A light transmissive flexible substrate surface useful for condensing water and method of making

Abstract

The application provides a light-transmitting flexible substrate surface for condensation water collection and a preparation method, comprising a light-transmitting flexible PDMS substrate with micro-pillar structure or micro-pit structure and lubricating oil filled in the microstructure, and the lubricating oil forms a continuous lubricating interface on the substrate surface, so that the condensate droplets can quickly nucleate, grow and slip off. The method comprises the following steps: preparing a microstructure silicon wafer mold, forming a microstructure substrate by using PDMS reverse mold, performing oxygen plasma activation treatment on the substrate surface, and injecting lubricating oil by using dip coating or spin coating. The application can reduce the adhesion and pinning effect of the condensate droplets on the surface by constructing a microstructure array on the surface of the light-transmitting flexible PDMS substrate and injecting lubricating oil into the microstructure to form a continuous and stable lubricating interface, so that the condensate droplets can quickly slip off at a smaller size, thereby improving the refresh frequency of the condensation surface and strengthening the condensation heat exchange and water collection process.

Description

Technical Field

[0001] This invention relates to the field of condensation enhancement and water collection technology, and in particular to a transparent flexible substrate surface that can be used for condensation water collection and its preparation method. Background Technology

[0002] Condensation is widely used in power generation, refrigeration, seawater desalination, atmospheric water collection, and thermal management. Its heat and mass transfer efficiency directly affects system performance, energy consumption, and equipment scale. The key to improving condensation efficiency lies in maintaining a stable bead-like condensation state on the condensation surface, enabling condensate droplets to quickly nucleate, grow, and detach from the surface, thereby continuously refreshing the condensation surface and reducing heat transfer resistance. In existing technologies, surface modification is often achieved through physical or chemical methods to obtain a condensation surface with bead-like condensation. Although traditional hydrophobic surfaces can promote the formation of discrete bead-like droplets, due to surface microstructure defects or chemical inhomogeneities, the droplets are prone to large contact angle hysteresis and pinning effects. They usually need to grow to a large size before they can detach, resulting in a low surface renewal frequency and limited condensation heat transfer and water collection efficiency.

[0003] To address the aforementioned issues, slippery liquid-infused porous surfaces (SLIPS) are developed by injecting a lubricant that is immiscible with the condensing liquid into the micro-nano structure. This creates a continuous lubrication interface on the surface, thereby reducing droplet adhesion and contact angle hysteresis, promoting the rapid sliding and detachment of small droplets, and demonstrating good potential for condensation enhancement.

[0004] However, existing SLIPS still have shortcomings in practical applications: some substrates are made of metallic or inorganic rigid porous materials, which have poor flexibility and are difficult to adapt to curved or complex surfaces; although some flexible substrates have a certain deformation capacity, their condensation and water collection efficiency is still low; at the same time, existing lubricating surfaces still suffer from lubricant loss under long-term condensation or disturbance conditions, affecting their stability and service life. To address these issues, this invention proposes a transparent flexible substrate surface for condensation and water collection and its preparation method. Summary of the Invention

[0005] This invention provides a transparent flexible substrate surface that can be used for condensation and water collection, and a method for preparing it, in order to solve or alleviate specific technical problems existing in the prior art, or at least provide a beneficial technical option for solving such problems.

[0006] The technical solution of the present invention is as follows: a light-transmitting flexible substrate surface that can be used for condensation water collection includes a light-transmitting flexible PDMS substrate and a liquid-filled super-lubricating microstructure layer disposed on at least one side surface of the PDMS substrate; the liquid-filled super-lubricating microstructure layer includes a microstructure array on the surface of the PDMS substrate and lubricating oil injected into the microstructure array; the microstructure array is composed of multiple spaced micropillar structures or micropit structures to form a liquid storage space for accommodating the lubricating oil between adjacent micropillars or inside the micropits; the lubricating oil is held in the liquid storage space and covers the functional surface of the PDMS substrate to form a continuous lubrication interface, allowing condensate droplets to nucleate, grow and slide off on the continuous lubrication interface, thereby realizing condensation water collection.

[0007] More preferably, the microstructures in the microstructure array can be circular, square, hexagonal, or star-shaped, and the arrangement of the microstructure array can be periodic, staggered, quasi-periodic, or random; the characteristic size of the microstructure array is 5–95 μm, and the depth of the microstructure is 5–100 μm. By controlling the morphology, size, and arrangement of the microstructures, lubricant retention capacity, droplet mobility, and light transmittance can be balanced, thereby obtaining a condensate collection surface with superior performance.

