Laser structured hydrophobic self-cleaning cement-based radiative cooling material and method of making the same

Abstract

The application belongs to the technical field of cement-based materials, and discloses a laser-structured hydrophobic self-cleaning cement-based radiation refrigeration material and a preparation method thereof. The cement-based radiation refrigeration material comprises the following components in mass fractions: cement, 50-70 parts; rutile titanium dioxide, 7.5-18 parts; barium sulfate, 5-12 parts; hollow glass microbeads, 2.5-6 parts. The surface of the cement-based radiation refrigeration material has hierarchical micro-nano structures, which comprise grooves with a depth of 5-20 microns and a width of 50-100 microns and protrusions with an edge length of 100-500 nanometers. The grooves are located between adjacent protrusions. The surface of the hierarchical micro-nano structures is modified by a hydrophobic modifier to form a silane modified layer. The cement-based radiation refrigeration material can simultaneously meet the requirements of high radiation refrigeration performance, excellent matrix mechanical properties and long-term outdoor service stability.

Description

Technical Field

[0001] This invention belongs to the field of cement-based materials technology, specifically relating to a laser-structured hydrophobic self-cleaning cement-based radiation cooling material and its preparation method. Background Technology

[0002] Among existing technologies, passive daytime radiative cooling (PDRC) requires no additional energy input. Through its intrinsic optical characteristics of high solar spectrum reflectivity and high infrared emission via atmospheric transparency, it dissipates building heat into outer space via infrared radiation, achieving zero-energy cooling. This is one of the core technologies for reducing building cooling energy consumption and achieving low-carbon development. Cement-based materials, as the most widely used and extensively applied substrate in building engineering, can benefit significantly from PDRC technology, reducing cooling energy consumption while improving structural durability, thus possessing substantial engineering and economic value.

[0003] Currently, cement-based radiative cooling materials mainly follow two technical paths, both of which suffer from intractable core defects: The first is the internally added functional filler type, which improves the material's solar reflectance and infrared emission performance by incorporating functional fillers such as rutile titanium dioxide, barium sulfate, and hollow glass microspheres into the cement matrix. This approach is simple and adaptable to existing engineering construction processes, but its core drawbacks are: efflorescence from cement hydration products and easy dust accumulation in surface pores lead to a 10%-20% decrease in solar reflectance within 3-6 months of outdoor service, resulting in a significant reduction in cooling efficiency. Furthermore, the addition of hydrophobic agents to address efflorescence and water absorption hinders the hydration process of the cement matrix, significantly reducing mechanical properties and failing to meet engineering application requirements. The second approach is the surface coating type, which involves coating the cement substrate with a polymer-based radiative cooling coating, achieving excellent initial cooling performance. However, its core drawbacks are: poor adhesion between the organic coating and the cement substrate, which makes it prone to wear, cracking and peeling during outdoor service, resulting in serious lack of durability; in addition, the organic coating has poor resistance to ultraviolet aging, and its optical performance continues to decline after long-term service. At the same time, it adds extra construction procedures and overall costs, limiting its large-scale application.

[0004] For example, patent document CN121107788A discloses a long-lasting cooling sheet material and its preparation method of a carbon nitride-coated cement-based material. This technology composites a carbon nitride (g-C3N4) coating layer onto the surface of a white cement-based radiation cooling substrate, achieving synergistic passive cooling and pollutant degradation, and exhibiting a certain self-cleaning effect. However, this existing technology does not address the inherent interface risks of the layered structure, and there is still a risk of thin-layer shedding of the functional layer during long-term use. As an independent functional thin layer, the wear resistance and UV aging resistance of the coating layer directly affect the long-term service performance of the material, and the process is complex and energy-intensive. Summary of the Invention

[0005] The purpose of this invention is to provide a laser-structured hydrophobic self-cleaning cement-based radiation cooling material and its preparation method, so as to solve the technical problem that the existing technology is unable to simultaneously meet the requirements of high radiation cooling performance, excellent matrix mechanical properties, and long-term outdoor service stability.

[0006] The laser-structured hydrophobic self-cleaning cement-based radiation cooling material comprises, by weight, the following components: Cement, 50-70 parts; Rutile titanium dioxide, 7.5-18 parts; Barium sulfate, 5-12 parts; Hollow glass microspheres, 2.5-6 parts; The surface of the cement-based radiative cooling material has a hierarchical micro-nano structure, which includes trenches with a depth of 5-20 μm and a width of 50-100 μm and protrusions with a side length of 100-500 nm. The trenches are located between adjacent protrusions. The surface of the hierarchical micro-nano structure is modified with a hydrophobic modifier to form a silane modified layer.

[0007] Preferably, the rutile titanium dioxide has a particle size of 0.2-0.25 μm; the barium sulfate has a particle size of 0.3-0.5 μm; and the hollow glass microspheres have a particle size of 10-50 μm and a wall thickness of 1-2 μm.

[0008] Preferably, the water contact angle of the silane-modified layer is ≥140° and the roll-off angle is ≤5°.

[0009] Preferably, the laser-structured hydrophobic self-cleaning cement-based radiation cooling material further comprises, by weight parts: Hydroxypropyl methylcellulose ether, 0.05-0.1 parts; Polycarboxylate superplasticizer, 0.8-1.2 parts.

