Radiation refrigeration cement-based material with metasurface as well as preparation method and application of radiation refrigeration cement-based material

Abstract

The invention discloses a radiation refrigeration cement-based material with a metasurface and a preparation method and application thereof.The radiation refrigeration cement-based material with the metasurface is prepared from, by mass, cementitious material particles, water and an additive according to the mass fraction ratio of (1-2): (0.4-0.6): (0.01-0.02). Bubbles are guided to be spontaneously arranged and grow on the surface of cement-based material slurry which is not completely hardened, complete hardening of a matrix and stability of surface microbubbles are finally achieved by combining the rheological property of the cement-based material, the super-surface cement-based material which is excellent in optical performance and provided with orderly-arranged cavities in the surface is finally obtained, passive cooling can be efficiently achieved, and the service life of the super-surface cement-based material is prolonged. Use of active refrigeration equipment such as an air conditioner is reduced, and the system is suitable for being applied to building walls which are under sun irradiation for a long time in medium and low latitude areas and have cooling requirements, contributes to reduction of building energy consumption, and realizes low-carbon sustainable development.

Description

Technical Field

[0001] The invention relates to a radiation cooling cement-based material with a super surface and a preparation method and application thereof, belonging to the technical field of building materials. Background Art

[0002] In recent years, the challenge of global climate change has become increasingly severe and urgent. With the acceleration of urbanization, the proportion of building energy consumption has continued to rise, and the construction industry has become a "major carbon emitter", exacerbating climate change. At present, building refrigeration accounts for about 20% of the total energy consumption. The use of existing cooling and heating equipment such as air conditioners, refrigerators and other household appliances, whose refrigeration medium Freon will destroy the ozone layer, cause ozone holes, and aggravate the greenhouse effect and urban heat island effect. The problems make my country and even the world face two major problems: energy shortage and climate warming. Therefore, in order to achieve the goal of carbon neutrality, the construction industry is a top priority. Efficient and energy-saving building cooling methods are necessary technologies and key difficulties to alleviate energy problems and achieve the "carbon peak" and "carbon neutrality" strategies.

[0003] Radiative cooling plays an important role in energy conservation. It is considered to be one of the most attractive concepts in the 21st century. It does not require external energy input, can reduce building energy consumption, thereby saving energy, and does not produce pollution. It meets the requirements of today's sustainable development and is a green and environmentally friendly passive cooling method. Radiative cooling technology includes both reflection (reflect) and radiation (emit). The temperature of the universe is close to absolute zero and can be regarded as a "pool" that absorbs heat. Objects on the earth can transfer heat to outer space in the form of electromagnetic waves (mainly 8μm-13μm) through radiation, and at the same time reflect most of the sunlight (mainly 0.25μm-2.5μm) that reaches the surface of the earth to achieve the effect of heat dissipation and cooling. The two most important parameters for measuring the refrigeration performance of radiative cooling materials are: the reflectivity R solar and the radiance ε of the atmospheric band LWIR Solar radiation is mainly distributed within 0.25μm-2.5μm, which accounts for more than 98% of the total solar radiation energy, and the total radiation intensity is as high as 993W◆m -2, including the ultraviolet region (UV, 0.25μm-0.4μm), the visible region (VIS, 0.4μm-0.78μm) and the near-infrared region (NIR, 0.78μm-2.5μm), which are the main sources of heat in buildings. Therefore, high solar reflectivity indicates that the material can reflect most of the sunlight to achieve a cooling effect on the surface. The atmosphere between the earth and outer space is a complex mixture of various gases, some of which are semi-transparent media for electromagnetic waves under certain conditions, which will hinder the cooling effect to a certain extent. However, in the mid-infrared band (MIR) of 8μm–13μm, the atmosphere is highly transparent (high transmittance) to thermal radiation, and most electromagnetic waves can pass through it, so it is also called the "atmospheric window"; at the same time, this atmospheric window also coincides with the peak value of blackbody thermal radiation at room temperature. Therefore, high infrared emissivity indicates that it can dissipate more heat through thermal radiation on the surface of the object, thereby achieving a cooling effect.

[0004] Cement is the largest and most widely used material at present, and it is also the main building structural material. Survey data show that from a high altitude, the concrete coverage rate (including pavement, parking lots and building side walls) in a certain city in the United States is about 39%. Due to the complex surface structure of urban buildings, the overall reflectivity of the city is lower than that of the surrounding rural areas, and due to the low reflectivity of concrete and other traditional building materials, up to nearly 90% of the sunlight is absorbed by the surface. Therefore, the surface of the building composed of cement products will absorb more heat, causing the surface temperature of the building to rise, thereby exacerbating the urban heat island effect. The rise in urban temperature has exacerbated the energy consumption and environmental pollution caused by the use of refrigeration equipment such as air conditioners, increased the demand for electricity and the city's carbon footprint, and is also a threat to human comfort and health. If this technology is applied to buildings, it will have a huge impact. According to relevant calculations, for every 1% increase in surface reflectivity, global carbon dioxide emissions will be reduced by 44Gt per year. Significantly improve the reflectivity R of the structural material itself solar and the emissivity ε LWIR , achieving the performance target of building structure radiation cooling, can open up a new way for building cooling and building energy conservation in the field of civil engineering materials. Advanced building materials with multiple uses and green environmental protection are an important topic that needs to be realized in the current field of building energy conservation and emission reduction. Efficient radiation cooling methods need to be combined with cement for application.

