Superhydrophilic / super-slippery region distributed silicon-based surface and preparation method thereof

Abstract

The application relates to a super-hydrophilic / super-slippery region-distributed silicon-based surface and a preparation method thereof, and belongs to the technical field of surface treatment. The preparation method comprises the following steps: spin coating photoresist on the surface of a silicon substrate, performing silver-assisted chemical etching treatment after photoetching to obtain a sample with a strip-shaped micron-level rough structure; performing silver-assisted chemical etching treatment on the sample again to increase a nanowire structure on the basis of the micron-level rough structure, thereby obtaining a sample with a micro-nano composite structure; spin coating photoresist on the surface of the sample again, and plating silver on the concave strip surface of the sample through a magnetron sputtering technology, thereby obtaining a sample with a barrier layer and a micro-nano composite structure; and immersing lubricating oil on the surface of the sample and performing acid pickling to obtain a silicon-based surface. The silicon-based surface has excellent hydrophilicity and super-slippery characteristics, the super-hydrophilic surface has the characteristics of rapid droplet nucleation and transportation, the super-slippery surface has a small hysteresis angle, and the obtained region-distributed surface can quickly collect and transport water in mist.

Description

Technical Field

[0001] This invention belongs to the field of surface treatment technology, and particularly relates to a silicon-based surface with a super-affinity / super-slippery region distribution and its preparation method. Background Technology

[0002] With freshwater resources becoming increasingly scarce due to pollution, obtaining usable freshwater from other sources has become particularly important. Seawater desalination technology has long been widely used in arid regions worldwide. However, environmental limitations and high costs prevent many areas from benefiting from seawater desalination. To address the challenge of providing clean water for a growing population and economic activities, it is essential to design widely applicable, simple, and cost-effective freshwater collection systems. Fog is well-known as a potentially abundant water resource that can be extracted from the surrounding environment using existing technologies. Therefore, fog harvesting technology has been proposed as a method for collecting water in arid and semi-arid regions. Collecting water from moist air involves many important processes: heat transfer, water transport, water collection, and water removal. For dew harvesting, the water collection stage is particularly challenging because water is scarce in environments where such systems are most needed. Dew is crucial for flora and fauna in arid climates, and an increasing amount of dew is being collected for human use. Only through careful design of surface properties can the capture rate of moisture from the air be maximized. Ideal surfaces facilitate the condensation of water from moist air and the rapid transport of condensed droplets to a collector. According to Volmer's nucleation theory, the nucleation rate of droplets on hydrophilic surfaces should be relatively fast. However, once there, the droplets will not slide until they grow large enough that their gravity is sufficient to overcome capillary forces. The magnitude of this resistance increases with the contact angle, hysteresis angle, and liquid-solid contact area. For a fixed droplet size, the liquid-solid contact area on a hydrophilic surface is large. Therefore, the droplet must reach a larger critical mass to begin moving on the hydrophilic surface, which may offset the faster nucleation rate. Superlubricated surfaces overcome the effects of hydrophilicity and hysteresis to some extent, but the isotropic nature of water droplets makes it impossible to control the direction of droplet transport. In recent years, many methods for artificially preparing biomimetic surfaces have emerged both domestically and internationally, but most of these methods have some drawbacks, such as expensive equipment, complex and difficult-to-control processes, and environmentally unfriendly materials. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention provides a silicon-based surface with a super-affinity / super-lubricating region distribution and its preparation method. The method involves constructing a micro / nano structure by combining photolithography and chemical etching, depositing a barrier layer on the surface, and finally immersing the barrier layer in lubricating oil to remove the barrier layer, thereby preparing a super-affinity / super-lubricating region distribution surface for water collection.

[0004] The first objective of this invention is to provide a method for preparing a silicon-based surface with a super-affinity / super-lubricity region distribution, comprising the following steps:

[0005] (1) Photoresist was spin-coated onto the surface of a silicon substrate, and silver-assisted chemical etching was performed after photolithography to obtain a sample with a striped micron-level rough structure.

[0006] (2) The sample with striped micron-level rough structure described in step (1) is subjected to silver-assisted chemical etching again to add nanowire structure on the basis of micron-level rough structure to obtain a sample with micro-nano composite structure.

[0007] (3) Photoresist is spin-coated again on the surface of the sample with micro-nano composite structure described in step (2), and silver is deposited on the surface of the concave stripes of the sample by magnetron sputtering technology to obtain a sample with a barrier layer and micro-nano composite structure.

[0008] (4) The sample surface with the barrier layer and micro-nano composite structure described in step (3) is wetted with lubricating oil and acid washed to obtain the silicon-based surface with the super-affinity / super-slippery region distribution.

