One-step method for the preparation of durable, repairable superhydrophobic surfaces

Abstract

The application discloses a method for preparing a durable and repairable super-hydrophobic surface in one step, which comprises the following steps: (1) after polishing a metal material, a femtosecond laser beam is used to burn the metal base material in an air environment, laser ablation is performed to remove, and a lotus leaf-like surface papilla structure is obtained on the metal surface; (2) on the periodic papilla structure spacing, a wall structure higher than the base material itself is constructed by using a laser melting accumulation method, and a rectangular wall structure is formed by controlling a laser path to guide the accumulation; (3) after the multilayer microstructure treated in steps (1) and (2) is modified by a low surface energy, a multilayer super-hydrophobic surface with durability and repairability is obtained. The multilayer super-hydrophobic surface is prepared by combining the methods of laser ablation and laser melting accumulation, and still has high super-hydrophobicity after friction. After failure, the super-hydrophobic phenomenon is still maintained after repair by modification of a low surface energy substance.

Description

Technical Field

[0001] This invention belongs to the field of superhydrophobic surface processing and laser processing technology, and specifically relates to a one-step method for preparing a durable and repairable superhydrophobic surface. Background Technology

[0002] Application-oriented superhydrophobic surfaces not only need excellent liquid repellency but also good stability, including mechanical stability such as wear resistance and impact resistance, as well as chemical and thermal durability. Among these, mechanical stability should be the primary consideration. In practical applications, the surface faces potential friction and wear risks during transportation and installation, as well as the impact of sand and gravel that may be encountered during use, all of which test the surface's wear resistance.

[0003] Currently, many scholars and research groups have conducted related work to obtain stable and durable superhydrophobic surfaces. For example, Qian et al. prepared a superhydrophobic coating on a magnesium alloy surface by high-temperature spraying of a mixture containing micron- and nano-sized FAS-modified silica particles. After coating, the sample was further treated at 100°C for 1 hour, and the contact angle of the coated magnesium alloy was 159°, showing good corrosion resistance. However, the mechanical stability of thin coatings is easily affected. She et al. successfully prepared a robust and stable superhydrophobic surface with a pinecone-like layered structure on AZ91D magnesium alloy by electrodepositing nickel, and the resulting surface had a CA as high as 163.3±0.7°. However, the deposited nickel element has certain toxicity, and it is especially unsuitable for use in superhydrophobic surfaces of medical alloys. Zhang created a superhydrophobic aluminum alloy with a 155° contact angle by etching an aluminum alloy to form a rough surface with protrusions and pits, and then spraying an alcohol solution composed of hydrophobic silica NPs and methyl silicate precursors. While the rough surface created by the protrusions and pits of the substrate can protect nanoparticles from damage, the process is complex, and the precision of etching the protrusions and pits is uncontrollable. Furthermore, the destruction of the superhydrophobic structure through these methods is accompanied by changes in the micro / nano structure, making it difficult to restore the superhydrophobic state after further modification.

[0004] Therefore, how to quickly and easily prepare durable, repairable, and pollution-free superhydrophobic surfaces is a problem that needs to be solved. Summary of the Invention

[0005] To overcome the above technical problems, the present invention aims to provide a one-step method for preparing a durable and repairable superhydrophobic surface. This method constructs a multi-layer superhydrophobic structure by adjusting the scanning speed and scanning power in the femtosecond laser preparation parameters and using a top-down laser ablation and bottom-up molten material deposition method.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A one-step method for preparing a durable and repairable superhydrophobic surface includes the following steps;

[0008] Step 1: After grinding and polishing the metal material, the metal substrate is burned in the air with a femtosecond laser beam. After laser ablation, a lotus leaf-like surface papillary structure is obtained on the metal surface.

[0009] By controlling the laser path, periodic lotus leaf-like surface papillae structures were obtained. Specifically, the structures are micron-scale conical structures and nanoscale structures on the surface of micron-scale conical structures. The bottom of the conical structure is 10 to 15 μm in size, and the top size is 2 to 3 μm in size.

[0010] Step 2: On the nipple structure spacing of the lotus leaf-like surface, a wall structure higher than the substrate itself is constructed by laser melting deposition. The laser path is controlled to guide the deposition to form a rectangular wall structure with a width of 30 to 40 μm and a height of 10 to 15 μm. At the same time, the surface is accompanied by nanoscale structures; thus, a multi-layered microstructure is obtained.

[0011] The metal material in step 1 is AZ31B magnesium alloy, but it also includes aluminum alloy, stainless steel or titanium alloy.

