A mechanically durable superhydrophobic mist collection surface and its preparation method

Abstract

A mechanically durable superhydrophobic mist collection surface and its preparation method are disclosed. The surface includes a groove array structure on a substrate material surface, and a protrusion array structure on the grooves. Specifically, protrusion structures reinforced and connected by the substrate material are formed on the ridges between the groove structures. The preparation method involves first preparing the groove array structure on the substrate material surface, then preparing the protrusion array structure on the grooves, and finally placing the substrate material in a constant-temperature drying oven for temperature-controlled aging treatment. The constant-temperature heating promotes the adsorption of hydrophobic organic functional groups from the air by the mechanically durable superhydrophobic structure surface, reducing the surface free energy and achieving a superhydrophobic state. This invention can improve mist collection efficiency, increase the transport capacity of collected droplets (i.e., the drainage rate), and simultaneously improve mechanical durability. It has advantages such as environmental friendliness, efficient large-area manufacturing, and increased application stability.

Description

Technical Field

[0001] This invention relates to the field of superhydrophobic micro / nano structure manufacturing technology, specifically to a mechanically durable superhydrophobic mist collection surface and its preparation method. Background Technology

[0002] Water collection holds immense potential in alleviating the global water crisis. Due to the extremely low adhesion of superhydrophobic surfaces to droplets, their application in water collection is receiving increasing attention. Since the advent of micro-nano manufacturing technology, techniques such as photolithography, chemical etching, and sol-gel methods have made various advancements, but they still suffer from drawbacks such as environmental pollution and uncontrollable size and morphology. Meanwhile, novel processing technologies, such as femtosecond lasers, are widely used for the precision machining of superhydrophobic water collection surfaces due to their maskless operation, environmental friendliness, extremely small heat-affected zone, and high processing precision. Various typical structured surfaces exhibit excellent Cassie-state superhydrophobic properties, with contact angles even exceeding 170°. Because the actual application environment of water collection is complex (arid regions such as deserts and Gobi often experience severe sandstorms), the durability (impact resistance and abrasion resistance) of superhydrophobic water collection surfaces is also crucial.

[0003] Studies have shown that controlling the morphology of micro and nano surface structures often significantly alters the performance indicators of functional surfaces, including durability. In ultrafast laser processing, conventional methods for controlling the morphology include changing the scanning speed and number of scans, as well as different path planning. However, the morphologies prepared by these methods (such as those in application CN201810316726.4, entitled "A Super-Daphery Metal Surface with Three-Dimensional Distribution of Nanostructures and Its Preparation Method"; and application CN201810757967.2, entitled "A Femtosecond Laser Dot Marking Method Based on Anti-Reflection Microstructures") do not possess intrinsic mechanical durability.

[0004] Currently, almost all publications on superhydrophobic surfaces focus solely on wettability characterization before and after durability testing. Furthermore, research on mechanical durability typically relies on sandpaper abrasion as a method. Even if wettability remains largely unchanged, the actual mechanical properties of the structure itself can significantly alter. This change further weakens the stability of superhydrophobic surface applications, potentially leading to complete damage to the micro / nano structure under external forces. This is an inherent defect of most current superhydrophobic surfaces (e.g., application number CN201810316726.4, entitled "A Superhydrophobic Metal Surface with Three-Dimensional Distribution of Nanostructures and Its Preparation Method"). Moreover, while superhydrophobic surfaces offer advantages over hydrophilic materials in mist collection, their high nucleation barriers often prevent them from capturing a sufficient number of droplets. Even when composite structures are used to increase droplet nucleation rates, the pinning effect prevents timely removal of captured droplets. Therefore, how to use femtosecond lasers to prepare superhydrophobic surfaces with mechanical durability and improved mist collection efficiency is of great significance for improving and expanding the stability and scope of superhydrophobic surface applications. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the present invention aims to provide a mechanically durable superhydrophobic mist collection surface and its preparation method, which can improve the mist collection efficiency, the droplet transport capacity (i.e., the drainage rate), and the mechanical durability, and has the advantages of being environmentally friendly, capable of efficient large-area manufacturing, and increasing application stability.

