A method for preparing a super-lyophobic hole array structure based on modulating femtosecond laser pulse width

Abstract

A method for preparing a super-liquid-repellent hole array structure based on modulated femtosecond laser pulse width, wherein the base material is first pretreated, and then a re-entry concave angle hole array structure is prepared, and finally the super-liquid-repellent re-entry concave angle hole array structure is constructed; while the structure is manufactured by picosecond laser texturing technology, the surface wettability of the composite base material is regulated to achieve the preparation of the super-liquid-repellent re-entry concave angle hole array structure; in addition to the concave angle feature of the hole edge generated by the melt deposition effect, the super-liquid-repellent re-entry concave angle hole array structure also generates a "spiral" groove structure from top to bottom on the inner wall of the hole, indirectly forming a re-entry concave angle feature structure on the inner wall of the hole, and has a primary re-entry concave angle structure feature generated by the melt deposition effect at the hole edge and a secondary "spiral" groove re-entry concave angle structure feature formed by the inner wall of the hole through laser and material impact strengthening; the double re-entry concave angle structure and the presence of air pockets in the hole enable the structure to achieve excellent super-liquid-repellent performance.

Description

Technical Field

[0001] The invention relates to the technical field of super-liquid-repellent micro-nano structure manufacturing, and in particular to a method for preparing a super-liquid-repellent hole array structure based on modulating femtosecond laser pulse width. Background Art

[0002] Surfaces with a static contact angle of more than 150° and a rolling angle of less than 10° are usually called super-hydrophobic surfaces, which have a wide range of applications and prospects due to their extreme wetting properties. In 2007, a scholar innovatively proposed a super-liquid reentry angle structure, which not only has excellent super-hydrophobic properties, but also can repel organic liquids with a surface energy lower than that of water. This structure greatly expands the application range of extreme wettability surfaces, such as self-cleaning, oil droplet transportation, and corrosion resistance. Therefore, it has been extensively studied by scholars. As far as the preparation method is concerned, the current super-liquid repellent surface preparation methods mainly include chemical etching, photolithography, and chemical solution oxidation. However, the above methods often have the disadvantages of complicated processes, chemical pollution, low processing efficiency, and poor control of structural characteristics, which makes wettability very difficult to control, thus limiting the further promotion of super-liquid repellent surfaces.

[0003] In recent years, femtosecond laser processing has emerged. Due to its mask-free, environmentally friendly, extremely small heat-affected zone, and high processing precision, it has been widely used in the preparation of micro-nano structures on non-metallic and metal surfaces, and has strong universality. However, the femtosecond laser beam is usually a Gaussian beam, which has the characteristics of higher energy in the center of the spot and lower energy at the edge. Therefore, the structures usually processed (such as Chinese patent application number CN201810316726.4, named a super-amphiphobic metal surface with three-dimensional distribution of nanostructures and its preparation method; Chinese patent application number CN202110276386.9, named a method for preparing a super-hydrophobic surface based on comprehensive regulation of femtosecond laser and temperature control aging; paper Yuhu Chen, The JOURNAL OF PHYSICALCHEMISTRY C, 2021.) show conical features (conical grooves, cones, conical holes), and after low surface energy treatment, they show excellent super-hydrophobic properties. The conical feature structure usually does not have a re-entry concave angle feature, so it cannot show hydrophobic properties to most liquids with surface energy lower than water. Therefore, how to utilize the processing advantages of femtosecond laser to efficiently and environmentally friendly prepare super-liquid-reentrant concave corner structures with controllable structural characteristics is still a challenging problem. Summary of the invention

[0004] In order to overcome the defects of the above-mentioned prior art, the purpose of the present invention is to provide a method for preparing a super-hydrophobic hole array structure based on modulating the femtosecond laser pulse width. While realizing structure manufacturing through picosecond laser texturing technology, the surface wettability of the composite substrate material is regulated, and finally the preparation of a super-hydrophobic re-entry concave corner hole array structure is realized, which has significant advantages in expanding the application of super-hydrophobic surfaces and improving process convenience and efficiency.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A method for preparing a super-liquid-repellent hole array structure based on modulating femtosecond laser pulse width comprises the following steps:

[0007] 1) Preprocessing:

[0008] 1.1) Select the required base material according to the actual functional application and technical working conditions;

[0009] 1.2) Polishing the substrate material to make the surface smooth and easy to programmatically design and manufacture the functional structure;