[0010] The present invention also provides a method for preparing the laser-structured hydrophobic self-cleaning cement-based radiation cooling material as described above, comprising the following steps: Step 1: Prepare cement-based radiative cooling matrix. Weigh each component raw material according to the designed mass proportions, stir and mix, and then perform matrix molding, curing and pretreatment to obtain cement-based radiative cooling matrix. Step 2: Laser structuring is performed on the substrate surface. Based on the size requirements of the hierarchical micro-nano structure, the pretreated cement-based radiation cooling substrate surface is laser etched in a horizontal-vertical cross grid scanning mode to form a hierarchical micro-nano structure. Step 3: The hierarchical micro / nano structure is modified with low surface energy hydrophobicity by coating the surface of the hierarchical micro / nano structure with a hydrophobic modifier, thereby forming a silane modified layer, which is then cured at room temperature to obtain the finished product.

[0011] Preferably, step one includes the following sub-steps: (1) Dry material mixing: Weigh out the dry materials such as cement, rutile titanium dioxide, barium sulfate, hollow glass microspheres, and hydroxypropyl methylcellulose ether according to the designed mass parts, put them into a planetary mixer and dry mix them until they are evenly mixed to obtain the mixed dry material; (2) Wet material mixing: Weigh out the polycarboxylate superplasticizer and mixing water according to the designed mass parts, mix and stir evenly, add the resulting liquid to the mixed dry material, and stir evenly to obtain cement paste; (3) Molding and curing: The cement slurry is injected into the mold and vibrated to form the mold. After curing in the mold, it is demolded and then cured again to obtain the cured cement-based radiation cooling matrix. (4) Substrate pretreatment: Dry the cement-based radiation cooling substrate after curing to constant weight, then grind to remove surface laitance and loose layer, then blow it clean with compressed air, then ultrasonically clean it with anhydrous ethanol, and dry it again for later use.

[0012] Preferably, step two includes: laser etching using a pulsed laser, which is a 355nm ultraviolet nanosecond or femtosecond laser, and the etching depth is achieved by adjusting the "laser power-scanning rate-scanning number" in a linked manner, and the power and rate are finely adjusted after fixing the number of scans.

[0013] Preferably, the laser power used in step two etching is 5-15W, the scanning rate is 500-2000mm / s, the line spacing is 50-100μm, the spot diameter is 20-50μm, the number of scans is 1-2, and the pulsed laser parameters are any one of the following: 1) Nanosecond laser: pulse width 10-30ns, repetition frequency 20-50kHz; 2) Femtosecond laser: pulse width 100-500 fs, repetition frequency 100-200 kHz.

[0014] Preferably, step three includes the following sub-steps: (1) Preparation of hydrophobic modifier: Weigh out octyltriethoxysilane, anhydrous ethanol and glacial acetic acid by mass, mix them evenly, and then hydrolyze them in a dark environment at room temperature to obtain the hydrophobic modifier. (2) Coating and curing: The hydrophobic modifier is uniformly coated on the surface of the cement-based radiation cooling substrate by spraying or impregnation to modify the surface of the hierarchical micro-nano structure. After curing at room temperature, the finished product is obtained.

[0015] Preferably, in step three, the pH value of the hydrophobic modifier is 4-5, and the coating amount of the hydrophobic modifier is 80 g / m². 2 The hydrolysis time is 30 minutes, and the hydrolysis solidification is carried out at room temperature with a relative humidity (RH) of 40-60%.

[0016] The technical advantages of this invention are as follows: This invention only performs laser structuring treatment on a shallow 5-20μm layer on the surface of the cement matrix, without altering the hydration process and microstructure inside the cement matrix. This completely avoids the defects of decreased matrix mechanical properties and hindered hydration caused by traditional internal admixture modification, ensuring the core engineering application performance of cement-based materials. The hierarchical micro / nano structure formed by laser etching is the physical structure of the cement matrix itself, integrally formed with the matrix. It does not suffer from the problems of poor interfacial adhesion and easy wear and detachment found in traditional coating materials, exhibiting extremely high structural stability.

[0017] This invention can also form a silane-modified layer, which bonds to the cement matrix via -Si-O-Si- covalent bonds, rather than through traditional physical coating. Therefore, it exhibits extremely strong anchoring force, can withstand long-term rain erosion, UV aging, and freeze-thaw cycles, and is less prone to hydrophobic layer peeling, resulting in excellent durability. Simultaneously, the structure is precisely controllable; by adjusting laser process parameters, the size and morphology of the surface micro / nano structures can be precisely controlled, simultaneously achieving an optimal match between radiation-cooling optical properties and hydrophobic self-cleaning properties. The combination of self-cleaning function and strong durability effectively ensures the long-term service performance of the material.

[0018] The aforementioned technical advantages are present simultaneously, enabling the cement-based radiative cooling material of the present invention to simultaneously meet the requirements of high radiative cooling performance, excellent matrix mechanical properties, and long-term outdoor service stability. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of a method for preparing a laser-structured hydrophobic self-cleaning cement-based radiation cooling material according to the present invention; Figure 2 This is a schematic diagram illustrating the principle of a laser-structured hydrophobic self-cleaning cement-based radiation cooling material according to the present invention. Detailed Implementation

[0020] The following detailed description of the embodiments, with reference to the accompanying drawings, will further illustrate the specific implementation of the present invention, in order to help those skilled in the art to have a more complete, accurate, and in-depth understanding of the inventive concept and technical solution of the present invention.