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

[0007] A mechanically durable superhydrophobic mist collection surface includes a groove array structure on the surface of a substrate material, and a protrusion array structure on the grooves, that is, protrusion structures formed on the ridges between the groove structures and reinforced by the substrate material.

[0008] A method for preparing a mechanically durable superhydrophobic mist collection surface includes the following steps:

[0009] 1) Preprocessing:

[0010] 1.1) Select the substrate material according to the actual engineering application requirements;

[0011] 1.2) Sand the surface of the base material with sandpaper to achieve a mirror-like finish;

[0012] 1.3) The polished substrate material was cleaned in sequence with acetone, anhydrous ethanol and deionized water using an ultrasonic bath, and dried with nitrogen.

[0013] 2) Preparation of a superhydrophobic mist collection surface with enhanced mechanical durability:

[0014] 2.1) Construct a femtosecond laser micro / nano manufacturing system, collimate and correct the optical path to ensure that the femtosecond laser beam is transmitted to the processing back end without distortion; at the same time, finely adjust the femtosecond laser spot to ensure that the femtosecond laser spot presents a uniform Gaussian energy distribution, and finally set the relevant processing and manufacturing parameters (repetition frequency and single pulse energy, etc.).

[0015] 2.2) Design the functional structure of the processing path in the software interface that controls the laser scanning trajectory;

[0016] 2.3) Place the surface of the substrate material at the processing rear end and on the focal plane of the femtosecond laser beam;

[0017] 2.4) Perform programmed texturing in the X direction according to the manufacturing parameters designed in step 2.1) and the machining path designed in step 2.2) to form a groove array structure;

[0018] 2.5) Set a low laser power value, and perform programmed texturing in the Y direction according to the processing and manufacturing parameters designed in step 2.1) and the processing path designed in step 2.2) to form a protrusion array structure on the groove;

[0019] 2.6) After processing is completed, use a cleaning air blower to clean the residual ablation residue on the texture surface;

[0020] 2.7) The processed micro-nano structures were sequentially cleaned with acetone, anhydrous ethanol, and deionized water using an ultrasonic bath, and then dried with nitrogen.

[0021] 3) Construction of mechanically durable superhydrophobic structure surface: The mechanically durable superhydrophobic mist collection surface prepared in step 2) is placed in a constant temperature drying oven for temperature-controlled aging treatment to promote the adsorption of hydrophobic organic functional groups from the air and reduce the surface free energy to achieve a superhydrophobic state; the final mechanically durable superhydrophobic mist collection surface has good superhydrophobicity and excellent mist collection performance.

[0022] The substrate material is aluminum and its alloys, titanium and its alloys, copper and other materials.

[0023] The aforementioned enhanced mechanical durability refers to the enhanced mechanical properties of the superhydrophobic structure, such as increased resistance to shear and impact. This enhanced mechanical durability is caused by the geometric characteristics of the superhydrophobic structure itself.

[0024] The processing path in step 2.2) adopts a raster scanning method.

[0025] Step 2.4) programmed texture X-direction processing and step 2.5) programmed texture Y-direction processing are respectively the vertical and horizontal linear array extension directions in the raster scan path.

[0026] In step 2.5), setting a low laser power value still requires ensuring that the laser pulse energy density is above the ablation threshold of the substrate material. Only in this way can the substrate material be effectively etched.

[0027] Step 3) Temperature-controlled aging treatment involves placing the substrate material with the enhanced mechanical durability and superhydrophobic mist collection surface in a drying oven and heating it at a constant temperature for a set time. In addition to using the constant temperature heating to absorb organic functional groups in the air and reduce the surface energy of the enhanced mechanical durability and superhydrophobic structure surface, it can also play a secondary curing role on the mechanical properties of the structure.

[0028] In step 3), good superhydrophobicity means that even after the mechanically durable superhydrophobic mist collection surface is mechanically worn, the superhydrophobicity in the groove morphology will be further maintained due to the existence of the groove structure.