[0010] 1.3) Use acetone, anhydrous ethanol, and deionized water in an ultrasonic bath for 15 minutes, and use nitrogen to dry at the same time;

[0011] 2) Preparation of reentry concave hole array structure:

[0012] 2.1) Perform preliminary adjustments to the femtosecond laser micro-nano processing optical system based on the processing and manufacturing requirements, including alignment and correction, adjustment of relevant processing and manufacturing laser parameters, i.e., repetition frequency and single pulse energy; set the pulse width of the femtosecond laser to the picosecond level through the femtosecond laser parameter control panel on the computer;

[0013] 2.2) Design and plan the functional structure processing path trajectory through the integrated control interactive interface of the femtosecond laser micro-nano processing optical system;

[0014] 2.3) Placing the surface of the substrate material to be processed on the processing platform and in the focal plane of the laser beam, and performing programmed texturing processing according to the pre-designed laser parameters and processing planning path;

[0015] 2.4) After the processing is completed, use clean air to clean the remaining ablation residues on the texture surface;

[0016] 2.5) The processed reentrant corner hole array structure was cleaned in acetone, anhydrous ethanol, and deionized water ultrasonic bath for 15 minutes in sequence, and then dried with nitrogen;

[0017] 3) Construction of a super-hydrophobic reentrant concave corner hole array structure: The reentrant concave corner hole array structure prepared by laser in step 2) is placed in a constant temperature drying oven for temperature-controlled aging treatment, thereby utilizing the effect of constant temperature heating to promote the adsorption of hydrophobic organic groups from the air on the texture surface to reduce the surface energy and achieve a super-hydrophobic state.

[0018] The substrate material is metal and its alloy material, including aluminum and its alloy, titanium and its alloy.

[0019] The prepared super-liquid-repellent reentrant concave corner hole array structure monomer exists in the form of micron holes. The edge of the micron hole structure is partially covered by a portion of the molten substrate material, thereby reducing the diameter of the micron hole, and combining with the internal space of the hole to form the reentrant concave corner structure characteristics.

[0020] The prepared super-liquid-repellent re-entry concave corner hole array structures are all located below the initial surface of the substrate. In addition to the re-entry concave corner features generated at the hole edge due to the melt deposition effect, a "spiral" groove structure is generated from top to bottom on the inner wall of the hole due to the impact strengthening effect between the high-energy laser and the substrate material. The "spiral" groove structure has a certain depth, so the re-entry concave corner feature structure on the inner wall of the hole is indirectly formed. Therefore, the prepared super-liquid-repellent re-entry concave corner hole array structure has a double re-entry concave corner feature, that is, the primary re-entry concave corner structure feature generated by the melt deposition effect at the hole edge and the secondary "spiral" groove re-entry concave corner structure feature formed by the laser and material impact strengthening of the inner wall of the hole; the double re-entry concave corner structure and the presence of cavitations in the hole enable the structure to achieve excellent super-liquid-repellent performance.

[0021] The super-lyophobic reentrant concave corner hole array structure is not only hydrophobic, but also liquids with surface tension lower than water, including oils with polyols and aromatic hydrocarbons as main components, whose surface tension is in the range of 30 to 40 mN / m. For oils with alkanes as main components, their surface tension is lower than 30 mN / m, or even lower than 20 mN / m.

[0022] The single pulse energy in step 2.1) is adjusted to 40-50 μj.

[0023] The step 2.3) of planning the path trajectory refers to realizing equidistant dot patterning processing on the surface of the substrate material.

[0024] Compared with the existing technology, the present invention has the following advantages and beneficial effects:

[0025] First, the present invention adopts a laser-prepared super-liquid-reentrant concave-angle hole array structure surface. Laser processing has a series of advantages such as high processing accuracy, no mask, environmental friendliness, and flexible and controllable structural morphology. The subsequent low surface energy treatment is carried out by heating in a temperature-controllable drying oven. Compared with other commonly used methods such as silanization, it does not produce chemical waste that pollutes the environment. At the same time, according to the characteristics of the galvanometer path planning at the rear end of the super-liquid-reentrant concave-angle hole array structure processing, the processing efficiency is improved by 3 to 4 times compared with the conventional path (horizontal and vertical cross-type grid scanning) processing, which is suitable for large-area processing on the substrate surface.