[0009] In one embodiment of the present invention, in step (1), the silicon substrate is a smooth surface polished on one side with a single crystal orientation.

[0010] In one embodiment of the present invention, in step (1), the stripe width of the striped micron-scale rough structure is 100μm-800μm.

[0011] In one embodiment of the present invention, in step (1), the spin coating speed of the photoresist is 2000 r / min-5000 r / min, the drying temperature is 80℃-120℃, and the drying time is 1 min-2 min.

[0012] In one embodiment of the present invention, in step (1), the ultraviolet exposure time for photolithography is 10s-20s, and the development time is 1min-2min. The photolithography and photoresist will leave a rectangular stripe array on the surface of the silicon substrate, with the unexposed and exposed portions having the same width and length.

[0013] In one embodiment of the present invention, in step (1), the silver-assisted chemical etching process includes a deposition process and an etching process; the deposition process uses a deposition solution that is a mixture of silver nitrate, hydrofluoric acid, and water; the molar ratio of silver nitrate to hydrofluoric acid is 0.5-1:4.8; the etching process uses an etching solution that is a mixture of hydrogen peroxide, hydrofluoric acid, and water; the molar ratio of hydrogen peroxide to hydrofluoric acid is 0.1-0.5:4.8. By changing the concentration of the deposition solution and the deposition time, the thickness of the deposited silver can be freely controlled within a certain range; by changing the concentration of the etching solution and the etching time, the depth of the micron stripes can be freely controlled.

[0014] In one embodiment of the present invention, in step (2), the silver-assisted chemical etching process includes a deposition process and an etching process; the deposition process uses a mixed solution of silver nitrate, hydrofluoric acid, and water; the molar ratio of silver nitrate to hydrofluoric acid is 0.1-0.5:4.8; the etching process uses a mixed solution of hydrogen peroxide, hydrofluoric acid, and water; the molar ratio of hydrogen peroxide to hydrofluoric acid is 0.1-0.5:4.8. Due to the presence of nanowires and the presence of hydrophilic groups on the etched surface, the sample exhibits a superhydrophilic state. Furthermore, the structure of the etched nanowires makes it easier for the lubricant to remain and less prone to loss.

[0015] In one embodiment of the present invention, the deposition treatment time is 30s-70s to form Ag particles with a certain density distribution on the sample surface, which is beneficial to the next step of chemical etching; the etching treatment time is 10min-30min to form trenches of a certain depth.

[0016] In one embodiment of the present invention, in step (3), the parameters of the magnetron sputtering technology are as follows: cavity gas pressure is 0.5 Pa-1.5 Pa, radio frequency power is 30 W-50 W, nitrogen flow rate is 3 mL / min-5 mL / min, and sputtering time is 5 min-20 min. This is to form a dense Ag barrier layer of a certain thickness for subsequent lubricant impregnation.

[0017] In one embodiment of the present invention, in step (4), the lubricating oil is one or more of silicone oil, fluorinated polyether oil and DuPont oil.

[0018] In one embodiment of the present invention, in step (4), the acid washing uses a nitric acid solution with a concentration of 30wt%-50wt% to remove the silver film barrier layer on the surface and then rinses with deionized water, the washed-off part being the superhydrophilic region.

[0019] A second objective of this invention is to provide a silicon-based surface with a super-affinity / super-lubricity region distribution prepared by the method, wherein the super-affinity / super-lubricity region distribution silicon-based surface comprises: a silicon substrate, a micron-scale stripe-like rough structure disposed on the silicon substrate surface, and a nanowire rough structure distributed on the stripe structure.

[0020] A third objective of this invention is to provide an application of the aforementioned super-affinity / super-slippery region distribution on a silicon-based surface in mist collection and seawater desalination.

[0021] The technical solution of the present invention has the following advantages compared with the prior art:

[0022] (1) The preparation method described in this invention uses a combination of photolithography and chemical etching to prepare micro-nano composite structures on a silicon substrate with freely adjustable stripe width and depth. After photolithography, a silver barrier layer is magnetron sputtered on the substrate, and a lubricant is spin-coated. The lubricant wetting area can be selectively controlled to form a regionalized distribution surface with super-affinity and super-lubricity alternating with the unwetted area.

