A method for laser preparation of superhydrophobic fractal microstructures

Abstract

The present invention belongs to the technical field of the preparation of fractal micro-textures, and specifically discloses a method for laser preparation of superhydrophobic fractal micro-textures. First, a Peano fractal micro-texture with a certain length and a certain spacing is generated through Matlab programming. After several iterations, a Peano fractal micro-texture pattern is obtained. Secondly, the surface of a metal or an alloy is pretreated. Then, a Peano fractal micro-texture is prepared on the surface by using laser processing technology. Finally, the surface of the Peano fractal micro-texture is modified with low surface energy by using perfluorodecyltriethoxysilane, and finally a superhydrophobic metal or alloy surface is obtained. The Peano fractal micro-texture pattern provided by the present invention has the characteristics of equal length, equal spacing, uniform distribution, and high controllability. The contact angle of the fractal micro-texture surface reaches more than 150°, and it has good superhydrophobic performance and can be used in the fields of solar energy, construction engineering, biomedicine, etc.

Description

Technical Field

[0001] The present invention relates to the field of laser processing on the surface of metals or alloys, and particularly to a method for laser preparation of superhydrophobic fractal microstructures. Background Art

[0002] In marine equipment, aircraft and aerospace, aluminum alloys are widely used due to their excellent properties such as low density and good corrosion resistance, such as ship equipment, aircraft hulls, etc.; in the field of biomedicine, titanium alloys have good biocompatibility, excellent corrosion resistance and fatigue resistance, and are often used to make various internal fixation devices for fractures, artificial joints, artificial heart valves, etc. However, the surface of metals or alloys has good wettability by itself and is extremely prone to corrosion failure in a humid environment, seriously affecting the structural strength and various properties of the material and reducing its service life.

[0003] In order to improve the service performance of the surface of high-end equipment, a laser technique can be used to prepare a superhydrophobic microstructure on the surface of metals or alloys to improve their surface corrosion resistance. Superhydrophobic generally refers to a surface with a contact angle greater than 150° and a rolling angle less than 10°. When a material has superhydrophobic characteristics, the liquid is more likely to roll off the surface, reducing the contact time between the surface and the liquid, so that the material surface has a certain corrosion resistance. Laser processing has the advantages of a wide processing range, high processing accuracy, simple processing, stability, etc., and can process any pattern structure with high precision. Therefore, the laser technique is selected for microtexture processing.

[0004] Nowadays, the patterns of traditional microtexture processing are mostly cylinders and square columns, which are first-order microtextures and can achieve superhydrophobicity, but the hydrophobic ability is small, while multi-order microtextures have better hydrophobicity. Summary of the Invention

[0005] To solve the problems of small hydrophobicity and low service life of traditional hydrophobic microtextures, the present invention provides a method for laser preparation of superhydrophobic fractal microstructures. By programming in Matlab to generate Peano fractal microstructures, using the laser technique to prepare the fractal microstructures on the surface of metals or alloys, and using perfluorodecyltriethoxysilane for low surface energy modification to obtain a superhydrophobic metal or alloy fractal microstructure surface, so that its surface has good corrosion resistance and anti-fouling self-cleaning performance.

[0006] The technical solution adopted by the present invention to solve its technical problems is as follows:

[0007] A method for laser preparation of superhydrophobic fractal microstructures specifically includes the following steps:

[0008] (1) Generate Peano fractal microstructures with a certain length and a certain spacing through Matlab programming. After several iterations, obtain a Peano fractal microstructure pattern. The formation process of the Peano fractal microstructures is as follows:

[0009] S1. Define 4 empty matrices to store the initial elements of the Peano fractal, namely A = [], B = [], C = [], D = [];

[0010] S2. Define 4 direction line segments of unit length, namely north = [0 a], east = [a 0], south = [0 -a], west = [-a 0], where a is the side length of the Peano fractal microtexture;

[0011] S3. Define 4 initial Peano elements, namely

[0012] AA = [ B; north ; A ; east ; A ; south ; C];

[0013] BB = [A ; east ; B ; north ; B ; west ; D];

[0014] CC = [D ; west ; C ; south ; C ; east ; A];

[0015] DD = [C ; south ; D ; west ; D ; north ; B];

[0016] S4. Assign the 4 initial elements to the corresponding matrices, i.e.,

[0017] A = AA; B = BB; C = CC; D = DD;

[0018] S5. Repeat the operations of S3 and S4, define it as an iteration step, and perform multiple iterations;

[0019] S6. After the iteration is completed, output the Peano fractal pattern;