[0005] At present, the design of radiative cooling is mostly focused on the application of high-temperature resistant metal oxides, organic matter and micro-nano particles with reflective effects. The resulting forms are mostly film-like and coating-like, and some require the use of precise technology to prepare micro-nano-level coatings and super-surfaces with fine microstructures. Existing designs are mostly oriented towards photovoltaic devices, personal thermal management fabrics, etc. CN119243472A discloses a method for preparing a nanofiber membrane with sustainable cooling sensation, and CN119194733A discloses a fiber membrane with adjustable radiative cooling performance. Both of them can be used as fabrics to perform thermal management on the human body. CN118980190A discloses a structurally colored photonic crystal radiative cooling device, which needs to be prepared using a photolithography method, has a high cost, can only be applied to high-precision instruments, and is not suitable for large-scale scenes of buildings. The method of applying radiative cooling to buildings is still in the exploratory stage. CN118852813A discloses a porous polymer-based radiation cooling material, which is a plate-like structure or a film-like structure; CN118598539A discloses a multilayer film structure for radiation cooling of building glass; CN118325368A discloses a method for preparing a radiation cooling coating for building energy saving, which can be applied on a substrate to form a radiation cooling coating for building energy saving. However, the above three designs are all polymer-based film or coating structures, which can only be attached to the outer surface of the building to play a role. The durability problem becomes a challenge, and it fails to solve the essential problem that the building material itself has low reflectivity and is easy to absorb heat in summer, thereby causing the internal temperature to rise. Therefore, there is an urgent need to develop advanced radiation cooling cement-based metamaterials with "high reflectivity, high emissivity, large-scale preparation, strong plasticity, and strong structural integrity" to achieve nano-micro-macro multi-scale performance coordinated regulation, large-scale material preparation, and multi-scenario material integrated design and functional application, while meeting structural requirements such as structural strength, thermal insulation, protection and durability, achieving the goal of self-radiative cooling of building structures, and meeting the urgent needs of the construction of people's livelihood and commercial infrastructure projects such as building structure roofs and exterior walls, alleviating the need to use traditional refrigeration systems, reducing energy consumption and carbon emissions, mitigating the "heat island effect", promoting discipline development, and promoting the "dual carbon" process. Summary of the invention

[0006] Purpose of the invention: The first purpose of the present invention is to provide a radiant cooling cement-based material with a super surface. The second purpose of the present invention is to provide a method for preparing the super surface radiant cooling cement-based material. The third purpose of the present invention is to provide an application of the method for preparing the super surface radiant cooling cement-based material in unsupported 3D printed buildings.

[0007] Technical solution: The present invention discloses a radiant cooling cement-based material with a super surface, wherein the base material comprises the following components in a mass fraction ratio: the mass ratio of cementitious material particles: water: admixture is (1-2): (0.4-0.6): (0.01-0.02), and the super surface is prepared by combining the template method with the method of gas volume expansion driven by a pressure gradient to act on the base material.

[0008] Furthermore, the cementitious material particles are unhydrated cement particles.

[0009] Furthermore, the elements of the unhydrated cement particles include one or more of calcium, silicon, aluminum, sulfur, oxygen or iron.

[0010] Furthermore, the unhydrated cement particles are at least one of white silicate cement, black silicate cement, white sulphoaluminate cement and black sulphoaluminate cement.

[0011] Furthermore, the water is purified water.

[0012] Furthermore, the admixture is a water reducing agent.

[0013] Furthermore, the water reducer is at least one of a carboxylic acid type polycarboxylic acid water reducer, a sulfonic acid type polycarboxylic acid water reducer, a hydroxyl type polycarboxylic acid water reducer, and a carboxylic acid-sulfonic acid composite water reducer.

[0014] The method for preparing the radiative cooling cement-based material with a super surface according to the present invention comprises the following steps:

[0015] (1) preparing a silicon master mold having a columnar microstructure on the surface by photolithography, and performing a surface hydrophobic treatment;

[0016] (2) pouring a thermosetting or thermoplastic organic material onto the silicon master mold obtained in step (1), drying and forming the material, and peeling the material off to obtain an organic material template;

[0017] (3) pouring the matrix material slurry in an ordinary cement slurry mold, covering the matrix material slurry with an organic template, placing it in a vacuum drying oven, evacuating the air, standing it for curing, hardening it into shape, peeling off the organic template, and continuing to cure it to obtain a radiant cooling cement-based material with a super surface.

[0018] Furthermore, in step (1), the silicon master mold is a single crystal silicon wafer.

[0019] Furthermore, in step (1), the surface of the obtained silicon master mold has a plurality of columnar microstructures, the diameter of the columnar microstructures is 25-100 μm, the depth is 25-100 μm, and the spacing between adjacent columnar microstructures is 50-200 μm. The diameter: spacing is (1:1) to (1:3), preferably the diameter: spacing = 1:2.

[0020] Furthermore, the plurality of columnar microstructures are arranged hexagonally.

[0021] Furthermore, in step (2), the thermosetting or thermoplastic organic matter is at least one of polydimethylsiloxane (PDMS), polyethylene (PE), and polytetrafluoroethylene (PTFE).

[0022] Furthermore, thermosetting polydimethylsiloxane (PDMS) is composed of a main agent (polydimethylsiloxane prepolymer) and a curing agent (siloxane cross-linking agent).

[0023] Furthermore, when thermosetting polydimethylsiloxane (PDMS) is prepared, the mass ratio of the main agent to the curing agent is (8-12):1, preferably 10:1.

[0024] Furthermore, polyethylene (PE) and polytetrafluoroethylene (PTFE) are prepared by hot pressing of particles.

[0025] Furthermore, polydimethylsiloxane (PDMS) is used to prepare an organic template, the temperature for stirring the main agent and the curing agent is room temperature, the curing temperature is 60-80° C., and the curing time is more than 2 hours.

[0026] Furthermore, when polyethylene (PE) and polytetrafluoroethylene (PTFE) are used to prepare organic templates, the melting temperature is 150-200° C., preferably 180° C., and the organic templates are solidified after being cooled to room temperature.

[0027] Furthermore, in step (3), the air pressure extracted during vacuuming is at least one value between 10 and 90 kPa, preferably between 20 and 80; and the curing conditions are all standard curing conditions.

[0028] Furthermore, in step (3), the curing is performed for more than 12 hours and further for more than 72 hours.

[0029] Furthermore, the ambient temperature during preparation of the matrix material slurry is 15-25° C., and the stirring speed is 400-500 rpm.

