Method for improving hydrophobicity by combining picosecond and femtosecond lasers to prepare micro-nano structure

Abstract

A method for preparing micro / nano structures with enhanced hydrophobicity using a combination of picosecond and femtosecond lasers is disclosed. The method involves pre-treating a TC4 titanium alloy substrate to obtain a clean and smooth surface; using a picosecond laser to ablate the surface of the TC4 titanium alloy substrate to prepare a periodically arranged array of micron-sized square truncated pyramids as a primary microstructure; selectively irradiating the top platform of the micron-sized square truncated pyramids with a femtosecond laser to induce the formation of a periodic nanograting structure as a secondary nanostructure, thereby forming a micro / nano composite structure; and finally, cleaning and drying to obtain a superhydrophobic TC4 titanium alloy surface with a micro / nano composite structure.

Description

Technical Field

[0001] This invention relates to the field of TC4 titanium alloy technology, and to a method for preparing micro-nano structures with improved hydrophobicity using a combination of picosecond and femtosecond lasers. Background Technology

[0002] TC4 titanium alloy, due to its high specific strength, excellent corrosion resistance, and good biocompatibility, is widely used in cutting-edge fields such as aerospace, biomedical implants, and marine engineering. However, in many applications, the intrinsic surface properties of TC4 titanium alloy cannot meet the stringent requirements. For example, in the aerospace field, icing on wing surfaces can severely affect aerodynamic performance; in the biomedical field, protein adsorption and bacterial adhesion on implant surfaces may trigger immune rejection and infection; and in the marine environment, biofouling on ship hull surfaces increases drag. Developing TC4 titanium alloy surfaces with superhydrophobic properties is of great significance for solving these problems. Superhydrophobic surfaces (water contact angle >150°, roll-off angle <10°) can achieve functions such as droplet self-cleaning, anti-icing, drag reduction, and anti-bioadhesion. Currently, methods for preparing superhydrophobic surfaces are mainly divided into chemical and physical methods. Chemical methods, such as chemical etching, sol-gel methods, and chemical vapor deposition, usually require modification with low surface energy fluorine-containing or silane-containing substances. These methods suffer from drawbacks such as complex processes, environmental pollution from chemical reagents, weak adhesion between the resulting hydrophobic coating and the substrate, and susceptibility to wear and failure, limiting their long-term application under harsh conditions. As an advanced physical processing method, ultrafast laser (picosecond, femtosecond laser) processing technology shows great potential in the fabrication of functional micro / nano structures due to its "cold processing" characteristics, high precision, and material versatility. While femtosecond lasers alone can fabricate micro / nano composite structures on material surfaces in one step through precise material ablation and self-organization effects, their material removal rate is low. When processing large-area surfaces (above the square centimeter scale) to fabricate micron-scale deep structures, the processing efficiency is extremely low and the processing time is too long, failing to meet the requirements of industrial production. Picosecond lasers alone have relatively long pulse widths and relatively significant thermal effects. Although they offer high material removal rates and are suitable for rapidly constructing micron-scale structures, they are difficult to precisely fabricate subwavelength, almost thermally damage-free periodic nanograting structures (such as LIPSS). Therefore, how to combine the unique advantages of lasers with different pulse widths to develop a surface modification method that can both ensure processing efficiency and achieve precise construction of micro-nano structures in order to obtain a superhydrophobic TC4 titanium alloy surface with stable performance and high durability is a technical problem that urgently needs to be solved in this field.

[0003] The information disclosed in the background section is only intended to enhance the understanding of the background of the present invention, and therefore may contain information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0004] To address the shortcomings or defects of existing technologies, a method for fabricating micro / nano structures with enhanced hydrophobicity using a combination of picosecond and femtosecond lasers is provided. By combining the high efficiency of picosecond lasers with the high precision of femtosecond lasers, micro / nano composite structures with excellent superhydrophobic properties can be controllably fabricated on the surface of TC4 titanium alloy, solving the problem of balancing efficiency and precision in the fabrication of efficient and stable large-area hydrophobic surfaces using single laser processing techniques.

[0005] The objective of this invention is achieved through the following technical solutions.

[0006] A method for fabricating micro / nano structures using a combination of picosecond and femtosecond lasers to improve hydrophobicity includes:

[0007] A clean and smooth machined surface is obtained by pre-treating the TC4 titanium alloy substrate.

