A cooling and water-saving coupled refrigeration film based on a biomimetic micro-nano structure and a preparation method thereof

Abstract

The present application relates to a kind of cooling water-saving coupling refrigeration film based on bionic micro-nano structure and its preparation method, belong to the technical field of facility agriculture covering material.To solve the problem that existing technology cannot realize efficient refrigeration, atmospheric water collection, green preparation and agricultural adaptation simultaneously, the present application provides a kind of cooling water-saving coupling refrigeration film based on bionic micro-nano structure, including flexible composite substrate, the surface of flexible composite substrate has regularly arranged micro-pyramid array structure, and the inside of flexible composite substrate is uniformly dispersed with nano-particle of high emissivity to infrared light and high transmissivity to visible light;The top of micro-pyramid array is hydrophilic area, and the body and substrate are hydrophobic area, to form hydrophilic and hydrophobic hetero micro area.The present application has excellent radiative refrigeration, high-efficiency water collection capacity, self-cleaning weather resistance through bionic micro-nano structure and function synergistic design, preparation process is simple and controllable, energy-saving emission-reduction benefit is remarkable, adapts greenhouse application, and has practicality and industrialization potential.

Description

Technical Field

[0001] This invention belongs to the field of facility agriculture covering materials technology, and particularly relates to a cooling and water-saving coupled refrigeration film based on a biomimetic micro-nano structure and its preparation method. Background Technology

[0002] As a core carrier of modern agriculture, facility agriculture faces key bottlenecks hindering its development, including high summer temperatures, high energy consumption for cooling, and water shortages for irrigation. Traditional greenhouses rely on active cooling methods such as fans, evaporative cooling pads, and shade nets, resulting in enormous annual electricity consumption, high operating costs, and significant humidity fluctuations that negatively impact crop growth. Conventional irrigation methods also suffer from low water resource utilization, a problem particularly acute in arid and semi-arid regions. Against this backdrop, passive radiative cooling coupled with atmospheric water collection technology has emerged as a crucial development direction for achieving zero-energy cooling and in-situ water-saving irrigation.

[0003] However, existing agricultural covering materials and cooling and water collection technologies generally suffer from problems such as limited functionality, low integration, and significant performance bottlenecks, making it difficult to meet the needs of efficient and green development in facility agriculture. Traditional agricultural films only possess basic functions such as heat preservation, light transmission, and anti-fogging, lacking efficient cooling capabilities. Conventional radiative cooling materials, on the other hand, focus only on solar reflection and infrared radiation heat dissipation, without integrating water collection and irrigation functions, failing to achieve integrated cooling and water resource recycling, and struggling to cope with the dual pressures of high temperatures and water scarcity. Furthermore, there is a clear antagonistic mechanism between cooling and water collection. High-performance radiative cooling requires high solar reflectivity and a smooth surface to ensure optical performance, but such surfaces are not conducive to water vapor nucleation and adhesion. Conversely, the porous hydrophilic surface required for water collection easily forms a water film that blocks the light path, significantly reducing solar reflectivity and cooling efficiency, making it difficult to achieve both simultaneously. Furthermore, existing micro-nano structures are mostly designed for optical targets and do not take into account the need for rapid water droplet transport in agricultural scenarios. Condensate is easily pinned and retained on the surface, causing secondary evaporation, resulting in extremely low water collection efficiency. Moreover, the structure is prone to clogging and has poor weather resistance, making it unsuitable for long-term outdoor use in greenhouses. High-end radiation cooling films mostly use complex processes such as vacuum coating and photolithography etching, which are costly and have rigid substrates. They cannot meet the requirements of flexibility, rollability, and large-area application for agricultural films. Some processes also use toxic reagents, which do not meet the standards for green agricultural production. Summary of the Invention

[0004] To address the limitations of existing technologies in simultaneously achieving efficient cooling, atmospheric water collection, green manufacturing, and agricultural compatibility, this invention provides a cooling and water-saving coupled cooling film based on a biomimetic micro / nano structure and its preparation method.

[0005] The technical solution of the present invention:

[0006] A cooling and water-saving coupled refrigeration film based on biomimetic micro-nano structures includes a flexible composite substrate. The surface of the flexible composite substrate has a regularly arranged micro pyramid array structure. The interior of the flexible composite substrate is uniformly dispersed with nanoparticles that have high emissivity to infrared light and high transmittance to visible light. The top of the micro pyramid array is a hydrophilic region, while the body and the substrate are hydrophobic regions, forming a hydrophilic-hydrophobic heterogeneous micro-region.

[0007] Furthermore, the thickness of the flexible composite substrate is 50~300μm, and the side length of the array unit substrate of the micro pyramid array structure is 3~5μm, and the height is 2.1~3.5μm.

[0008] Furthermore, the static water contact angle of the hydrophilic region is 60~75°, and the contact angle of the hydrophobic region is 115~130°.

[0009] Furthermore, the nanoparticles include SiO2 nanoparticles and ITO nanoparticles, wherein the SiO2 nanoparticles have a particle size of 200-400 nm and the ITO nanoparticles have a particle size of 50-100 nm; the flexible composite substrate is composed of polydimethylsiloxane doped with SiO2 and ITO nanoparticles.

[0010] A method for preparing a cooling and water-saving coupled refrigeration thin film based on a biomimetic micro / nano structure includes the following steps:

[0011] Step 1: Prepare a silicon master template with a regular micro pyramid array;

[0012] Step 2: Cast a curable polysiloxane mixture doped with SiO2 and ITO nanoparticles onto the surface of a silicon master template, control the coating thickness with a scraper, then cure and demold to obtain a flexible composite substrate with a surface replicating a micro pyramid structure and the nanoparticles uniformly dispersed inside.

[0013] Step 3: Perform an overall vapor phase hydrophobic treatment on the flexible composite substrate obtained in Step 2 to make the pyramid body and base area hydrophobic.

[0014] Step 4: Selectively hydrophilically modify the top of the pyramid of the flexible composite substrate obtained in Step 3 to make the top region hydrophilic, forming a hydrophilic-hydrophobic heterogeneous micro-region.