[0021] like Figures 1-2 As shown, this invention provides a laser-structured hydrophobic self-cleaning cement-based radiation cooling material, comprising the following components by mass parts: Cement, 50-70 parts; Rutile titanium dioxide, 7.5-18 parts; Barium sulfate, 5-12 parts; Hollow glass microspheres, 2.5-6 parts; The surface of the cement-based radiative cooling material has a hierarchical micro-nano structure, which includes trenches with a depth of 5-20 μm and a width of 50-100 μm and protrusions with a side length of 100-500 nm. The trenches are located between adjacent protrusions. The surface of the hierarchical micro-nano structure is modified with a hydrophobic modifier to form a silane modified layer.

[0022] The rutile titanium dioxide (purity ≥98%) has a particle size of 0.2-0.25 μm; the barium sulfate (purity ≥98%) has a particle size of 0.3-0.5 μm; and the hollow glass microspheres have a particle size of 10-50 μm and a wall thickness of 1-2 μm. When preparing the cement paste, the water-cement ratio of the mixing water to the cement is 0.42-0.48.

[0023] The particle size matching of rutile titanium dioxide and barium sulfate is the optimal particle size for Mie scattering in the solar band, achieving high reflectivity across the entire solar spectrum. The hollow glass microspheres have the combined effect of enhancing solar scattering and strengthening infrared emission through the atmospheric window, while also reducing the thermal conductivity of the material and improving the cooling effect.

[0024] The reason for controlling the depth of the hierarchical micro-nano structure to 5-20μm is that if the depth is less than 5μm, the hierarchical micro-nano structure is easily covered by dust, and the self-cleaning effect fails; if the depth is greater than 20μm, it will damage the dense layer on the surface of the cement matrix, resulting in increased water absorption, decreased freeze-thaw resistance, and a reduction in laser processing efficiency of more than 30%.

[0025] The groove depth, width, and protrusion size of the hierarchical micro-nano structure are matched with the solar spectrum. On the one hand, it can significantly enhance the full-band reflection of the solar spectrum (0.3-2.5μm) through the Mie scattering effect, minimizing solar heat input. On the other hand, the micro-nano structure can enhance the infrared emission capability of cement hydration products and functional fillers in the atmospheric transparent window (8-13μm) through the photon tunneling effect, dissipating the heat of the matrix into outer space in the form of infrared radiation, achieving passive cooling with zero energy consumption during the day.

[0026] The silane-modified layer is a covalently bonded hydrophobic layer with a self-cleaning effect. Moreover, the structure of this layer is bonded to the cement matrix through -Si-O-Si- covalent bonds, rather than traditional physical coating. It has extremely strong anchoring force and can withstand long-term rain erosion, ultraviolet aging, and freeze-thaw cycles without the problems of hydrophobic layer peeling off or performance degradation.

[0027] Simultaneously, the low surface energy chemical modification with silane achieves a Cassie-Baxter wetting state with a water contact angle ≥140° and a roll-off angle ≤5°. This allows dust on the hierarchical micro / nano structure surface to be completely removed by natural rainwater runoff, achieving a self-cleaning effect and fundamentally solving the problem of optical performance degradation caused by outdoor dust accumulation. Furthermore, the hydrophobic layer blocks the migration path of moisture within the cement, inhibits efflorescence of hydration products, and ensures long-term stable optical performance.

[0028] The components of the aforementioned cement-based radiant cooling material, by mass parts, also include: 0.05-0.1 parts of hydroxypropyl methylcellulose ether (HPMC); and 0.8-1.2 parts of polycarboxylate-based high-efficiency water-reducing agent. The water-reducing agent has a solid content of 40%, a water reduction rate of ≥30%, and an HPMC viscosity of 4000 mPa. Adding these additives ensures the workability of freshly mixed slurry and the density of the hardened matrix, reduces surface porosity, and lowers the risk of ash accumulation and efflorescence from the source.

[0029] The hollow glass microspheres are hollow borosilicate glass microspheres, and the hydrophobic modifier is a mixture of octyltriethoxysilane (purity ≥97%), anhydrous ethanol (AR grade), and glacial acetic acid (AR grade). The cement used as the cementing material is 42.5 grade white cement, or a certain amount of 42.5 grade ordinary Portland cement can be added to the 42.5 grade white cement.

[0030] This invention also provides a method for preparing the above-mentioned laser-structured hydrophobic self-cleaning cement-based radiation cooling material, comprising the following steps: Step 1: Prepare cement-based radiative cooling matrix. Weigh each component raw material according to the designed mass proportions, stir and mix, and then perform matrix molding, curing and pretreatment to obtain cement-based radiative cooling matrix.

[0031] Step one includes the following sub-steps: (1) Dry material mixing: Weigh out the cement, rutile titanium dioxide, barium sulfate, hollow glass microspheres, and hydroxypropyl methylcellulose ether according to the designed mass fractions, put them into a planetary mixer and dry mix until uniform to obtain the mixed dry material. The dry mixing time is 3 minutes.