[0026] Secondly, unlike most other convex super-liquid-repellent surface structures such as nanoparticles deposited on a cone and an inverted cone, the super-liquid-repellent reentrant concave angle hole array structure prepared by the present invention is almost all located below the initial surface of the substrate. In addition to the reentrant concave angle feature generated by the molten deposition effect at the edge of the hole, a "spiral" groove structure is generated from top to bottom on the inner wall of the hole due to the impact strengthening effect between the high-energy laser and the material. The "spiral" groove structure has a certain depth, so the reentrant concave angle feature structure on the inner wall of the hole is indirectly formed. Therefore, the super-liquid-repellent reentrant concave angle hole array structure prepared by the present invention has a double concave angle feature, that is, the primary reentrant concave angle structure feature generated by the molten deposition effect at the edge of the hole and the secondary "spiral" groove formed on the inner wall of the hole by laser and material impact strengthening. The groove re-entry concave angle structure features; the double re-entry concave angle structure and the existence of air pockets in the holes enable the structure to achieve excellent super-liquid-repellent performance; at the same time, thanks to the double re-entry concave angle feature, the super-liquid-repellent re-entry concave angle hole array structure of the present invention also has good super-liquid-repellent stability. It is known from the literature that the re-entry concave angle structure itself can increase the energy barrier for the transition of droplets on the textured surface from the Cassie state to the Wenzel state and generate an upward supporting force for the droplets, so the double re-entry concave angle structure can further increase the barrier threshold of the wettability transition. Therefore, the double re-entry concave angle structure can greatly increase the stability of wettability, and even if it is impacted by heavy rain or wind disturbance, it can increase the possibility that the wettability stability will not be destroyed, which is of great significance to the promotion of super-liquid-repellent surfaces. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a schematic diagram of femtosecond laser processing in Example 1 of the present invention.

[0028] Figure 2 This is the processing path of the laser on the surface of the substrate material in Example 1 of the present invention. Each monomer area in the figure is formed by the laser beam directly striking the material surface (not rotary cutting).

[0029] Figure 3Schematic diagram of three-dimensional software modeling of the super-liquid-repellent reentry recessed corner hole array structure prepared in Example 1 of the present invention; wherein a is a top view; b is a cross-sectional view including the features of the primary reentry recessed corner structure and the secondary reentry recessed corner structure; c is an isometric view; d is a local enlarged view; and e is a side view.

[0030] Figure 4 This is an electron microscope image of the super-liquid-reentrant concave corner hole array structure prepared in Example 1 of the present invention, magnified 700 times.

[0031] Figure 5 This is an electron microscope image of the super-liquid-reentrant concave corner hole array structure prepared in Example 1 of the present invention, which is magnified 3.5k times.

[0032] Figure 6 In the figure, a, b, and c are the static contact angles of the super-lyophobic reentrant concave angle hole array structure prepared in Example 1 of the present invention with water, soybean oil, and dodecane, respectively.

[0033] Figure 7 This is an electron microscope image of the super-liquid-reentrant concave corner hole array structure prepared in Example 2 of the present invention, magnified 1k times.

[0034] Figure 8 In the figure, a, b, and c are the static contact angles of the super-lyophobic reentrant concave angle hole array structure prepared in Example 2 of the present invention with water, soybean oil, and dodecane, respectively. DETAILED DESCRIPTION

[0035] The present invention is described in detail below with reference to the embodiments and the accompanying drawings.

[0036] Embodiment 1, a method for preparing a super-liquid-repellent hole array structure based on modulating femtosecond laser pulse width, comprising the following steps:

[0037] 1) Preprocessing:

[0038] 1.1) According to the actual engineering application requirements, the area is selected as 25×25mm 2 , 6061 aluminum alloy with a thickness of 3 mm is used as the base material of the super-liquid-repellent reentrant concave corner hole array structure. 6061 aluminum alloy is widely used in decoration, packaging, construction, transportation, electronics, aviation, aerospace, weapons and other industries;

[0039] 1.2) Polishing the substrate material to make the surface smooth and easy to programmatically design and manufacture the functional structure;

[0040] 1.3) Use acetone, anhydrous ethanol, and deionized water in an ultrasonic bath for 15 minutes, and use nitrogen to dry at the same time;

[0041] 2) Preparation of reentry concave hole array structure:

[0042] 2.1) Perform preliminary adjustments to the femtosecond laser micro-nano processing optical system based on the processing and manufacturing requirements, including alignment and correction, adjustment and design of relevant processing and manufacturing laser parameters (repetition frequency and single pulse energy, etc.); set the pulse width of the femtosecond laser to the picosecond level through the femtosecond laser parameter control panel on the computer;

