Study on the surface characteristics and infiltration mechanism of banana leaf

Objective  The wetting behavior of the front and back surfaces of banana leaves at different growth stages of the banana tree canopy was studied, in order to provide a basis for the regulation mechanism of pesticide droplets retention on the surface of banana leaves.

Method  The static wetting properties of the banana leaf surface were characterized by a contact angle measuring instrument, the dynamic wetting behavior of droplets on the surface of the banana leaf was recorded by a high-speed camera, and the structural information of the banana leaf surface was observed by a field emission scanning electron microscope. The surface chemical composition was analyzed using the Fourier transform infrared spectrometer. The surface microstructure model of banana leaf was constructed based on the Wenzel and Cassie wetting theory, and the wetting equation was established to describe its wetting mechanism.

Result  Scanning electron microscopic observation showed that the front surface of banana leaves presented a micro-nano-scale double-layer composite structure, the micro-scale protrusion structure was covered with nano-scale papillary structures with a density of about 4.6 pieces/µm², the strip-like protrusion width was (16.03±3.48) µm, the average diameter of papillae was (0.116±0.068) µm, the size of micron-scale strip-like protrusions on the back of banana leaves was larger than that of the front, and the width was (74.25±9.80) μm, the nano-scale structure had mesh-like protrusions with a width of (2.35±0.49) μm, and the wettability of the back of banana leaves was generally higher than that of the front. For banana leaves at different growth stages, the front of flag leaves showed hydrophilicity with contact angle of 71.46°±6.02°, while the front and back of banana leaves at other stages showed weak hydrophobicity, indicating that the front surface of young leaves had stronger wetting and spreading ability. By constructing the Wenzel and Cassie wetting models for the front surface of mature banana leaves, the intrinsic contact angle of the front surface of mature banana leaves was 20.76° showed super-hydrophilic based on analysis and calculation, indicating that its nano-scale papillary structure was polysaccharide.

Conclusion  The combination of the hydrophobic micro-nano bilayer composite structure and the hydrophilic chemical components on the surface of banana leaves leads to the wet state of weak hydrophobicity on the surface, and the polysaccharide of the nano-papillary structure is responsible for hydrophilic effect and high adhesion effect of the banana leaf surface.