[0032] (2) Wet material mixing: Weigh the polycarboxylate superplasticizer according to the designed mass fraction, weigh the mixing water according to the set water-cement ratio, add the weighed polycarboxylate superplasticizer to the mixing water and mix evenly. Then add the resulting liquid to the mixed dry material and mix evenly to obtain cement paste. The mixing method is to first mix at low speed for 2 minutes, and then mix at high speed for 1 minute.

[0033] (3) Molding and curing: The cement slurry is injected into the mold and vibrated to form the mold. After curing in the mold for 24 hours, the mold is removed and then cured for another 28 days to obtain the cement-based radiant cooling matrix after curing. The cement-based radiant cooling matrix after demolding should be placed in a standard curing room with a temperature of 20±2℃ and a relative humidity of ≥95% for post-demolding curing.

[0034] (4) Substrate pretreatment: The cured cement-based radiant cooling substrate is dried to constant weight, then ground to remove surface laitance and loose layer. After that, it is first blown clean with compressed air, then ultrasonically cleaned with anhydrous ethanol. After cleaning, it is dried again for use. The temperature of the first drying is kept constant at 60℃. Grinding is done with 2000-grit sandpaper. After grinding, it is dried to constant weight, and the surface roughness Ra after grinding is controlled to be ≤1.6μm. Anhydrous ethanol ultrasonic cleaning is carried out for 3 minutes under the action of an ultrasonic generator at 100W power. Finally, it is dried to a moisture content ≤0.5%.

[0035] Step 2: Laser structuring is performed on the substrate surface. Based on the size requirements of the hierarchical micro-nano structure, the pretreated cement-based radiation cooling substrate surface is laser etched in a horizontal-vertical cross-grid scanning mode to form a hierarchical micro-nano structure.

[0036] This laser etching step uses a pulsed laser, specifically a 355nm ultraviolet nanosecond or femtosecond laser, in a horizontal-vertical cross-grid scanning mode to etch the surface of the cement substrate pretreated in the previous step. The etching depth is strictly controlled between 5-20μm, achieved through the coordinated adjustment of "laser power-scanning rate-scanning count," preferentially using a fixed number of scans (1 or 2 times) with fine-tuning of power and rate.

[0037] The following are the essential steps and key control parameters for forming this target structure, and the impact of parameter deviations on the structure and performance are clarified. Step two specifically employs a 355nm ultraviolet nanosecond / femtosecond pulsed laser for etching, using a horizontal-vertical 90° cross-grid scanning mode. The laser power used for etching is 5-15W, the scanning rate is 500-2000mm / s, the line spacing is 50-100μm, the spot diameter is 20-50μm, and the number of scans is 1-2. Under these conditions, a low-power shallow etching process is performed on the substrate surface, forming 50-100μm micrometer-level ordered trenches and 100-500nm nanometer-level protrusions in a shallow 5-20μm layer on the substrate surface, thus forming a hierarchical micro / nano structure. This structure is the core foundation for simultaneously achieving enhanced Mie scattering of the solar spectrum, enhanced infrared emission through the atmospheric window, and anchoring of the hydrophobic structure.

[0038] 355nm is a suitable wavelength for cold processing of cement-based materials. Using a 1064nm infrared laser would primarily result in thermal ablation, causing the cement surface to melt and clump, preventing the formation of 100-500nm nanometer-scale protrusions. Using 266nm deep ultraviolet light would result in an excessively fast etching rate, easily penetrating the shallow surface layer and damaging the internal structure of the matrix. Furthermore, the laser type must be pulsed; continuous lasers will generate sustained heat accumulation, leading to the decomposition of cement hydration products and surface carbonization and blackening. The parameters of the pulsed laser can be any of the following: 1) Nanosecond laser: pulse width 10-30ns, repetition frequency 20-50kHz; 2) Femtosecond laser: pulse width 100-500 fs, repetition frequency 100-200 kHz.

[0039] Step 3: The hierarchical micro / nano structure is modified with low surface energy hydrophobicity by coating the surface of the hierarchical micro / nano structure with a hydrophobic modifier, thereby forming a silane modified layer, which is then cured at room temperature to obtain the finished product.

[0040] Step three specifically includes the following sub-steps: (1) Preparation of hydrophobic modifier: Weigh out the raw materials octyltriethoxysilane, anhydrous ethanol and glacial acetic acid according to the mass fraction, mix them evenly, and then hydrolyze them in a dark environment at room temperature for 30 minutes to obtain a silane solution, which is the hydrophobic modifier.

[0041] The hydrophobic modifier comprises the following components by mass: 5-10 parts of octyltriethoxysilane, 89-94 parts of anhydrous ethanol, and 1 part of glacial acetic acid. The pH of the hydrophobic modifier is 4-5.

[0042] (2) Coating and curing: The hydrolyzed silane solution (hydrophobic modifier) ​​is uniformly sprayed onto the surface of the laser-structured cement-based radiation cooling substrate, and then cured at room temperature to obtain the finished product, namely the laser-structured hydrophobic self-cleaning cement-based radiation cooling material.

[0043] In this step, the coating amount of the hydrophobic modifier is 80 g / m². 2 The curing time is 24 hours, the ambient temperature is room temperature, and the relative humidity (RH) is 40-60%. This step can also be replaced by an impregnation method, in which the surface of the cement-based radiation-cooled substrate is impregnated with a corresponding hydrophobic modifier to modify the surface of the hierarchical micro / nano structure.

