Journal of Hebei University of Science and Technology (Feb 2018)
Wettability measurement and hydrophobicity mechanism analysis of leaf surface of Hylotelephium erythrostictum
Abstract
To search a bionic prototype for fabrication of superhydrophobic surfaces, the wettability of water droplets on leaf surfaces of Hylotelephium erythrostictum is measured, and the micromorphology of these leaf surfaces is examined by scanning electron microscope and three-dimensional shape, and the characteristic parameter is extracted. Based on the Wenzel equation and Cassie-Baxter equation, theoretical models are proposed to analyze the leaf surface's hydrophobicity mechanism. Results present that the contact angles change remarkably with the variation of leaf types, the contact angle of water droplets on up side and low side of the fresh young leaf are recorded as (147.25 ± 3.79)° and (137.46 ± 4.03)°, and the greatest value is recorded as 152.54° when the water droplet contact with fresh young leaf's low side, demonstrating the fresh young leaf possesses superhydrophobic property. The leaf's surface morphology consists of convex halls and wax coverings, the ellipsoidal convex halls from young leaf show a continuous and dense arrangement with the similar height, the significant different distribution density and projected area. The wax coverings emerge as discernible platelet-formed wax crystals with an irregular pattern and overlap each other to generate numerous cavities, and the wax crystal's geometrical parameters from both sides of the young leaf exhibit extremely similar values. Both the micro-scaled convex halls and the nano-scaled wax crystals serve the function of making the leaf surface present hydrophobic property, but the wax crystals play an extremely important role. The theoretical model proposed based on the Cassie-Baxter equation can adequately elucidate the hydrophobic mechanism of leaf surface in Hylotelephium erythrostictum, and provides theoretical support for the bionic fabrication of superhydrophobic surface.
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