[0030] Application of the radiant cooling cement-based material with a super surface of the present invention or the preparation method of the radiant cooling cement-based material with a super surface of any one of claims 7 to 9 in unsupported 3D printed buildings

[0031] The present invention provides a cement-based radiant cooling material with a super surface, which not only has excellent optical regulation performance, but also has the characteristics of structural integration and high strength, providing a new solution for building energy conservation and green construction. The material achieves a perfect combination of function and structural performance, and can be used as a functional coating for the surface modification of existing buildings, and can also be used as a structural material for the overall design and construction of future green buildings.

[0032] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0033] (1) Excellent radiative cooling performance: The present invention constructs an orderly arranged micro-cavity structure through a template replication method. The structure has high solar reflectivity (which can effectively reduce heat absorption) and high infrared emissivity (which can quickly dissipate heat to the outside), significantly improving the passive cooling effect. Both the solar reflectivity and mid-infrared emissivity can reach 96%, fundamentally changing the heat absorption characteristics of cement-based materials. Compared with existing coating-type radiative cooling materials, the present invention can provide more efficient and lasting cooling performance.

[0034] (2) Innovative preparation process: The present invention adopts a template method combined with a pressure gradient driven gas expansion process to prepare a super surface structure with micro cavities on the surface, which is simple to operate and easy to industrialize. Compared with traditional complex and expensive micro-nano processing technology, the present invention has low cost and high efficiency, and is suitable for large-scale promotion and application.

[0035] (3) High mechanical properties and durability: Compared with traditional functional materials, the present invention uses cement-based materials as the matrix, which has high compressive strength and weather resistance (14-day compressive strength can reach 100MPa), can resist erosion in complex environments such as high temperature, humidity, wind and sand for a long time, and maintain the stability and service life of the material.

[0036] (4) Integration of structure and function: Through optimized design, the present invention organically combines the microstructural function of radiant cooling with the high strength and durability of cement-based materials, overcoming the problems of easy detachment of the coating and performance degradation caused by the separation of the functional coating and the base material in the prior art, thus achieving long-term use of the material.

[0037] (5) Multifunctionality and wide applicability: As a functional coating, it can be applied to the energy-saving renovation of existing buildings, with simple construction and strong adaptability; as a structural material, it can be directly applied to new green buildings to achieve functional and structural integration, simplify the construction process, and improve overall performance. This dual application capability broadens the application scenarios of the material.

[0038] (6) Green environmental protection and low-carbon sustainability: This invention provides an efficient passive cooling solution for the cooling needs of buildings in low- and mid-latitude areas that are exposed to strong solar radiation for a long time, reduces the dependence on high-energy air-conditioning systems, and reduces energy consumption and carbon emissions in building operations through passive cooling. At the same time, inorganic white gelling materials and environmentally friendly processes are selected in the material production process, further reducing the environmental burden of the production process, which is in line with the development trend of green building materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a schematic diagram of the method of gas volume expansion driven by the template method and the pressure gradient in the process of preparing the super surface of the present invention;

[0040] Figure 2 This is a picture of pouring PDMS slurry onto a silicon master mold;

[0041] Figure 3 is a SEM image of the PDMS organic template obtained in Example 1;

[0042] Figure 4 1 is a real picture of the PDMS template prepared in Example 1, wherein A is a picture of a PDMS template that can be freely spliced ​​and expanded, and B is a picture of a light and thin PDMS template;

[0043] Figure 5 It is the SEM image of the super surface microstructure of the radiant cooling cement-based material with a super surface prepared in Examples 1-3; wherein A is the SEM image of the surface microstructure of the radiant cooling cement-based material prepared in Example 1, B is the SEM image of the surface microstructure of the radiant cooling cement-based material prepared in Example 2, and C is the SEM image of the surface microstructure of the radiant cooling cement-based material prepared in Example 3. DETAILED DESCRIPTION

[0044] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0045] Example 1

[0046] 1. Prepare a silicon master mold with a columnar microstructure on the surface by photolithography, and perform surface hydrophobic treatment;

[0047] First, a single crystal silicon wafer with a microstructure on the surface is prepared as a master mold. The single crystal silicon wafer is ultrasonically cleaned and dried, and a layer of photoresist (SU-8) is spin-coated on the clean and dry surface of the single crystal silicon wafer. The spin coating parameters are 3000rpm, 60 seconds to obtain a uniform photoresist layer, and baked at 90°C for 25 minutes to remove the solvent. Subsequently, ultraviolet exposure is performed through a mask (circular diameter of 25μm, depth of 25μm), and the exposure dose is controlled at 200mJ / cm2 to transfer the columnar microstructure pattern to the photoresist layer. After exposure, a developer (SU-8 developer) is used for development, and the development time is controlled at 25 minutes to obtain a high-fidelity microstructure pattern. Next, the silicon wafer is etched by deep reactive ion etching (DRIE) or wet etching (such as KOH solution) to form a columnar microstructure on the surface of the silicon wafer. The etching depth is controlled at 50μm, and then the residual photoresist is removed and cleaned to obtain a silicon master mold with a columnar microstructure on the surface (the diameter of the surface columnar microstructure is 25μm, the depth is 25μm, the spacing is 50μm, and the hexagonal arrangement). Finally, the etched silicon wafer is placed in a chemical vapor deposition (CVD) device, and the surface is modified using 1H, 1H, 2H, 2H-perfluorooctyltriethoxysilane (FOTS) or trifluoromethylsilane (TFMS), and treated at 150°C for 30 to 60 minutes to form a low surface energy coating on the surface of the silicon wafer, making it super-hydrophobic, so as to reduce the adhesion during the subsequent PDMS demolding process.

[0048] 2. 100g white silicate cement, 40g pure water, 1g polycarboxylate water reducer, the surface of the single crystal silicon master mold has a hexagonal columnar microstructure (diameter 25μm, depth 25μm, spacing 50μm), the organic template material is PDMS (polydimethylsiloxane), containing 10g main agent (α,ω-dihydroxypolydimethylsiloxane), 1g curing agent (polymethylhydrogensiloxane).