[0043] like Figure 1 As shown, the femtosecond laser micro-nano processing optical system of this embodiment includes a femtosecond laser 1, a reflector 2, a beam expander 3, a two-axis scanning galvanometer 4, a processing platform 5 for placing a substrate material, and an integrated control system 6; the Gaussian beam with a wavelength of 1030nm and an adjustable pulse width (the default is 240fs) output by the femtosecond laser 1 sequentially passes through the reflector 2, the beam expander 3 and the two-axis scanning galvanometer 4 and is focused on the surface of the substrate material to be processed on the processing platform 5; the optical path components are adjusted to obtain a spot beam quality suitable for processing, and at the same time, the plane where the laser beam focus is located is found by using the step-by-step scribing method, and the spot focus diameter focused on the surface of the substrate material to be processed on the processing platform is about 30 microns;

[0044] In this embodiment, the femtosecond laser is first set to output Gaussian light with a wavelength of 1030nm, and then the repetition frequency is 100kHz, the single pulse energy is 50μJ, and the pulse width is tuned from 240fs to 6ps;

[0045] 2.2) Design and plan the functional structure processing path trajectory through the integrated control interactive interface of the femtosecond laser micro-nano processing optical system;

[0046] 2.3) The surface of the substrate material to be processed is placed on the processing platform and is located on the focal plane of the laser beam emitted from the field lens, and programmed texturing processing is performed according to the pre-designed laser parameters and processing planning path;

[0047] In this example, the Figure 2 The dot structure with a pitch of 35μm shown needs to be processed by laser direct punching, and the action point between the laser and the surface of the substrate material needs to have a certain extension time. According to the experimental exploration rules, it is set to 3.6ms, the number of processing repetitions is 1, and the processing order is "bow"-shaped line-by-line scanning;

[0048] 2.4) After the processing is completed, use clean air to clean the remaining ablation residues on the texture surface for further cleaning work;

[0049] 2.5) The processed reentrant concave hole array structure is cleaned in acetone, anhydrous ethanol, and deionized water ultrasonic bath for 15 minutes in sequence, and then dried with nitrogen to lay the foundation for subsequent processes;

[0050] 3) Construction of super-hydrophobic reentrant concave corner hole array structure: placing the reentrant concave corner hole array structure prepared by laser in step 2) in a constant temperature drying oven for temperature controlled aging treatment, thereby utilizing the effect of constant temperature heating to promote the adsorption of hydrophobic organic groups from the air on the texture surface to reduce the surface energy and achieve a super-hydrophobic state;

[0051] In this embodiment, the substrate is heated at 150° C. for 3.5 hours in a forced air drying oven. The heating promotes the adsorption of hydrophobic organic functional groups in the air on the surface of the reentrant corner hole array structure of the substrate material, so that its wettability is changed from superhydrophilic to superlyophobic.

[0052] The beneficial effects of this embodiment are as follows: firstly, a relatively uniformly distributed double reentry concave hole array structure can be prepared by using a femtosecond laser micro-nano processing optical system, such as Figure 3 , Figure 4 , Figure 5 As shown in the figure, the entrance diameter of the hole is about 25 microns, which is compared with the laser focus spot diameter of 30 microns, indicating that the entrance diameter of the hole is reduced to a certain extent, that is, a primary reentry concave angle structure is generated. When observing the inner wall of the hole, it is found that there is a "spiral" groove reentry concave angle structure, that is, a secondary reentry concave angle structure. Therefore, the femtosecond laser after tuning the pulse width interacts with the surface of the 6061 aluminum alloy to complete the physical structure mechanism transformation of the super-liquid-repellent extreme wettability surface; by characterizing the wettability of the reentry concave angle structure modified by temperature control and aging, it is found that the contact angles for water, soybean oil, and dodecane are 166°, 159°, and 156°, respectively. Figure 6 As shown, it has excellent super-lyophobic properties (the surface tension of dodecane is 25.5 mN / m at room temperature and pressure, so the static contact angle for liquids with surface tension higher than that of dodecane can also reach a super-lyophobic state).