[0023] (2) The preparation method described in this invention is a silver-assisted wet chemical etching method. Inspired by pitcher plants and nano-desert beetles, a hydrophilic super-slippery pattern for fog collection is prepared on a single-crystal silicon substrate. Single-crystal silicon has a thermal conductivity of ~149 W / m K, making it a non-metallic material with high thermal conductivity. Fog collection is carried out through condensation, and the high thermal conductivity of the silicon substrate is beneficial for heat conduction, thereby improving the efficiency of fog collection. At the same time, the hydrophilic super-slippery surface can accurately guide the movement of water droplets due to the presence of grooves, and the alternating super-hydrophilic and super-slippery stripe structure has a Laplace pressure difference, which is suitable for efficient water transport and collection during fog collection.

[0024] (3) The silicon-based surface with superhydrophilic / superlubricating regional distribution described in this invention has excellent hydrophilicity and superlubricating properties. The superhydrophilic surface has the characteristics of rapid droplet nucleation and transport, while the superlubricating surface has a small hysteresis angle. The regional distribution surface obtained by combining the two can quickly collect and transport water in the mist due to the presence of the Laplace pressure difference and the stripe structure.

[0025] (4) In practical applications, the interface between droplets and the stripe pattern on the silicon-based surface with the superhydrophilic / superlubricated region distribution described in this invention is complex, including the droplet-stripe interface and the droplet-lubricant interface. When a droplet slides along the stripes, it needs to overcome the viscous forces at the droplet-water interface on the stripes and the droplet-lubricant interface on the surrounding sliding plates. Since the droplet sliding speed is low, the viscous forces can be ignored, making it easy for the droplet to slide along the stripes. However, the droplet must break the surface tension of the droplet-water interface from the stripes in order to slide in a direction perpendicular to the stripes. The droplet is elongated, indicating that the droplet tends to diffuse along the stripes under the action of capillary force, while it tends to be vertically constrained under the action of the energy barrier formed by the stripes. The parallel contact angle and the vertical contact angle of the droplet on the surface are 32° and 82°, respectively, indicating that the static contact angle is significantly anisotropic. Due to the Laplace pressure difference, once the droplet nucleates on the superlubricated region and comes into contact with the sliding surface, the condensate will converge and be discharged under the action of gravity, thus transferring to the superhydrophilic pattern. Attached Figure Description

[0026] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein:

[0027] Figure 1 The following are characterization images from Test Example 1 of the present invention, wherein (a) is an optical image of the silicon-based surface with superphilic / superlubricated regions distributed therein; (b)-(d) are cross-sectional microscopic morphology images of the sample with micro-nano composite structure.

[0028] Figure 2 The following are characterization images of the sample with a striped micron-level rough structure in Test Example 2 of the present invention, wherein (a) is a surface microstructure image of Example 1; (b) is a surface microstructure image of Example 2; (c) is a cross-sectional microstructure image of Example 1; and (d) is a cross-sectional microstructure image of Example 3.

[0029] Figure 3 This is a schematic diagram of the contact angle of the silicon-based surface with the distribution of super-affinity / super-slippery regions in Test Example 3 of the present invention, wherein (a) is the super-slippery region; and (b) is the super-affinity region.

[0030] Figure 4 The diagram shows the contact angle anisotropy of the three surfaces in Test Example 3 of the present invention and the comparison diagram of mist collection efficiency. (a) is a schematic diagram of static contact angle anisotropy; (b) is a comparison diagram of mist collection efficiency test.

[0031] Figure 5 The image shows the surface cross-section of a silicon-based surface with a super-sensitive / super-slippery region distribution, representing the delay in water droplet motion in Test Example 3 of this invention. Detailed Implementation

[0032] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0033] In this invention, unless otherwise specified, the UV photoresist is model RZJ-304-25, and the corresponding developer is a NaOH solution with a mass fraction of 1‰.

[0034] In this invention, unless otherwise specified, the silicon substrate is selected as a smooth surface polished on one side with a single crystal orientation. The surface is ultrasonically cleaned sequentially with acetone, ethanol, and deionized water, and then dried with nitrogen gas.

[0035] In this invention, unless otherwise stated, the lubricating oil is hydroxyl-terminated polydimethylsiloxane with a viscosity of 25.

[0036] Example 1

[0037] A silicon-based surface with super-affinity / super-lubricity region distribution and its preparation method, specifically including the following steps:

[0038] (1) A UV photoresist was spin-coated on the surface of a silicon substrate at a speed of 3000 r / min. After drying at 100°C for 1 min, the silicon substrate was fixed on the photolithography machine for photolithography. The mask stripe width was 600 μm and the UV exposure time was 15 s. After the photolithography was completed, the substrate was immediately placed in the developer corresponding to the photoresist for 1 min. After development, the substrate was rinsed with deionized water and dried to obtain the photolithographic sample.

