Fabrication of biomimetic superhydrophobic surface based on nanosecond laser-treated titanium alloy surface and organic polysilazane composite coating

Nanosecond Laser Fabrication of Novel Micro-/Nanostructured Metal Surfaces: A Dual-Functional Supersurface Combining Antireflectivity and Superhydrophobic Properties

The research and applications in the field of micro/nano surface manufacturing are progressively shifting their focus toward multifunctional surfaces. In practical applications, objects often need to operate under demanding environmental conditions, and single-function surfaces have inherent limitations in terms of performance, adaptability, and longevity. In this paper, a micro-/nanolayered structural strategy with dual functions of ultrahigh antireflective properties and superhydrophobicity was created on the surface of titanium alloy by using nanosecond pulsed laser processing, and two structural modes of periodic honeycomb and lattice with controllable shapes were designed. In addition, the morphology and formation mechanism of multilevel micro-/nanostructures were investigated in depth, combining laser texturization and silanization of substrate microstructures. The effects of the micro-/nanostructured morphology on the reflection and wettability properties were evaluated with different pulse widths and lateral overlap index. This study also demonstrated that water droplets exhibit excellent bouncing and rolling behavior on superhydrophobic surfaces, further verifying the excellent hydrophobic properties of the prepared samples. Furthermore, in addressing the challenges of susceptibility to dust contamination and performance degradation in extreme environments associated with antireflective surfaces, a series of durability and mechanical stability tests were conducted on controllability periodic micro-/nanostructured surfaces. Successfully meeting this challenge will open up great potential and opportunities for significant improvements in equipment performance and stable operation under extreme operating conditions.

Recent Advances in Dual-Function Superhydrophobic Antibacterial Surfaces

Bacterial adhesion and subsequent biofilm formation on the surfaces of synthetic materials imposes a significant burden in various fields, which can lead to infections in patients or reduce the service life of industrial devices. Therefore, there is increasing interest in imbuing surfaces with antibacterial properties. Bioinspired superhydrophobic surfaces with high water contact angles (>150°) exhibit excellent surface repellency against contaminations, thereby preventing initial bacterial adhesion and inhibiting biofilm formation. However, conventional superhydrophobic surfaces typically lack long-term durability and are incapable of achieving persistent efficacy against bacterial adhesion. To overcome these limitations, in recent decades, dual-function superhydrophobic antibacterial surfaces with both bacteria-repelling and bacteria-killing properties have been developed by introducing bactericidal components. These surfaces have demonstrated improved long-term antibacterial performance in addressing the issues associated with surface-attached bacteria. This review summarizes the recent advancements of these dual-function superhydrophobic antibacterial surfaces. First, a brief overview of the fabrication strategies and bacteria-repelling mechanism of superhydrophobic surfaces is provided and then the dual-function superhydrophobic antibacterial surfaces are classified into three types based on the bacteria-killing mechanism: i) mechanotherapy, ii) chemotherapy, and iii) phototherapy. Finally, the limitations and challenges of current research are discussed and future perspectives in this promising area are proposed.

Rich CuO Nanowires Fabrication via Laser Post-Treatment of Laser-Textured Copper Substrate

The superhydrophobic and anti-icing properties of copper-based materials have been widely concerned. Laser texturing followed by thermal oxidation is a method to prepare durable CuO nanowires on Cu substrate. Rich CuO nanowires on micro-structures are required to meet its applications for anti-icing based on sustaining better Cassie–Baxter state stability. In this paper, dense CuO nanowires are obtained by additional laser post-treatment between the laser texturing and thermal oxidation. Uniform Cu2O and CuO layers form on the micro-structures by the laser post-treatment, which serves as the precursors for the growth of nanowires. The density of CuO nanowire increases from 44.3% to 61.4%, resulting in excellent superhydrophobicity and anti-icing performance. The delayed freezing time increases from 17 s to 1519 s at the temperature of −10 °C, which is more than 80 times longer compared to pure Cu substrate. The resulting anti-icing property shows durability through icing–melting cycles and taping tests. This feasible method opens new possibilities for enhanced anti-icing property on copper-based equipment used in low-temperature environments.

Investigation and Prediction on Regulation of Hydrophobicity of Polymethyl Methacrylate (PMMA) Surface by Femtosecond Laser Irradiation

This study presents the contact angle prediction model of a trapezoidal groove structure based on the laser irradiation on polymethyl methacrylate (PMMA). The trapezoidal groove structure was designed and proposed according to the characteristics of a femtosecond laser. First, the complete wetting model and incomplete wetting model which were compatible with the characteristics of the laser mechanism were constructed based on the Gibbs free energy and the structural parameters of the trapezoidal groove structure. Then, based on the contact angle prediction models constructed, the samples were divided into two groups according to the designed structural parameters, and the experimental investigations were carried out. The result demonstrated that the incomplete wetting prediction model was more in line with the actual situation. The convex width and the top edge length of spacing of the trapezoidal groove structure both affected the contact angle prediction results. From both the experimental contact angles and the contact angles predicted by the incomplete wetting model, it could be known that the contact angle reached 138.09° when the ratio of the convex width to the top edge length of spacing was 0.25, indicating that the smaller the ratio of the convex width to the top edge length of spacing, the better the hydrophobicity of PMMA.

Research on the Hydrophobicity of Square Column Structures on Monocrystalline Silicon Fabricated Using Micro-Machining

The theoretical prediction models of contact angle were constructed by considering the interface free energy. Then, the square column structure on monocrystalline silicon was fabricated using micro-milling. The rationality of prediction models was validated by regulating the parameters of the square column. It should be mentioned that the whole construction process was facile and efficient. After processing, the hydrophobicity of monocrystalline silicon with the square column structure was improved. The static contact angle of the processed monocrystalline silicon reached 165.8° when the side length of the square column was 60 μm. In addition, the correctness of the prediction models was verified from the perspective of molecular dynamics. The prediction models of contact angle were of great value for the practical application.