[0008] More preferably, the lubricating oil is an immiscible lubricating medium that can be stably maintained within the microstructure, preferably a perfluoropolyether oil, and more preferably Krytox VPF-1514. This lubricating oil has suitable interfacial tension parameters, which allows condensate droplets to remain on the surface of the lubricating layer during condensation without being encapsulated by the lubricating oil, thereby reducing the loss of lubricating oil with the droplets during droplet detachment and improving the long-term lubrication stability of the surface.

[0009] Further preferably, the PDMS substrate has good transparency and flexible deformation capability, which can be attached to curved or irregular surfaces and maintain the integrity of the continuous lubrication interface in the attached state, thus making it suitable for applications such as curved surface condensation water collection, flexible water collection, and applications requiring light transmittance.

[0010] The present invention also provides a method for preparing the above-mentioned transparent flexible substrate surface that can be used for condensation and water collection, comprising the following steps: S1. Prepare a silicon wafer mold with a microstructure array; S2. After mixing the PDMS prepolymer with the curing agent, the mixture is poured onto the surface of the silicon wafer mold. After degassing, curing, and peeling, a PDMS substrate with opposite microstructure arrays is obtained. S3. Perform oxygen plasma activation treatment on the surface of the PDMS substrate; S4. Lubricating oil is injected into the activated PDMS substrate microstructure using dip coating or spin coating, so that the lubricating oil fills and is maintained in the liquid storage space formed by the microstructure array, thereby obtaining the light-transmitting flexible substrate surface.

[0011] More preferably, in step S1, the silicon wafer mold is prepared by photolithography and dry etching processes, which may include: cleaning and drying the silicon wafer in sequence; spin-coating an adhesion promoter and photoresist on the surface of the silicon wafer and pre-baking; transferring the preset microstructure pattern to the photoresist layer by photolithography exposure; after development and post-baking hardening, dry etching is performed to obtain a silicon wafer mold with a microstructure array.

[0012] More preferably, in step S2, the PDMS prepolymer and curing agent are mixed at a mass ratio of 10:1, poured onto the surface of the silicon wafer mold, and then vacuum degassed and cured at 60~100 ℃ for 2~5 hours to obtain a transparent PDMS substrate with opposite microstructure arrays.

[0013] More preferably, in step S3, the power of the oxygen plasma activation treatment is 50~120 W and the treatment time is 60~180 seconds, so as to enhance the oleophilicity and lubricant retention ability of the PDMS substrate surface.

[0014] More preferably, in step S4, when the dip coating method is used, the activated PDMS substrate is completely immersed in lubricating oil and transferred to a vacuum chamber. After soaking for 30 to 180 minutes, it is taken out and then left to stand vertically for more than 12 hours to remove excess lubricating oil from the surface. When the spin coating method is used, the sample is transferred to a vacuum chamber so that the lubricating oil fills the microstructure pores of the PDMS substrate. Then, the excess lubricating oil on the surface is removed by spin coating and centrifugation to obtain a transparent flexible substrate surface with uniformly distributed lubricating oil.

[0015] The embodiments of the present invention have the following advantages due to the adoption of the above technical solutions: I. This invention constructs a microstructure array on the surface of a transparent flexible PDMS substrate and injects lubricating oil into the microstructure to form a continuous and stable lubrication interface. This reduces the adhesion and pinning effect of condensate droplets on the surface, allowing condensate droplets to quickly slide off at a smaller size. This improves the refresh frequency of the condensation surface, enhances condensation heat transfer and water collection processes. The water collection efficiency per unit area of ​​the surface of this invention can reach 0.31 ± 0.026 g / cm³ within 8 hours. 2 It offers a significant improvement over traditional condensation surfaces.

[0016] Second, this invention forms a stable liquid storage space by processing micro-pillar or micro-pit structures, which allows the lubricating oil to be stably maintained in the microstructure of the substrate surface. Combined with the selection of lubricating oil that does not form a coating layer on the surface of condensed water droplets, the lubricating oil loss during the shedding of condensed water droplets is reduced, thereby improving the surface lubrication stability and long-term performance. The contact angle hysteresis of the surface of this invention is still less than 6° after 8 hours of condensation, and the amount of lubricating oil loss is low.