[0015] Furthermore, the silicon master template mentioned in step one uses... <100> The crystal-oriented single-crystal silicon wafer is prepared by wet etching; the etching solution contains potassium hydroxide and isopropanol, wherein the mass concentration of potassium hydroxide is 5%, the volume concentration of isopropanol is 2%, the etching temperature is 80℃, and the etching time is 30~40min.

[0016] Furthermore, the preparation method of the curable polysiloxane mixture doped with SiO2 and ITO nanoparticles in step two is as follows: First, tetraethyl orthosilicate, anhydrous ethanol, and deionized water are reacted under the catalysis of ammonia to obtain a siloxane sol. Then, SiO2 and ITO nanoparticles are added, and after dispersion and solvent removal, a functional filler concentrate is obtained. Finally, the functional filler concentrate is mixed evenly with PDMS prepolymer and PDMS curing agent in a certain proportion, and then degassed. The silicon master template is subjected to anti-sticking treatment before casting. The silicon master template and hydrophobic treatment agent are placed together in a sealed container and heat-treated at 70~90℃ for 1~3h to form a hydrophobic layer on the template surface. The coating thickness is 50~100μm. The curing temperature is 60℃ and the curing time is 4h.

[0017] Furthermore, the preparation method of the functional filler concentrate is as follows: anhydrous ethanol, deionized water, and tetraethyl orthosilicate are mixed in a volume ratio of 8~12:1.5~2.5:0.8~1.2, and after stirring, ammonia water is added dropwise as a catalyst. The amount of ammonia water is 0.3~0.8% of the total volume of the reaction solution. The mixture is stirred at room temperature for 1~3 hours to obtain a transparent sol. Nanoparticles are added to the sol to make the concentration of SiO2 nanoparticles in the sol 0.07~0.12 g / mL and the concentration of ITO nanoparticles 0.04~0.08 g / mL. After magnetic stirring, the mixture is ultrasonically dispersed in an ice bath for 0.5~1.5 hours. Then, the solvent is removed to obtain the functional filler concentrate. The mass ratio of the functional filler concentrate, PDMS prepolymer, and PDMS curing agent is 1.5~3:10:1.

[0018] Furthermore, the method for the vapor-phase hydrophobication treatment described in step three is as follows: The flexible composite substrate obtained in step two is irradiated under ultraviolet light for activation treatment. The ultraviolet wavelength is 150~300nm and the irradiation intensity is 1~20mW / cm². 2 The irradiation distance is 1~20mm and the irradiation time is 5~20min. The UV-activated flexible composite substrate and the hydrophobic treatment agent are placed together in a sealed container. The flexible composite substrate is suspended with the pyramid face down and does not contact the hydrophobic treatment agent. Vapor deposition is carried out at 70~90℃ for 1~2h. After taking it out, it is heat-treated at 100~130℃ for 20~40min to complete the crosslinking and curing.

[0019] Further, the selective hydrophilic modification method described in step four is as follows: Prepare a 1-3 mg / mL dopamine hydrochloride solution using a pH=8.0-9.0, 8-12 mmol / L Tris-HCl buffer solution. Coat the dopamine hydrochloride solution uniformly onto a clean, UV-activated glass slide. Control the coating thickness to 10-30 μm using a scraper. Allow the slide to stand at room temperature in the dark for 3-8 minutes to form an adhesive coating. Place the flexible composite substrate (after hydrophobic treatment in step three) with its pyramidal face down, ensuring the pyramid apex contacts and adheres to the resulting adhesive coating. Apply pressure to the back of the flexible composite substrate to ensure a smooth, adhered fit. Allow the slide to stand at room temperature in the dark for 10-20 minutes. After smoothly peeling off the flexible composite substrate, rinse 2-4 times with deionized water to remove unpolymerized dopamine. Dry with nitrogen and dry at 50-70°C for 20-40 minutes to obtain the finished cooling and water-saving coupled refrigeration film.

[0020] The beneficial effects of this invention are:

[0021] This invention achieves excellent spectral modulation capabilities through the synergistic effect of the geometric scattering effect of the biomimetic micro-nano pyramid array structure and the Mie scattering of SiO2 and ITO nanoparticles. Experimental tests show that the infrared emissivity of the film of this invention can reach 95.3% in the 8-13μm atmospheric window band, and the transmittance in the 400-700nm photosynthetically active light band can reach 87.6%, which can both ensure the light requirements of crops and efficiently reflect thermal radiation. Outdoor tests show that the film of this invention can achieve a maximum temperature reduction of 8.1℃ during the midday high temperature period, with an average cooling power of 89.6W / m. 2 Peak value reaches 128W / m 2 Taking Riyadh, a tropical desert climate, as an example, a 100-square-meter greenhouse using this material can save 16,788 kilowatt-hours of electricity annually, equivalent to reducing CO2 emissions by 10,311 kg.

[0022] This invention utilizes the naturally formed V-shaped microchannels between adjacent units of a micro-pyramid array, combined with a hydrophilic (hydrophilic at the top, contact angle approximately 67.8°) and hydrophobic (hydrophobic at the body and base, contact angle approximately 124.5°) heterogeneous micro-region design, to achieve directional guidance and efficient collection of condensate droplets. In a sealed humidity chamber with 60% relative humidity and an ambient temperature of 25°C, the membrane of this invention can achieve a water collection capacity of 1244g per square meter per night, with a 2m... 2 The total water collection volume of the test sample reached 2488g. Even in a dry environment with a relative humidity as low as 45%, it can still achieve a water collection volume of 386g per square meter per night.

[0023] This invention integrates the radiative cooling function achieved by uniformly dispersed nanoparticles within a flexible composite substrate with a water collection structure, realizing a closed-loop synergy of cooling, condensation, water collection, and irrigation: the film surface effectively lowers its own temperature to approximately 6.9°C below the dew point, providing a driving force for water vapor condensation; the water collection structure promptly guides condensate away from the surface, preventing water film formation from blocking infrared radiation, thereby simultaneously improving both cooling and water collection efficiency. Compared to traditional PE films, this invention achieves a higher nighttime radiative cooling power (110.1 W / m²). 2 The efficiency was improved by 317%; compared with traditional cooling membranes, the water collection efficiency was improved by 120%.

