Water-vapor separation device based on PDMS super-hydrophobic membrane and preparation method and device of PDMS super-hydrophobic membrane

Abstract

The application discloses a water-gas separation device based on a PDMS super-hydrophobic film, and a preparation method and device of the PDMS super-hydrophobic film, and relates to the technical fields of functional surface processing and marine gas resource collection. The separation device comprises a dynamic flow field generating unit and a static interface selecting unit. The dynamic flow field generating unit generates an upward flow field through a spiral blade to promote the rapid upward floating of bubbles. The static interface selecting unit adopts an inverted V-shaped PDMS film with a super-hydrophobic lower surface and a super-hydrophilic upper surface to realize efficient gas-liquid separation. The device is equipped with a self-adaptive floating system, and the PDMS film is always kept at the optimal working position through a floating plate and an adjusting mechanism. The double-sided super-hydrophobic / super-hydrophilic porous PDMS film is obtained through a template copying method. The problems of water pressure penetration and low efficiency in the bubble collection process are effectively solved, and the device has the advantages of stable structure, high collection efficiency and the like, and is particularly suitable for methane bubble collection in a marine environment, and can effectively reduce greenhouse gas emissions and realize energy recycling.

Description

Technical Field

[0001] This invention relates to the fields of micro / nano structure surface engineering and gas-liquid interface control technology, and particularly to a water-gas separation device based on PDMS superhydrophobic film and a method and apparatus for preparing PDMS superhydrophobic film. Background Technology

[0002] In nature, most methane (CH4) exists on the seabed as a solid gas hydrate. Directly releasing methane into the atmosphere exacerbates the greenhouse effect, causing changes in terrestrial and aquatic ecosystems and thus having a significant impact on global ecosystems, economies, and societies. Meanwhile, the large amounts of methane bubbles from the seabed can also be considered a valuable energy source, as methane combustion produces only a small amount of carbon dioxide, without pollutants such as sulfides and particulate matter. Unfortunately, collecting methane bubbles from the seabed for further utilization also faces challenges such as slow bubble rise and easy dispersion. In still water, bubble rise is constrained by buoyancy and viscous drag, and the collection path is unstable. Furthermore, conventional collection methods often overlook incomplete water-gas separation and the influence of material surface properties on bubble behavior. Therefore, elucidating the mechanisms of efficient bubble adsorption and directional transport, and developing bubble collection devices with long-term stability, is of significant value for theoretical innovation and engineering practice in deep-sea resource development and greenhouse gas emission reduction.

[0003] Domestic and international scholars have conducted some research on the preparation of underwater bubble collection devices. Patent application CN202320613341.0 uses a first pump to regulate the water flow speed, simulating the impact of sediments under different hydraulic conditions to release methane bubbles. Utilizing the Venturi effect and the airflow redirection in the bend, methane and water are effectively separated, and the gas is finally collected in a gas collecting bottle. Patent application CN201621153648.3 uses a molecular sieve trap to dry bubbles in geothermal water, then a syringe delivers them to a sampler. A high-precision diaphragm flowmeter is used for pressure testing to ensure the collected pressure is above one atmosphere, preventing air pollution. Its advantages overcome the problems of high humidity, difficulty in accurately measuring gas volume, and potential environmental pollution caused by low pressure in conventional exhaust methods. However, the molecular sieve trap needs frequent replacement, increasing operational complexity and cost. Furthermore, the sealing of the injector can affect the accuracy of gas collection.