[0044] After the above silane solution is hydrolyzed for 30 minutes under pH 4-5 conditions, its hydrolysis products undergo a dehydration reaction with the hydroxyl groups on the surface of cement hydration products (CSH gel, calcium hydroxide) to form -Si-O-Si- covalent bonds, thus constructing a uniform, dense, hydrophobic, and self-cleaning layer that is chemically bonded to the matrix on the entire surface of the hierarchical micro-nano structure (including the inner walls of the grooves and the surface of the nano-protrusions).

[0045] The following raw materials were used in specific embodiments of the present invention: Cementing materials: Grade 42.5 white cement and Grade 42.5 ordinary Portland cement, conforming to GB 175-2007 standard; Functional fillers: rutile titanium dioxide (particle size 0.2-0.25μm, purity ≥98%), barium sulfate (particle size 0.3-0.5μm, purity ≥98%), hollow borosilicate glass microspheres (particle size 10-50μm, wall thickness 1-2μm). Admixtures: Polycarboxylate superplasticizer (solid content 40%, water reduction rate ≥30%), hydroxypropyl methylcellulose ether (HPMC, viscosity 4000 mPa) s); Hydrophobic modifiers: octyltriethoxysilane (purity ≥97%), anhydrous ethanol (AR grade), glacial acetic acid (AR grade).

[0046] The specific embodiments of the invention are as follows: Example 1 This embodiment provides a laser-structured hydrophobic self-cleaning cement-based radiation cooling material and its preparation method. The preparation method includes the following steps: Step 1: Prepare the cement-based radiation cooling matrix. This includes the following sub-steps: (1) Dry material mixing: Weigh 55 parts of 42.5 grade white cement, 25 parts of rutile titanium dioxide (particle size: 0.2-0.25μm), 15 parts of barium sulfate (particle size: 0.3-0.5μm), 5 parts of hollow glass microspheres and 0.08 parts of HPMC according to the mass fraction, put them into a planetary mixer and dry mix for 3 minutes to obtain the mixed dry material.

[0047] (2) Wet material mixing: Weigh the mixing water according to the water-binder ratio of 0.45, add 1.0 part of polycarboxylate superplasticizer (by mass), mix and stir evenly, then add the mixed dry material, stir at low speed for 2 minutes, then stir at high speed for 1 minute to obtain cement paste.

[0048] (3) Molding and curing: The cement slurry is injected into a 40mm×40mm×160mm mold and a 300mm×300mm×50mm flat mold respectively, and then vibrated to form. After curing in the mold for 24 hours, it is demolded and then placed in a standard curing room with a temperature of 20±2℃ and a relative humidity of ≥95% for demolding and curing for 28 days to obtain the cement-based radiant cooling matrix after curing.

[0049] (4) Substrate pretreatment: The cured cement-based radiation cooling substrate is dried at 60°C to constant weight, and then the surface laitance and loose layer are removed by wet grinding with 2000-grit sandpaper. The surface roughness Ra after grinding is controlled to be ≤1.6μm. After that, it is first blown clean with compressed air, and then ultrasonically cleaned with anhydrous ethanol at 100W power for 3 minutes. After cleaning, it is dried again until the moisture content is ≤0.5% for later use.

[0050] Step 2: Laser structuring is performed on the substrate surface. Based on the size requirements of the hierarchical micro-nano structure, the pretreated cement-based radiation cooling substrate surface is laser etched in a horizontal-vertical cross-grid scanning mode to form a hierarchical micro-nano structure.

[0051] The process parameters for laser structuring include: laser power 10W, scanning rate 1000mm / s, line spacing 80μm, one scan, spot diameter 30μm, etching depth 10-15μm, and ultrasonic cleaning power 100W. The parameters for the pulsed laser are as follows: Nanosecond laser: pulse width 10-30ns, repetition frequency 20-50kHz; Femtosecond laser: pulse width 100-500 fs, repetition frequency 100-200 kHz.

[0052] Step 3: Perform low surface energy hydrophobic modification on the hierarchical micro / nano structure: Coat the surface of the hierarchical micro / nano structure with a hydrophobic modifier to form a silane modified layer, and obtain the finished product after curing at room temperature.

[0053] Step three specifically includes the following sub-steps: (1) Preparation of hydrophobic modifier: Weigh 8 parts by mass of octyltriethoxysilane, 91 parts by mass of anhydrous ethanol and 1 part by mass of glacial acetic acid, mix them evenly, and then hydrolyze them in a dark environment at room temperature for 30 minutes to obtain a silane solution, which is the hydrophobic modifier. At this time, the pH value of the hydrophobic modifier is 4-5.

[0054] (2) Coating and Curing: The hydrolyzed silane solution (hydrophobic modifier) ​​is uniformly sprayed onto the surface of the laser-structured cement-based radiation cooling substrate, and then cured at room temperature to obtain the finished product, namely, the laser-structured hydrophobic self-cleaning cement-based radiation cooling material. The coating amount of the hydrophobic modifier is 80 g / m². 2 The cement-based radiative cooling material of this invention is obtained by allowing the material to be left at room temperature for 24 hours to completely hydrolyze and solidify (with an ambient relative humidity of 40-60%).