[0024] After the pyramidal body and substrate of the thin film of this invention are treated with superhydrophobicity, the static water contact angle reaches 124.5° and the roll-off angle is less than 5°. It has excellent self-cleaning properties and can effectively cope with outdoor rain and dust pollution, ensuring the stability of optical performance during long-term use.

[0025] This invention utilizes a flexible PDMS substrate, allowing the film to be rolled up and cut, and is fully compatible with existing greenhouse film installation systems. The fabrication process employs silicon template etching, PDMS molding, and selective hydrophilic modification, eliminating the need for complex and expensive equipment such as vacuum deposition and photolithography. The raw materials are readily available, the process is environmentally friendly, and costs are controllable, making it potential for large-scale industrial production. Based on national estimates for the promotion of facility agriculture, extending this to 1% of the area could save 1.67 billion kilowatt-hours of electricity annually, reduce carbon emissions by 1.34 million tons, save 44.8 million tons of water, and meet approximately 30% of irrigation water needs, demonstrating significant energy-saving, emission-reduction, and agricultural application benefits. Attached Figure Description

[0026] Figure 1 This is a top view of the silicon master template obtained by etching in Example 1 using a scanning electron microscope;

[0027] Figure 2 A scanning electron microscope top view of the PDMS flexible composite substrate prepared in Example 1;

[0028] Figure 3 A scanning electron microscope side view of the PDMS flexible composite substrate prepared in Example 1;

[0029] Figure 4 This is a side view of the static water contact angle of the hydrophobic region of the flexible composite substrate after vapor-phase hydrophobication treatment in Example 1.

[0030] Figure 5 The image shows a comparison of the nighttime radiative cooling power of the biomimetic micro / nano structure-based cooling and water-saving coupled refrigeration film and the traditional PE film at different surface temperatures, as prepared in Example 1. A represents the cooling and water-saving coupled refrigeration film, and B represents the traditional PE film.

[0031] Figure 6 Transmittance comparison of the cooling and water-saving coupled refrigeration thin film based on biomimetic micro / nano structure prepared in Example 1;

[0032] Figure 7 A photograph of the testing device used to detect outdoor daytime cooling performance;

[0033] Figure 8 A comparison of daytime temperature changes inside the testing device for outdoor daytime cooling performance under different film coverings;

[0034] Figure 9 A comparison of atmospheric water collection under different humidity environments for the biomimetic micro-nano structure-based cooling and water-saving coupled refrigeration film prepared in Example 1.

[0035] Figure 10 Comparison of energy-saving and carbon-reduction benefits of the biomimetic micro-nano structure-based cooling and water-saving coupled refrigeration film prepared in Example 1 for application in the tropical Riyadh climate zone;

[0036] Figure 11 Comparison of energy-saving and carbon-reduction benefits of the biomimetic micro-nano structure-based cooling and water-saving coupled refrigeration film prepared in Example 1 for the subtropical Cape Town climate zone;

[0037] Figure 12 A comparison of the energy-saving and carbon-reduction benefits of the biomimetic micro-nano structure-based cooling and water-saving coupled refrigeration film prepared in Example 1 for application in the temperate Beijing climate zone. Detailed Implementation

[0038] The technical solution of the present invention will be further described below with reference to embodiments, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention. In the following embodiments, the process equipment or apparatus not specifically specified are all conventional equipment or apparatus in the art. Unless otherwise specified, the raw materials used in the embodiments of the present invention are all commercially available; unless otherwise specified, the technical means used in the embodiments of the present invention are all conventional means well known to those skilled in the art.

[0039] Example 1

[0040] This embodiment provides a method for preparing a cooling and water-saving coupled refrigeration thin film based on a biomimetic micro / nano structure. The specific preparation steps are as follows:

[0041] Step 1: Fabrication of a silicon master template with a regular micro-pyramid array:

[0042] (1) Silicon wafer cleaning: cleaning N-type silicon wafers <100> The crystal-oriented monocrystalline silicon wafers were ultrasonically cleaned for 15 minutes each with acetone, anhydrous ethanol, and deionized water. Then, a piranha solution, which is a mixture of concentrated sulfuric acid and 30% hydrogen peroxide in a volume ratio of 3:1, was added and treated in an 80°C water bath for 20 minutes to remove organic matter and impurities from the surface. After removal, the wafers were rinsed with deionized water and dried with nitrogen gas for later use.

[0043] (2) Preparation of etching solution: Add 5% KOH aqueous solution by mass to a polytetrafluoroethylene beaker, and then add 2% isopropanol (IPA) by volume as etching aid. After stirring evenly, place it in a water bath and keep it at a constant temperature of 80°C. Be careful to seal it to prevent the isopropanol from evaporating.

[0044] (3) Wet etching: The cleaned silicon wafer with the polished side facing up is completely immersed in the constant temperature etching solution and etched for 40 minutes, during which the temperature is kept constant.

[0045] Monocrystalline silicon in <100> Significant anisotropic etching characteristics exist between the {111} and {111} crystal plane families, with the {111} crystal plane exhibiting an extremely low etching rate. When <100> When a single-crystal silicon wafer with a specific crystal orientation is wet-etched in a potassium hydroxide etching solution, <100> The crystal facets are rapidly etched, and the four exposed {111} crystal facets form a natural corrosion termination surface. These four {111} crystal facets self-assemble to form a square pyramid with a square base, i.e., a micro pyramid structure.

[0046] (4) Termination of etching and post-processing: After etching is completed, the silicon wafer is immediately removed, rinsed with a large amount of deionized water to terminate the etching, then ultrasonically cleaned with anhydrous ethanol for 5 minutes, and dried with nitrogen to obtain a silicon master template with a regular micro-nano pyramid array.

[0047] Figure 1 This is a scanning electron microscope top view of the etched silicon master template. Figure 1 The surface of the silicon master template shows a recessed structure of an inverted pyramid array with sharp edges, arranged in a periodic and orderly manner. The base side length of the pyramid array unit is about 4 μm and the height is about 2.8 μm.

