Polyethylene-polysiloxane-based organic-inorganic hybrid porous coating based on thermal radiation and its preparation method and application

Abstract

The present invention discloses a polyethylene-polysiloxane-based organic-inorganic hybrid porous coating, its preparation method, and application. The porous coating has a three-dimensional random network skeleton structure oriented parallel to the surface direction; in the coating, the skeleton packing density along the out-of-plane direction is higher than the skeleton packing density along the surface direction (or in-plane direction). The polyethylene-polysiloxane-based organic-inorganic hybrid porous coating prepared by the present invention can simultaneously possess significant mechanical robustness, optical stability, and excellent PDRC performance, providing a powerful solution to the practical challenges of PDRC materials for low-cost, large-scale applications.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-reflection and high-infrared-emission materials, and in particular relates to a polyethylene-polysiloxane-based organic-inorganic hybrid porous coating based on thermal radiation, and a preparation method and application thereof. Background Art

[0002] Since the Industrial Revolution, global warming caused by the greenhouse effect has become an increasingly serious environmental problem, significantly impacting people's production and lifestyles. Passive daytime radiative cooling (PDRC), an emerging technology, reduces solar thermal energy input by utilizing materials' high reflectivity in the solar radiation band (0.3-2.5μm). Simultaneously, through radiative heat exchange with outer space (approximately 3K, with virtually no infrared radiation) in the mid-infrared atmospheric window band (8-13μm), the material captures the cosmic cold source, resulting in a net heat loss and a daytime or all-day cooling effect. This technology can be used in energy-saving buildings, photovoltaics, factories, automobiles, electronic products, and personal thermal management systems. It is expected to partially replace traditional active cooling technologies such as air conditioners and refrigerators, reducing the significant energy consumption and environmental costs associated with traditional cooling technologies, thereby mitigating the greenhouse effect and urban heat island effect.

[0003] In 2014, Raman et al. designed an inorganic nanophotonic crystal material that achieved a power output of 850W m by utilizing 97% of the solar radiation band reflectivity and selective high infrared emissivity in the atmospheric window band. -2 The sub-ambient temperature drop of 4.9°C and 40.1W m -2Net cooling power (i.e., net heat loss) is achieved. However, inorganic photonic crystal materials are constrained by high manufacturing costs and difficulty in large-scale preparation. In recent years, polymer-based materials have been widely developed and applied due to their availability, ease of processing, and multifunctionality (such as superhydrophobicity and superthermal insulation) while meeting the optical properties required for PDRC. As one of the most common preparation methods, micro-nano inorganic particles such as titanium dioxide (TiO2), barium sulfate (BaSO4), and aluminum oxide (Al2O3) utilize their inherent high refractive index to form high-reflectivity organic-inorganic hybrid coatings for PDRC by simply blending with polymers. Alternatively, micron-sized silica (SiO2) particles of a specific size can be blended with polymers to produce high-infrared emissivity films in the atmospheric window band for PDRC, leveraging their resonance enhancement effect in the atmospheric window band. However, the micro-nano particles used in these preparation methods are generally fine powder particles. In production and daily life, the environmental pollution and health issues caused by fine powder particles have long attracted widespread attention. What is more serious is that TiO2 nanoparticles, which are the most widely used in high-reflectivity polymer coatings, have been listed as suspected potential carcinogens by the European Union in 2020. The porous polymer films / fabrics for radiative cooling obtained by electrospinning are composed of discontinuous nanofibers, and may still have bio-environmental toxicity problems similar to those caused by fine powder particles during large-scale production and use. Solution processing technology based on phase separation method has also received attention in the field of PDRC in recent years. It grows a three-dimensional continuous random network skeleton through the phase separation behavior of the system induced in the film formation process of the polymer solution, and utilizes the refractive index difference (n polymer / n air ≈1.5) to efficiently scatter incident sunlight, while leveraging the skeleton itself to achieve high infrared emissivity or high infrared transmittance (the latter is used for human radiative cooling, as high infrared emissivity comes from human skin). Phase separation-based solution processing avoids the preparation and environmental cost issues associated with using particulate pigments.