[0039] (2) The photolithographic sample was placed in a mixed solution containing 1M silver nitrate and 4.8M hydrofluoric acid to deposit silver for 1 min; the sample after silver deposition was placed in a mixed solution containing 0.2M hydrogen peroxide and 4.8M hydrofluoric acid to etch for 15 min; after etching, it was immediately placed in a 50wt% nitric acid solution to wash away the silver, and then ultrasonically cleaned with acetone, anhydrous ethanol and deionized water for 10 min in sequence and purged with nitrogen gun for 2 min to obtain a sample with a striped micron-level rough structure.

[0040] (3) The sample with striped micron-level rough structure was placed in a mixed solution containing 0.1M silver nitrate and 4.8M hydrofluoric acid to deposit silver for 1 min; the silicon substrate after silver deposition was placed in a mixed solution containing 0.1M hydrogen peroxide and 4.8M hydrofluoric acid to etch for 15 min; after etching, it was immediately placed in a 50wt% nitric acid solution to wash away the silver particles, and then washed with deionized water and dried with a nitrogen gun to obtain a sample with micro-nano composite structure.

[0041] (4) Spin-coat UV photoresist onto the sample surface with micro-nano composite structure, expose the recessed stripes with the same mask for photolithography, and deposit a silver protective layer on the sample surface by magnetron sputtering. The parameters of the magnetron sputtering technology are: cavity pressure of 1.5 Pa, radio frequency power of 40 W, nitrogen flow rate of 5 mL / min, and sputtering time of 15 min. Then wash away the photoresist and the exposed silver film with acetone to obtain a sample with a barrier layer and micro-nano composite structure.

[0042] (5) Use a micropipette to drop an appropriate amount of lubricating oil onto the sample surface with the barrier layer and micro-nano composite structure until the surface is completely wetted; spin coat at 4500 r / min for 40 s to remove excess lubricating oil from the surface. The part not covered by the silver barrier layer is the super-slippery area; after spin coating, use 50 wt% nitric acid solution to acid wash away the barrier layer, and then wash with deionized water to obtain a silicon-based surface with super-affinity / super-slippery area distribution.

[0043] Example 2

[0044] The process is basically the same as in Example 1, except that in step (1), the mask stripe width is 400 μm during exposure.

[0045] Example 3

[0046] The process is basically the same as in Example 1, except that the etching time in step (2) is 30 min.

[0047] Comparative Example 1

[0048] The process is basically the same as in Example 1, except that after step (3), steps (4) and (5) are not performed, resulting in a micro-nano composite structure sample with superphilic properties, which changes the surface wettability without altering the surface structure.

[0049] Comparative Example 2

[0050] The process is basically the same as in Example 1, except that after step (3), step (4) is not performed, i.e., no barrier layer is deposited on the surface, and silicone oil is directly injected onto the surface of the micro-nano composite structure sample to obtain a homogeneous super-slippery sample.

[0051] Test Example 1

[0052] The sample with micro / nano composite structure in Example 1 and the silicon-based surface with superphilic / superlubricated region distribution were characterized, and the results are as follows: Figure 1 As shown, from Figure 1 It can be seen that a striped micro-nano composite structure was successfully prepared by combining silver-assisted chemical etching and photolithography.

[0053] Test Example 2

[0054] The samples with striped micron-scale rough structures in Examples 1-3 were characterized, and the results are as follows: Figure 2 As shown, from Figure 2 It can be seen that the stripe width and trench depth on the sample surface can be easily adjusted by adjusting the mask stripe width and the silver-assisted chemical etching time.

[0055] Test Example 3

[0056] The contact angle of the silicon-based surface with the super-affinity / super-lubricity region distribution prepared in Example 1 was tested using a contact angle meter, and the results are as follows: Figure 3-4 As shown in (a). From Figure 3 It can be seen that the contact angle between the superlubricated region and water is 73.3°, while the contact angle between the superhydrophilic region and water is less than 5°. From... Figure 4 (a) It can be seen that the 10 μL droplet has obvious anisotropy on the silicon-based surface distributed in the superphilic / superlubricated region. The contact angle in the vertical direction is about 82° and the contact angle in the parallel direction is about 33°. No anisotropy is shown on the homogeneous superphilic and superlubricated samples. The contact angles in the vertical and parallel directions are similar.

[0057] Figure 4 (b) Fog collection tests were conducted on three different samples under the following conditions: ambient temperature 24°C, ambient humidity 90%, and substrate cooling temperature -5°C. Figure 4 (b) It can be seen that the silicon-based surface with superphilic / superlubricated regions has a significantly improved mist collection rate compared to the superphilic and superlubricated samples.

