Banana Leaf Surface’s Janus Wettability Transition from the Wenzel State to Cassie–Baxter State and the Underlying Mechanism

Abstract

Janus wettability plays an important role in certain special occasions. In this study, field emission scanning electron microscopy (FESEM) was used to observe the surface microstructure of banana leaves, the static wettability of the banana leaf surface was tested, and the dynamic response of water droplets falling at different heights and hitting on the adaxial and abaxial sides was studied. The study found that the nanopillars on the adaxial and abaxial sides of the banana leaf were different in shape. The nanopillars on the adaxial side were cone-shaped with large gaps, showing hydrophilicity (Wenzel state), and the heads of the nanopillars on the abaxial side were smooth and spherical with small gaps, showing weak hydrophobicity (Cassie–Baxter state). Banana leaves show Janus wettability, and the banana leaf surface has high adhesion properties. During the dynamic impact test, the adaxial and abaxial sides of the banana leaves showed different dynamic responses, and the wettability of the adaxial side of the banana leaves was always stronger than the abaxial side. Based on the structural parameters of nanopillars on the surface of the banana leaf and the classical wetting theory model, an ideal geometric model around a single nanopillar on both sides of the banana leaf was established. The results show that the established model has high accuracy and can reflect the experimental results effectively. When the apparent contact angle was 76.17°, and the intrinsic contact angle was 81.17° on the adaxial side of the banana leaf, steady hydrophilicity was shown. The abaxial side was similar. The underlying mechanism of Janus wettability on the banana leaf surface was elucidated. This study provides an important reference for the preparation of Janus wettability bionic surfaces and the efficient and high-quality management of banana orchards.

Wetting and deposition characteristics of air-assisted spray droplet on large broad-leaved crop canopy

“…A large number of studies have used artificial collectors such as Mylar and water-sensitive paper (WPS) to visualize spray droplet distribution (Li et al, 2022a;Wang et al, 2022). However, due to the different wettability of natural plant leaves, artificial collectors cannot truly reflect the spray coverage and droplet density on the target leaf surface, which has also confirmed by our previous research (Xiang, 2020;Jiang et al, 2021;Jiang et al, 2022b). Therefore, in this study, banana leaves were directly used as collectors rather than any artificial collectors.…”

“…The wettability difference between the adaxial and abaxial sides was mainly affected by the microstructure and chemical composition of the surface. As shown in Figure 2, the sharp and large-spacing nanopillars structure on the adaxial side and the round and small-spacing nanopillars structure on the abaxial sides make them show Janus wettability (Jiang et al, 2021;Jiang et al, 2022b). The difference in wettability between pesticides is due to the active ingredients of different solutions.…”

Liquid Metal-Based Angle Detection Sensor

“…This change in diameter corresponds to a transition in the state of the LM in the fiber from the Wenzel state to the Cassie state. 31,32 The adhesion of the oxide layer on the LM gradually decreases as the contact area between the LM and fiber decreases. In this study, the geometry of the fiber sensor is modeled using an axisymmetric cylindrical tube, and a theoretical model can be established from a two-dimensional case (as shown in Figure 1c).…”

“…As shown in Figure c, there is a significant reduction in the diameter of the LM inside the fiber from 187 to 133 μm, as one moves from F to E. Additionally, a moderate downward trend can be observed in the M section. This change in diameter corresponds to a transition in the state of the LM in the fiber from the Wenzel state to the Cassie state. , The adhesion of the oxide layer on the LM gradually decreases as the contact area between the LM and fiber decreases. In this study, the geometry of the fiber sensor is modeled using an axisymmetric cylindrical tube, and a theoretical model can be established from a two-dimensional case (as shown in Figure c).…”

Effect of Microstructure on Mechanical Properties of Cornstalk

“…With the rapid development of modern technology, there are more and more studies on the microscopic scale of plants with the help of modern instrumental analysis technology [7,8]. In the study of cornstalks, Zhao carried out the surface characterization of the physicochemical properties of ultra-fine powder of cornstalks with different particle sizes [9].…”