[0020] (2) Pre-treat the metal or alloy specimen, that is, embed the metal or alloy specimen in a metallographic silica gel soft mold with epoxy resin CM4, and then successively polish it with sandpapers of different mesh numbers, polish it with a polishing agent, and clean it for standby;

[0021] (3) Place the pre-treated metal or alloy specimen on the laser scanning platform, adjust the relative distance between the processing surface and the laser lens so that the processing surface is at the focus of the laser; adjust the laser processing parameters, import the Peano fractal microtexture pattern into the laser marking machine for processing, and then perform ultrasonic cleaning and drying treatment with absolute ethanol;

[0022] (4) Immerse the prepared peano fractal micro-textured surface in an ethanol solution of 1H,1H,2H,2H-perfluorodecyltriethoxysilane for modification, and then dry it at 50 °C to obtain a superhydrophobic fractal micro-texture on the metal or alloy surface.

[0023] Further, the present invention also defines the dimensions of the peano fractal micro-texture in step (1): its side length is 50 μm to 200 μm, the number of iterations is 6 to 8 times, and the depth is 10 μm to 40 μm.

[0024] Further, the present invention also defines the process of pre-treating the metal or alloy specimen in step (2) as follows:

[0025] S1. Cut the metal or alloy specimen into samples of 15 mm × 15 mm × 3 mm in size, place them in a metallographic silica gel soft mold with an inner diameter of 30 mm, and embed them with epoxy resin CM4 until solidification;

[0026] S2. Polish the embedded samples successively with sandpapers of 180 mesh, 400 mesh, 800 mesh, 1200 mesh, 1500 mesh, 2000 mesh, and 4000 mesh, then polish them with diamond spray polishing agents with particle sizes of 3.5 μm, 2.5 μm, 1.5 μm, and 0.5 μm respectively. Finally, clean them with an ultrasonic cleaner using acetone, absolute ethanol, and deionized water, and dry them with a hair dryer.

[0027] Further, the present invention also defines the laser processing parameters in step (3): the relative distance between the processing surface and the laser lens is 176 mm, the laser power is 5 W to 8 W, the laser frequency is 20 kHz to 40 kHz, the scanning speed is 300 mm / s to 1000 mm / s, the laser pulse width is 100 ns, and the wavelength is 1064 nm.

[0028] Further, the present invention also defines that the volume ratio of 1H,1H,2H,2H-perfluorodecyltriethoxysilane to ethanol in the ethanol solution of 1H,1H,2H,2H-perfluorodecyltriethoxysilane in step (4) is 1:100.

[0029] Further, the present invention also defines that the immersion time for modification in step (4) is 15 - 20 min, preferably 20 min.

[0030] The beneficial effects of the present invention are as follows: The present invention prepares a peano fractal micro-texture on the metal or alloy surface by laser, and uses 1H,1H,2H,2H-perfluorodecyltriethoxysilane for low surface energy modification to obtain a superhydrophobic surface. The peano fractal micro-texture pattern has the characteristics of equal length, equal spacing, uniform distribution, and high controllability, and the surface contact angle reaches more than 150°. The surface has excellent corrosion resistance and anti-fouling self-cleaning performance. Description of the Drawings

[0031] Figure 1 It is a schematic diagram of the size of the Peano fractal micro-texture in Embodiment 1 of the present invention;

[0032] Figure 2 It is the Peano fractal micro-texture pattern in Embodiment 1 of the present invention;

[0033] Figure 3 It is a specimen of the Peano fractal micro-texture processed by laser in Embodiment 1 of the present invention;

[0034] Figure 4 It is a three-dimensional topography map with a 20-fold magnification of the surface of the Peano micro-texture in Embodiment 1;

[0035] Figure 5 It is the pattern of the cylindrical fractal processed micro-texture of the present invention;

[0036] Figure 6 It is the pattern of the square-column fractal processed micro-texture of the present invention;

[0037] Figure 7 It is a schematic diagram for measuring the contact angle of the surface of the Peano fractal micro-texture with a side length of 50 μm in Embodiment 2;

[0038] Figure 8 It is a schematic diagram for measuring the contact angle of the surface of the Peano fractal micro-texture with a side length of 100 μm in Embodiment 1;

[0039] Figure 9 It is a schematic diagram for measuring the contact angle of the surface of the Peano fractal micro-texture with a side length of 150 μm in Embodiment 3;

[0040] Figure 10 It is a schematic diagram for measuring the contact angle of the surface of the Peano fractal micro-texture with a side length of 200 μm in Embodiment 4;

