana leaf surfaces and help explore the potential application of efficient and high-quality pesticide spraying in banana orchards.