[0029] In step 3), the excellent mist collection performance refers to having both a high droplet nucleation and growth rate and a high drainage rate. The increase in droplet nucleation and growth rate is the result of the interaction between the protruding structure and the mist flow, while the increase in drainage rate is caused by the combined effect of gravity and the directional wicking effect of the groove structure.

[0030] Compared with existing technologies, the present invention has the following advantages and beneficial effects:

[0031] First, the micro-nano structure of the present invention is prepared using a femtosecond laser processing system, which has the advantage of precise and controllable processing. Furthermore, the subsequent low surface energy treatment is carried out by heating in a temperature-controlled drying oven. Compared with other commonly used methods such as silanization, it does not produce chemical waste that pollutes the environment, and the collected water will not be subject to secondary pollution.

[0032] Secondly, the superhydrophobic surface structure proposed in this invention has the advantage of enhanced intrinsic mechanical durability, mainly due to the strengthening connection between the structures by the intrinsic substrate material. While strengthening the connection by the substrate material appears to be simply achieved by increasing the spacing between microstructures, existing research has shown that increasing the spacing between microstructures lowers the energy barrier for the transition from the Cassie state to the Wenzel state, thus easily leading to a loss of low-adhesion superhydrophobic properties, which is detrimental to mist collection applications. However, the structure proposed in this invention is based on a trench array structure, which has long been proven to have excellent anisotropic superhydrophobic properties. Therefore, using a trench array structure as a basis does not result in a loss of superhydrophobicity. Furthermore, by controlling the laser power, protrusions strengthened by the substrate material are formed on the ridges (formed on the intrinsic substrate surface) between the trench structures. Therefore, the trench protrusion array structure has the dual advantages of maintaining superhydrophobicity and enhanced intrinsic mechanical durability.

[0033] Finally, during mist collection operations, these protrusions increase the contact area between the structure and the mist. Although they do not increase the nucleation rate of droplets as much as hydrophilic protrusions, compared with other superhydrophobic (structures without protrusion features) surfaces, these micro-protrusions change the way the surrounding mist flows, allowing the mist to be deposited on the surface of the micro-protrusions as much as possible. At the same time, the groove structure can also play a role in the directional transport of droplets collected by the micro-protrusions due to the wicking effect. Attached Figure Description

[0034] Figure 1 This is Embodiment 1 of the present invention. SOLIDWORKS Modeling schematic diagram, where (a) is an isometric view, (b) is a partial enlarged view of (a), (c) is the smallest unit of the array; and (d) is the structural feature parameters.

[0035] Figure 2 This is a three-dimensional contour diagram of the structure prepared in Example 1 of the present invention.

[0036] Figure 3 This is an electron microscope image of the structure prepared in Example 1 of the present invention.

[0037] Figure 4 The image shows the contact angle test diagram of the structure prepared in Embodiment 1 of the present invention.

[0038] Figure 5 for Figure 3 A magnified view of a portion of the image.

[0039] Figure 6 This is a mist collection process on the surface of the substrate material in Embodiment 1 of the present invention, wherein (a) is a structural surface morphology diagram before the mist collection experiment, and (b), (c), and (d) are optical images of mist deposition on the surface after 15 seconds, 30 seconds, and 45 seconds of the experiment, respectively.

[0040] Figure 7 The image shows the three-dimensional morphology of the structure prepared by laser confocal imaging in Example 2 of this invention.

[0041] Figure 8 Figure (b) is an enlarged view of the structure prepared in Example 2 of the present invention.

[0042] Figure 9 The contact angle is that of the structure prepared in Example 2 of the present invention.

[0043] Figure 10 A three-dimensional laser confocal image of the intrinsic mechanical durability enhancement structure prepared in Example 3 of the present invention.

[0044] Figure 11 Figure (b) is an enlarged view of the structure prepared in Example 3 of the present invention.

[0045] Figure 12 This is a contact angle test diagram of the structure prepared in Example 3 of the present invention. Detailed Implementation

[0046] The present invention will now be described in detail with reference to the embodiments and accompanying drawings.