[0041] Figure 11 It is a schematic diagram for measuring the contact angle of the surface of the Peano fractal micro-texture with a side length of 250 μm in Embodiment 5;

[0042] Figure 12 It is a schematic diagram for measuring the contact angle of the cylindrical micro-texture surface;

[0043] Figure 13 It is a schematic diagram for measuring the contact angle of the square-column micro-texture surface. Embodiments

[0044] The present invention will be further described below in conjunction with the drawings of the specification, but the protection scope of the present invention is not limited thereto:

[0045] Example 1 A method for laser preparation of superhydrophobic Peano fractal microstructures, comprising the following steps:

[0046] (1) Design of Peano fractal microstructures

[0047] Generate Peano fractals through Matlab programming, design the side length of the microstructures to be 100 μm, and iterate 7 times; the specific steps are as follows:

[0048] S1. Define 4 empty matrices to store the initial elements of the Peano fractal, namely A = [], B = [], C = [], D = [];

[0049] S2. Define the lengths of 4 direction line segments as the side length of the microstructures, with a length of 0.1 mm, that is, the side length is 100 μm, namely north = [0 0.1], east = [0.1 0], south = [0 -0.1], west = [-0.1 0];

[0050] S3. Define 4 Peano initial elements, respectively

[0051] AA = [ B; north ; A ; east ; A ; south ; C];

[0052] BB = [A ; east ; B ; north ; B ; west ; D];

[0053] CC = [D ; west ; C ; south ; C ; east ; A];

[0054] DD = [C ; south ; D ; west ; D ; north ; B];

[0055] S4. Assign the 4 initial elements to the corresponding matrices, that is

[0056] A = AA; B = BB; C = CC; D = DD;

[0057] S5. Repeat the operations of S3 and S4, define it as an iteration step, and perform 7 iterations;

[0058] S6. After the iteration is completed, output the Peano fractal pattern. The schematic diagram of the processed microstructure size is as Figure 1 shown, and the processed microstructure pattern is as Figure 2 shown;

[0059] (2) Pretreatment of pure aluminum specimens

[0060] S1. Cut the pure aluminum sheet into samples of 15 mm×15 mm×3 mm with an HT400 wire electrical discharge machine, and then place the samples in a metallographic silica gel soft mold with an inner diameter of 30 mm and embed them with epoxy resin CM4. Wait for it to solidify (4 hours).

[0061] S2. Polish the embedded samples with sandpapers of 180 mesh, 400 mesh, 800 mesh, 1200 mesh, 1500 mesh, 2000 mesh, and 4000 mesh respectively, and then polish them with diamond spray polishing agents with particle sizes of 3.5 μm, 2.5 μm, 1.5 μm, and 0.5 μm respectively. Clean them with an ultrasonic cleaner using acetone, absolute ethanol, and deionized water, and dry them with a hair dryer.

[0062] (3) Laser preparation of Peano fractal micro-texture

[0063] Place the cleaned sample in step (2) on the laser scanning platform, adjust the relative distance between the processing surface and the laser lens to 176 mm, and make the processing surface at the focus of the laser; adjust the laser processing parameters: laser power is 6 W, laser frequency is 20 KHz, scanning speed is 500 mm / s, pulse width is 100 ns, wavelength is 1064 nm, import the Peano fractal into the Heshen laser marking machine HSG-1A20W for processing. The processed sample is as Figure 3 shown, and its three-dimensional morphology is as Figure 4 shown;

[0064] (4) Fluorosilane modification

[0065] Use 1H,1H,2H,2H-perfluorodecyltriethoxysilane as the low surface energy modification material, and configure a fluorosilane ethanol solution. Among them, the volume ratio of fluorosilane to ethanol is 1:100. Immerse the surface of the sample obtained in step (3) in the fluorosilane ethanol solution for 20 min to modify the surface, and then dry it at a temperature of 50 °C to obtain a Peano micro-textured superhydrophobic pure aluminum surface. Example 2

[0066] In this example, in step (1), design a Peano fractal micro-texture with a side length of 50 μm; step S2 is specifically: define the lengths of the line segments in 4 directions as the side length of the micro-texture, with a length of 0.05 mm, that is, the side length is 50 μm, which are north = [0 0.05], east = [0.05 0], south = [0 -0.05], west = [-0.05 0]; other steps are the same as in Example 1 to obtain a Peano micro-textured superhydrophobic pure aluminum surface with a side length of 50 μm. Example 3