[0012] In step 1, the burning path of the lotus leaf-like surface papillae structure is an array-like grid structure, and its processing method includes the following steps:

[0013] 1) Perform periodic ablation removal along the X direction, with a distance of 15 μm between the two laser beams, and each cycle consists of 63 paths, with a distance of 40 μm between each cycle.

[0014] 2) After processing in step 1), perform periodic ablation removal along the Y direction. The distance between the two beams is 15um, and each cycle consists of 63 paths. The distance between each cycle is 40um. This completes the processing of the lotus leaf-like surface papilla structure.

[0015] The wall structure fusion deposition path in step 2 is a perimeter wall structure, and its processing method includes the following steps:

[0016] 1) Melting and stacking occurs along the X direction in the middle of the periodic interval, and the stacking path is the periodic interval;

[0017] 2) After the processing in step 1), melt deposition is carried out in the middle of the periodic interval along the Y direction; at this point, the wall structure is completed; the surface of the overall multi-layer superhydrophobic structure is completed.

[0018] The femtosecond laser pulse width for step 1, which forms the papillary structure on the surface of a lotus leaf, is 223 fs, with a repetition frequency of 60 kHz, a wavelength of 1030 nm, a lens focal length of 17 mm, a scanning speed of 100-300 mm / s, and a power of 1 W. The process is repeated twice to fabricate the structure.

[0019] The femtosecond laser used in step 2 for the wall structure has a pulse width of 223 fs, a repetition frequency of 60 kHz, a wavelength of 1030 nm, a lens focal length of 17 mm, a scanning speed of 10-20 mm / s, and a power of 5 W.

[0020] After the multilayer microstructure obtained through steps 1 and 2 is modified with low surface energy, a superhydrophobic surface with durability and repairability is obtained.

[0021] The specific steps for low surface energy modification are as follows: after laser processing, the sample is placed in anhydrous ethanol solution for ultrasonic cleaning, and then immersed in 0.5 mol / L stearic acid ethanol low surface energy solution for 30 minutes. After immersion, the sample is taken out and dried with hot air.

[0022] In the above method, the laser processing paths for the lotus leaf-like surface papillae structure and the wall structure are obtained through computer programming to prepare a multi-layered microstructure in one step. The wall structure is a rectangular structure with a spacing of 1 cm.

[0023] The beneficial effects of the present invention.

[0024] (1) This invention constructs a multilayer superhydrophobic structure by adjusting the scanning speed and scanning power in the femtosecond laser preparation parameters, using a top-down laser ablation and bottom-up molten material deposition method. The laser-guided deposition of the wall structure can effectively protect the internal lotus leaf-like surface papillary structure from damage, thereby achieving the purpose of durability.

[0025] (2) The multilayer superhydrophobic structure of the present invention can repair the superhydrophobic surface to a certain extent after wear through the repair of low surface energy.

[0026] (3) The process of this invention is simple. It is based on femtosecond laser one-step processing without introducing other substances. It has the characteristics of fast processing speed, environmental protection and no pollution, and is especially suitable for medical metal surfaces. Attached image description:

[0027] Figure 1 This is a schematic diagram of the processing flow of the multilayer superhydrophobic structure of the present invention.

[0028] Figure 2 This is a scanning electron microscope image of the multilayer superhydrophobic structure of the present invention.

[0029] Figure 3 This is a surface morphology diagram of the multilayer superhydrophobic structure of the present invention.

[0030] Figure 4 This is a measurement diagram of the contact angle of the multilayer superhydrophobic structure of the present invention.

[0031] Figure 5 This is a scanning electron microscope image of the multilayer superhydrophobic structural wall of the present invention.

[0032] Figure 6 This is a scanning electron microscope image of the papillary structure on the surface of a multilayer superhydrophobic structure resembling a lotus leaf, as described in this invention.

[0033] Figure 7 This is a schematic diagram of the friction and wear experiment of the present invention.

[0034] Figure 8 This is a schematic diagram of the wall structure after wear in this invention.

[0035] Figure 9 This is a measurement diagram of the contact angle of the multilayer superhydrophobic structure of the present invention after wear.

[0036] Figure 10 This is a measurement diagram of the contact angle after repair according to the present invention. Detailed Implementation

[0037] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] The basic principle of the fabrication method employed in this invention is to construct a multilayer superhydrophobic structure by adjusting the scanning speed and scanning power in the femtosecond laser fabrication parameters, using a top-down laser ablation and bottom-up molten material deposition approach. Its mechanical durability mechanism lies in the fact that the continuous enclosure structure effectively prevents the wear of the internal lotus leaf-like surface papillae, thus preserving the superhydrophobic function of the magnesium alloy surface.