[0017] Third, this invention uses PDMS as the substrate material, which makes the resulting surface have both good optical transparency and flexible deformation ability. It can not only meet the application scenarios with high light transmission requirements, but also be attached to curved or irregular surfaces. It overcomes the problem of poor adaptability to complex surfaces of some existing rigid SLIPS surfaces, thereby broadening the application range of condensate collection surfaces. IV. The preparation method of the present invention is based on photolithography, etching, PDMS molding, surface activation and lubricating oil injection and other process steps. The overall process route is clear and has good repeatability, which makes it easy to prepare large-area, flexible and transparent condensation surfaces. It has good engineering application prospects and promotion value. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram illustrating the preparation process of the transparent flexible substrate surface that can be used for condensation and water collection according to the present invention; Figure 2 These are photographs of the water droplet contact angle, surface deformation, and condensation behavior on the surface of the transparent flexible substrate of the present invention. Figure 3 This is a graph showing the efficiency of the transparent flexible substrate surface of the present invention during condensation and water collection. Figure 4 This is a diagram showing the lubricating oil loss per unit area on different condensation surfaces according to the present invention. Detailed Implementation

[0020] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of the invention. Therefore, the drawings and description are considered to be exemplary in nature and not restrictive.

[0021] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0022] like Figures 1-4 As shown, this invention provides a transparent flexible substrate surface and its preparation method for condensate water collection. PDMS is used as the transparent flexible substrate. A stable liquid storage space is provided by constructing a microstructure array. A continuous lubrication interface is formed by combining this with a lubricating oil that is immiscible with condensate water. This reduces the adhesion and pinning of condensate droplets on the surface, allowing droplets to slide and detach quickly at a smaller size, thereby improving the refresh frequency of the condensate surface and the water collection efficiency per unit area. Simultaneously, the microstructure's ability to retain the lubricating oil, combined with the selection of a lubricating oil that does not form a coating layer on the condensate droplet surface, reduces the loss of lubricating oil under long-term condensation or external disturbance conditions, thus balancing transparency, flexibility, and long-term stability.

[0023] Figure 2 The markings are specifically (a) the water contact angle on a SLIPS with a pit diameter of 90 μm; (b) SLIPS attached to the outer wall of a cylindrical test tube; and (c) the condensation behavior on the SLIPS on the outer wall of a cylindrical test tube.

[0024] Figure 3 The mark P in the text represents the micropillar structure, the number represents the diameter of the micropillar (μm), and Glaco Silicon represents the surface of a conventional Glaco superhydrophobic coated flat silicon wafer.

[0025] Figure 4 In this context, P represents the micropillar structure, C represents the micropit structure, the number represents the diameter of the micropillar (μm), and F-LIS represents the porous foam substrate lubricating surface in the literature.

[0026] Example 1: Fabrication of a translucent flexible substrate surface with a regular micropillar array In this embodiment, a transparent PDMS substrate with a regular micropillar array structure on its surface is prepared, and lubricating oil is injected by dip coating method to obtain a light-transmitting flexible substrate surface for condensation and water collection.