[0049] Stir α,ω-dihydroxy polydimethylsiloxane and polymethylhydrogensiloxane at 15-25°C, remove the internal gas by vacuum degassing, and then cast on a single crystal silicon master mold (such as Figure 2 The PDMS organic template obtained in this example was analyzed by scanning electron microscopy. The results are as follows: Figure 3 shown. Figure 3 is a SEM image of the PDMS organic template obtained in Example 1. Figure 3 It can be seen that after one molding process, concave columns with diameters of 25 μm and 50 μm and arranged hexagonally are uniformly present on the PDMS membrane.

[0050] On the other hand, stir white silicate cement, pure water, and carboxylic acid-type polycarboxylate water-reducing agent at 15-25°C at a speed of 400-500rpm for 2 minutes until evenly mixed to obtain an unhardened matrix material slurry. Pour the unhardened matrix material slurry into an ordinary cement slurry mold, and then cover the PDMS mold on the unhardened matrix material slurry so that the surface with the microstructure is in contact with the unhardened matrix material slurry. Put it in a vacuum drying oven and connect the vacuum pump. Turn on the vacuum pump, draw 80kPa air pressure and then close the valve. Let it stand for curing and wait for the internal slurry to harden. After 12 hours, open the vacuum drying oven, peel off the PDMS template, and move the whole into standard curing conditions for continued curing to obtain a cement-based radiant refrigeration material with a super surface. The experimental process is as follows Figure 1 The prepared PDMS template is shown in the figure. Figure 4 shown. Figure 4 These are actual photos of the PDMS template prepared in Example 1, wherein A is a photo of a PDMS template that can be freely spliced ​​and expanded, and B is a photo of a light and thin PDMS template.

[0051] Comparative Example 1

[0052] The experimental process is the same as in Example 1, except that no supersurface is prepared, as follows:

[0053] 100g white Portland cement, 40g pure water, 1g polycarboxylate water reducer. Stir white Portland cement, pure water, polycarboxylate water reducer at 15-25℃, stir at 400-500rpm for 2min until uniform, obtain unhardened slurry, pour into ordinary cement slurry mold, demould after 24h, and cure.

[0054] Example 2

[0055] The experimental process is the same as that of Example 1, except that the columnar microstructure on the surface of the single crystal silicon master mold is changed to (diameter 50 μm, depth 50 μm, spacing 100 μm, hexagonal arrangement), as follows:

[0056] 100g white silicate cement, 40g pure water, 1g polycarboxylic acid water reducer, the surface of the single crystal silicon master mold has a columnar microstructure (diameter 50μm, depth 50μm, spacing 100μm, hexagonal arrangement), the organic template material is PDMS (polydimethylsiloxane), containing 10g main agent (α,ω-dihydroxypolydimethylsiloxane), 1g curing agent (polymethylhydrogensiloxane).

[0057] Stir α,ω-dihydroxy polydimethylsiloxane and polymethylhydrogensiloxane at 15-25℃, vacuum degassing to remove internal gas, then cast on a single crystal silicon master mold, put into an oven at 60℃, dry for 2h, take out, and peel off to obtain a PDMS mold. On the other hand, stir white silicate cement, pure water, and carboxylic acid type polycarboxylic acid water reducer at 15-25℃, stir at a speed of 400-500rpm for 2min until uniform, obtain an unhardened matrix material slurry, cast the unhardened matrix material slurry in an ordinary cement slurry mold, and then cover the PDMS mold on the unhardened matrix material slurry so that the surface with microstructure is in contact with the unhardened matrix material slurry, put it into a vacuum drying oven, and connect a vacuum pump. Turn on the vacuum pump, draw 80kPa air pressure, close the valve, and let it stand for curing until the internal slurry hardens. After 12h, open the vacuum drying oven, peel off the PDMS template, and move the whole into standard curing conditions for continued curing to obtain a cement-based radiative cooling material with a super surface.

[0058] Example 3

[0059] The experimental process is the same as that of Example 1, except that the size of the mask when preparing the single crystal silicon template is changed, so that the columnar microstructure on the surface of the single crystal silicon master mold is changed to (diameter of 100 μm, depth of 100 μm, spacing of 200 μm, hexagonal arrangement), as follows:

[0060] 100g white silicate cement, 40g pure water, 1g polycarboxylic acid water reducer, the surface of the single crystal silicon master mold has a columnar microstructure (diameter 100μm, depth 100μm, spacing 200μm, hexagonal arrangement), the organic template material is PDMS (polydimethylsiloxane), containing 10g main agent (α,ω-dihydroxypolydimethylsiloxane), 1g curing agent (polymethylhydrogensiloxane).

[0061] Stir α,ω-dihydroxy polydimethylsiloxane and polymethylhydrogensiloxane at 15-25℃, vacuum degassing to remove internal gas, then cast on a single crystal silicon master mold, put into an oven at 60℃, dry for 2h, take out, and peel off to obtain a PDMS mold. On the other hand, stir white silicate cement, pure water, and carboxylic acid type polycarboxylic acid water reducer at 15-25℃, stir at a speed of 400-500rpm for 2min until uniform, obtain an unhardened matrix material slurry, cast the unhardened matrix material slurry in an ordinary cement slurry mold, and then cover the PDMS mold on the unhardened matrix material slurry so that the surface with microstructure is in contact with the unhardened matrix material slurry, put it into a vacuum drying oven, and connect a vacuum pump. Turn on the vacuum pump, draw 80kPa air pressure, close the valve, and let it stand for oxidation to wait for the internal slurry to harden. After 12h, open the vacuum drying oven, peel off the PDMS template, and move the whole into standard curing conditions for continued curing to obtain a cement-based radiative cooling material with a super surface.

[0062] The radiative cooling cement-based materials with super surface prepared in Examples 1-3 were analyzed by scanning electron microscope. The results are as follows: Figure 5 shown. Figure 5 It is the SEM image of the ultra-surface microstructure of the radiant cooling cement-based material with ultra-surface prepared in Examples 1-3. Among them, A is the SEM image of the surface microstructure of the radiant cooling cement-based material finally prepared in Example 1 when the diameter of the organic template is 25μm, the depth is 25μm, the spacing is 50μm, and the hexagonal arrangement is; B is the SEM image of the surface microstructure of the radiant cooling cement-based material finally prepared in Example 2 when the diameter of the organic template is 50μm, the depth is 50μm, the spacing is 100μm, and the hexagonal arrangement is; C is the SEM image of the surface microstructure of the radiant cooling cement-based material finally prepared in Example 3 when the diameter of the organic template is 100μm, the depth is 100μm, the spacing is 200μm, and the hexagonal arrangement is. By Figure 5 It can be seen that by changing the mask size, changing the single crystal silicon mold, and thus changing the organic template, the bubble growth can be guided under the action of negative pressure, and ultimately the microstructure and morphology of the cement-based material surface can be changed.

