ABSTRACT
The wettability, surface energy, structure, and morphology of a material's surface will affect the interaction process between the material and the organism. Moreover, these factors are not independent of each other, but will affect each other, which together determine the biological surface of the material. Although two classic theories of surface wettability control have been established, including the Wenzel model and the Cassie-Baxter model, the mechanism of the microstructure parameters on the surface wettability has not been considered. This paper established a two-dimensional mathematical model of the composite wetting pattern based on microstructure parameters, revealed the mechanism of the microstructure parameters on the surface wettability, and then used ultra-precision cutting and molding composite preparation methods to quickly and efficiently prepare bionic structures, and the hydrophobic character of the microstructure was characterized by the contact angle meter, which provides theoretical support and preparation technology for the modification of the hydrophobic character of the material.
ABSTRACT
The current research on gecko-inspired dry adhesives is focused on micropillar arrays with different terminal shapes, such as flat, spherical, mushroom, and spatula tips. The corresponding processing methods are mostly chemical methods, including lithography, etching, and deposition, which not only are complex, expensive, and environmentally unfriendly, but also cannot completely ensure microstructural integrity or performance stability. The present study demonstrates a high-precision, high-efficiency, and green method for the fabrication of a gecko-inspired surface, which can promote its application in dexterous robot hands and mechanical grippers. Based on the bendable lamellar structures of the gecko, annular wedge adhesive surfaces that stick to the finger surfaces of dexterous robot hands to improve their load capacity are proposed and fabricated via a suitable combined processing method of ultraprecision machining and replica molding. The greater the width, the higher the replication integrity, and when the minimum width is 20 µm, the replication error is less than 5.5% due to the superior processing performance of the nickel-phosphorus (Ni-P) plating of the master mold. The fabricated annular wedge structures with an optimized width of 20 µm not only exhibit a strong friction force of up to 35.48 mN under a preload of 20 mN in the GCr15/poly(dimethylsiloxane) (PDMS) friction pair but also demonstrate an obviously improved anisotropic friction characteristic of up to λ = 1.36, as the molecular force exhibits a stronger increase as compared to the decrease of the mechanical force of the structure with a small width.