[0058] To further investigate the reasons for the improved mist collection efficiency, the motion of droplets on the composite surface was photographed, and the results are as follows: Figure 5 As shown, A represents the superhydrophilic region, and B represents the superlubricated region. From Figure 5 It can be seen that when the droplet comes into contact with the super-lubricated surface on the super-affinity surface, it moves rapidly toward the super-affinity region under the influence of the Laplace pressure difference. The whole process lasts only 64ms, which leads to the rapid transport and collection of water droplets and improves the mist collection efficiency.

[0059] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a silicon-based surface with a super-affinity / super-lubricity region distribution, characterized in that, Includes the following steps, (1) Photoresist was spin-coated onto the surface of a silicon substrate, and silver-assisted chemical etching was performed after photolithography to obtain a sample with a striped micron-level rough structure. (2) The sample with striped micron-level rough structure described in step (1) is subjected to silver-assisted chemical etching again to add nanowire structure on the basis of micron-level rough structure to obtain a sample with micro-nano composite structure. (3) Photoresist is spin-coated again on the surface of the sample with micro-nano composite structure described in step (2), and silver is deposited on the surface of the concave stripes of the sample by magnetron sputtering technology to obtain a sample with a barrier layer and micro-nano composite structure. (4) The sample surface with the barrier layer and micro-nano composite structure described in step (3) is wetted with lubricating oil and acid washed to obtain the silicon-based surface with the super-affinity / super-slippery region distribution.

2. The method for preparing a silicon-based surface with a super-affinity / super-lubricating region distribution according to claim 1, characterized in that, In step (1), the stripe width of the striped micron-scale rough structure is 100μm-800μm.

3. The method for preparing a silicon-based surface with a super-affinity / super-lubricity region distribution according to claim 1, characterized in that, In step (1), the spin coating speed of the photoresist is 2000r / min-5000r / min, the drying temperature is 80℃-120℃, and the drying time is 1min-2min.

4. The method for preparing a silicon-based surface with a super-affinity / super-lubricity region distribution according to claim 1, characterized in that, In step (1), the silver-assisted chemical etching process includes a deposition process and an etching process; the deposition process uses a deposition solution that is a mixture of silver nitrate, hydrofluoric acid and water; the molar ratio of silver nitrate and hydrofluoric acid is 0.5-1:4.8; the etching process uses an etching solution that is a mixture of hydrogen peroxide, hydrofluoric acid and water; the molar ratio of hydrogen peroxide and hydrofluoric acid is 0.1-0.5:4.

8.

5. The method for preparing a silicon-based surface with a super-affinity / super-lubricating region distribution according to claim 1, characterized in that, In step (2), the silver-assisted chemical etching process includes a deposition process and an etching process; the deposition process uses a mixture of silver nitrate, hydrofluoric acid and water as the deposition solution; the molar ratio of silver nitrate and hydrofluoric acid is 0.1-0.5:4.8; the etching process uses a mixture of hydrogen peroxide, hydrofluoric acid and water as the etching solution; the molar ratio of hydrogen peroxide and hydrofluoric acid is 0.1-0.5:4.

8.

6. The method for preparing a silicon-based surface with a super-affinity / super-lubricity region distribution according to claim 4 or 5, characterized in that, The deposition process takes 30-70 seconds; the etching process takes 10-30 minutes.

7. The method for preparing a silicon-based surface with a super-affinity / super-lubricity region distribution according to claim 1, characterized in that, In step (3), the parameters of the magnetron sputtering technology are as follows: cavity gas pressure is 0.5Pa-1.5Pa, radio frequency power is 30w-50w, nitrogen flow rate is 3mL / min-5mL / min, and sputtering time is 5min-20min.

8. The method for preparing a silicon-based surface with a super-affinity / super-lubricity region distribution according to claim 1, characterized in that, In step (4), the lubricating oil is one or more of silicone oil, fluorinated polyether oil and DuPont oil.

9. The method for preparing a silicon-based surface with a super-affinity / super-lubricating region distribution according to claim 1, characterized in that, In step (4), the pickling is performed using a nitric acid solution with a concentration of 30wt%-50wt%.

10. The silicon-based surface with a super-affinity / super-lubricity region distribution prepared by the method according to any one of claims 1-9, characterized in that, The silicon-based surface with the super-affinity / super-lubricity region distribution includes: a silicon substrate, a micron-scale striped rough structure disposed on the silicon substrate surface, and a nanowire rough structure distributed on the striped structure.

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