[0063] Example 4

[0064] The experimental process is the same as that of Example 1, except that the cementitious material particles are replaced with black silicate cement particles, as follows:

[0065] 100g black silicate cement, 40g pure water, 1g polycarboxylic acid water reducer, the surface of the single crystal silicon master mold has a columnar microstructure (diameter 25μm, depth 25μm, spacing 50μm, hexagonal arrangement), the organic template material is PDMS (polydimethylsiloxane), containing 10g main agent (α,ω-dihydroxypolydimethylsiloxane), 1g curing agent (polymethylhydrogensiloxane).

[0066] Stir α,ω-dihydroxy polydimethylsiloxane and polymethylhydrogensiloxane at 15-25℃, vacuum degassing to remove internal gas, then cast on a single crystal silicon master mold, put into an oven at 60℃, dry for 2h, take out, and peel off to obtain a PDMS mold. On the other hand, stir white silicate cement, pure water, and carboxylic acid type polycarboxylic acid water reducer at 15-25℃, stir at a speed of 400-500rpm for 2min until uniform, obtain an unhardened matrix material slurry, cast the unhardened matrix material slurry in an ordinary cement slurry mold, and then cover the PDMS mold on the unhardened matrix material slurry so that the surface with microstructure is in contact with the unhardened matrix material slurry, put it into a vacuum drying oven, and connect a vacuum pump. Turn on the vacuum pump, draw 80kPa air pressure, close the valve, and let it stand for curing until the internal slurry hardens. After 12h, open the vacuum drying oven, peel off the PDMS template, and move the whole into standard curing conditions for continued curing to obtain a cement-based radiative cooling material with a super surface.

[0067] Comparative Example 2

[0068] The experimental process is the same as that of Example 2, except that no supersurface is prepared, as follows:

[0069] 100g black silicate cement, 40g purified water, 1g polycarboxylate water reducer. Stir white silicate cement, purified water, polycarboxylate water reducer at 15-25℃, stir at 400-500rpm for 2min until uniform, obtain unhardened slurry, pour into ordinary mold, demould after 24h, and cure.

[0070] Example 5

[0071] The experimental process is the same as that of Example 2, except that the size of the mask when preparing the single crystal silicon template is changed, so that the columnar microstructure on the surface of the single crystal silicon master mold is changed to (diameter 50 μm, depth 50 μm, spacing 100 μm, hexagonal arrangement), as follows:

[0072] 100g black silicate cement, 40g pure water, 1g polycarboxylic acid water reducer, the surface of the single crystal silicon master mold has a columnar microstructure (diameter 50μm, depth 50μm, spacing 100μm, hexagonal arrangement), the organic template material is PDMS (polydimethylsiloxane), containing 10g main agent (α,ω-dihydroxypolydimethylsiloxane), 1g curing agent (polymethylhydrogensiloxane).

[0073] Stir α,ω-dihydroxy polydimethylsiloxane and polymethylhydrogensiloxane at 15-25℃, vacuum degassing to remove internal gas, then cast on a single crystal silicon master mold, put into an oven at 60℃, dry for 2h, take out, and peel off to obtain a PDMS mold. On the other hand, stir white silicate cement, pure water, and carboxylic acid type polycarboxylic acid water reducer at 15-25℃, stir at a speed of 400-500rpm for 2min until uniform, obtain an unhardened matrix material slurry, cast the unhardened matrix material slurry in an ordinary cement slurry mold, and then cover the PDMS mold on the unhardened matrix material slurry so that the surface with microstructure is in contact with the unhardened matrix material slurry, put it into a vacuum drying oven, and connect a vacuum pump. Turn on the vacuum pump, draw 80kPa air pressure, close the valve, and let it stand for curing until the internal slurry hardens. After 12h, open the vacuum drying oven, peel off the PDMS template, and move the whole into standard curing conditions for continued curing to obtain a cement-based radiative cooling material with a super surface.

[0074] Example 6

[0075] The experimental process is the same as that of Example 2, except that the size of the mask when preparing the single crystal silicon template is changed, so that the columnar microstructure on the surface of the single crystal silicon master mold is changed to (diameter of 100 μm, depth of 100 μm, spacing of 200 μm, hexagonal arrangement), as follows:

[0076] 100g black silicate cement, 40g pure water, 1g polycarboxylate water reducer, the surface of the single crystal silicon master mold has a columnar microstructure (diameter 100μm, depth 100μm, spacing 200μm, hexagonal arrangement), the organic template material is PDMS (polydimethylsiloxane), containing 10g main agent (α,ω-dihydroxypolydimethylsiloxane), 1g curing agent (polymethylhydrogensiloxane).

[0077] Stir α,ω-dihydroxy polydimethylsiloxane and polymethylhydrogensiloxane at 15-25℃, vacuum degassing to remove internal gas, then cast on a single crystal silicon master mold, put into an oven at 60℃, dry for 2h, take out, and peel off to obtain a PDMS mold. On the other hand, stir white silicate cement, pure water, and carboxylic acid type polycarboxylic acid water reducer at 15-25℃, stir at a speed of 400-500rpm for 2min until uniform, obtain an unhardened matrix material slurry, cast the unhardened matrix material slurry in an ordinary cement slurry mold, and then cover the PDMS mold on the unhardened matrix material slurry so that the surface with microstructure is in contact with the unhardened matrix material slurry, put it into a vacuum drying oven, and connect a vacuum pump. Turn on the vacuum pump, draw 80kPa air pressure, close the valve, and let it stand for curing until the internal slurry hardens. After 12h, open the vacuum drying oven, peel off the PDMS template, and move the whole into standard curing conditions for continued curing to obtain a cement-based radiative cooling material with a super surface.