[0067] In this embodiment, step S2 of the design of the Peano fractal micro-texture with a side length of 150 μm in step (1) is specifically as follows: Define the lengths of the line segments in 4 directions as the side lengths of the micro-texture, with a length of 0.15 mm, that is, the side length is 150 μm, which are north = [0 0.15], east = [0.15 0], south = [0 -0.15], west = [-0.15 0]; other steps are the same as those in Embodiment 1 to obtain a superhydrophobic pure aluminum surface with a Peano micro-texture with a side length of 150 μm. Embodiment 4

[0068] In this embodiment, step S2 of the design of the Peano fractal micro-texture with a side length of 200 μm in step (1) is specifically as follows: Define the lengths of the line segments in 4 directions as the side lengths of the micro-texture, with a length of 0.20 mm, that is, the side length is 200 μm, which are north = [0 0.2], east = [0.2 0], south = [0 -0.2], west = [-0.2 0]; other steps are the same as those in Embodiment 1 to obtain a superhydrophobic pure aluminum surface with a Peano micro-texture with a side length of 200 μm. Embodiment 5

[0069] In this embodiment, step S2 of the design of the Peano fractal micro-texture with a side length of 250 μm in step (1) is specifically as follows: Define the lengths of the line segments in 4 directions as the side lengths of the micro-texture, with a length of 0.25 mm, that is, the side length is 250 μm, which are north = [0 0.25], east = [0.25 0], south = [0 -0.25], west = [-0.25 0]; other steps are the same as those in Embodiment 1 to obtain a superhydrophobic pure aluminum surface with a Peano micro-texture with a side length of 250 μm.

[0070] Comparative Example 1 Laser preparation method for superhydrophobic cylindrical micro-textures

[0071] Step S1 of the processing in step (1) is specifically as follows: Design the diameter of the cylinder to be 100 μm and the spacing to be 100 μm, and process the micro-texture pattern as Figure 5 shown; other steps are the same as those in Embodiment 1 to obtain a pure aluminum surface with cylindrical micro-textures.

[0072] Comparative Example 1 Laser preparation method for superhydrophobic square-column micro-textures

[0073] Step S1 of the processing in step (1) is specifically as follows: Design the side length of the square column to be 100 μm and the spacing to be 100 μm, and process the micro-texture pattern as Figure 6 shown to obtain a pure aluminum surface with square-column micro-textures.

[0074] The superhydrophobic pure aluminum surfaces with Peano microtextures having side lengths of 50 μm, 100 μm, 150 μm, 200 μm, and 250 μm obtained in the present invention were subjected to contact angle measurements with the pure aluminum surfaces with cylindrical microtextures and the pure aluminum surfaces with square column microtextures. Specifically: A DSA30S contact angle tensiometer (manufactured by Kruss GmbH, Germany) was used to measure the contact angles of the pure aluminum surfaces with different microtextures after processing. The volume of the test droplet was 4 μL. The measurement method was the sessile drop method, and the fitting method was the Young-Laplace method. The contact angle measurement experiment was repeated three times and the average value was taken. Figures 7 - 11 Shown are the pure aluminum surfaces with Peano fractal microtextures having side lengths of 50 μm, 100 μm, 150 μm, 200 μm, and 250 μm. Figures 12 - 13 Shown are the contact angle measurement values of the pure aluminum surfaces with cylindrical microtextures and the pure aluminum surfaces with square column microtextures. As Figures 7 - 11 can be seen, the contact angles of the pure aluminum surfaces with Peano fractal microtextures having side lengths of 50 μm, 100 μm, 150 μm, 200 μm, and 250 μm are 154.2°, 162.7°, 158.5°, 153.2°, and 144.0° respectively. It can be seen that the pure aluminum surface with a Peano fractal microtexture having a side length of 100 μm has better hydrophobic performance.

[0075] The pure aluminum surface with a Peano fractal microtexture having a side length of 100 μm was compared with the pure aluminum surface with a cylindrical microtexture and the pure aluminum surface with a square column microtexture. As Figures 12 - 13 shown, the contact angle of the pure aluminum surface with a cylindrical microtexture is 159.7°, and the contact angle of the pure aluminum surface with a square column microtexture is 158.1°. The contact angle of the pure aluminum surface with a Peano fractal microtexture having a side length of 100 μm is 162.7°. Compared with the pure aluminum surface with a cylindrical microtexture, it has increased by 2.8°, and compared with the pure aluminum surface with a square column microtexture, it has increased by 4.6°. It can be seen that the Peano fractal microtexture has better hydrophobic performance.