[0027] A microstructured silicon wafer mold was prepared using a 4-inch single-sided polished silicon wafer as the substrate. The wafer was sequentially cleaned with acetone, ethanol, and deionized water to remove organic contaminants, particulate impurities, and residual ions. After cleaning, it was dried with high-purity nitrogen and baked on a 120°C hot plate for 10 minutes to ensure complete drying. Subsequently, hexamethyldisilane adhesion promoter was spin-coated onto the wafer surface at 3000 rpm for 30 minutes, followed by drying on a 90°C hot plate for 10 minutes to improve the adhesion of the subsequent photoresist to the wafer surface. Then, positive photoresist was spin-coated at 3000 rpm for 30 seconds. After spin-coating, it was pre-baked on a 90°C hot plate for 10 minutes to remove solvent from the photoresist and form a stable adhesive layer. In this embodiment, a mask containing circular micro-pit structure patterns of different sizes is used for exposure. The micro-structure patterns include a circular array with a diameter of 25–90 μm and a center-to-center spacing of 100 μm. The silicon wafer coated with photoresist is placed in an ultraviolet lithography machine for contact exposure for 9 seconds to accurately transfer the mask pattern to the photoresist layer. After exposure, the silicon wafer is immersed in a 0.5% NaOH aqueous solution for 40 seconds to remove the photoresist in the exposed area, exposing the silicon substrate at the corresponding location. After development, the wafer is thoroughly rinsed with deionized water and dried with nitrogen gas, and then post-baked on a hot plate at 120 °C for 30 minutes to improve the etching resistance of the photoresist layer and the clarity of the pattern boundaries. After the photolithographic pattern transfer is completed, dry etching is performed to form a mold with a regular micro-pit structure. In this embodiment, the preferred etching depth is 50 μm. After etching, a microstructure array with high uniformity, clear boundaries, and relatively steep sidewalls is formed on the surface of the silicon wafer. After etching, the silicon wafer is ultrasonically cleaned with acetone, ethanol, and deionized water in sequence to remove residual photoresist and etching byproducts. Finally, it is dried with nitrogen to obtain a microstructure silicon wafer master mold that can be used for casting. Subsequently, a PDMS substrate with opposite microstructures was prepared using the aforementioned silicon wafer master mold. PDMS raw materials were taken, and the prepolymer and curing agent were mixed at a weight ratio of 10:1 and stirred thoroughly. The mixture was then slowly poured onto the surface of the microstructured silicon wafer master mold and degassed in a vacuum chamber. After degassed, the sample and mold were placed in a 90 ℃ oven for 5 hours to allow the PDMS to fully crosslink and solidify. After curing, the PDMS layer was smoothly peeled off from the surface of the silicon wafer mold to obtain a transparent PDMS substrate with an array of reverse microstructures; that is, the silicon wafer mold is an array of micropits, and the obtained PDMS substrate is an array of micropillars. After the stripped PDMS substrate is cut to a size suitable for testing or application, it is placed in an oxygen plasma treatment instrument and treated at 100 W power for 120 seconds. After treatment, the surface energy of the PDMS surface is increased, which is more conducive to the subsequent entry of lubricating oil into the microstructure and its stable retention on the substrate surface. Regarding the selection of lubricating oil, this embodiment uses Krytox VPF-1514 perfluoropolyether oil as the lubricating phase; this lubricating oil is immiscible with condensate and has good thermal and chemical stability; its oil-gas interfacial tension... Approximately 20 mN·m -1 Water-oil interfacial tension Approximately 54.6 mN·m -1 Water-air interfacial tension Approximately 72 mN·m -1 ; Therefore, the spreading coefficient of water at the oil-gas interface is calculated as follows:

[0028] because This indicates that the water droplets generated during condensation are not completely enveloped by the lubricating oil, but rather form a coating layer on the outside of the droplets, existing in a spherical shape on the lubricating oil film. This characteristic effectively reduces the lubricating oil loss when condensed droplets detach, thereby improving the long-term lubrication stability of the surface.

[0029] In this embodiment, the lubricating oil is injected using the dip-coating method. The specific procedure is as follows: The PDMS substrate, activated by oxygen plasma, was completely immersed in Krytox VPF-1514 lubricating oil and transferred to a vacuum chamber for 30 minutes to remove the original air inside the microstructure. This allowed the lubricating oil to fully fill the reservoir space of the microstructure under capillary action and pressure difference. After immersion, the sample was removed and stood vertically for at least 12 hours, allowing excess lubricating oil not retained by the microstructure to gradually flow away under gravity. This resulted in a uniform, continuous, and appropriately thick lubricating interface on the PDMS substrate surface, yielding a transparent flexible substrate surface suitable for condensation and water collection.

[0030] The surface prepared in this embodiment retains the original transparency of the PDMS substrate on a macroscopic level, while forming a liquid-filled superlubricating interface composed of microstructures and lubricating oil on a microscopic level. This structure relies on the microstructure array to contain and restrict the loss of lubricating oil, and on the lubricating oil to form a low-adhesion interface on the surface, allowing condensed water droplets to slide off quickly.

[0031] Example 2: Fabrication of a transparent flexible substrate surface with a regular micro-pit array The main difference between this embodiment and Embodiment 1 is that the silicon wafer mold adopts a regular micropillar array pattern, thereby replicating a regular micro-pit array structure on the PDMS substrate surface; and the lubricating oil injection method adopts spin coating.