[0048] Step 2: Fabrication of a flexible composite substrate replicating the micro pyramid structure:

[0049] (1) Preparation of functional filler concentrate: 10 mL of anhydrous ethanol, 2 mL of deionized water, and 1 mL of tetraethyl orthosilicate were added sequentially to a clean beaker. After magnetic stirring for 5 min, 0.1 mL of 25% ammonia solution was added dropwise for catalysis. The mixture was then stirred in a sealed container at room temperature for 2 h to obtain a transparent siloxane sol. 1.2 g of SiO2 nanoparticles with a particle size of 300 nm and 0.8 g of ITO nanoparticles with a particle size of 80 nm were added to the obtained sol. After magnetic stirring at room temperature for 30 min, the mixture was ultrasonically dispersed in an ice bath for 1 h to obtain a uniformly dispersed sol containing nanoparticles. The obtained dispersion was placed in a low-temperature oven to remove the ethanol solvent, resulting in a functional filler concentrate with high solid content and modified silanol content on the surface, without obvious agglomeration or precipitation.

[0050] (2) Preparation of hybrid functional precursor: The curable polysiloxane mixture in this embodiment is a polydimethylsiloxane (PDMS) system, purchased from Dow Chemical Company, USA, model SYLGARD. TM 184.

[0051] The functional filler concentrate, PDMS prepolymer, and PDMS curing agent were mixed at a mass ratio of 3:10:1. First, the PDMS prepolymer and curing agent were mixed at a mass ratio of 10:1 and magnetically stirred at room temperature until completely homogeneous and degassed. Then, the functional filler concentrate was slowly added dropwise to the PDMS mixture while continuously stirring at high speed. After the addition was completed, stirring was continued at room temperature for 30 minutes until completely homogeneous. Then, the mixture was placed in a vacuum dryer for degassed for 30 minutes to obtain a homogeneous, bubble-free hybrid functional precursor.

[0052] (3) Anti-adhesion treatment of silicon template: Place the silicon template obtained in step one in a petri dish, add 2 drops of hexadecyltrimethoxysilane (HDTMS), seal the petri dish with plastic wrap with small holes, and then place it in an oven at 80°C for 2 hours to form a hydrophobic layer on the template surface, which facilitates subsequent demolding.

[0053] (4) Molding and curing: The degassed hybrid functional precursor is slowly poured onto the silicon master template. The coating thickness is controlled to be 90 μm by a scraper to make the precursor layer uniform. It is then placed in a vacuum dryer to remove air bubbles, and then placed in a 60℃ oven for curing for 4 hours. This allows the platinum-catalyzed hydrosilanization crosslinking of the PDMS system and the condensation crosslinking of the siloxane sol to be completed simultaneously, forming a homogeneous film with a chemically interpenetrating network structure.

[0054] (5) Demolding: After curing, the film is cooled to room temperature and carefully peeled off from the silicon template with tweezers to obtain a flexible composite substrate with a surface replicating a micro-nano pyramid array structure and uniformly dispersed SiO2 and ITO nanoparticles inside. In this embodiment, the thickness of the flexible composite substrate is 86 μm.

[0055] Figure 2This is a scanning electron microscope top view of the obtained flexible composite substrate. Figure 2 The surface of the flexible composite substrate is an array of pyramidal protrusions.

[0056] Figure 3 This is a scanning electron microscope side view of the obtained flexible composite substrate. Figure 3 The top clearly shows the array of upright pyramids on the flexible composite substrate, with smooth sidewalls and regular morphology, proving that the silicon template molding process successfully replicated the target micro-nano structure; the bottom substrate cross-section is clearly visible, with a small number of tiny bubbles / pores inside. These are trace bubbles left over from the curing process, which are within the allowable range of the process and do not affect the flexibility and overall performance of the material.

[0057] Step 3: Perform overall vapor-phase hydrophobication treatment on the flexible composite substrate obtained in Step 2:

[0058] The flexible composite substrate obtained in step two was subjected to ultraviolet light irradiation for activation treatment. The ultraviolet wavelength was 200 nm and the irradiation intensity was 10 mW / cm². 2 The irradiation distance was 10 mm and the irradiation time was 10 min. Then, the flexible composite substrate was placed in a sealed culture dish with a glass slide containing 3 drops of HDTMS. The pyramid face of the flexible composite substrate was placed face down and suspended in the air without contacting the HDTMS liquid. Vapor deposition was carried out in an oven at 80℃ for 1.5 h. After removal, it was placed in an oven at 120℃ for 30 min for heat treatment to complete cross-linking and curing, so that the pyramid body and the base area of ​​the flexible composite substrate formed a superhydrophobic surface.

[0059] Figure 4 This is a side view of the static water contact angle of the hydrophobic region of the flexible composite substrate after vapor-phase hydrophobication treatment; the static water contact angle of the hydrophobic region is 124.5° as measured by a contact angle measuring instrument.

[0060] Step 4: Selectively hydrophilically modify the pyramid apex of the flexible composite substrate obtained in Step 3:

[0061] (1) Preparation of dopamine solution: Prepare a 2 mg / mL dopamine hydrochloride solution using pH=8.5, 10 mmol / L Tris-HCl buffer, and store it in the dark for later use.

[0062] (2) Preparation of glass slide coating: A clean glass slide was irradiated with ultraviolet light at a wavelength of 200 nm and an intensity of 10 mW / cm². 2 The irradiation distance was 10 mm. After UV activation for 10 min, dopamine solution was uniformly coated on its surface. The coating thickness was controlled to be about 20 μm with a scraper. The coating was left to stand at room temperature in the dark for 5 min to form a semi-polymerized viscous coating.

[0063] (3) Selective hydrophilic transfer: The flexible composite substrate after hydrophobic treatment in step four is placed with the pyramid face down, so that the top of the pyramid contacts and adheres to the dopamine adhesive coating on the glass slide. Another glass slide is placed on the back of the flexible composite substrate and uniform pressure is applied to make the two flat and adhered. It is left to stand at room temperature in the dark for 15 minutes to selectively graft dopamine onto the top of the pyramid, making the top area hydrophilic and forming a superhydrophobic surface with the body and the substrate area.