[0055] Example 2 This embodiment provides a laser-structured hydrophobic self-cleaning cement-based radiation cooling material and its preparation method. The basic steps are basically the same as those in Example 1, but the difference from Example 1 is as follows: Step one includes: (1) Dry material mixing: Weigh 60 parts of 42.5 grade white cement, 20 parts of rutile titanium dioxide (particle size: 0.2-0.25μm), 12 parts of barium sulfate (particle size: 0.3-0.5μm), 8 parts of hollow glass microspheres and 0.1 parts of HPMC according to the mass fraction, put them into a planetary mixer and dry mix for 3 minutes to obtain the mixed dry material.

[0056] (2) Wet material mixing: Weigh the mixing water according to the water-cement ratio of 0.42, add 1.2 parts of polycarboxylate superplasticizer (by mass), mix and stir evenly, then add the mixed dry material, stir at low speed for 2 minutes, then stir at high speed for 1 minute to obtain cement paste. Other process steps in this step are the same as in Example 1.

[0057] In step two, the process parameters for laser structuring include: laser power 12W, scanning rate 1500mm / s, line spacing 100μm, number of scans 2, spot diameter 40μm, and etching depth 15-20μm. Other process steps in this step are the same as in Example 1.

[0058] In step three, the mass concentration of the low surface energy hydrophobic modifier (silane solution) is 10%, and the coating amount is 100 g / m². 2 The other process steps in this step are the same as in Example 1.

[0059] Example 3 This embodiment provides a laser-structured hydrophobic self-cleaning cement-based radiation cooling material and its preparation method. The basic steps are basically the same as those in Example 1, but the difference from Example 1 is as follows: Step one includes: (1) Dry material mixing: Weigh out 50 parts of 42.5 grade ordinary Portland cement, 10 parts of 42.5 grade white cement, 18 parts of rutile titanium dioxide (particle size: 0.2-0.25μm), 18 parts of barium sulfate (particle size: 0.3-0.5μm), 4 parts of hollow glass microspheres, and 0.05 parts of HPMC by weight, and put them into a planetary mixer for dry mixing for 3 minutes to obtain a uniform dry material. Other sub-steps of this step are the same as in Example 1.

[0060] (2) Wet material mixing: Weigh the mixing water according to the water-binder ratio of 0.48, add 0.8 parts of polycarboxylate superplasticizer (by mass), mix and stir evenly, then add the mixed dry material, stir at low speed for 2 minutes, then stir at high speed for 1 minute to obtain cement paste.

[0061] In step two, the process parameters for laser structuring include: laser power 8W, scanning rate 800mm / s, line spacing 50μm, number of scans 1, spot diameter 20μm, and etching depth 5-10μm. Other process steps in this step are the same as in Example 1.

[0062] In step three, the mass concentration of the low surface energy hydrophobic modifier (silane solution) is 5%, and the coating amount is 50 g / m². 2 The other process steps in this step are the same as in Example 1.

[0063] To verify the technical effects of the present invention, the following comparative examples were also provided: Comparative Example 1 This comparative example provides a common cement-based radiation cooling material (without laser etching and hydrophobic modification). Its matrix formulation and preparation method are basically the same as in Example 1. The difference compared to Example 1 is: The preparation method omits steps two and three, and does not perform laser structuring treatment or silane hydrophobic modification, directly obtaining ordinary cement-based radiation cooling materials.

[0064] Comparative Example 2 This comparative example provides a cement-based radiative cooling material (without hydrophobic modification), whose matrix formulation and preparation method are basically the same as those in Example 1. The difference between Example 1 and Example 1 is as follows: The preparation method omits step three, does not perform silane hydrophobic modification, and directly obtains ordinary cement-based radiation cooling material that has only undergone laser etching treatment.

[0065] Comparative Example 3 This comparative example provides a cement-based radiation cooling material (without laser etching), whose matrix formulation and preparation method are basically the same as those in Example 1. The difference between Example 1 and Example 1 is as follows: The preparation method does not include step two, and does not perform laser structuring treatment, directly obtaining a cement-based radiation cooling material that has only undergone silane hydrophobic modification.

[0066] Only silane hydrophobic modification (no laser structuring treatment) The matrix preparation and silane hydrophobic modification process are exactly the same as in Example 1; without laser structuring treatment, cement-based radiation cooling material modified only with silane is directly obtained.

[0067] Comparative Example 4 This comparative example provides a cement-based radiative cooling material, whose matrix formulation and preparation method are basically the same as those in Example 1. The difference between Example 1 and Example 1 is as follows: The matrix formulation also includes 1.5 parts of calcium stearate hydrophobic agent. The preparation method does not include steps two and three, and does not undergo laser structuring treatment and silane hydrophobic modification, directly obtaining a traditional cement-based radiation cooling material with internal hydrophobic agent.

[0068] Comparative Example 5 This comparative example provides a cement-based radiative cooling material, whose matrix formulation and preparation method are basically the same as those in Example 1. The difference between Example 1 and Example 1 is as follows: The preparation method omits steps two and three, and does not perform laser structuring treatment or silane hydrophobic modification. The preparation method involves uniformly coating the substrate surface with a commercially available acrylic-based radiation cooling coating at a coating amount of 200 g / m², and curing at room temperature for 7 days to obtain a surface-coated cement-based radiation cooling material.