[0032] Specifically, the preparation steps of the silicon wafer mold are basically the same as in Example 1, except that the mask pattern is preferably a micropillar array structure, the pattern shape can be circular, the feature size can be selected from 25 to 90 μm, and the etching depth is controlled within the range of 45 to 65 μm. In this example, it is preferably 50 μm. After completing the PDMS molding, degassing, and curing and peeling, a transparent flexible PDMS substrate with a regular micro-pit array is obtained.

[0033] Subsequently, the PDMS substrate was activated by oxygen plasma under the same conditions as in Example 1. After activation, lubricating oil was introduced into the gaps between the micro-pit arrays in a vacuum chamber, so that the lubricating oil could fully fill the reservoir space formed inside the micro-pits. Then, the sample was centrifuged by spin coating to remove excess lubricating oil from the surface, leaving only the lubricating oil layer effectively maintained by the microstructure array. After spin coating, the sample surface still retains a continuous lubrication interface, and the excess oil layer on the surface is more controllable, which is conducive to obtaining a more uniform interface state. The surface prepared in this embodiment also has good transparency, flexibility and super-slip properties, and can be used for condensation and water collection; compared with dip coating, spin coating is more suitable for rapid adjustment and control of the surface oil film thickness, and is suitable for application scenarios that require control of the amount of residual oil on the surface; Example 3: Application under curved surface attachment conditions To verify the flexible adaptability of the surface of the present invention, the light-transmitting flexible substrate surface prepared in Example 1 or Example 2 was attached to the outer wall of a cylindrical test tube (radius of curvature of 1.45 cm). Since the PDMS substrate itself has good flexibility and a relatively thin overall thickness, the surface can bend and fit in accordance with the curvature change without causing obvious cracking, delamination or interruption of the lubrication interface due to bending. As attached Figure 2 As shown in (b), the resulting surface adheres tightly to the outer wall of the cylindrical test tube while maintaining good interfacial integrity; as shown in the attached diagram. Figure 2 As shown in (c), under condensation conditions, the surface attached to the curved outer wall can still achieve nucleation, growth, migration and collection of condensate droplets, indicating that the surface of the present invention is not only suitable for planar condensation water collection, but also for water collection conditions of curved surfaces and irregularly shaped transparent surfaces; this characteristic makes it have good application value in scenarios with transparent components such as solar water collection covers, curved heat exchangers, ships and RVs.

[0034] Test Example 1: Apparent Wettability and Superlubricity Test To verify the wettability and droplet migration ability of the surface of the present invention, static contact angle and contact angle hysteresis tests were performed on the samples prepared in the examples, with deionized water droplets as the test objects; Test results show that, as attached Figure 2 As shown in (a), water droplets exhibit a distinctly spherical shape on the SLIPS surface prepared according to this invention, with a static contact angle of approximately 105.8°–106.2°. Although this contact angle is lower than that of some conventional superhydrophobic surfaces, the contact angle hysteresis of the surface of this invention is less than 3°, indicating that the difference between the advancing and retreating contact angles of the droplets on this surface is small, and the adhesion resistance between the droplets and the surface is low. Under slight tilting or the action of a small external force, small-sized droplets can move and detach quickly, demonstrating that the surface of this invention has excellent super-slippery properties.

[0035] Furthermore, after 8 hours of continuous condensation operation, the surface was tested again, and its contact angle hysteresis was still less than 6°. This indicates that after a certain period of condensation, the surface can still maintain good low adhesion characteristics and droplet slippage ability, reflecting the good long-term stability of the surface of the present invention.

[0036] Test Example 2: Condensation Water Collection Performance Test To verify the condensation enhancement and water collection performance of the surface of the present invention, the surface of the present invention was compared with the unstructured surface of a traditional hydrophobic coating under the same condensation test conditions; the test period was 8 hours, and the water collection per unit area was recorded.

[0037] During the experiment, it was observed that the condensation droplets on the surface of the present invention could slide or detach when they grew to a relatively small critical size (~3.8±0.8 mm), and the exposed surface area could quickly re-participate in the subsequent condensation process, thus resulting in a high surface renewal frequency. In contrast, the condensation droplets on the traditional hydrophobic control surface were more likely to remain and pin, and needed to continue growing to a larger size before they could roll off by gravity. This resulted in some surfaces being occupied by droplets for a long time, reducing the effective condensation area and continuous water collection capacity.