[0064] (4) Post-processing: The flexible composite substrate is peeled off smoothly, and the unpolymerized dopamine is removed by rinsing with deionized water three times. The substrate is dried with nitrogen and then dried in an oven at 60°C for 30 minutes to obtain the finished cooling and water-saving coupled refrigeration film.

[0065] The static water contact angle of the hydrophilic region at the top of the pyramid, as measured by a contact angle meter, is 67.8°. The hydrophilic / hydrophobic heterogeneous micro-regions of the water-collecting functional layer exhibit gradient wetting characteristics. The static water contact angle at the top of the pyramid is 67.8°, classifying it as a hydrophilic region, providing preferential sites for dew nucleation and growth. The static water contact angle in the pyramid body and base region is 124.5°, classifying it as a hydrophobic region, allowing water droplets to flow rapidly away from the membrane surface. This cross-design of hydrophilic and hydrophobic micro-regions enables efficient water conduction, ensuring that dew cannot remain on the membrane surface, allowing for a continuous and efficient cycle of water collection and conduction.

[0066] Example 2

[0067] This embodiment provides a method for preparing a cooling and water-saving coupled refrigeration thin film based on a biomimetic micro / nano structure. The specific steps are as follows:

[0068] Step 1: Fabrication of a silicon master template with a regular micro-pyramid array:

[0069] (1) Silicon wafer cleaning: cleaning N-type silicon wafers <100> The crystal-oriented monocrystalline silicon wafers were ultrasonically cleaned for 15 minutes each with acetone, anhydrous ethanol, and deionized water. Then, a piranha solution, which is a mixture of concentrated sulfuric acid and 30% hydrogen peroxide in a volume ratio of 3:1, was added and treated in an 80°C water bath for 20 minutes to remove organic matter and impurities from the surface. After removal, the wafers were rinsed with deionized water and dried with nitrogen gas for later use.

[0070] (2) Preparation of etching solution: Add 5% KOH aqueous solution by mass to a polytetrafluoroethylene beaker, and then add 2% isopropanol (IPA) by volume as etching aid. After stirring evenly, place it in a water bath and keep it at a constant temperature of 80°C. Seal to prevent the isopropanol from evaporating.

[0071] (3) Wet etching: The cleaned silicon wafer with the polished side facing up is completely immersed in the constant temperature etching solution and etched for 35 minutes, during which the temperature is kept constant.

[0072] (4) Termination of etching and post-processing: After etching, the silicon wafer was immediately removed and rinsed with a large amount of deionized water to terminate the reaction. Then, it was ultrasonically cleaned with anhydrous ethanol for 5 minutes and dried with nitrogen to obtain a silicon master template with a regular micro-nano pyramid array. The surface of the obtained silicon master template is an inverted pyramid recess array, which is periodically and orderly arranged. The base side length of the pyramid array unit is about 3.5 μm and the height is about 2.5 μm.

[0073] Step 2: Fabrication of a flexible composite substrate replicating the micro pyramid structure

[0074] (1) Preparation of functional filler concentrate: 8 mL of anhydrous ethanol, 1.5 mL of deionized water, and 0.8 mL of tetraethyl orthosilicate were added sequentially to a clean beaker. The mixture was magnetically stirred for 5 min, and 0.08 mL of ammonia was added dropwise for catalysis. The mixture was stirred at room temperature for 1 h to obtain a transparent siloxane sol. 1.2 g of SiO2 nanoparticles with a particle size of 200 nm and 0.8 g of ITO nanoparticles with a particle size of 50 nm were added to the sol. The mixture was magnetically stirred for 30 min and ultrasonically dispersed in an ice bath for 0.5 h to obtain a uniformly dispersed sol containing nanoparticles. The obtained dispersion was placed in a low-temperature oven to remove the ethanol solvent, thus obtaining the functional filler concentrate.

[0075] (2) Preparation of hybrid functional precursors: Polydimethylsiloxane (PDMS, SYLGARD) was used. TM 184) System: PDMS prepolymer and PDMS curing agent are mixed at a mass ratio of 10:1 and magnetically stirred for 30 min until homogeneous. The above functional filler concentrate is then mixed with PDMS prepolymer and PDMS curing agent at a mass ratio of 3:10:1, magnetically stirred for 30 min until homogeneous, and vacuum degassed for 30 min to obtain the hybrid functional precursor.

[0076] (3) Anti-adhesion treatment of silicon template: Place the silicon template in a petri dish, add 2 drops of hexadecyltrimethoxysilane (HDTMS), seal with holes, and place in a 70℃ oven for heat treatment for 2.5h to form a hydrophobic layer on the template surface.

[0077] (4) Molding and curing: The degassed hybrid functional precursor is slowly poured onto the silicon master template. The coating thickness is controlled to be 90μm by a scraper to make the precursor layer uniform. After secondary degasing, it is placed in a 60℃ oven for curing for 4h.

[0078] (5) Demolding: After cooling at room temperature, carefully peel off the film to obtain a flexible composite substrate with a surface replicating a micro pyramid array and a uniformly dispersed nanoparticle inside. The substrate thickness is 86 μm.

[0079] Step 3: Overall vapor phase hydrophobic treatment. The flexible composite substrate was activated under ultraviolet light with a wavelength of 254 nm, an irradiation intensity of 5 mW / cm², an irradiation distance of 15 mm, and an irradiation time of 15 min. It was then sealed together with a glass slide containing 3 drops of HDTMS, suspended with the pyramid face down, and vapor-phase deposited at 70 °C for 2 h. After removal, it was heat-treated at 100 °C for 40 min to complete cross-linking and curing. The static water contact angle of the hydrophobic region was 121.3°.

[0080] Step 4: Selective hydrophilic modification:

[0081] (1) Preparation of dopamine solution: Prepare 1 mg / mL dopamine hydrochloride solution with pH=8.0, 8 mmol / L Tris-HCl buffer, and keep it away from light for later use.

