Objective Silicon carbide (SiC) is widely used in fields such as functional ceramics, power electronics, and photovoltaics owing to its excellent physical and chemical properties. However, the intrinsically hydrophilic properties of SiC make it easy to adsorb dirt. Moreover, the SiC surface can readily freeze in low- temperature environments, which undermines the performance of SiC components and results in significant economic losses. Therefore, the extension of SiC applications has been limited owing to these drawbacks. Traditional preparation of superhydrophobic surfaces includes coating, chemical etching, and electroplating. However, most of these processes have distinct restrictions owing to the use of hazardous chemicals, complex processing, low processing efficiency, high requirements for the nature and size of the material, and non- environmental friendliness. To address these problems, we obtain a superhydrophobic surface by modifying the surface of SiC using a laser- silicone oil- heat treatment composite process combined with a bionic design. This superhydrophobic SiC surface presents excellent self-cleaning, anti- icing, and mechanical durability properties. Hence, the obtained surface is expected to expand the application prospects of SiC. Methods The surface texturing shape is designed and optimized using the microstructural characteristics of natural loach and shark skins (Fig. 1). The composite process (Fig. 2) includes the following steps: First, the SiC surface is processed using laser surface processing to construct a regular array with multilevel micro/nanostructures which result in a wettability shift from hydrophilicity to superhydrophilicity. Subsequently, a pre- configured mixed solution consisting of silicone oil and isopropanol (IPA) of approximately 50 mu L is dripped onto the superhydrophilic surface. After the solution completely infiltrates the laser- processed area, the superhydrophilic surface is heated on a heating plate at 200 degrees C for 10 min, followed by ultrasonic cleaning with isopropanol and air- drying. Subsequently, the superhydrophilic surface is transformed into superhydrophobicity. Furthermore, the physical and chemical properties of the surface are tested. Laser confocal microscope and scanning electron microscope are employed to characterize the micro/nanostructure of the superhydrophobic SiC sample surface. The chemical element composition of the surface is analyzed using X-ray photoelectron spectroscopy. The contact angle is measured using a contact angle measuring instrument with a high- resolution complementary metal- oxide- semiconductor transistor (CMOS) camera. Finally, chemical stability, self-cleaning, anti- icing, and sandpaper cyclic friction experiments are designed to evaluate the long-term stability, self-cleaning performance, anti- icing performance, and friction and wear performance of the superhydrophobic SiC samples, respectively. Results and Discussions By adjusting the laser processing parameters, periodic biomimetic structural surfaces with different densities and roughness are prepared (Fig. 3). The experimental results show that the laser parameters are important for forming micro/nanostructures. Furthermore, the micro/nanostructures processed using laser are composed of a combination of densely grown oxide nanopapillae structure and " fence " structure (Fig. 4). Surface chemical analysis shows that the contents of C and O elements are important for the regulation of wettability. A large number of nonpolar carbon- containing hydrophobic groups (-CH2- , -CH3, C=C) are deposited on the laser- processed surface after silicone oil- heat treatment, and the full deposition of Si elements on the surface further strengthens the hydrophobicity of the laser processed surface after heat treatment (Fig. 5). The wettability results indicate that the untreated SiC surface (with a contact angle of 70.3 degrees +/- 1.2 degrees) after laser processing transitions to the Wenzel state (with a contact angle of 0 degrees). Subsequently, the wettability of the SiC surface shifts from superhydrophilicity to hydrophobicity via silicone oil treatment and simultaneously, the wetting state of the surface transforms from Wenzel state to C- B state. After IPA cleaning, the hydrophilic surface transforms into superhydrophobicity (Fig. 6). By changing the laser processing parameters, the wettability of the SiC surface can be adjusted, and superhydrophobicity is guaranteed when using the laser processing parameters in the following range: scanning speed of 20 -200 mm/s and scanning spacing of 100 -150 mu m (Fig. 8). Performing chemical stability, self-cleaning, anti- icing, and sandpaper cyclic friction experiments demonstrate that the superhydrophobic SiC samples exhibit excellent long-term stability, friction and wear resistance, self-cleaning, and anti- icing properties (Figs. 9-12). Conclusions In this study, by mimicking the microstructure characteristics of loach and shark skins in nature, multilevel micro/ nanostructures are successfully fabricated on the surface of SiC samples using a laser- silicone oil- heat treatment composite process. Laser surface processing is first utilized to induce surface micro/nanostructures. Through the subsequent silicone oil- heat treatment and isopropanol cleaning, the surface energy of SiC can be effectively reduced. In addition, the SiC surface can be transformed from superhydrophilicity to superhydrophobicity (contact angle of 158.8 degrees +/- 0.6 degrees and sliding angle of 7.0 degrees +/- 0.5 degrees ), which can effectively help achieve superhydrophobicity and low surface adhesion. The experimental results indicate that the superhydrophobic SiC surface prepared in this study exhibits excellent long-term stability, self-cleaning, and anti- icing properties. Furthermore, it is expected to be widely used in aerospace and intelligent manufacturing fields. In addition, the post- process treatment duration of the laser- silicone oil- heat treatment composite process developed by this study is significantly reduced compared with those of previous methods. Meanwhile, the process is low-cost, nontoxic, and environmentally friendly, which can render a series of applications.