[0039] The size of the wall is controlled by adjusting the spacing of the laser beams to regulate the spacing of the wall structures. After grinding and polishing modification, the contact angle of the magnesium alloy surface is 81°; the hydrophobic angle of the modified lotus leaf-like surface papilla structure is 163°; and the contact area calculated by Cassie-Baxter is 3.7%. A superhydrophobic contact angle of 150° and a contact area of ​​11.6% are achieved. From this, we can see that the wall width is 30 to 40 μm. After wear, the nanostructure of the wall is worn away. We designed the wall spacing to be 1 cm, and verified through the Cassie-Baxter equation that its hydrophobic angle is within 150°. Therefore, the superhydrophobic surface can regain its hydrophobicity after wear.

[0040] Cassie-Baxter equations:

[0041] f represents the solid-liquid contact volume fraction, the static contact angle of the multilayer surface, and θ represents the contact angle of the polished magnesium alloy surface.

[0042] Example 1: Fabrication of multilayer superhydrophobic structures

[0043] (1) Pretreatment process: Use sandpaper to grind the AZ31B magnesium alloy sheet (30mm*30mm*1mm) from 1000 grit to 5000 grit to remove surface impurities and oxide and hydroxide layers. Then, use alcohol and deionized water for ultrasonic cleaning for 10 minutes respectively.

[0044] (2) Figure 1 As shown, a femtosecond laser was used to ablate the sample surface in an air environment. First, the focused laser beam scanned along the X-axis, with a distance of 15 μm between the two linear laser ablation paths. The wavelength was 1030 nm, the pulse width was 223 fs, the scan speed was 300 mm / s, the power was 1 W, and the frequency was 60 kHz. Each scan cycle consisted of 63 paths, with a cycle interval of 40 μm. Next, the same laser parameters were used to scan along the Y-axis, maintaining the 15 μm distance between the two linear laser ablation paths. This process was repeated twice to complete the fabrication of the lotus leaf-like surface papillae structure. Finally, the power and speed were changed: the power was increased from 1 W to 5 W, and the speed was decreased from 300 mm / s to 15 mm / s, while other parameters remained unchanged. The execution path was the middle path with a cycle interval of 40 μm for perimeter ablation.

[0045] (3) After the above process is completed, the magnesium alloy sample is ultrasonically cleaned in anhydrous ethanol solution for 5 minutes, and then immersed in 0.5 mol / L stearic acid ethanol low surface energy solution for 30 minutes. After immersion, the sample is taken out and dried with hot air.

[0046] (4) The hydrophobic angle measured by the hydrophobic angle measuring instrument is 163°.

[0047] Example 2: Mechanical Stability and Recoverability

[0048] (1) Wear test

[0049] The sandpaper abrasion test is often used to test the mechanical stability of superhydrophobic structures, and the modified multilayer superhydrophobic structure is taken as the research object. Figure 7 This diagram illustrates a superhydrophobic wear test. Using 2000-grit sandpaper as the wear surface, the multilayer superhydrophobic structure under test faces the sandpaper. Under a 100g load, the structure moves along a straight line at 1cm / s for a distance of 10cm. The contact angle of the multilayer superhydrophobic structure surface is then measured. This process is considered one wear cycle. After 10 wear cycles, the droplet becomes spherical on the surface, with a hydrophobic angle of approximately 145°.

[0050] (2) Repairability

[0051] After the worn superhydrophobic structure was placed in a 0.5 mol / L stearic acid solution and left to stand for 30 minutes, it was ultrasonically cleaned in alcohol for 5 minutes. The hydrophobic angle was measured to be 151° by a contact angle meter, and it was restored to the superhydrophobic state.

[0052] like Figure 1 As shown: the processing path of the multi-layer superhydrophobic structure. The thin solid line is the processing path of the lotus leaf-like surface papilla structure, and the dashed line is the processing path of the wall structure. First, the lotus leaf-like surface papilla structure is completed by ablation on both sides along the X and Y directions, and then the wall structure is processed.

[0053] like Figure 2 The image shown is a scanning electron microscope image of a multilayer superhydrophobic structure, which clearly shows the fabricated multilayer superhydrophobic structure.

[0054] like Figure 3 As shown: a three-dimensional topographic image of a multilayer superhydrophobic structure. It can be seen from the image that the wall structure is higher than the nipple structure on the surface of the lotus leaf. The distance between the two wall structures is 1 cm, and the height of the wall is 10 to 15 μm.

[0055] like Figure 4 As shown, the contact angle of the multilayer superhydrophobic structure, measured by a contact measuring instrument, is 163°.

[0056] like Figure 5 As shown: Scanning electron microscope image of a multilayer superhydrophobic wall structure, with nanoscale structures accompanying the surface of the wall structure.