[0069] Based on the finished product samples obtained from the above embodiments and comparative examples, the following performance tests were conducted to obtain the corresponding performance indicators.

[0070] Test standard description: 1. Mechanical property testing was conducted according to GB / T 17671-2021 "Test Method for Strength of Cement Mortar (ISO Method)", testing the 28-day compressive strength and flexural strength; 2. Solar spectral reflectance was measured using an ultraviolet-visible-near-infrared spectrophotometer (UV-Vis-NIR), with a test wavelength range of 0.3-2.5μm. The weighted calculation was based on the AM1.5 standard solar spectrum. 3. Infrared emissivity was measured using a Fourier transform infrared spectrometer (FTIR) in the 8-13 μm band, and the weighted calculation was based on the atmospheric transparency window emissivity standard. 4. Hydrophobicity test was conducted using a contact angle measuring instrument to measure the static water contact angle and roll-off angle at 25℃, with a water droplet volume of 5μL. 5. The radiative cooling performance test was conducted according to ASTM E1980-20 standard, and the steady-state temperature drop was tested under standard 1-sun (1000W / m²) irradiation. 6. The ultraviolet aging test was conducted in accordance with GB / T 16422.3-2014, using a UVB-313 lamp with an irradiance of 0.71 W / m² for 500 hours. 7. The freeze-thaw cycle test is conducted according to GB / T 50082-2009, using the rapid freezing method, and involves 100 freeze-thaw cycles. 8. Rainwater erosion test according to GB / T 9276-1996, using artificial rain device, erosion intensity of 100mm / h, continuous 1000 cycles; 9. The efflorescence resistance test is conducted according to GB / T 25181-2010, using the accelerated efflorescence method, and the efflorescence level is tested after 7 days. 10. The chloride ion penetration resistance test was conducted according to GB / T 50082-2009, using the electrical flux method, and the electrical flux was tested over 56 days. 11. The carbonization resistance test is conducted according to GB / T 50082-2009, testing the carbonization depth after 28 days; 12. Thermal conductivity was tested according to GB / T 10294-2008, using the protective hot plate method, at 25℃.

[0071] The resulting performance indicators are shown in Table 1.

[0072] Table 1 Performance Index Test Results

[0073] By comparing and analyzing the comparative examples and embodiments in Table 1, it can be seen that: Comparative Example 1 (no laser, no modification): The initial performance was the worst, and the long-term performance degradation was the most severe, proving the necessity of laser structuring and hydrophobic modification.

[0074] Comparative Example 2 (laser only): The optical performance was improved, but the hydrophobicity was poor, and the problems of dust accumulation and alkali bloom could not be solved. The long-term performance degradation was obvious.

[0075] Comparative Example 3 (Silane only): Hydrophobicity was improved, but lacking micro / nano structure support, it could not achieve superhydrophobic self-cleaning, and its optical performance was not significantly improved.

[0076] Comparative Example 4 (with internal hydrophobic agent): The mechanical properties decreased significantly, and both the hydrophobic and optical properties were poor, demonstrating the inherent defects of traditional internal doping modification.

[0077] Comparative Example 5 (Surface Coating): It has excellent initial performance, but its long-term performance deteriorates the most. In particular, after freeze-thaw cycles and rain erosion, the coating cracks and peels off, proving that the traditional coating solution is not durable enough.

[0078] A comparison of Examples 2 and 3 with Example 1 shows that: Example 2: The content of white cement and hollow glass microspheres was increased, while the total content of functional fillers was reduced. Simultaneously, the laser etching depth and silane coating amount were increased. Results showed a slight improvement in mechanical properties, a decrease in thermal conductivity, and better hydrophobicity, but a slight decrease in solar reflectivity. This makes it suitable for cold regions where higher insulation and durability requirements are needed.

[0079] Example 3: A composite system of ordinary silicate cement and white cement was used to reduce the laser etching depth and silane coating amount. The results showed a slight decrease in solar reflectivity and mechanical properties, and a slight increase in thermal conductivity, but the requirements for engineering applications were still met. This significantly reduced raw material costs and is suitable for cost-sensitive large-scale municipal engineering applications.

[0080] Analysis of the various embodiments in conjunction with comparative examples shows that: Examples 1-3 all exhibit compressive strength ≥40MPa, comparable to ordinary cement matrix, and significantly higher than Comparative Example 4's 31.5MPa. After 1000 rain washes, the contact angle retention rate is ≥96%, and the reflectivity retention rate is ≥97%, significantly higher than Comparative Example 5. The efflorescence resistance grade reaches 0, and after 500 hours of UV aging, the reflectivity retention rate is ≥96%, significantly higher than all comparative examples. Therefore, the technical solutions formed in each example can simultaneously achieve high-radiative cooling, long-term self-cleaning, excellent mechanical properties, and durability, overcoming the corresponding technical problems existing in the prior art.

[0081] The present invention has been described above by way of example with reference to the accompanying drawings. Obviously, the specific implementation of the present invention is not limited to the above-described manner. Any non-substantial improvements made using the inventive concept and technical solution of the present invention, or the direct application of the inventive concept and technical solution of the present invention to other occasions without modification, are all within the protection scope of the present invention.