[0082] (2) Preparation of glass slide coating: Clean glass slides are activated by ultraviolet light for 10 min, dopamine solution is uniformly coated, the thickness is controlled to 10 μm with a scraper, and the slides are left to stand at room temperature in the dark for 8 min to form a semi-polymerized adhesive coating.

[0083] (3) Selective hydrophilic transfer: The coating is applied to the flexible composite substrate with the pyramid side facing down, and pressure is applied to the back side. It is left to stand at room temperature in the dark for 20 minutes.

[0084] (4) Post-treatment: The flexible composite substrate was smoothly peeled off, rinsed twice with deionized water, dried with nitrogen, and dried in an oven at 50°C for 40 min to obtain the finished film. The static water contact angle of the hydrophilic zone at the top of the tower of the obtained film was 65.2°.

[0085] Example 3

[0086] This embodiment provides a method for preparing a cooling and water-saving coupled refrigeration thin film based on a biomimetic micro / nano structure. The specific steps are as follows:

[0087] Step 1: Fabrication of a silicon master template with a regular micro-pyramid array:

[0088] (1) Silicon wafer cleaning: cleaning N-type silicon wafers <100> The crystal-oriented monocrystalline silicon wafers were ultrasonically cleaned with acetone, anhydrous ethanol, and deionized water for 15 minutes each, treated with piranha solution in an 80°C water bath for 20 minutes, rinsed with deionized water, and dried with nitrogen gas for later use.

[0089] (2) Preparation of etching solution: Add 5% KOH aqueous solution by mass to a polytetrafluoroethylene beaker, then add 2% isopropanol (IPA) by volume, stir evenly and keep the temperature constant to 80°C, then seal for later use.

[0090] (3) Wet etching: The silicon wafer is immersed in the etching solution with the polished side facing up for 30 minutes and kept at a constant temperature.

[0091] (4) Termination of etching and post-processing: The etching was terminated by rinsing with deionized water, ultrasonically cleaning with anhydrous ethanol for 5 min, and drying with nitrogen to obtain the silicon master template. The substrate side length of the obtained silicon master template pyramid array unit is about 3.0 μm and the height is about 2.1 μm.

[0092] Step 2: Fabrication of a flexible composite substrate replicating the micro pyramid structure

[0093] (1) Preparation of functional filler concentrate: 12 mL of anhydrous ethanol, 2.5 mL of deionized water, and 1.2 mL of tetraethyl orthosilicate were added sequentially to a clean beaker. The mixture was magnetically stirred for 5 min, and 0.12 mL of ammonia was added dropwise for catalysis. The mixture was stirred at room temperature for 3 h to obtain a transparent siloxane sol. 1.2 g of SiO2 nanoparticles with a particle size of 200 nm and 0.8 g of ITO nanoparticles with a particle size of 50 nm were added to the sol. The mixture was magnetically stirred for 30 min and ultrasonically dispersed in an ice bath for 0.5 h to obtain a uniformly dispersed sol containing nanoparticles. The obtained dispersion was placed in a low-temperature oven to remove the ethanol solvent, thus obtaining the functional filler concentrate.

[0094] (2) Preparation of hybrid functional precursors: Polydimethylsiloxane (PDMS, SYLGARD) was used. TM 184) System: PDMS prepolymer and PDMS curing agent are mixed at a mass ratio of 10:1 and magnetically stirred for 30 min until homogeneous. The above functional filler concentrate is then mixed with PDMS prepolymer and PDMS curing agent at a mass ratio of 3:10:1, magnetically stirred for 30 min until homogeneous, and vacuum degassed for 30 min to obtain the hybrid functional precursor.

[0095] (3) Anti-adhesion treatment of silicon template: Place the silicon template in a petri dish, add 2 drops of hexadecyltrimethoxysilane (HDTMS), seal with holes, and place in a 90℃ oven for 1 hour to form a hydrophobic layer on the template surface.

[0096] (4) Molding and curing: The degassed hybrid functional precursor is slowly poured onto the silicon master template. The coating thickness is controlled to be 90μm by a scraper to make the precursor layer uniform. After secondary degasing, it is placed in a 60℃ oven for curing for 4h.

[0097] (5) Demolding: After cooling at room temperature, carefully peel off the film to obtain a flexible composite substrate with a surface replicating a micro pyramid array and a uniformly dispersed nanoparticle inside. The substrate thickness is 86 μm.

[0098] Step 3: Overall vapor phase hydrophobic treatment. The flexible composite substrate was activated under ultraviolet light with a wavelength of 254 nm, an irradiation intensity of 5 mW / cm², an irradiation distance of 15 mm, and an irradiation time of 15 min. It was then sealed together with a glass slide containing 3 drops of HDTMS, suspended with the pyramid face down, and vapor-phase deposited at 90 °C for 1 h. After removal, it was heat-treated at 130 °C for 20 min to complete cross-linking and curing. The static water contact angle of the hydrophobic region was 126.7°.

[0099] Step 4: Selective hydrophilic modification:

[0100] (1) Preparation of dopamine solution: Prepare a 3 mg / mL dopamine hydrochloride solution using pH=9.0, 12 mmol / L Tris-HCl buffer and store it away from light.

[0101] (2) Preparation of glass slide coating: activate glass slide with ultraviolet light for 10 min, coat with dopamine solution, control the thickness to 30 μm with a scraper, and let stand at room temperature in the dark for 3 min to form an adhesive coating.

[0102] (3) Selective hydrophilic transfer: The coating is applied to the flexible composite substrate with the pyramid face down, pressurized, and left to stand at room temperature in the dark for 10 minutes.

[0103] (4) Post-treatment: The flexible composite substrate was peeled off, rinsed with deionized water 4 times, dried with nitrogen, and dried in an oven at 70°C for 20 min to obtain the finished film. The static water contact angle of the hydrophilic zone at the top of the tower of the obtained film was 72.5°.