[0004] Gibson and Ashby pointed out that the mechanical properties of porous materials (modulus E, strength σ, etc.) and their apparent density ρ have a power law relationship: E / E S ∝(ρ / ρ S ) m or σ / σ S ∝(ρ / ρ S ) m , the parameter m is determined by the deformation behavior of the porous material skeleton structure under stress, and its value range is usually 1 to 4; E s , σ s and ρ sare the intrinsic modulus, intrinsic strength and intrinsic density of the material skeleton respectively. Among them, the E-related power law of random open-pore porous materials is usually 2, and the σ-related power law is usually 1.5. At the same time, the porosity (1-ρ / ρ s ) is also one of the important parameters that determine the optical properties of PDRC, and it mainly affects the reflectivity to the intensity of solar radiation. The experimental and simulation results of Wang et al. show that within the porosity range of the porous structure they studied (less than 0.8), the reflectivity increases with the increase of porosity (the decrease of apparent density). In the same type of porous material, choosing the highest possible porosity can obtain better optical properties. Obviously, the mechanical properties of the material and the apparent density will significantly attenuate with the increase of porosity under a power law relationship greater than 1 or even a square. Mechanical properties or mechanical robustness are crucial for PDRC materials that serve outdoors for a long time. Therefore, the preparation of polymer-based materials that have both good mechanical and optical properties and are environmentally friendly and low-cost should be one of the main challenges that the PDRC field needs to address in future research. Summary of the Invention

[0005] In order to improve the above technical problems, the present invention provides a polyethylene-polysiloxane-based organic-inorganic hybrid porous coating having a three-dimensional random network skeleton structure oriented parallel to the surface direction;

[0006] In the porous coating layer, the skeleton packing density along the out-of-plane direction is higher than the skeleton packing density along the surface direction (or in-plane direction).

[0007] In the present invention, the direction along the surface refers to a direction parallel to the surface of the porous coating layer.

[0008] According to an embodiment of the present invention, the porous coating layer has a long rod-like structure along an out-of-plane direction.

[0009] According to an embodiment of the present invention, the thickness of the porous coating layer is 80-1400 μm, preferably 97-1110 μm, for example, 97 μm, 118 μm, 164 μm, 219 μm, 293 μm, 350 μm, 590 μm or 1108 μm.

[0010] According to an embodiment of the present invention, the reflectivity of the porous coating layer is 80-99%, preferably 94-99% at a wavelength of 0.3-2.5 μm. Preferably, the reflectivity of the porous coating layer is 90-99%, preferably 94-99% at a wavelength of 0.4-1.1 μm.

[0011] Preferably, when the porous coating has a thickness of 590 μm, the average total sunlight reflectivity in the solar radiation band (i.e., wavelength of 0.3-2.5 μm) reaches up to 95%, and the average total infrared emissivity in the atmospheric window band (i.e., wavelength of 8-13 μm) reaches up to 96%.

[0012] In the present invention, the reflectivity refers to the reflectivity at a specific wavelength; the average total sunlight reflectivity refers to the average reflectivity in the entire wavelength range of 0.3-2.5 μm.

[0013] According to an embodiment of the present invention, the skeleton component of the three-dimensional random network skeleton structure is a polyethylene-polysiloxane double cross-linked hybrid polymer network. Preferably, the mass ratio of the organic component to the inorganic component is 1:1, wherein polyethylene is the organic component and polysiloxane is the inorganic component.

[0014] According to an embodiment of the present invention, the pore size of the three-dimensional random network skeleton structure is 0.1-0.5 μm, the average pore size is 0.34 μm in the in-plane (along the surface) direction, and 0.19 μm in the out-of-plane (cross-section) direction, and the skeleton size of the three-dimensional random network skeleton structure is 0.28 μm.

[0015] According to an embodiment of the present invention, the skeleton volume filling rate of the porous coating layer is 40-70%.

[0016] According to an embodiment of the present invention, the porosity of the porous coating layer is 30-60%.

[0017] According to an embodiment of the present invention, the refractive index of the porous coating layer is 1.2-1.7, preferably 1.5.