[0004] The main defects and drawbacks of the current technology are: the complex structure of the device leads to high manufacturing and maintenance costs; the risk of cross-contamination of gases is significant; the water-gas separation is incomplete, which easily leads to a decline in the quality of methane gas collection; at the same time, the device is difficult to adapt to changes in different hydraulic conditions, lacks the flexibility of operating condition adjustment, and has low collection efficiency, which limits its promotion in practical application scenarios. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a water-air separation device based on a PDMS superhydrophobic membrane, as well as a method and apparatus for preparing the PDMS superhydrophobic membrane. It utilizes an underwater superhydrophobic / hydrophilic unidirectional transport porous membrane to intercept air bubbles, enabling efficient collection and utilization of underwater methane bubbles. The PDMS membrane is prepared using a laser-electrochemical deposition continuous processing method. A micro / nano composite structure with abundant nano-nickel pyramids is fabricated on a copper surface. The laser scanning gap is adjusted to maximize the contact angle of the superhydrophobic surface, achieving the most stable superhydrophobic state. A PDMS membrane with the same properties is replicated using a template method. A uniform array of conical micropores is fabricated on the other side of the PDMS membrane, and this side is modified with a superhydrophilic reagent, resulting in a PDMS membrane with a superhydrophilic upper surface and a superhydrophobic lower surface.

[0006] The present invention achieves the above-mentioned technical objectives through the following technical means.

[0007] A water-air separation device based on a PDMS superhydrophobic membrane includes a container, a PDMS membrane, and a floating plate. The container is a hollow cavity, placed in seawater, and suspended by the floating plate. A gas delivery pipe is connected to the upper end of the container, and a PDMS membrane is placed at the lower end of the container. The upper surface of the PDMS membrane is superhydrophilic, and the lower surface is superhydrophobic. Gas passing through the PDMS membrane is collected into a gas storage container through the gas delivery pipe.

[0008] In the above scheme, the container has an inverted V-shaped structure with a slope angle of 10° to 20°; the PDMS membrane has an inverted V-shaped structure with a slope angle of 3° to 5°.

[0009] In the above scheme, the floating plate is fitted onto the outer ring of the container by a support frame. The floating plate has a hollow honeycomb structure and a lateral dimension L of 0.6 to 1.2 m.

[0010] In the above scheme, a negative pressure suction device is installed inside the gas transmission pipe.

[0011] In the above scheme, the container is also provided with a rigid linkage mechanism, and a spiral blade is connected to the rigid linkage mechanism. The spiral blade is positioned below the PDMS membrane and is used to agitate the seawater so that the bubbles can quickly reach the PDMS membrane.

[0012] A template-assisted laser-electrochemical deposition method for preparing PDMS superhydrophobic / hydrophilic double-sided porous membranes includes the following steps:

[0013] Step 1) Prepare a superhydrophobic copper surface micro / nano composite structure;

[0014] Step 2) Based on the superhydrophobic copper surface micro-nano composite structure obtained in Step 1, a superhydrophobic micro-nano structure surface is prepared on one side of the PDMS film using a replication method;

[0015] Step 3) Use a nanolaser to process a uniform conical micropore array on the PDMS film, and use a superhydrophilic reagent to modify the surface of the PDMS film where the uniform conical micropore array is processed to obtain superhydrophilic properties, thus obtaining a superhydrophilic surface, and finally obtaining a PDMS film with a superhydrophilic upper surface and a superhydrophobic lower surface.

[0016] In the above scheme, step one includes mechanical polishing, laser ablation, electrochemical polishing, and electrochemical deposition.

[0017] In the above scheme, the wavelength of the laser is 1000-1200nm, the pulse width is 10-15ps, the repetition frequency is 1MHz, the output power is 10-25W, the scanning speed is set to 150-300mm / s, the number of scans is 25-30, the diameter of the focused spot is 20-30μm, and the laser scanning gap is equal to the diameter of the focused spot.

[0018] In the above scheme, in step three, the gap between two adjacent holes is set to 300-500 μm, the diameter of the micropores is 100-150 μm, and the conical micropore array covers the entire effective area of ​​the film in a hexagonal close-packed (HCP) configuration.

[0019] An apparatus for realizing a template-assisted laser-electrochemical deposition method for inducing superhydrophobic / hydrophilic double-sided porous PDMS films is characterized by comprising a picosecond pulsed laser system for ablating micron-sized structures, an electrochemical polishing system for growing nanostructures, and an electrochemical deposition system. The picosecond pulsed laser system is used to ablate the workpiece. In the electrochemical polishing system, the workpiece is connected to the positive terminal of a power supply, a lead plate is connected to the negative terminal, and the workpiece is placed in a polishing solution. In the electrochemical deposition system, the workpiece is placed in an electrolyte, the workpiece is connected to the negative terminal, and a nickel block is connected to the positive terminal. Micro / nano composite structures are obtained through electrochemical polishing and electrochemical deposition.