[0038] The experimental results are attached. Figure 3 As shown, the water collection efficiency per unit area of ​​the surface of the present invention reaches 0.31 ± 0.026 g / cm³ over 8 hours. 2 The water collection efficiency of a traditional Glaco superhydrophobic coating on a flat silicon wafer surface is 0.24 ± 0.015 g / cm³. 2 Compared to traditional control surfaces, the water collection efficiency per unit area of ​​the surface of this invention is increased by approximately 27.4%. The above results demonstrate that the present invention, through the synergistic design of the microstructure liquid storage and lubrication interface, significantly improves the migration and detachment behavior of condensate droplets on the surface, thereby effectively improving the condensation and water collection efficiency.

[0039] Test Example 3: Lubricating Oil Loss Test To verify the surface's ability to retain lubricating oil, a centrifugal loss simulation test was conducted. During the test, the prepared sample was vacuum-adsorbed onto the center of the spin coater's turntable. The rotation speed was set to 2000–7000 rpm and continued for 10 seconds to simulate the loss of lubricating oil adhering to the surface under shear or disturbance conditions using the centrifugal force generated by the high-speed rotation. The sample mass was measured using a precision electronic balance before and after the test, and the difference was taken as the amount of lubricating oil loss.

[0040] The experimental results are attached. Figure 4As shown, compared with the porous foam-based lubricating surface (F-LIS) in the literature, the translucent flexible substrate surface of the present invention exhibits significantly lower lubricant loss mass under the same centrifugal conditions. Under higher centrifugal force conditions, the surface of the present invention can reduce lubricant loss by 23.7% to 28.2% compared with the F-LIS surface. This result indicates that the present invention, by constructing a regular microstructure array on the PDMS substrate surface, enables lubricant to be stored more stably in the reservoir space formed by the microstructure, thereby exhibiting better resistance to lubricant loss.

[0041] The reason why this invention can simultaneously achieve condensation water collection efficiency, lubrication stability, and flexible transparency is mainly due to the synergistic effect of the following aspects: Firstly, the microstructure array provides a stable reservoir for lubricating oil. Whether it is a micropillar array or a micropit array, it can keep the lubricating oil in the surface area through spatial confinement, preventing the lubricating oil from flowing out quickly during use, and at the same time providing a basis for the formation of a continuous lubrication interface on the surface.

[0042] Secondly, the lubricant selection and interfacial tension relationship were matched. When Krytox VPF-1514 was used as the lubricant, it met the requirements of interfacial tension with condensate. Under the condition of the spreading coefficient, the water droplets formed by condensation will not be wrapped by the oil film, but exist in the surface of the lubricating layer in the shape of a spherical cap and slide off quickly, reducing the loss of lubricating oil when the droplets fall off.

[0043] Thirdly, the PDMS substrate itself possesses excellent optical transparency, flexibility, and formability. On the one hand, PDMS can accurately obtain microstructures complementary to the silicon wafer mold by etching the microstructures on the silicon wafer through molding, facilitating the fabrication of highly consistent functional surfaces. On the other hand, the PDMS surface can adapt to certain curvature changes, making the surface of this invention suitable not only for planar condensation water collection but also for water collection applications on curved, arc-shaped, and other irregularly shaped surfaces. Implementation Description In the above embodiments, the shape of the microstructure can be selected as circular, square, hexagonal, or star-shaped according to application requirements, and its arrangement can be periodic array, staggered arrangement, quasi-periodic distribution, or random distribution; the characteristic size of the microstructure can be selected in the range of 5–95 μm, and the depth can be adjusted in the range of 5–100 μm. Different sizes and arrangements of microstructures will affect the lubricating oil retention capacity, condensate droplet slippage behavior, and light transmittance. Those skilled in the art can make reasonable selections within the scope of this invention based on specific working conditions.

[0044] Similarly, the lubricating oil injection method is not limited to the above-mentioned dip coating and spin coating methods. Provided that the lubricating oil can stably enter the microstructure and form a continuous lubrication interface, other filling methods that can achieve similar effects can also be used. The size, thickness and specific attachment method of the PDMS substrate can also be adjusted according to the actual application.

[0045] This embodiment prepared and verified a liquid-filled super-lubricating porous surface that combines high condensation efficiency, long-term lubrication stability, optical transparency, and good flexibility. Experimental data show that this surface effectively solves the main bottleneck of SLIPS technology in practical condensation applications, namely, lubricating oil loss and condensation efficiency reduction during long-term condensation. It provides a reliable and promising technical solution for developing the next generation of efficient and durable condensation water collection, mist collection, and thermal management systems.