[0008] Picosecond lasers were used to ablate the surface of the TC4 titanium alloy substrate to prepare a periodically arranged micron-scale square truncated array as a primary microstructure.

[0009] On the top platform of a micron-sized square truncated pyramid, selective irradiation with a femtosecond laser is used to induce the generation of a periodic nanograting structure as a secondary nanostructure, thereby forming a micro-nano composite structure.

[0010] After processing, the surface of the superhydrophobic TC4 titanium alloy with a micro-nano composite structure is obtained by cleaning and drying.

[0011] In a preferred embodiment of the method, the surface pretreatment includes sequential mechanical grinding and polishing, followed by ultrasonic cleaning in acetone and anhydrous ethanol, and finally drying with nitrogen.

[0012] In a preferred embodiment of the method, in the micron-scale square frustum array, each frustum has a bottom side length of 80-120 μm, a top side length of 60-90 μm, a height of 50-80 μm, and a center-to-center distance between adjacent frustums of 100-150 μm.

[0013] In a preferred embodiment of the method, the processing parameters of the picosecond laser are: wavelength 1064nm, pulse width 10ps, repetition frequency 500kHz, average power 20-50W, scanning speed 1000mm / s, and filling scanning ablation is performed through a galvanometer system.

[0014] In a preferred embodiment of the method, the femtosecond laser is focused on the top of each micrometer-sized square truncated pyramid and scanned unidirectionally along a direction perpendicular to the laser polarization direction with a line spacing of 5 μm, thereby inducing the formation of a periodic nanograting structure.

[0015] In a preferred embodiment of the method, the processing parameters of the femtosecond laser are: wavelength 1030nm, pulse width 290fs, repetition frequency 200kHz, average power 0.8-2.5W, focused spot diameter 35μm, and scanning speed 150mm / s.

[0016] In a preferred embodiment of the method, the entire processing is carried out in an air environment without the use of chemical modifiers or low surface energy coatings, and the resulting superhydrophobic structure is integrally formed with the substrate.

[0017] In a preferred embodiment of the method, post-processing cleaning and drying includes ultrasonic cleaning in anhydrous ethanol for 5 minutes and drying with nitrogen gas.

[0018] A superhydrophobic TC4 titanium alloy surface with a micro-nano composite structure is prepared by combining picosecond and femtosecond lasers to improve its surface hydrophobicity. Its surface static water contact angle is greater than 155° and roll-off angle is less than 5°.

[0019] Compared with existing technologies, the beneficial effects of this invention are as follows: This invention adopts a hierarchical laser processing strategy: First, the efficient material removal capability of picosecond lasers is used to rapidly construct a micron-scale frustum framework, significantly improving processing efficiency; then, the ultra-fine "cold processing" characteristics of femtosecond lasers are used to superimpose functional nanostructures (LIPSS) in key areas (the top of the frustum), balancing macroscopic efficiency and microscopic precision, providing a feasible industrial path for the large-area preparation of high-performance hydrophobic surfaces. This micro-nano composite structure, formed directly on a TC4 titanium alloy substrate, significantly increases surface roughness. By capturing a large amount of macroscopic and microscopic air to form a stable "air cushion," it easily achieves the Cassie-Baxter state, thus exhibiting excellent superhydrophobicity, with a static contact angle >155° and a roll-off angle <5°. Because the structure is integrally formed with the substrate, it has extremely high mechanical strength and durability, is wear-resistant and erosion-resistant, and the entire processing is completed in air, requiring no chemical reagents, making it environmentally friendly. The superhydrophobic titanium alloy surface prepared by this technology has broad application potential in fields such as aerospace anti-icing, medical anti-adhesion, fluid drag reduction, and instrument anti-fouling and self-cleaning.

[0020] The description provided is merely an overview of the technical solution of this invention. In order to make the technical means of this invention clearer and more understandable, so that those skilled in the art can implement it according to the contents of the specification, and to make the described and other objects, features and advantages of this invention more obvious and understandable, specific embodiments of this invention are described below. Attached Figure Description

[0021] Various other advantages and benefits of the present invention will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. It is obvious that the drawings described below are merely some embodiments of the invention, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort. Furthermore, the same reference numerals denote the same parts throughout the drawings.