[0020] Beneficial effects:

[0021] 1. In this invention, the rotation of the helical blades can create a dynamic flow field, which accelerates the upward movement of bubbles, breaks the limitations of traditional bubble collection under still water conditions, avoids the accumulation and retention of bubbles in specific areas, and significantly improves the efficiency of bubble capture.

[0022] 2. In this invention, the top of the container is designed as an inverted V-shape with rounded corners to reduce gas accumulation and retention caused by the formation of eddies and turbulence, making it easier for the gas to float and accumulate on the inclined surface. The negative pressure extraction device is connected to the top of the container through a gas supply pipe. The extraction device accelerates the extraction of the collected methane gas, further improving the collection efficiency and utilization rate of methane gas, thereby effectively alleviating environmental pollution and energy problems.

[0023] 3. This invention constructs a bubble collection device that integrates a dynamic flow field generation module (spiral blade), a static interface selection module (double-sided superhydrophobic / superhydrophilic PDMS membrane), and a drag-reducing container configuration, achieving efficient enrichment and continuous separation of bubbles through multi-physics field synergistic coupling.

[0024] 4. Traditional devices that utilize superhydrophobic properties to collect bubbles often assume that the lower surface of the membrane is superhydrophobic and that water-air separation can be directly achieved after the membrane is perforated. In practical applications, water can seep in through the pores, affecting the bubble collection efficiency. In this invention, the floating plate adopts a hollow honeycomb structure to achieve a precise balance between buoyancy and gravity, keeping the lower surface of the membrane at the water surface boundary and preventing hydrostatic pressure from damaging the PDMS membrane. The lateral dimension of the floating plate (L=1.2m) is much larger than the wave wavelength (typical ocean wave λ≈0.5m), and the resonance response is suppressed by utilizing the wave frequency detuning principle, reducing the membrane heave amplitude by about 70%. Furthermore, the lower surface is superhydrophobic, while the upper surface of the PDMS membrane is modified with superhydrophilic properties and features a sloping design. Through the synergistic effect of the surface superhydrophobicity and gravity-driven drainage, when some bubbles rise with the water flow to the PDMS membrane, the water spreads on the superhydrophilic surface and slides down the sloping surface, effectively solving the problem of water seeping in through the membrane pores and achieving dual protection for water-air separation.

[0025] 5. In the PDMS film preparation method of this invention, the copper-based template prepared by laser-electrochemical deposition has excellent mechanical durability and can achieve more than 30 repeated transfers of PDMS film, thereby greatly improving preparation efficiency and reducing production costs. This invention utilizes a template etching method in the preparation of PDMS films. The template method has a simple preparation process, requires no complex and cumbersome processing equipment, and the template can be reused multiple times, saving costs. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the water vapor separation device based on PDMS superhydrophobic membrane involved in the present invention.

[0027] Figure 2 This is a schematic diagram of the experimental apparatus for preparing superhydrophobic copper surface micro / nano composite structures according to the present invention.

[0028] Figure 3 A schematic diagram of the overall continuous fabrication process for multi-scale micro / nano composite structures and 3D concave corner structures on superhydrophobic copper surfaces.

[0029] Figure label:

[0030] 1-Negative pressure suction device; 2-Gas delivery pipe; 3-Container; 4-PDMS membrane; 5-Rigid linkage mechanism; 6-Bubble; 7-Helical blade; 8-Seawater; 9-Floating plate; 10-Support frame; 11-Workpiece; 12-Pulse power supply; 13-Lead plate; 14-Polishing fluid; 15-Electrolyte; 16-Nickel block; 17-Focusing lens; 18-Reflector; 19-Aperture; 20-Nanosecond laser; 21-Power supply. Detailed Implementation

[0031] The embodiments of the present invention are described in detail below. The embodiments described below with reference to the accompanying drawings are merely illustrative and intended to explain the present invention, and should not be construed as limiting the present invention.