Claims

1. A laser-structured hydrophobic self-cleaning cement-based radiation cooling material, characterized in that, Based on parts by mass, it includes the following components: Cement, 50-70 parts; Rutile titanium dioxide, 7.5-18 parts; Barium sulfate, 5-12 parts; Hollow glass microspheres, 2.5-6 parts; The surface of the cement-based radiative cooling material has a hierarchical micro-nano structure, which includes trenches with a depth of 5-20 μm and a width of 50-100 μm and protrusions with a side length of 100-500 nm. The trenches are located between adjacent protrusions. The surface of the hierarchical micro-nano structure is modified with a hydrophobic modifier to form a silane modified layer.

2. The laser-structured hydrophobic self-cleaning cement-based radiation cooling material according to claim 1, characterized in that, The particle size of rutile titanium dioxide is 0.2-0.25 μm; the particle size of barium sulfate is 0.3-0.5 μm; and the particle size of hollow glass microspheres is 10-50 μm with a wall thickness of 1-2 μm.

3. The laser-structured hydrophobic self-cleaning cement-based radiation cooling material according to claim 1, characterized in that, The water contact angle of the silane-modified layer is ≥140°, and the roll-off angle is ≤5°.

4. The laser-structured hydrophobic self-cleaning cement-based radiation cooling material according to claim 1, characterized in that, It also includes the following components by parts by mass: Hydroxypropyl methylcellulose ether, 0.05-0.1 parts; Polycarboxylate superplasticizer, 0.8-1.2 parts.

5. A method for preparing a laser-structured hydrophobic self-cleaning cement-based radiation cooling material according to any one of claims 1-4, characterized in that, Includes the following steps: Step 1: Prepare cement-based radiative cooling matrix. Weigh each component raw material according to the designed mass proportions, stir and mix, and then perform matrix molding, curing and pretreatment to obtain cement-based radiative cooling matrix. Step 2: Laser structuring is performed on the substrate surface. Based on the size requirements of the hierarchical micro-nano structure, the pretreated cement-based radiation cooling substrate surface is laser etched in a horizontal-vertical cross grid scanning mode to form a hierarchical micro-nano structure. Step 3: The hierarchical micro / nano structure is modified with low surface energy hydrophobicity by coating the surface of the hierarchical micro / nano structure with a hydrophobic modifier to form a silane modified layer, which is then cured at room temperature to obtain the finished product.

6. The method for preparing a laser-structured hydrophobic self-cleaning cement-based radiation cooling material according to claim 5, characterized in that, Step one includes the following sub-steps: (1) Dry material mixing: Weigh out the dry materials such as cement, rutile titanium dioxide, barium sulfate, hollow glass microspheres, and hydroxypropyl methylcellulose ether according to the designed mass parts, put them into a planetary mixer and dry mix them until they are evenly mixed to obtain the mixed dry material; (2) Wet material mixing: Weigh out the polycarboxylate superplasticizer and mixing water according to the designed mass parts, mix and stir evenly, add the resulting liquid to the mixed dry material, and stir evenly to obtain cement paste; (3) Molding and curing: The cement slurry is injected into the mold and vibrated to form the mold. After curing in the mold, it is demolded and then cured again to obtain the cured cement-based radiation cooling matrix. (4) Substrate pretreatment: Dry the cement-based radiation cooling substrate after curing to constant weight, then grind to remove surface laitance and loose layer, then blow it clean with compressed air, then ultrasonically clean it with anhydrous ethanol, and dry it again for later use.

7. The preparation method of a laser-structured hydrophobic self-cleaning cement-based radiation cooling material according to claim 5, characterized in that, Step two includes: laser etching uses pulsed laser, which is a 355nm ultraviolet nanosecond or femtosecond laser. The etching depth is achieved by adjusting the "laser power-scanning rate-scanning number" in a linked manner. After fixing the number of scans, the power and rate are finely adjusted.

8. The method for preparing a laser-structured hydrophobic self-cleaning cement-based radiation cooling material according to claim 7, characterized in that, Step two etching uses a laser power of 5-15W, a scanning rate of 500-2000mm / s, a line spacing of 50-100μm, a spot diameter of 20-50μm, and 1-2 scans. The pulsed laser parameters can be any of the following: 1) Nanosecond laser: pulse width 10-30ns, repetition frequency 20-50kHz; 2) Femtosecond laser: pulse width 100-500 fs, repetition frequency 100-200 kHz.

9. The preparation method of a laser-structured hydrophobic self-cleaning cement-based radiation cooling material according to claim 5, characterized in that, Step 3 includes the following sub-steps: (1) Preparation of hydrophobic modifier: Weigh out octyltriethoxysilane, anhydrous ethanol and glacial acetic acid by mass, mix them evenly, and then hydrolyze them in a dark environment at room temperature to obtain the hydrophobic modifier. (2) Coating and curing: The hydrophobic modifier is uniformly coated on the surface of the cement-based radiation cooling substrate by spraying or impregnation to modify the surface of the hierarchical micro-nano structure. After curing at room temperature, the finished product is obtained.

10. The method for preparing a laser-structured hydrophobic self-cleaning cement-based radiation cooling material according to claim 9, characterized in that, In step three, the pH value of the hydrophobic modifier is 4-5, and the coating amount of the hydrophobic modifier is 80g / m². 2 The hydrolysis time is 30 minutes, and the hydrolysis solidification is carried out at room temperature with a relative humidity (RH) of 40-60%.

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