[0047] Example 1: A mechanically durable superhydrophobic mist collection surface includes a groove array structure on the surface of a substrate material, and a protrusion array structure on the grooves, that is, a protrusion structure reinforced and connected by the intrinsic substrate material is formed on the ridges between the groove structures.

[0048] The method for preparing a mechanically durable, superhydrophobic mist collection surface includes the following steps:

[0049] 1) Preprocessing:

[0050] 1.1) Based on the actual engineering application requirements, an area of ​​25×25 mm is selected. 2 2mm thick 6061 aluminum alloy is used as the substrate material for femtosecond laser processing and is widely used in the electronics, aviation, aerospace, and weaponry industries.

[0051] 1.2) Grind the surface of the base material with 500 grit, 1000 grit, and 1500 grit sandpaper in sequence to make the surface have a mirror-like appearance, and ensure that the processing differences in different locations are minimized.

[0052] 1.3) The polished substrate material was subjected to an ultrasonic bath for 15 minutes in sequence with acetone, anhydrous ethanol and deionized water, and was dried with nitrogen gas at the same time.

[0053] 2) Preparation of a superhydrophobic mist collection surface with enhanced mechanical durability:

[0054] 2.1) Construct a femtosecond laser micro / nano processing optical system, collimate and correct the optical path to focus the femtosecond laser beam on the processing platform at the location to be processed. Simultaneously, the following tasks are performed: adjusting optical path components to obtain a suitable beam quality for processing; finding the plane containing the focal point of the femtosecond laser beam using a step-by-step scribing method; the focal diameter of the focused beam at the processing platform is approximately 35 micrometers; using a computer control system, first set the femtosecond laser output wavelength to 1030 nm Gaussian light, then the repetition frequency to 100 kHz and the single pulse energy to 30 μJ.

[0055] 2.2) Design the functional structure of the processing path in the interactive software interface that controls the laser scanning trajectory;

[0056] 2.3) Place the surface of the substrate material at the processing end position and on the focal plane of the femtosecond laser beam;

[0057] 2.4) Perform programmed texturing X-direction processing according to the processing and manufacturing parameters designed in step 2.1) and the processing path designed in step 2.2). Set the X-direction to scan 10 times and the scanning speed to 10 mm / s to form a groove array structure.

[0058] 2.5) Set the laser single pulse energy to 20uJ, keep other laser parameters unchanged, and perform programmed texturing in the Y direction according to the processing and manufacturing parameters designed in step 2.1) and the processing path designed in step 2.2) to form a protrusion array structure on the groove; set the Y direction to scan 10 times and the scanning speed to 10mm / s;

[0059] 2.6) After processing is completed, use a cleaning air blower to clean the residual ablation residue on the fabric surface to facilitate further cleaning work.

[0060] 2.7) The processed micro-nano structures were sequentially ultrasonically cleaned with acetone, anhydrous ethanol, and deionized water for 15 minutes, then dried with nitrogen and heated at 150°C for 6 hours in a forced-air drying oven to prepare for subsequent processes.

[0061] 3) Construction of a mechanically durable superhydrophobic structure surface: The substrate material with a mechanically durable superhydrophobic mist collection surface prepared in step 2) was placed in a constant temperature drying oven for temperature-controlled aging treatment. The constant temperature heating promoted the adsorption of hydrophobic organic functional groups from the air, reducing the surface free energy and achieving a superhydrophobic state, thus obtaining a mechanically durable groove protrusion structured superhydrophobic mist collection surface. Characterized by the seat drop method, the static contact angle of this surface with deionized water is greater than 150°, indicating good superhydrophobicity. For mist collection characterization, the substrate material with the mechanically durable groove protrusion structured superhydrophobic mist collection surface was fixed on a support at a 45° angle at room temperature. An atomizer capable of generating nano-droplet mist with an airflow velocity of 10 cm / s was placed 10 cm in front of the support. The mist collection process on the sample surface was observed and analyzed using an optical microscope.