[0076] The embodiments are only for illustrating the technical idea of the present invention and cannot be used to limit the protection scope of the present invention. Any modification made on the basis of the technical solution according to the technical idea proposed by the present invention falls within the protection scope of the present invention.

Claims

1. A method for laser preparation of superhydrophobic fractal microstructures, characterized in that It includes the following steps: (1) Generate Peano fractal micro-textures with a certain length and spacing through Matlab programming. After several iterations, obtain the Peano fractal micro-texture pattern. The formation process of the Peano fractal micro-texture is as follows: S1. Define 4 empty matrices to store the initial elements of the Peano fractal, namely A = [], B = [], C = [], D = []; S2. Define 4 direction line segments with a unit length, namely north = [0 a], east = [a 0], south = [0 -a], west = [-a 0], where a is the side length of the Peano fractal micro-texture; S3. Define 4 Peano initial elements, which are respectively AA = [ B; north ; A ; east ; A ; south ; C]; BB = [A ; east ; B ; north ; B ; west ; D]; CC = [D ; west ; C ; south ; C ; east ; A]; DD = [C ; south ; D ; west ; D ; north ; B]; S4. Assign the 4 initial elements to the corresponding matrices, that is A = AA; B = BB; C = CC; D = DD; S5. Repeat the operations of S3 and S4, define it as an iteration step, and perform multiple iterations; S6. After the iteration is completed, output the Peano fractal pattern; (2) Pre-treat the metal or alloy sample, that is, embed the metal or alloy sample in a metallographic silica gel soft mold with epoxy resin CM4, and then successively polish it with sandpapers of different meshes, polish it with a polishing agent, and clean it for standby; (3) Place the pre-treated metal or alloy sample on the laser scanning platform, adjust the relative distance between the processing surface and the laser lens so that the processing surface is at the focus of the laser; adjust the laser processing parameters, import the Peano fractal micro-texture pattern into the laser marking machine for processing, and then perform ultrasonic cleaning and drying treatment with anhydrous ethanol; (4) Immerse the prepared Peano fractal micro-texture surface in a 1H,1H,2H,2H-perfluorodecyltriethoxysilane ethanol solution for modification treatment, and then dry it at 50 °C to obtain a superhydrophobic fractal micro-texture on the metal or alloy surface; The size of the Peano fractal micro-texture in step (1): its side length is 100 μm to 150 μm, the number of iterations is 6 to 8 times, and the depth is 10 μm to 40 μm; The laser processing parameters in step (3): the relative distance between the processing surface and the laser lens is 176 mm, the laser power is 5 W to 8 W, the laser frequency is 20 kHz to 40 kHz, the scanning speed is 300 mm / s to 1000 mm / s, the laser pulse width is 100 ns, and the wavelength is 1064 nm.

2. The method for laser preparation of a super-hydrophobic fractal microstructure according to claim 1, wherein The size of the Peano fractal micro-texture in step (1): its side length is 100 μm.

3. A method for laser preparation of a superhydrophobic fractal microstructure according to claim 1, characterized in that The process of pre-treating the metal or alloy sample in step (2) is as follows: S1. Cut a metal or alloy specimen into a sample with a size of 15 mm × 15 mm × 3 mm, place it in a metallographic silica gel soft mold with an inner diameter of 30 mm, and embed it with epoxy resin CM4 until solidified; S2. Polish the embedded sample successively with 180-mesh, 400-mesh, 800-mesh, 1200-mesh, 1500-mesh, 2000-mesh, and 4000-mesh sandpapers, then polish it with diamond spray polishing agents with particle sizes of 3.5 μm, 2.5 μm, 1.5 μm, and 0.5 μm respectively. Finally, clean it with an ultrasonic cleaner using acetone, absolute ethanol, and deionized water, and dry it with a hair dryer.

4. A method for laser preparation of a superhydrophobic fractal microstructure according to claim 1, characterized in that In step (4), the feeding volume ratio of 1H,1H,2H,2H-perfluorodecyltriethoxysilane to ethanol in the 1H,1H,2H,2H-perfluorodecyltriethoxysilane ethanol solution is 1:

100.

5. A method for laser preparation of a super-hydrophobic fractal microstructure according to claim 1, characterized in that In step (4), the immersion time for the modification treatment is 15 - 20 min.

6. A method for laser preparation of a superhydrophobic fractal microstructure according to claim 1, characterized in that In step (4), the immersion time for the modification treatment is 20 min.

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