[0032] Combined with appendix Figure 1 As shown, a water-air separation device based on a PDMS superhydrophobic membrane includes a container 3, a PDMS membrane 4, and a floating plate 9. The container 3 is a hollow cavity, placed in seawater 8, and suspended by the floating plate 9. The upper end of the container 3 is connected to a gas delivery pipe 2, and the lower end of the container 3 is provided with a PDMS membrane 4. The upper surface of the PDMS membrane 4 is superhydrophilic, and the lower surface is superhydrophobic. The gas passing through the PDMS membrane 4 is collected into a gas storage container through the gas delivery pipe 2.

[0033] The container 3 is made of transparent and durable material to facilitate observation of the movement of the bubbles 6. The bottom of the container is designed as a V-shaped structure with an angle of about 160°, that is, the angle of the slope is 10° to 20°. The folds are rounded to reduce the formation of eddies and turbulence, making it easier for the gas to float and accumulate on the slope. The container is placed upside down underwater.

[0034] The prepared double-sided superhydrophobic / superhydrophilic PDMS membrane 4 is cut into a suitable size and shape and subjected to bevel design. It is then folded from the middle to form a V-shaped structure with an angle of about 170°, i.e., a bevel angle of 3° to 5°. The folded part is rounded to facilitate the spread and sliding of water on the superhydrophilic surface. The designed PDMS membrane 4 is installed on the uncovered side of the container to ensure that the membrane is tightly attached to the container.

[0035] An annular floating plate 9 with a hollow honeycomb structure is installed on the upper outer side of container 3, and is connected to the container via a support frame 10. The horizontal dimension of the floating plate is L = 1.2m, and it is made of low-density composite material with a density of 0.3~0.5g / cm³. 3The support frame is manufactured with an adjustment accuracy of ≤±1mm, and its inner diameter is 10-15cm larger than the outer diameter of the container, providing additional buoyancy without affecting bubble observation. Through dynamic buoyancy compensation of the floating plate, it can automatically adapt to different water depths and wave conditions, maintaining stable system operation.

[0036] The top of the container is connected to the negative pressure pumping device 1 via the gas supply pipe 2. Its function is to ensure that the gas can be output faster. The negative pressure pumping device is located above the water surface.

[0037] The lower part of the container is connected to the helical blades 7 via a rigid linkage mechanism 5, which is used to break the still water state and form a dynamic flow field. This reduces the relative velocity between the bubbles and the water, thereby reducing the resistance of the water and the influence of surface tension.

[0038] Experimental procedures and bubble collection:

[0039] The spiral blade 7 rotates, causing the seawater 8 to form an upward flow field; water containing methane bubbles is poured into a container, and the rising of bubbles and water-gas separation are observed; when the methane gas accumulates to a certain amount on the inclined plane, the negative pressure pump is turned on to extract the gas and collect it into a designated gas storage container; the purity and flow rate of the collected methane gas are tested to ensure that they meet the application requirements.

[0040] A template-assisted laser-electrochemical deposition method for water vapor separation using PDMS superhydrophobic films includes the following steps:

[0041] 1) Continuous fabrication of superhydrophobic copper surface multi-scale micro / nano composite structures and 3D concave corner structures:

[0042] Combined with appendix Figure 3 The illustrated embodiment shows a continuous preparation process including mechanical polishing, laser ablation, electrochemical polishing, and electrochemical deposition;

[0043] Mechanically polish the copper surface to a mirror finish:

[0044] In this embodiment, combined with the appendix Figure 2As shown, during laser ablation, an ultrashort pulse laser in the near-infrared band is used to periodically scan the copper substrate. The laser scanning gap is approximately equal to the diameter of the focused spot to achieve the maximum contact angle. By precisely controlling the laser energy density, scanning rate, and scanning strategy, a regular micron-scale trench array structure is formed on the copper surface. Specifically, during laser ablation, the laser wavelength is 1000–1200 nm, and the pulse width is 10–15 ps, exhibiting a short pulse duration. The repetition frequency is set to 1 MHz to ensure high-frequency laser action. The output power is 10–25 W. The scanning speed is set to 150–300 mm / s to achieve rapid and uniform scanning. The number of scans is 25–30 to ensure sufficient laser action. The diameter of the focused spot is approximately 20–30 μm. The laser scanning gap is adjusted so that it equals the diameter of the focused spot. At this point, the contact angle of the superhydrophobic surface reaches its maximum value and the roll-off angle reaches its minimum value at room temperature. The nanostructure allows the composite structure to capture more air, allowing water droplets to contact the sample surface through the air. Abundant submicron-nano pyramids enhance the ability to trap air and reduce the contact area between water droplets and the substrate to achieve a stable Cassie state.

[0045] During the electrochemical polishing process, workpiece 11, a copper sample, serves as the anode, and 99.99% pure lead plate 13 is used as the cathode. The polishing solution 14 contains an alkaline electrolyte and a surfactant. Subsequently, the copper sample is activated by immersion in an acidic solution for 20 seconds, rinsed with deionized water, and then transferred to the electrochemical deposition step.

[0046] During deposition, the copper sample serves as the cathode, the high-purity nickel block 16 as the anode, and the electrolyte 15 contains Ni. 2+ Ion source, pH buffer and crystallization modifier, the pH of electrolyte is adjusted to a weakly acidic range by adding the solution, and the process is carried out under constant temperature of about 65℃.

[0047] The deposition process is divided into two stages: a step-by-step current control method is used, in which the current density parameter is adjusted in stages to first form a primary nanocone array on the surface of the laser-ablated micron structure, and then a secondary nanopyramid is constructed on the surface of the primary structure, finally obtaining a composite structure with micron-submicron-nano three-level hierarchical characteristics.

[0048] 2) Template method for replicating superhydrophobic PDMS surfaces

[0049] After mixing the polydimethylsiloxane prepolymer and curing agent at a specific mass ratio and homogenizing them thoroughly, the mixture is transferred to a vacuum degassing device to complete gradient degassing. A polydimethylsiloxane (PDMS) film with high mechanical stability and controllable rheological properties is then formed through a precise temperature-controlled curing process.

[0050] Using the superhydrophobic copper surface obtained in step 1) as a template, it is shaped into a container shape using a mold. A thin layer of release agent is coated on its surface, and the prepared liquid PDMS is cast onto the copper surface for replication. After being left to solidify naturally for 24 hours, the template is peeled off to obtain a transparent PDMS film with a micro-nano layered composite structure.

[0051] 3) Preparation of superhydrophobic / hydrophilic double-sided porous PDMS membrane:

[0052] During the processing, a nanosecond laser is used to fabricate a uniform array of conical micropores on the PDMS film. In this embodiment, the gap between two adjacent pores is set to approximately 500 μm. The conical micropore array covers the entire effective area of ​​the film, and the micropore diameter is 100 μm. A high surface energy superhydrophilic reagent is used to modify the other side of the PDMS film. After the reagent evaporates, this side will become superhydrophilic, thus obtaining a porous PDMS film with one superhydrophobic side and the other superhydrophilic side.

[0053] The gap between two adjacent pores is set to about 300-500 μm, the diameter of the micropores is 100-150 μm, and the conical micropore array covers the entire effective area of ​​the film in a hexagonal close-packed (HCP) configuration.

[0054] Combined with appendix Figure 2 As shown, an apparatus for preparing superhydrophobic copper surface micro / nano composite structures comprises a picosecond pulsed laser system for preparing micron-sized structures and an electrochemical polishing and electrochemical deposition system for preparing nano-sized structures. The picosecond pulsed laser system is used to ablate a workpiece 11. In the electrochemical polishing system, the workpiece 11 is connected to the positive terminal of a power supply 12, and a lead plate 13 is connected to the negative terminal of the power supply 12. The workpiece 11 is placed in a polishing solution 14. In the electrochemical deposition system, the workpiece 11 is placed in an electrolyte 15, and the workpiece 11 is connected to the negative terminal of the power supply 12. A nickel block 16 is connected to the positive terminal of the power supply 12. The micro / nano composite structure is obtained after electrochemical polishing and electrochemical deposition.