[0062] The beneficial effects of this embodiment are as follows: First, the use of femtosecond lasers to fabricate micro / nano structures has a smaller thermal impact effect, which provides a basis for precise control of the micro / nano structure size, and its processing flexibility also allows for the fabrication of various different morphologies. Second, the adjustment of laser power enables the fabrication of a micro-protrusion array structure on the ridges of the groove array structure. The micro-protrusions are reinforced and connected by an intrinsic material substrate, improving the structural mechanical stability. Typically, groove structures have good anisotropic superhydrophobicity, while micro-protrusion structures with larger spacing have poor hydrophobicity. The structure fabricated in this embodiment combines the advantages of the anisotropy of the groove array structure and the enhanced intrinsic mechanical durability of the micro-protrusion structure with larger spacing, that is, enhancing its intrinsic mechanical durability while maintaining anisotropic superhydrophobicity.

[0063] Reference Figure 1 , Figure 1 Example 1 SOLIDWORKS The modeling diagram is shown in (a) as an isometric view and (b) as a magnified view of (a). Figures (a) and (b) show that the groove structure and the protruding structures on it are evenly distributed, with the protruding structures reinforced by the intrinsic material matrix. (c) shows the array elements, as indicated by the black rectangular boxes. (d) provides some explanation of the structural characteristic parameters, which can be used to represent the solid-liquid contact area fraction. and the surface roughness of the structural model Thus, while ensuring enhanced intrinsic mechanical durability, hydrophobicity is controlled;

[0064]

[0065]

[0066] in, This represents the solid-liquid contact area fraction. For the surface roughness of the structural model, This represents the actual solid-liquid contact area within a structural unit. This represents the projected area of ​​the solid-liquid contact region within a structural unit. Meaning as Figure 1 As indicated by the d mark, all examples are... , .

[0067] Reference Figure 2 , Figure 2 The figure shows a three-dimensional contour diagram of the structure prepared in Example 1, which shows a regularly arranged array of groove protrusions.

[0068] Reference Figure 3 The image shows an electron microscope image of the structure prepared in Example 1. It can be seen from the image that protrusions reinforced and connected by the intrinsic material substrate are distributed on the ridges of the trench array structure.

[0069] Reference Figure 4 , Figure 5 , Figure 4 The image shows the contact angle test results of the structure prepared in Example 1. As can be seen from the image, the contact value is greater than 150°, indicating a superhydrophobic state. Figure 5 for Figure 3 The enlarged view of the electron microscope image shows that nanoscale features are distributed on the ridge-like structure and microprotrusions. These nanoscale features are formed by the interaction between the laser and the material substrate.

[0070] Reference Figure 6 , Figure 6 This document describes the mist collection process on the substrate material surface in Example 1. Image (a) shows the surface morphology before the mist collection experiment. Images (b), (c), and (d) show the deposition optical images of mist on the surface after 15, 30, and 45 seconds, respectively. Image (b) shows a large amount of tiny droplets deposited on the surface, a result of the interaction between the micron-sized protrusions and the small droplets in the mist. Furthermore, as the mist collection process continues, the droplets in image (b) continue to grow, as shown in image (c). When the droplets reach a certain size, under the influence of gravity and the wicking effect of the groove array structure, the collected droplets begin to roll off the surface parallel to the grooves on the sample surface. The rolling trajectory of the droplets is clearly visible in image (d). The mist collection experiment demonstrates that within a short period of tens of seconds, a large number of small droplets in the mist are deposited and grown on the substrate material surface until they are rapidly transported away from the surface under the combined effect of gravity and wicking. The newly exposed substrate material surface then undergoes the next mist collection cycle.

[0071] Example 2: The substrate material in step 1) was replaced with copper, the single-pulse energy in step 2.1) was set to 40 μJ, and the single-pulse energy in step 2.5) was set to 30 μJ, while other steps remained unchanged. The resulting structure morphology is as follows. Figure 7 and Figure 8 As shown, the wettability characteristics are as follows: Figure 9 As shown in the figure, the contact angle is greater than 150°, exhibiting a superhydrophobic state; when conducting mist collection experiments, similar benefits to those in Example 1 can be achieved.