[0104] Basic material performance tests and results:

[0105] (a) Cooling power test

[0106] Taking the biomimetic micro / nano structure-based cooling and water-saving coupled refrigeration film prepared in Example 1 as an example, and using a traditional PE film as a control, its radiative cooling performance was further quantified, and the nighttime radiative cooling power at different surface temperatures was theoretically calculated. The calculations were performed under ambient temperatures of 303.15 K (30°C) and dry air conditions, simulating different non-radiative heat transfer coefficients (hc = 0, 2, 4, 6, 8 W / m). 2 Under K), the net radiative cooling power of the cooling and water-saving coupled cooling film of the present invention at night is as follows: Figure 5 As shown.

[0107] Figure 5 The results show that the cooling power of the cooling and water-saving coupled refrigeration film of this invention increases with the increase of the non-radiative heat transfer coefficient hc. When the material and ambient temperature are at the same level (temperature difference is 0), there is no non-radiative heat transfer. At this point, the nighttime radiative cooling power of the material of this invention and the traditional PE film are 110.1 W / m², respectively. 2 and 26.4 W / m 2The nighttime radiative cooling power of the material of this invention is increased by approximately 317% compared to traditional PE films, indicating that this material has excellent nighttime radiative cooling effect and can effectively reduce the temperature of the space covered by the film.

[0108] (ii) Spectral transmittance test

[0109] The transmittance of the biomimetic micro / nanostructure-based cooling and water-saving coupled refrigeration film prepared in Example 1, containing ITO+SiO2 nanoparticles, was tested, along with the solar spectral transmittance of the biomimetic micro / nanostructure-based cooling and water-saving coupled refrigeration films prepared using the same method but containing only ITO nanoparticles or only SiO2 nanoparticles. The results are as follows: Figure 6 As shown.

[0110] The results show that the cooling and water-saving coupled cooling film prepared by the present invention has better solar spectral transmittance and better transmittance of light in the photosynthetic band, making it better suited for agricultural greenhouse applications.

[0111] (III) Outdoor daytime cooling performance test

[0112] To further verify the practical application advantages of the biomimetic micro-nano structure cooling and water-saving coupled refrigeration film of this invention in agricultural scenarios, three commonly used traditional greenhouse films in facility agriculture—PE polyethylene film, PO polyolefin film, and PVC polyvinyl chloride film—were selected as parallel control groups for simultaneous outdoor control testing.

[0113] Testing devices for detecting outdoor daytime cooling performance, such as Figure 7 As shown in the figure, the comparison of daytime temperature changes inside the device under different film coverage is as follows: Figure 8 As shown.

[0114] The results show that the internal temperatures of the devices covered by PE, PO, and PVC films are basically the same, all significantly higher than those of the devices covered by the cooling and water-saving coupled refrigeration film of this invention. The cooling and water-saving coupled refrigeration film of this invention exhibits good cooling effects during the daytime, and the cooling effect increases with increasing solar irradiance. During the midday high-temperature period of the experiment (11:00-13:00), the average temperature of the devices covered by the cooling and water-saving coupled refrigeration film of this invention is 9.05℃, 9.91℃, and 7.02℃ lower than that of the devices covered by PE, PO, and PVC films, respectively, verifying the excellent cooling capability of the cooling and water-saving coupled refrigeration film of this invention during extreme high-temperature periods.

[0115] (iv) Atmospheric water collection performance test

[0116] Basic tests were conducted on the condensation nucleation and water collection performance of the biomimetic micro / nano structure cooling and water-saving coupled refrigeration film of this invention in a closed humidity chamber with a relative humidity of 60% and an ambient temperature of 25°C, and in an arid environment with a humidity of less than 45%. The test area was 2m².2 During the continuous 12-hour test, the results were as follows: Figure 9 As shown.

[0117] The results show that the cooling and water-saving coupled refrigeration film of this invention achieves a water collection capacity of 1244g per square meter per night, with a 2m... 2 The test sample collected a total of 2488g of water, which can fully meet the in-situ irrigation and water replenishment needs of vegetable greenhouses. In a dry environment with relative humidity as low as 45%, the material can still collect 386g of water per square meter per night, which is 120% more efficient than traditional atmospheric water collection devices in low humidity environments.

[0118] (V) Simulation of annual energy consumption and environmental benefits

[0119] To verify the universal application value of the biomimetic micro / nano structure cooling and water-saving coupled refrigeration film of this invention in different climate zones around the world, the annual energy consumption simulation analysis was carried out using the energy consumption analysis software EnergyPlus for traditional greenhouse buildings in three typical climate zones: tropical (Riyadh), subtropical (Cape Town), and temperate (Beijing). The results are as follows: Figure 10 , Figure 11 and Figure 12 As shown.

[0120] The results show that applying the biomimetic micro-nano structure cooling and water-saving coupled refrigeration film of this invention to the building envelope of greenhouses can significantly reduce the operating energy consumption of the heating and cooling system. Its energy-saving benefits can be simultaneously converted into reductions in electricity, natural gas, and standard coal consumption, as well as carbon emissions. Taking Riyadh, a tropical desert climate, as an example, a 100-square-meter greenhouse model, after applying this material, can save 16,788 kWh of electricity, or 2,803 cubic meters of natural gas, or 5,370 kg of standard coal annually, equivalent to a reduction of 10,311 kg of CO2 emissions. This demonstrates extremely outstanding energy-saving and carbon-reduction benefits in high-temperature and high-radiation regions.

Claims

1. A cooling and water-saving coupled refrigeration thin film based on a biomimetic micro / nano structure, characterized in that, The invention includes a flexible composite substrate, the surface of which has a regularly arranged micro pyramid array structure, and the interior of which is uniformly dispersed nanoparticles with high emissivity to infrared light and high transmittance to visible light; the top of the micro pyramid array is a hydrophilic region, and the body and the substrate are hydrophobic regions, forming a hydrophilic-hydrophobic heterogeneous micro-region.

2. The cooling and water-saving coupled refrigeration thin film based on biomimetic micro / nano structure according to claim 1, characterized in that, The thickness of the flexible composite substrate is 50~300μm, and the side length of the array unit substrate of the micro pyramid array structure is 3~5μm, and the height is 2.1~3.5μm.