[0022] In the attached diagram:

[0023] Figure 1 This is a schematic diagram of a micron-scale square frustum array formed after picosecond laser processing in an embodiment of the present invention;

[0024] Figure 2 This is a schematic diagram of the micro-nano composite structure formed after femtosecond laser composite processing in an embodiment of the present invention;

[0025] Figure 3 This is a schematic diagram of the water droplet wetting state on the superhydrophobic surface prepared according to an embodiment of the present invention;

[0026] Figure 4 This is a process flow diagram of an embodiment of the present invention.

[0027] The present invention will be further explained below with reference to the accompanying drawings and embodiments. Detailed Implementation

[0028] Specific embodiments of the invention will now be described in more detail with reference to the accompanying drawings. While specific embodiments of the invention are shown in the drawings, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the invention and to fully convey the scope of the invention to those skilled in the art.

[0029] It should be noted that certain terms are used in the specification and claims to refer to specific components. Those skilled in the art will understand that different terms may be used to refer to the same component. This specification and claims do not distinguish components based on differences in terminology, but rather on differences in function. The terms "comprising" or "including" used throughout the specification and claims are open-ended and should be interpreted as "comprising but not limited to." The following descriptions are preferred embodiments for carrying out the invention; however, these descriptions are for the purpose of understanding the general principles of the specification and are not intended to limit the scope of the invention. The scope of protection of this invention is determined by the appended claims.

[0030] To facilitate understanding of the embodiments of the present invention, the following will provide further explanation and description with reference to the accompanying drawings and several specific embodiments, and the accompanying drawings do not constitute a limitation on the embodiments of the present invention.

[0031] To better understand, such as Figures 1 to 4 As shown, the method includes:

[0032] A clean and smooth machined surface is obtained by pre-treating the TC4 titanium alloy substrate.

[0033] Picosecond lasers were used to ablate the surface of the TC4 titanium alloy substrate to prepare a periodically arranged micron-scale square truncated array as a primary microstructure.

[0034] On the top platform of a micron-sized square truncated pyramid, selective irradiation with a femtosecond laser is used to induce the generation of a periodic nanograting structure as a secondary nanostructure, thereby forming a micro-nano composite structure.

[0035] After processing, the surface of the superhydrophobic TC4 titanium alloy with a micro-nano composite structure is obtained by cleaning and drying.

[0036] In a preferred embodiment of the method, the surface pretreatment includes sequential mechanical grinding and polishing, followed by ultrasonic cleaning in acetone and anhydrous ethanol, and finally drying with nitrogen.

[0037] In a preferred embodiment of the method, in the micron-scale square frustum array, each frustum has a bottom side length of 80-120 μm, a top side length of 60-90 μm, a height of 50-80 μm, and a center-to-center distance between adjacent frustums of 100-150 μm.

[0038] In a preferred embodiment of the method, the processing parameters of the picosecond laser are: wavelength 1064nm, pulse width 10ps, repetition frequency 500kHz, average power 20-50W, scanning speed 1000mm / s, and filling scanning ablation is performed through a galvanometer system.

[0039] In a preferred embodiment of the method, the femtosecond laser is focused on the top of each micrometer-sized square truncated pyramid and scanned unidirectionally along a direction perpendicular to the laser polarization direction with a line spacing of 5 μm, thereby inducing the formation of a periodic nanograting structure.

[0040] In a preferred embodiment of the method, the processing parameters of the femtosecond laser are: wavelength 1030nm, pulse width 290fs, repetition frequency 200kHz, average power 0.8-2.5W, focused spot diameter 35μm, and scanning speed 150mm / s.

[0041] Example 1 (Optimal Example)

[0042] Step 1: Picosecond laser fabrication of micron-scale structures:

[0043] The pretreated TC4 titanium alloy sample was placed on a three-dimensional precision displacement stage of a picosecond laser micromachining system. The laser parameters were set as follows: center wavelength: 1064 nm, pulse width: 10 ps, ​​repetition rate: 500 kHz, average power: 30 W, focused spot diameter: 40 μm, scanning speed: 1000 mm / s. High-speed galvanometer scanning was employed, using a pre-defined CAD path for a fill-in scan to ablate the material between the square frustums, thus fabricating a periodically arranged array of square frustums (first-order microstructures) on the sample surface.