[0078] Example 7

[0079] The experimental process is the same as that of Example 1, except that the cementitious material particles are changed to white sulphoaluminate cement particles, as follows:

[0080] 100g white sulphoaluminate cement, 40g pure water, 1g polycarboxylic acid water reducer, the surface of the single crystal silicon master mold has a columnar microstructure (diameter 25μm, depth 50μm, spacing 50μm, hexagonal arrangement), the organic template material is PDMS (polydimethylsiloxane), containing 10g main agent (α,ω-dihydroxypolydimethylsiloxane), 1g curing agent (polymethylhydrogensiloxane).

[0081] Stir α,ω-dihydroxy polydimethylsiloxane and polymethylhydrogensiloxane at 15-25℃, vacuum degassing to remove internal gas, then cast on a single crystal silicon master mold, put into an oven at 60℃, dry for 2h, take out, and peel off to obtain a PDMS mold. On the other hand, stir white silicate cement, pure water, and carboxylic acid type polycarboxylic acid water reducer at 15-25℃, stir at a speed of 400-500rpm for 2min until uniform, obtain an unhardened matrix material slurry, cast the unhardened matrix material slurry in an ordinary cement slurry mold, and then cover the PDMS mold on the unhardened matrix material slurry so that the surface with microstructure is in contact with the unhardened matrix material slurry, put it into a vacuum drying oven, and connect a vacuum pump. Turn on the vacuum pump, draw 80kPa air pressure, close the valve, and let it stand for curing until the internal slurry hardens. After 12h, open the vacuum drying oven, peel off the PDMS template, and move the whole into standard curing conditions for continued curing to obtain a cement-based radiative cooling material with a super surface.

[0082] Comparative Example 3

[0083] The experimental process is the same as that of Example 7, except that no supersurface is prepared, as follows:

[0084] 100g white sulphoaluminate cement, 40g pure water, 1g polycarboxylate water reducer. Stir white silicate cement, pure water, carboxylic acid type polycarboxylate water reducer at 15-25℃, stir at 400-500rpm for 2min until uniform, obtain unhardened matrix material slurry, pour into ordinary mold, demould after 24h, and cure.

[0085] Example 8

[0086] The experimental process is the same as that of Example 7, except that the size of the mask when preparing the single crystal silicon template is changed, so that the columnar microstructure on the surface of the single crystal silicon master mold is changed to (diameter 50 μm, depth 50 μm, spacing 100 μm, hexagonal arrangement), as follows:

[0087] 100g white sulphoaluminate cement, 40g pure water, 1g polycarboxylic acid water reducer, the surface of the single crystal silicon master mold has a columnar microstructure (diameter 50μm, depth 50μm, spacing 100μm, hexagonal arrangement), the organic template material is PDMS (polydimethylsiloxane), containing 10g main agent (α,ω-dihydroxypolydimethylsiloxane), 1g curing agent (polymethylhydrogensiloxane).

[0088] Stir α,ω-dihydroxy polydimethylsiloxane and polymethylhydrogensiloxane at 15-25℃, vacuum degassing to remove internal gas, then cast on a single crystal silicon master mold, put into an oven at 60℃, dry for 2h, take out, and peel off to obtain a PDMS mold. On the other hand, stir white silicate cement, pure water, and carboxylic acid type polycarboxylic acid water reducer at 15-25℃, stir at a speed of 400-500rpm for 2min until uniform, obtain an unhardened matrix material slurry, cast the unhardened matrix material slurry in an ordinary cement slurry mold, and then cover the PDMS mold on the unhardened matrix material slurry so that the surface with microstructure is in contact with the unhardened matrix material slurry, put it into a vacuum drying oven, and connect a vacuum pump. Turn on the vacuum pump, draw 80kPa air pressure, close the valve, and let it stand for curing until the internal slurry hardens. After 12h, open the vacuum drying oven, peel off the PDMS template, and move the whole into standard curing conditions for continued curing to obtain a cement-based radiative cooling material with a super surface.

[0089] Example 9

[0090] The experimental process is the same as that of Example 7, except that the size of the mask when preparing the single crystal silicon template is changed, so that the columnar microstructure on the surface of the single crystal silicon master mold is changed to (diameter of 100 μm, depth of 100 μm, spacing of 200 μm, hexagonal arrangement), as follows:

[0091] 100g white sulphoaluminate cement, 40g pure water, 1g polycarboxylic acid water reducer, the surface of the single crystal silicon master mold has a columnar microstructure (diameter 100μm, depth 50μm, spacing 200μm, hexagonal arrangement), the organic template material is PDMS (polydimethylsiloxane), containing 10g main agent (α,ω-dihydroxypolydimethylsiloxane), 1g curing agent (polymethylhydrogensiloxane).

[0092] Stir α,ω-dihydroxy polydimethylsiloxane and polymethylhydrogensiloxane at 15-25℃, vacuum degassing to remove internal gas, then cast on a single crystal silicon master mold, put into an oven at 60℃, dry for 2h, take out, and peel off to obtain a PDMS mold. On the other hand, stir white silicate cement, pure water, and carboxylic acid type polycarboxylic acid water reducer at 15-25℃, stir at a speed of 400-500rpm for 2min until uniform, obtain an unhardened matrix material slurry, cast the unhardened matrix material slurry in an ordinary cement slurry mold, and then cover the PDMS mold on the unhardened matrix material slurry so that the surface with microstructure is in contact with the unhardened matrix material slurry, put it into a vacuum drying oven, and connect a vacuum pump. Turn on the vacuum pump, draw 80kPa air pressure, close the valve, and let it stand for curing until the internal slurry hardens. After 12h, open the vacuum drying oven, peel off the PDMS template, and move the whole into standard curing conditions for continued curing to obtain a cement-based radiative cooling material with a super surface.