[0053] Example 2: The substrate material in step 1.1) of Example 1 is replaced with copper, the single pulse energy in step 2.1) is adjusted to 40 μj, the extension time in step 2.3) is set to 3.3 ms, and the other steps remain unchanged. The structure morphology prepared is as follows: Figure 7 As shown, it can be seen that there are primary and secondary reentry concave structures similar to Example 1; the wettability is characterized by Figure 8 As shown, it can be seen that the static contact angles for water, soybean oil and dodecane are 165°, 155° and 154° respectively.

[0054] Example 3, the material in step 1.1) of Example 1 is replaced with titanium metal, the single pulse energy in step 2.1) is set to 45 μj, the extension time in step 2.3) is set to 3.5 ms, the temperature in step 3) is set to 200°C, and the other steps remain unchanged, so as to achieve similar beneficial effects as in Examples 1 and 2.

Claims

1. A method for preparing a super-lyophobic hole array structure based on modulating femtosecond laser pulse width, characterized in that: The following steps are involved: 1) Preprocessing: 1.1) Select the required base material according to the actual functional application and technical working conditions; 1.2) Polishing the substrate material to make the surface smooth and easy to programmatically design and manufacture the functional structure; 1.3) Use acetone, anhydrous ethanol, and deionized water in an ultrasonic bath for 15 min in sequence, and use nitrogen to dry at the same time; 2) Preparation of reentry concave hole array structure: 2.1) Perform preliminary adjustments to the femtosecond laser micro-nano processing optical system based on the processing and manufacturing requirements, including alignment and correction, adjustment of relevant processing and manufacturing laser parameters, i.e., repetition frequency and single pulse energy; set the pulse width of the femtosecond laser to the picosecond level through the femtosecond laser parameter control panel on the computer; 2.2) Design and plan the functional structure machining path trajectory through the integrated control interactive interface of the femtosecond laser micro-nano machining optical system; 2.3) Place the surface of the substrate material to be processed on the processing platform and in the focal plane of the laser beam, and perform programmed texturing processing according to the pre-designed laser parameters and processing planning path; 2.4) After processing is completed, use clean air to clean the remaining ablation residues on the texture surface; 2.5) The processed reentrant corner hole array structure was cleaned in acetone, anhydrous ethanol, and deionized water ultrasonic bath for 15 minutes in sequence, and then dried with nitrogen; 3) Construction of super-hydrophobic reentrant concave corner hole array structure: The reentrant concave corner hole array structure prepared by laser in step 2) is placed in a constant temperature drying oven for temperature-controlled aging treatment, thereby utilizing the effect of constant temperature heating to promote the adsorption of hydrophobic organic groups from the air on the texture surface to reduce the surface energy and achieve a super-hydrophobic state; The prepared super-liquid-repellent reentrant concave angle hole array structure monomer exists in the form of micron holes, and the edge of the micron hole structure is partially covered by a portion of the molten substrate material, thereby reducing the diameter of the micron hole, and combining with the internal space of the hole to form the reentrant concave angle structure characteristics; The prepared super-liquid-repellent re-entry concave angle hole array structures are all located below the initial surface of the substrate. In addition to the concave angle characteristics of the hole edge generated by the melt deposition effect, a "spiral" groove structure is generated from top to bottom on the inner wall of the hole due to the impact strengthening effect between the high-energy laser and the substrate material. The "spiral" groove structure has a certain depth, which indirectly forms a re-entry concave angle characteristic structure on the inner wall of the hole. Therefore, the prepared super-liquid-repellent re-entry concave angle hole array structure has a double re-entry concave angle characteristic, that is, the primary re-entry concave angle structure characteristic generated by the melt deposition effect at the hole edge and the secondary "spiral" groove re-entry concave angle structure characteristic formed by the laser and material impact strengthening of the inner wall of the hole; the double re-entry concave angle structure and the existence of air pockets in the hole enable the structure to achieve excellent super-liquid-repellent performance.

2. The method according to claim 1, characterized in that: The substrate material is metal and its alloy material, including aluminum and its alloy, titanium and its alloy.

3. The method according to claim 1, characterized in that: The super-lyophobic reentry concave angle hole array structure is super-lyophobic not only to water, but also to liquids with lower surface tension than water, including oils with polyols and aromatic hydrocarbons as main components.

4. The method according to claim 1, characterized in that: The single pulse energy in step 2.1) was adjusted to 40-50 μJ.

5. The method according to claim 1, characterized in that: The step 2.3) of planning the path trajectory refers to realizing equidistant dot patterning processing on the surface of the substrate material.

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