[0044] Step 2: Femtosecond laser fabrication of nanoscale structures:

[0045] The fabricated micron-sized samples were transferred to a femtosecond laser micromachining system, where a high-precision CCD coaxial vision positioning system precisely aligned the top platform of each micron-sized frustum. The laser parameters were set as follows: center wavelength: 1030 nm, pulse width: 290 fs, repetition rate: 200 kHz, average power: 1.5 W, focused spot diameter: 35 μm, and scanning speed: 150 mm / s. On the top platform of each frustum, unidirectional, equally spaced parallel lines perpendicular to the laser polarization direction were scanned to induce the generation of periodic nanograting structures (LIPSS, second-order nanostructures).

[0046] The sample, after undergoing two-step composite laser processing, was ultrasonically cleaned again in anhydrous ethanol for 5 minutes to remove surface ablation residue, and then dried with nitrogen. Using a contact angle meter, a 5 μL drop of deionized water was dropped onto the sample surface. The final static water contact angle was measured to be 161°, and the roll-off angle was 3.5°, demonstrating excellent superhydrophobic properties.

[0047] Examples 2-5 and Comparative Examples 1-4: The Influence of Key Laser Parameter Combinations on Superhydrophobic Properties

[0048] To verify the rationality and superiority of the picosecond and femtosecond laser power ranges defined in the claims of this invention, a series of experiments were conducted. In these experiments, except for the average power of the picosecond and femtosecond lasers, all other preparation conditions (such as materials, pretreatment, scanning speed, wavelength, etc.) were kept completely consistent with those in Example 1. Each set of parameters was used to fully execute the combined process of step one (picosecond processing) and step two (femtosecond processing), and then the performance of the final obtained surface was tested. The experimental results are summarized in Table 1.

[0049] Table 1

[0050]

[0051] In a preferred embodiment of the method, the entire processing is carried out in an air environment without the use of chemical modifiers or low surface energy coatings, and the resulting superhydrophobic structure is integrally formed with the substrate.

[0052] In a preferred embodiment of the method, post-processing cleaning and drying includes ultrasonic cleaning in anhydrous ethanol for 5 minutes and drying with nitrogen gas.

[0053] A superhydrophobic TC4 titanium alloy surface with a micro-nano composite structure is prepared by combining picosecond and femtosecond lasers to improve its surface hydrophobicity. Its surface static water contact angle is greater than 155° and roll-off angle is less than 5°.

[0054] In one embodiment, the method includes the following steps:

[0055] 1. Substrate pretreatment: The TC4 titanium alloy sample was mechanically ground and polished in sequence, then ultrasonically cleaned in acetone and anhydrous ethanol respectively, and finally dried with nitrogen to obtain a clean and flat surface to be processed.

[0056] 2. Picosecond Laser Fabrication of Micrometer Structures: Using a picosecond laser processing system, Gaussian beam shaping and high-speed galvanometer scanning are employed to ablate the surface of a pre-treated TC4 titanium alloy sample, fabricating a periodically arranged array of square frustums as a first-order micrometer structure. The square frustum array is composed of multiple independent square frustum units arranged at equal intervals on a two-dimensional plane.

[0057] 3. Femtosecond Laser Fabrication of Nanostructures: Building upon the fabrication of micron-sized structures, a femtosecond laser processing system is used to precisely align and focus the laser beam onto the top plane of each square truncated pyramid. By controlling the laser polarization direction and scanning path, a periodic grating nanostructure (LIPSS) is induced at the top of each truncated pyramid as a secondary nanostructure.

[0058] 4. Post-processing: The sample processed by composite laser is placed in anhydrous ethanol for ultrasonic cleaning to remove slag and particles generated during processing. Then it is dried with nitrogen to obtain a superhydrophobic TC4 titanium alloy surface with micro-nano composite structure.

[0059] The following example, using a "titanium alloy flat panel," details the specific steps of a method for enhancing the hydrophobicity of micro / nano structures using a combination of picosecond and femtosecond lasers:

[0060] Step 1: Substrate Pretreatment

[0061] A TC4 titanium alloy sheet with dimensions of 30mm × 30mm × 3mm was selected as the substrate. The surface of the sheet was progressively polished using 400#, 800#, 1200#, and 2000# metallographic sandpaper until no obvious scratches were visible. Subsequently, a diamond polishing slurry with a particle size of 0.05μm was used for fine polishing on a polishing machine to obtain a mirror finish. The polished sample was then placed in beakers containing acetone and anhydrous ethanol, respectively, and subjected to ultrasonic cleaning for 15 minutes each. Finally, the sample surface was dried with high-purity nitrogen gas and stored in a clean, dry environment for later use.