[0093] Example 10

[0094] The experimental process is the same as that of Example 7, except that the pressure extracted during the negative pressure driven bubble formation process is changed to 60 kPa, as follows:

[0095] 100g white sulphoaluminate cement, 40g pure water, 1g polycarboxylic acid water reducer, the surface of the single crystal silicon master mold has a columnar microstructure (diameter 25μm, depth 50μm, spacing 50μm, hexagonal arrangement), the organic template material is PDMS (polydimethylsiloxane), containing 10g main agent (α,ω-dihydroxypolydimethylsiloxane), 1g curing agent (polymethylhydrogensiloxane).

[0096] Stir α,ω-dihydroxy polydimethylsiloxane and polymethylhydrogensiloxane at 15-25℃, vacuum degassing to remove internal gas, then cast on a single crystal silicon master mold, put into an oven at 60℃, dry for 2h, take out, and peel off to obtain a PDMS mold. On the other hand, stir white silicate cement, pure water, and carboxylic acid type polycarboxylic acid water reducer at 15-25℃, stir at a speed of 400-500rpm for 2min until uniform, obtain an unhardened matrix material slurry, cast the unhardened matrix material slurry in an ordinary cement slurry mold, and then cover the PDMS mold on the unhardened matrix material slurry so that the surface with microstructure is in contact with the unhardened matrix material slurry, put it into a vacuum drying oven, and connect a vacuum pump. Turn on the vacuum pump, draw 60kPa air pressure, close the valve, and let it stand for curing until the internal slurry hardens. After 12h, open the vacuum drying oven, peel off the PDMS template, and move the whole into standard curing conditions for continued curing to obtain a cement-based radiative cooling material with a super surface.

[0097] Embodiment 11

[0098] The experimental process is the same as that of Example 7, except that the pressure extracted during the negative pressure driven bubble formation process is changed to 20 kPa, as follows:

[0099] 100g white sulphoaluminate cement, 40g pure water, 1g polycarboxylic acid water reducer, the surface of the single crystal silicon master mold has a columnar microstructure (diameter 25μm, depth 50μm, spacing 50μm, hexagonal arrangement), the organic template material is PDMS (polydimethylsiloxane), containing 10g main agent (α,ω-dihydroxypolydimethylsiloxane), 1g curing agent (polymethylhydrogensiloxane).

[0100] Stir α,ω-dihydroxy polydimethylsiloxane and polymethylhydrogensiloxane at 15-25℃, vacuum degassing to remove internal gas, then cast on a single crystal silicon master mold, put into an oven at 60℃, dry for 2h, take out, and peel off to obtain a PDMS mold. On the other hand, stir white silicate cement, pure water, and carboxylic acid type polycarboxylic acid water reducer at 15-25℃, stir at a speed of 400-500rpm for 2min until uniform, obtain an unhardened matrix material slurry, cast the unhardened matrix material slurry in an ordinary cement slurry mold, and then cover the PDMS mold on the unhardened matrix material slurry so that the surface with microstructure is in contact with the unhardened matrix material slurry, put it into a vacuum drying oven, and connect a vacuum pump. Turn on the vacuum pump, draw 20kPa air pressure, close the valve, and let it stand for curing until the internal slurry hardens. After 12h, open the vacuum drying oven, peel off the PDMS template, and move the whole into standard curing conditions for continued curing to obtain a cement-based radiative cooling material with a super surface.

[0101] Example 12

[0102] The experimental process is the same as that of Example 7, except that the organic template material is changed to PE (polyethylene) material, as follows:

[0103] 100g of white sulphoaluminate cement, 40g of purified water, 1g of polycarboxylate water reducer, the surface of the single crystal silicon master mold has a columnar microstructure (diameter 25μm, depth 50μm, spacing 50μm, hexagonal arrangement), the organic template material is PE (polyethylene), and 30-50μm particles are used. Two layers of PTFE membrane are laid on two metal plates as demoulding materials, and a layer of PE particles is laid in the middle. Put it in an oven at 190℃, wait for it to melt, put the silicon master mold on the melted PE, keep it for 2h, take it out, cool it at room temperature, and peel it off to get the PE mold. On the other hand, stir white sulphoaluminate cement, pure water and polycarboxylate water reducer at 15-25°C for 2 minutes at a speed of 400-500rpm until evenly mixed to obtain unhardened matrix material slurry, pour the unhardened matrix material slurry into an ordinary cement slurry mold, and then pour the unhardened matrix material slurry on a flat PDMS mold so that the surface with the microstructure is in contact with the unhardened matrix material slurry, put it into a vacuum drying oven, and connect a vacuum pump. Turn on the vacuum pump, draw 80kPa air pressure and close the valve, let it stand and wait for the internal slurry to harden. After 12 hours, open the vacuum drying oven, peel off the PE template, and move the whole into standard curing conditions for continued curing to obtain a cement-based radiant cooling material with a super surface.

[0104] Embodiment 13

[0105] 1. Solar reflectivity of cement-based radiant cooling materials

[0106] Solar reflectance (ratio) is defined as "the ratio of reflected to incident solar radiation energy flux" in GB / T 25261-2010 "Reflective Insulation Coatings for Buildings". Solar reflectance is in the band of 0.25-2.5nm, including ultraviolet (UV, 0.25-0.4nm), visible light (VIS, 0.4-0.78nm) and near infrared (NIR, 0.78-2.5nm), so it can also be called ultraviolet visible near infrared reflectance. This test uses the method specified in ASTM E903-20 "Solar Absorption, Reflectance and Material Transmittance Determination Method (Integrating Sphere)" to test the solar reflectance of powder samples and cement paste test blocks. The lambda 950 UV-Vis-NIR spectrophotometer produced by PerkinElmer is used, and the instrument is equipped with an integrating sphere. Since the test results are absolute values, the accuracy of the results is required to be high. In the experiment, a standard white plate is used for zero calibration, and then the reflectance value of the standard white plate on the spectrophotometer is measured.

[0107] The test result is the reflectivity of the sample at the corresponding wavelength in the 0.25-2.5nm band, with a step size of 5nm. solar The calculation is as follows:

[0108]

[0109] Among them, I solar (λ) is from the ASTM G173-03 (2020) standard table: Reference solar spectral irradiance - normal direct radiation and hemispherical radiation of a plane inclined at 37°, R(λ) is the reflectance corresponding to the wavelength λ.