[0046] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various variations or substitutions within the technical scope disclosed in the present invention, and these should all be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A transparent flexible substrate surface that can be used for condensation water collection, characterized in that, It includes a light-transmitting flexible PDMS substrate and a liquid-filled super-lubricated microstructure layer disposed on at least one side surface of the PDMS substrate; The fluid-filled super-lubricating microstructure layer includes a microstructure array formed on the surface of the PDMS substrate and lubricating oil injected into the microstructure array; The microstructure array consists of multiple spaced micropillar structures or micropit structures to form a reservoir space for containing the lubricating oil between adjacent micropillars or inside the micropits. The lubricating oil is held within the reservoir and covers the functional surface of the PDMS substrate to form a continuous lubrication interface, allowing condensate droplets to nucleate, grow, and slide off on the continuous lubrication interface, thereby achieving condensate collection.

2. The transparent flexible substrate surface for condensation water collection as described in claim 1, characterized in that, The microstructures in the microstructure array are circular, square, hexagonal, or star-shaped, and the microstructure array is arranged in a periodic array, staggered arrangement, quasi-periodic distribution, or random distribution.

3. The transparent flexible substrate surface for condensation water collection as described in claim 1, characterized in that, The microstructure array has a feature size of 5–95 μm and a depth of 5–100 μm.

4. The transparent flexible substrate surface for condensation water collection as described in claim 1, characterized in that, The lubricating oils include, but are not limited to, synthetic oils such as perfluoropolyether oil and dimethyl silicone oil, as well as mineral oil and bio-based oil.

5. The transparent flexible substrate surface for condensation water collection as described in claim 1, characterized in that, The PDMS substrate has flexible deformation capability, which can be attached to curved or irregular surfaces, and maintain the integrity of the continuous lubrication interface in the attached state for use in condensation and water collection on curved surfaces.

6. A method for preparing a transparent flexible substrate surface for condensation and water collection as described in any one of claims 1 to 5, characterized in that, Includes the following steps: S1. Prepare a silicon wafer mold with a microstructure array; S2. After mixing the PDMS prepolymer with the curing agent, the mixture is poured onto the surface of the silicon wafer mold. After degassing, curing and peeling, a PDMS substrate with opposite microstructure arrays is obtained. S3. Perform oxygen plasma activation treatment on the surface of the PDMS substrate; S4. Lubricating oil is injected into the activated PDMS substrate microstructure using dip coating or spin coating, so that the lubricating oil fills and is maintained in the liquid storage space formed by the microstructure array, thereby obtaining the light-transmitting flexible substrate surface.

7. The preparation method according to claim 6, characterized in that, Step S1 includes: The silicon wafers are cleaned and dried sequentially, and then an adhesion enhancer and photoresist are spin-coated onto the surface of the silicon wafers and pre-baked. A pre-defined microstructure pattern is transferred to a photoresist layer through photolithography exposure. After development and post-bake hardening, dry etching is performed to obtain a silicon wafer mold with a microstructure array.

8. The preparation method according to claim 6, characterized in that, In step S2, the PDMS prepolymer and curing agent are mixed at a mass ratio of 10:1, poured onto the surface of the silicon wafer mold, and then vacuum degassed and cured at 60~100 ℃ for 2~5 hours to obtain a light-transmitting flexible PDMS substrate with opposite microstructure arrays.

9. The preparation method according to claim 6, characterized in that, In step S3, the power of the oxygen plasma activation treatment is 50~120 W, and the treatment time is 60~180 seconds.

10. The preparation method according to claim 6, characterized in that, In step S4: When using the dip coating method, the activated PDMS substrate is completely immersed in lubricating oil and transferred to a vacuum chamber. After soaking for 30 to 180 minutes, it is removed and then left to stand vertically for more than 12 hours to remove excess lubricating oil from the surface. When using spin coating, the substrate is first left to stand in a vacuum chamber for 30 to 180 minutes to allow the lubricating oil to fill the microstructure pores of the PDMS substrate. Then, excess lubricating oil on the surface is removed by spin coating and centrifugation to obtain a transparent flexible substrate surface with uniformly distributed lubricating oil.

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