3. The cooling and water-saving coupled refrigeration thin film based on biomimetic micro / nano structure according to claim 1 or 2, characterized in that, The static water contact angle of the hydrophilic region is 60~75°, and the contact angle of the hydrophobic region is 115~130°.

4. The cooling and water-saving coupled refrigeration thin film based on biomimetic micro / nano structure according to claim 3, characterized in that, The nanoparticles include SiO2 nanoparticles and ITO nanoparticles, wherein the SiO2 nanoparticles have a particle size of 200-400 nm and the ITO nanoparticles have a particle size of 50-100 nm; the flexible composite substrate is composed of polydimethylsiloxane doped with SiO2 and ITO nanoparticles.

5. A method for preparing a cooling and water-saving coupled refrigeration thin film based on a biomimetic micro / nano structure as described in any one of claims 1-4, characterized in that, Includes the following steps: Step 1: Prepare a silicon master template with a regular micro pyramid array; Step 2: Cast a curable polysiloxane mixture doped with SiO2 and ITO nanoparticles onto the surface of a silicon master template, control the coating thickness with a scraper, then cure and demold to obtain a flexible composite substrate with a surface replicating a micro pyramid structure and the nanoparticles uniformly dispersed inside. Step 3: Perform an overall vapor phase hydrophobic treatment on the flexible composite substrate obtained in Step 2 to make the pyramid body and base area hydrophobic. Step 4: Selectively hydrophilically modify the top of the pyramid of the flexible composite substrate obtained in Step 3 to make the top region hydrophilic, forming a hydrophilic-hydrophobic heterogeneous micro-region.

6. The method for preparing a cooling and water-saving coupled refrigeration thin film based on a biomimetic micro / nano structure according to claim 5, characterized in that, The silicon master template mentioned in step one uses <100> The crystal-oriented single-crystal silicon wafer is prepared by wet etching; the etching solution contains potassium hydroxide and isopropanol, wherein the mass concentration of potassium hydroxide is 5%, the volume concentration of isopropanol is 2%, the etching temperature is 80℃, and the etching time is 30~40min.

7. The method for preparing a cooling and water-saving coupled refrigeration thin film based on a biomimetic micro / nano structure according to claim 5 or 6, characterized in that, The preparation method of the curable polysiloxane mixture doped with SiO2 and ITO nanoparticles in step two is as follows: First, tetraethyl orthosilicate, anhydrous ethanol, and deionized water are reacted under the catalysis of ammonia to obtain a siloxane sol. Then, SiO2 and ITO nanoparticles are added, and after dispersion and solvent removal, a functional filler concentrate is obtained. Finally, the functional filler concentrate is mixed evenly with PDMS prepolymer and PDMS curing agent in a certain proportion and degassing treatment is performed. The silicon master template is subjected to anti-sticking treatment before casting. The silicon master template and hydrophobic treatment agent are placed together in a sealed container and heat-treated at 70~90℃ for 1~3h to form a hydrophobic layer on the template surface. The coating thickness is 50~100μm. The curing temperature is 60℃ and the curing time is 4h.

8. The method for preparing a cooling and water-saving coupled refrigeration thin film based on a biomimetic micro / nano structure according to claim 7, characterized in that, The preparation method of the functional filler concentrate is as follows: Anhydrous ethanol, deionized water, and tetraethyl orthosilicate are mixed in a volume ratio of 8~12:1.5~2.5:0.8~1.

2. After stirring, ammonia water is added dropwise as a catalyst. The amount of ammonia water is 0.3~0.8% of the total volume of the reaction solution. The mixture is stirred at room temperature for 1~3 hours to obtain a transparent sol. Nanoparticles are added to the sol to make the concentration of SiO2 nanoparticles in the sol 0.07~0.12 g / mL and the concentration of ITO nanoparticles 0.04~0.08 g / mL. After magnetic stirring, the mixture is ultrasonically dispersed in an ice bath for 0.5~1.5 hours. Then the solvent is removed to obtain the functional filler concentrate. The mass ratio of the functional filler concentrate, PDMS prepolymer, and PDMS curing agent is 1.5~3:10:

1.

9. The method for preparing a cooling and water-saving coupled refrigeration thin film based on a biomimetic micro / nano structure according to claim 8, characterized in that, The method for vapor-phase hydrophobication treatment in step three is as follows: The flexible composite substrate obtained in step two is irradiated under ultraviolet light for activation treatment. The ultraviolet wavelength is 150~300nm and the irradiation intensity is 1~20mW / cm. 2 The irradiation distance is 1~20mm and the irradiation time is 5~20min. The UV-activated flexible composite substrate and the hydrophobic treatment agent are placed together in a sealed container. The flexible composite substrate is suspended with the pyramid face down and does not contact the hydrophobic treatment agent. Vapor deposition is carried out at 70~90℃ for 1~2h. After taking it out, it is heat-treated at 100~130℃ for 20~40min to complete the crosslinking and curing.

10. The method for preparing a cooling and water-saving coupled refrigeration thin film based on a biomimetic micro / nano structure according to claim 9, characterized in that, The selective hydrophilic modification method described in step four is as follows: Prepare a 1-3 mg / mL dopamine hydrochloride solution using a pH=8.0-9.0, 8-12 mmol / L Tris-HCl buffer solution. Coat the dopamine hydrochloride solution uniformly on a clean glass slide after UV activation. Use a scraper to control the coating thickness to 10-30 μm. Let it stand at room temperature in the dark for 3-8 minutes to form an adhesive coating. With the pyramid face down, place the flexible composite substrate (after hydrophobic treatment in step three) onto the obtained adhesive coating. Apply pressure to the back of the flexible composite substrate to make them flat and adhere. Let it stand at room temperature in the dark for 10-20 minutes. After smoothly peeling off the flexible composite substrate, rinse it 2-4 times with deionized water to remove unpolymerized dopamine. Blow it dry with nitrogen and dry it at 50-70℃ for 20-40 minutes to obtain the finished cooling and water-saving coupled refrigeration film.

Images