[0057] like Figure 6 The image shows a scanning electron microscope image of a lotus leaf-like surface papilla structure of a multilayer superhydrophobic structure. The structure consists of a micron-scale conical structure and a nanoscale structure on the surface of the micron-scale conical structure. The bottom of the conical structure is 10 to 15 μm in size, and the top size is 2 to 3 μm.

[0058] like Figure 7 The diagram shows a friction and wear experiment. 2000-grit sandpaper is used as the wear surface. The multilayer superhydrophobic structure to be tested faces the sandpaper wear surface and moves along a straight line at a speed of 1 cm / s for a distance of 10 cm under a load of 100g weight.

[0059] like Figure 8 As shown: Schematic diagram of the wall structure after wear. It can be seen that the nanoscale structure on the surface of the wall structure disappears after friction.

[0060] like Figure 9 The image shows the contact angle measurement of the multilayer superhydrophobic structure after wear. The contact angle after wear is approximately 145°.

[0061] like Figure 10 As shown: Contact angle measurement diagram after repair. The contact angle after repair is approximately 151°.

Claims

1. A one-step method for preparing a durable and repairable superhydrophobic surface, characterized in that, Includes the following steps; Step 1: After grinding and polishing the metal material, the metal substrate is burned in the air with a femtosecond laser beam. After laser ablation, a lotus leaf-like surface papillary structure is obtained on the metal surface. By controlling the laser path, periodic lotus leaf-like surface papillae structures were obtained. Specifically, the structures are micron-scale conical structures and micron-scale conical surface nanoscale structures. The bottom of the conical structure is 10 to 15 microns, and the top size is 2 to 3 microns. Step 2: On the nipple structure spacing of the lotus leaf-like surface, a wall structure higher than the substrate itself is constructed by laser melting and stacking. The stack is guided to form a rectangular wall structure by controlling the laser path. The wall structure is 30 to 40 micrometers wide and 10 to 15 micrometers high. At the same time, the surface is accompanied by nanoscale structures, thus obtaining a multi-layered microstructure. In step 1, the ablation path of the lotus leaf-like surface papillae structure is an array-like grid structure. The processing method for the lotus leaf-like surface papillae structure includes the following steps: 1) Perform periodic ablation removal along the X direction, with a distance of 15 μm between the two laser beams, and each cycle consists of 63 paths, with a distance of 40 μm between each cycle. 2) After processing in step 1), perform periodic ablation removal along the Y direction. The distance between the two beams is 15 μm, and each cycle consists of 63 paths. The distance between each cycle is 40 μm. This completes the processing of the lotus leaf-like surface papilla structure. The wall structure fusion deposition path in step 2 is a perimeter wall structure, and its processing method includes the following steps: 1) Melting and stacking occurs along the X direction in the middle of the periodic interval, and the stacking path is the periodic interval; 2) After processing in step 1), molten deposits are carried out along the Y direction at the midpoint of the periodic interval; at this point, the wall structure is completed; the surface of the overall multi-layer microstructure is completed. The femtosecond laser pulse width for step 1, which involves the formation of the papillary structure on the surface of a lotus leaf, is 223 fs, with a repetition frequency of 60 kHz, a wavelength of 1030 nm, a lens focal length of 17 mm, a scanning speed of 100-300 mm / s, and a power of 1 W. This process is repeated twice to fabricate the structure. The femtosecond laser used in step 2 for the wall structure has a pulse width of 223 fs, a repetition frequency of 60 kHz, a wavelength of 1030 nm, a lens focal length of 17 mm, a scanning speed of 10-20 mm / s, and a power of 5 W. The wall structure is higher than the nipple-like surface structure of the lotus leaf, the distance between the two wall structures is 1cm, and the height of the wall is 10 to 15um; The multilayer superhydrophobic structure with lotus leaf-like surface papillae consists of micron-scale conical structures and nanoscale structures with micron-scale conical surfaces. The bottom of the conical structure is 10 to 15 μm in size, and the top is 2 to 3 μm in size.

2. The method for preparing a durable and repairable superhydrophobic surface in one step according to claim 1, characterized in that, The metallic material used in step 1 is AZ31B magnesium alloy.

3. The method for preparing a durable and repairable superhydrophobic surface in one step according to claim 1, characterized in that, After the multilayer microstructure obtained by steps 1 and 2 is modified with low surface energy, a superhydrophobic surface with durability and repairability is obtained.

4. The method for preparing a durable and repairable superhydrophobic surface in one step according to claim 3, characterized in that, The specific steps for low surface energy modification are as follows: after laser processing, the sample is placed in anhydrous ethanol solution for ultrasonic cleaning, and then immersed in 0.5 mol / L stearic acid ethanol low surface energy solution for 30 minutes. After immersion, the sample is taken out and dried with hot air.

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