[0072] Example 3: The substrate material in step 1) was replaced with stainless steel, the single-pulse energy in step 2.1) was set to 50 μJ, the single-pulse energy in step 2.5) was set to 40 μJ, and the temperature-controlled aging temperature in step 3) was set to 200℃. All other steps remained unchanged, and the resulting structure morphology was as follows. Figure 10 and Figure 11 As shown, the wettability characteristics are as follows: Figure 12 As shown, it also possesses excellent superhydrophobicity; when conducting mist collection experiments, it can achieve similar benefits to Examples 1 and 2.

Claims

1. A method for preparing a mechanically durable, superhydrophobic mist collection surface, characterized in that: The mechanically durable superhydrophobic mist collection surface includes a groove array structure on the surface of the substrate material, a protrusion array structure on the grooves, and a protrusion structure reinforced and connected by the substrate material on the ridges between the groove structures. The method includes the following steps: 1) Preprocessing: 1.1) Select the substrate material according to the actual engineering application requirements; 1.2) Sand the surface of the base material with sandpaper to achieve a mirror-like finish; 1.3) Clean the polished base material and dry it with nitrogen. 2) Preparation of a superhydrophobic mist collection surface with enhanced mechanical durability: 2.1) Construct a femtosecond laser micro / nano manufacturing system, finely adjust the femtosecond laser spot to ensure that the femtosecond laser spot exhibits a uniform Gaussian energy distribution, and finally set relevant processing and manufacturing parameters, including repetition frequency and single pulse energy, with a single pulse energy of 30 μJ. 2.2) Design the functional structure of the processing path in the interactive software interface that controls the laser scanning trajectory; 2.3) Place the surface of the substrate material at the processing rear end and on the focal plane of the femtosecond laser beam; 2.4) Perform programmed texturing in the X direction according to the manufacturing parameters designed in step 2.1) and the machining path designed in step 2.2) to form a groove array structure; 2.5) Set the laser single pulse energy to 20 μJ, and perform programmed texturing Y-direction processing according to other processing and manufacturing parameters designed in step 2.1) and processing path designed in step 2.2), forming a protrusion array structure reinforced and connected by the substrate material on the ridges between the groove structures; 2.6) After processing is completed, use a cleaning air blower to clean the residual ablation residue on the texture surface; 2.7) The processed micro / nano structures are cleaned and then dried with nitrogen. 3) Construction of mechanically durable superhydrophobic structure surface: The mechanically durable superhydrophobic mist collection surface prepared in step 2) is placed in a constant temperature drying oven for temperature-controlled aging treatment to promote the adsorption of hydrophobic organic functional groups from the air on the surface, reduce the surface free energy and achieve a superhydrophobic state. The resulting mechanically durable superhydrophobic mist collection surface has good superhydrophobicity and excellent mist collection performance. The enhanced mechanical durability refers to the enhanced mechanical properties of the superhydrophobic structure, including enhanced shear and impact resistance; the good superhydrophobicity means that even after the enhanced mechanical durability superhydrophobic mist collection surface is mechanically worn, the presence of the groove structure will further maintain the superhydrophobicity of the groove morphology; the excellent mist collection performance means that it has both a high droplet nucleation and growth rate and a high drainage rate.

2. The method according to claim 1, characterized in that: The base material is aluminum and its alloys, titanium and its alloys, or copper.

3. The method according to claim 1, characterized in that: The processing path in step 2.2) adopts a raster scanning method.

4. The method according to claim 1, characterized in that: Step 2.4) programmed texture X-direction processing and step 2.5) programmed texture Y-direction processing are respectively the vertical and horizontal linear array extension directions in the raster scan path.

5. The method according to claim 1, characterized in that: Step 3) Temperature-controlled aging treatment involves placing the substrate material with a mechanically durable, superhydrophobic mist-collecting surface in a drying oven and heating it at a constant temperature for a set time.

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