[0062] Step 2: Fabrication of a micrometer-scale square truncated pyramid array using picosecond laser:

[0063] The pretreated TC4 titanium alloy sample was placed on a three-dimensional precision displacement stage of a picosecond laser micromachining system. The laser used in this system was a ytterbium-doped fiber picosecond laser. The laser parameters were set as follows: center wavelength: 1064 nm, pulse width: 10 ps, ​​repetition rate: 500 kHz, average power: 30 W, focused spot diameter: 40 μm, scanning speed: 1000 mm / s, and scanning method: high-speed galvanometer scanning, using a pre-set CAD path for a fill-in scan to ablate the material between the square frustums. Using these parameters, a periodically arranged array of square frustums was fabricated on the sample surface, such as... Figure 1 As shown. The geometric dimensions of each square frustum element are: bottom square side length 100μm, top square side length 70μm, frustum height 60μm, and center-to-center distance between adjacent frustums 120μm.

[0064] Step 3: Femtosecond laser fabrication of nanoscale LIPSS structures:

[0065] The samples with fabricated micron-sized structures were transferred to a femtosecond laser micromachining system. This system was equipped with a high-precision CCD coaxial vision positioning system to ensure that the laser beam was precisely aligned with the top platform of each micron-sized frustum. The laser parameters were set as follows: center wavelength: 1030 nm, pulse width: 290 fs, repetition rate: 200 kHz, average power: 1.5 W, laser polarization: linear polarization, focused spot diameter: 35 μm, scanning speed: 150 mm / s, and scanning path: unidirectional, equally spaced (5 μm line spacing) parallel line scanning along a direction perpendicular to the laser polarization on the top platform of each frustum.

[0066] like Figure 2 As shown, a low-energy femtosecond laser beam irradiates the top of the frustum, inducing the generation of a nanoscale LIPSS structure with consistent orientation and uniform period through interference and self-organization effects.

[0067] Step 4: Post-processing and performance testing:

[0068] The sample, after undergoing two laser processing steps, was placed again in anhydrous ethanol and ultrasonically cleaned for 5 minutes to thoroughly remove any ablation residue adhering to the surface. After drying with nitrogen, the final superhydrophobic TC4 titanium alloy sample was obtained. Its hydrophobic properties were tested: using a contact angle meter, a 5 μL drop of deionized water was dropped onto the sample surface. The measured static water contact angle was 161°, and the roll-off angle was 3.5°, demonstrating excellent superhydrophobic properties. Figure 3 As shown, the water droplet exhibits a typical Cassie-Baxter state on the micro-nano composite structure, with its bottom supported by a large number of trapped air layers, achieving an extremely low solid-liquid contact area.

[0069] Furthermore, this invention utilizes picosecond lasers to efficiently construct micron-scale arrays of square frustums, fully leveraging their high average power (20-50W) to achieve rapid, large-area material ablation on the surface of TC4 titanium alloy. This micron-scale structure not only significantly increases surface geometric roughness, but more importantly, its regularly arranged frustum morphology forms macroscopic "air trap" units, laying the foundation for subsequent stable Cassie-Baxter states. Compared to femtosecond lasers alone for fabricating microstructures, picosecond lasers improve processing efficiency by more than an order of magnitude, reducing the processing time for microstructures in square centimeter-scale areas from hours to minutes, meeting the efficiency requirements of industrial production.

[0070] Secondly, femtosecond lasers precisely induce LIPSS nanograting structures, utilizing the extremely low thermally affected region and strong nonlinear absorption characteristics brought about by the ultrashort pulse (290 fs) to perform localized and selective irradiation on the top platform of the pre-formed micron-sized frustum. By controlling the laser polarization direction and scanning path, LIPSS structures with good periodicity and consistent orientation can be generated in situ on the top of each microunit. This nanograting not only further improves the surface micro-roughness, but more importantly, its subwavelength scale can effectively enhance light-matter interaction and modulate solid-liquid interface energy, forming a multi-level "cushion" effect in conjunction with the micron-sized structure, significantly reducing the actual contact area of ​​water droplets, thereby achieving excellent superhydrophobic properties with a static contact angle >155° and a roll-off angle <5°.