[0110] 2. Hemispherical emissivity of cement-based radiant cooling materials

[0111] Hemispherical emissivity (hereinafter referred to as emissivity) is defined in GB / T 25261-2010 as "the ratio of the radiant emittance of a thermal radiator in the hemispherical direction to the radiant emittance of a total radiator (black body) at the same temperature". The hemispherical emissivity mainly considers the mid-infrared band range of 2.5-15μm, so it is also called mid-infrared emissivity. A Fourier transform infrared (FT-IR) spectrometer, model Nicolet 6700, is used. The spectrometer is equipped with a gold-plated integrating sphere. The two beams of light split by the beam splitter form an optical path difference and produce interference. After passing through the sample, the interference light containing the sample information reaches the detector, and then the signal is processed by Fourier transform, and finally an infrared absorption spectrum of transmittance or absorbance with wave number or wavelength is obtained. Hemispherical emissivity ε at temperature T T The calculation is as follows:

[0112]

[0113] According to Kirchhoff's law, 1-R(λ) is the radiance corresponding to the wavelength λ; P B (λ) is the blackbody spectral radiation power at wavelength λ, C1 and C2 are coefficients, C1 = 3.743 × 10 -16 W·m 2 , C2=1.4387×10 -2 m·K. T is the temperature. In this test, unless otherwise specified, the emissivity measured is at 25°C.

[0114] The above test results are shown in Table 1.

[0115] Table 1 Basic properties of polymer concrete paste obtained from Examples 1-12 and Comparative Examples 1-3

[0116]

[0117] The results in Table 1 show that in Examples 1, 4, 7, and Comparative Examples 1-3, changing the type of cementitious material can significantly change the radiative cooling performance, especially the reflectivity. Among them, white sulphoaluminate cement is the most helpful for improving the reflectivity, followed by white silicate cement, and black silicate cement has the worst performance. In Examples 1-12 and Comparative Examples 1-3, by changing the diameter, depth and spacing of the microstructure columns on the silicon master mold, the bubble size constituting the super surface of the cement-based material can be changed, thereby affecting the radiative cooling performance, especially the reflectivity. Among them, the smaller the diameter and depth, the higher the reflectivity; when the diameter: spacing = 1:2, the reflectivity is the highest. After analysis, micron-scale pores are conducive to the directional growth of crystals in the cement hydration product, thereby scattering light and promoting the improvement of reflectivity. When the diameter of the microstructure column on the silicon master mold is close to 100μm, the excessively large diameter can no longer induce crystal re-surface growth, so the effect is equivalent to the group without super surface preparation (Comparative Examples 1, 2, 3), and cannot play a role in improving the reflectivity. The pore structure of 25 μm is conducive to the growth of crystals, so Examples 1, 4, and 7 have higher reflectivity than the finished products made of the same gelling material and different organic template sizes. At the same time, according to Examples 7, 10, and 11, changing the extraction negative pressure value will change the bubble size to a certain extent, but will not significantly affect the overall performance; similarly, changing the type of organic template will not affect the bubble formation process, and therefore will not affect the optical performance (especially reflectivity).

Claims

1. A radiative cooling cement-based material with a super surface, characterized in that: The matrix material includes the following components in mass fraction ratio: the mass ratio of cementitious material particles: water: admixture is (1-2): (0.4-0.6): (0.01-0.02), and the metasurface is prepared by combining the template method with the pressure gradient driven gas volume expansion method to act on the matrix material.

2. The radiative cooling cement-based material with a super surface according to claim 1, characterized in that: Cementitious material particles are unhydrated cement particles.

3. The radiative cooling cement-based material with a super surface according to claim 2, characterized in that: The unhydrated cement particles are at least one of white silicate cement, black silicate cement, white sulphoaluminate cement and black sulphoaluminate cement.

4. The radiative cooling cement-based material with a super surface according to claim 1, characterized in that: The water is pure water and the admixture is a water reducing agent.

5. The radiative cooling cement-based material with a super surface according to claim 4, characterized in that: The water reducer is at least one of a carboxylic acid type polycarboxylic acid water reducer, a sulfonic acid type polycarboxylic acid water reducer, a hydroxyl type polycarboxylic acid water reducer, and a carboxylic acid-sulfonic acid composite water reducer.

6. The method for preparing the radiative cooling cement-based material with a super surface according to any one of claims 1 to 5, comprising the following steps: (1) preparing a silicon master mold having a columnar microstructure on the surface by photolithography, and performing a surface hydrophobic treatment; (2) pouring a thermosetting or thermoplastic organic material onto the silicon master mold obtained in step (1), drying and forming the material, and peeling the material off to obtain an organic material template; (3) pouring the matrix material slurry in an ordinary cement slurry mold, covering the matrix material slurry with an organic template, placing it in a vacuum drying oven, evacuating the air, standing it for curing, hardening it into shape, peeling off the organic template, and continuing to cure it to obtain a radiant cooling cement-based material with a super surface.

7. The method for preparing the radiative cooling cement-based material with a super surface according to claim 6, characterized in that: In step (1), the silicon master mold is a single crystal silicon wafer, and the surface of the obtained silicon master mold has a plurality of columnar microstructures, the diameter of the columnar microstructures is 25 to 100 μm, the depth is 25 to 100 μm, the spacing between adjacent columnar microstructures is 50 to 200 μm, and the diameter: spacing is (1:1) to (1:3).

8. The method for preparing the radiative cooling cement-based material with a super surface according to claim 6, characterized in that: In step (2), the thermosetting or thermoplastic organic matter is at least one of polydimethylsiloxane, polyethylene, and polytetrafluoroethylene.

9. The method for preparing the radiative cooling cement-based material with a super surface according to claim 6, characterized in that: In step (3), the air pressure extracted during vacuuming is at least one value between 10 and 90 kPa; and the curing conditions are all standard curing conditions.

10. Application of the radiant cooling cement-based material with a super surface as described in any one of claims 1 to 6 or the preparation method of the radiant cooling cement-based material with a super surface as described in any one of claims 7 to 9 in unsupported 3D printed buildings.

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