[0055] Compared to hydrophobic surfaces obtained by single laser ablation, the micro-protruding surfaces prepared by laser-electrochemical deposition are covered with dense nano-nickel pyramids, forming a multi-scale micro / nano composite structure and a 3D concave corner structure, which significantly improves hydrophobicity. By changing the scanning gap of laser ablation, the morphology of the micro / nano composite structure on the surface of the copper sample can be altered. When the laser scanning gap is equal to the spot diameter, the sample exhibits the optimal and most stable superhydrophobic properties, with a contact angle of up to 161° and a roll-off angle as low as 1°.

[0056] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0057] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention without departing from the principles and spirit of the present invention.

Claims

1. A water-air separation device based on a PDMS superhydrophobic membrane, characterized in that, The system includes a container (3), a PDMS membrane (4), and a floating plate (9). The container (3) is a hollow cavity, placed in seawater (8), and suspended by the floating plate (9). The upper end of the container (3) is connected to a gas supply pipe (2), and the lower end of the container (3) is provided with a PDMS membrane (4). The upper surface of the PDMS membrane (4) is superhydrophilic, and the lower surface is superhydrophobic. Gas passing through the PDMS membrane (4) is collected into a gas storage container through the gas supply pipe (2). The container (3) has an inverted V-shaped structure with an inclination angle of 10°~20°. The PDMS membrane (4) has an inverted V-shaped structure with an inclination angle of 3°~5°. The floating plate (9) is fitted onto the outer ring of the container (3) by a support frame (10). The floating plate (9) has a hollow honeycomb structure and a lateral dimension of 0.6~1.2 mm. m; The container (3) is also provided with a rigid linkage mechanism (5), and a spiral blade (7) is connected to the rigid linkage mechanism (5). The spiral blade (7) is positioned below the PDMS membrane (4). The spiral blade (7) is used to agitate the seawater (8) so that the bubbles (6) can quickly reach the PDMS membrane (4); The PDMS membrane is prepared by the following steps: Step 1) Prepare a superhydrophobic copper surface micro / nano composite structure; Step 2) Based on the superhydrophobic copper surface micro-nano composite structure obtained in Step 1, a superhydrophobic micro-nano structure surface is prepared on one side of the PDMS film using a replication method; Step 3) Use a nanosecond laser to process a uniform conical micropore array on the PDMS film, and use a superhydrophilic reagent to modify the surface of the PDMS film where the uniform conical micropore array is processed to obtain superhydrophilic properties, thereby obtaining a superhydrophilic surface, and finally obtaining a PDMS film with a superhydrophilic upper surface and a superhydrophobic lower surface (4).

2. The water-air separation device based on PDMS superhydrophobic membrane according to claim 1, characterized in that, The gas pipeline (2) is equipped with a negative pressure suction device (1).

3. The water-air separation device based on PDMS superhydrophobic membrane according to claim 1, characterized in that, Step 1, the preparation of the superhydrophobic copper surface micro / nano composite structure, includes mechanical polishing, laser ablation, electrochemical polishing, and electrochemical deposition.

4. The water-air separation device based on PDMS superhydrophobic membrane according to claim 1, characterized in that, The nanosecond laser has a wavelength of 1000~1200nm, a pulse width of 10~15ps, a repetition frequency of 1MHz, an output power of 10~25W, a scanning speed of 150~300mm / s, 25~30 scans, a focused spot diameter of 20~30μm, and a laser scanning gap equal to the focused spot diameter.

5. The water-air separation device based on PDMS superhydrophobic membrane according to claim 1, characterized in that, In step three, the gap between two adjacent holes in the conical micropore array is set to 300~500μm, the diameter of the micropore is 100~150μm, and the conical micropore array covers the entire effective area of ​​the film in a hexagonal close-packed configuration.

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