[0071] Third, the hierarchical composite processing strategy of "micro-first, nano-later" cleverly avoids the technical limitations of a single laser source: while femtosecond lasers can produce high-quality LIPSS, they are difficult to efficiently construct deep micron-level structures; while picosecond lasers are difficult to form clear and ordered nanogratings due to thermal accumulation effects. This invention optimizes the process sequence, allowing picosecond lasers to undertake the "skeleton building" task, while femtosecond lasers focus on "functional refinement," ensuring overall processing efficiency while maintaining nanometer precision in key areas, achieving an optimal balance between macroscopic efficiency and microscopic functionality.

[0072] Fourth, the resulting micro-nano composite structure is integrally formed with the substrate without any external coating or chemical modification, fundamentally solving the problems of easy peeling and poor wear resistance of traditional hydrophobic coatings. The micron-sized frustum and the substrate are continuous metallic phases, and the LIPSS is formed by laser-induced self-organization, resulting in high structural bonding strength. It can maintain stable hydrophobic properties under mechanical friction, fluid erosion, or long-term service conditions, and has excellent engineering applicability.

[0073] Finally, the entire process is completed in air at normal temperature and pressure, without the need for toxic solvents, low surface energy substances such as fluorosilanes, or vacuum environments, which conforms to the concept of green manufacturing. At the same time, it greatly simplifies the process flow and reduces production costs and environmental burden.

[0074] The basic principles of this application have been described above with reference to specific embodiments. However, it should be noted that the advantages, benefits, and effects mentioned in this application are merely examples and not limitations, and should not be considered as essential features of each embodiment of this application. Furthermore, the specific details disclosed above are for illustrative and facilitative purposes only, and are not limitations. These details do not limit the application to the necessity of employing the aforementioned specific details for implementation.

[0075] The above description has been given for purposes of illustration and description. Furthermore, this description is not intended to limit the embodiments of this application to the forms disclosed herein. Although numerous exemplary aspects and embodiments have been discussed above, those skilled in the art will recognize certain variations, modifications, alterations, additions, and sub-combinations thereof.

Claims

1. A method for enhancing the hydrophobicity of micro / nano structures prepared by combining picosecond and femtosecond lasers, characterized in that, It includes: A clean and smooth machined surface is obtained by pre-treating the TC4 titanium alloy substrate. Picosecond lasers were used to ablate the surface of the TC4 titanium alloy substrate to prepare a periodically arranged micron-scale square truncated array as a primary microstructure. On the top platform of a micron-sized square truncated pyramid, selective irradiation with a femtosecond laser is used to induce the generation of a periodic nanograting structure as a secondary nanostructure, thereby forming a micro-nano composite structure. After processing, the surface of the superhydrophobic TC4 titanium alloy with a micro-nano composite structure is obtained by cleaning and drying.

2. The method as described in claim 1, characterized in that, Preferably, the surface pretreatment includes sequential mechanical grinding and polishing, followed by ultrasonic cleaning in acetone and anhydrous ethanol, and finally drying with nitrogen.

3. The method as described in claim 1, characterized in that, In the micron-scale square frustum array, the bottom side length of each frustum is 80-120μm, the top side length is 60-90μm, the height is 50-80μm, and the center-to-center distance between adjacent frustums is 100-150μm.

4. The method as described in claim 1, characterized in that, The processing parameters of the picosecond laser are: wavelength 1064nm, pulse width 10ps, repetition frequency 500kHz, average power 20-50W, scanning speed 1000mm / s, and filling scanning ablation is performed through a galvanometer system.

5. The method as described in claim 1, characterized in that, The femtosecond laser is focused on the top of each micrometer-sized square truncated pyramid and scans unidirectionally along a parallel line perpendicular to the laser polarization direction with a line spacing of 5 μm, inducing the formation of a periodic nanograting structure.

6. The method as described in claim 1, characterized in that, The processing parameters of the femtosecond laser are: wavelength 1030nm, pulse width 290fs, repetition frequency 200kHz, average power 0.8-2.5W, focused spot diameter 35μm, and scanning speed 150mm / s.

7. The method as described in claim 1, characterized in that, The entire processing is carried out in an air environment without the use of chemical modifiers or low surface energy coatings, and the resulting superhydrophobic structure is integrally formed with the substrate.

8. The method as described in claim 1, characterized in that, After processing, cleaning and drying are performed, including ultrasonic cleaning in anhydrous ethanol for 5 minutes and drying with nitrogen gas.

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