[0018] According to an embodiment of the present invention, the porous coating layer has hydrophobicity.

[0019] The present invention also provides a method for preparing a polyethylene-polysiloxane-based organic-inorganic hybrid porous coating, the method comprising the following steps:

[0020] (1) Preparation of polyvinyl dimethyl ethoxy silane (PVDMES);

[0021] (2) mixing an organic solvent, an acidic compound, and a silicon-containing compound to react to obtain a polysilicic acid sol, and then adding a silane coupling agent to react to prepare an alkyl-modified polysiloxane sol;

[0022] (3) mixing the PVDMES in step (1) with the alkyl-modified polysiloxane sol in step (2) to prepare a mixed silica sol, coating the mixed silica sol on the surface of the substrate, and preparing the polyethylene-polysiloxane-based organic-inorganic hybrid porous coating by non-solvent-induced phase separation.

[0023] According to an embodiment of the present invention, in step (1), the preparation of polyvinyldimethylethoxysilane is carried out using conventional methods in the art, for example, the method described in document 10.1021 / acsnano.7b07117.

[0024] According to an embodiment of the present invention, in step (1), the number average molecular weight of the polyvinyl dimethyl ethoxy silane is 2×10 3 -5×10 3 g / mol, and the weight average molecular weight is 1×10 4 -5×10 4 g / mol, and the molecular weight distribution (weight average molecular weight / number average molecular weight) is 2-25.

[0025] According to an embodiment of the present invention, in step (2), the organic solvent is selected from at least one of ethanol, methanol, acetone, isopropanol, pentanol, N,N-dimethylformamide, dimethyl sulfoxide, and dioxane, preferably ethanol or methanol.

[0026] According to an embodiment of the present invention, in step (2), the acidic compound is selected from at least one of sulfuric acid, nitric acid, oxalic acid, citric acid, acetic acid, and aluminum chloride, preferably sulfuric acid or hydrochloric acid.

[0027] According to an embodiment of the present invention, in step (2), the silicon-containing compound is selected from at least one of tetraethyl silicate (TEOS), tetramethyl silicate (TMOS), tetraisopropyl silicate, tetrabutyl silicate, methyltrimethoxysilane (MTMS), methyltriethoxysilane (MTES), dimethyldimethoxysilane (DMDMS), dimethyldiethoxysilane (DMDES), trimethylmethoxysilane (TMMS), and trimethylethoxysilane (TMES). Preferably, tetraethyl silicate or tetramethyl silicate is selected.

[0028] According to an embodiment of the present invention, in step (2), the concentration of the acidic compound is 0.01-1 mol L -1 .

[0029] According to an embodiment of the present invention, in step (2), the mass volume ratio of the organic solvent, the acidic compound and the silicon-containing compound is (1-6) g: 1 g: (0.5-5) mL, preferably (1.5-4) g: 1 g: (1-2.8) mL.

[0030] According to an embodiment of the present invention, in step (2), the silane coupling agent is selected from at least one of n-octyltriethoxysilane (OCTEO), hexadecyltriethoxysilane, n-hexyltriethoxysilane, n-butyltriethoxysilane, n-octyltrimethoxysilane, dodecyltriethoxysilane, and phenyltriethoxysilane.

[0031] According to an embodiment of the present invention, in step (2), the volume ratio of the silicon-containing compound to the silane coupling agent is 1-10:1, preferably 2-9:1; illustratively, 2:1, 2.3:1, 3:1, 3.3:1, 4:1, 5:1, 6:1, 7:1, 8:1 or 9:1.

[0032] According to an embodiment of the present invention, in step (2), the reaction temperature during the preparation of the polysilicic acid sol is 20-35° C., such as room temperature; and the reaction time during the preparation of the polysilicic acid sol is 12-48 h, such as 24 h.

[0033] According to an embodiment of the present invention, in step (2), after adding the silane coupling agent, the reaction temperature is 15-35° C.; the reaction time is 12-72 h, for example, 48 h.

[0034] According to an embodiment of the present invention, in step (3), the mass of the PVDMES is 15-45 wt %, preferably 20-40 wt % of the alkyl-modified polysiloxane sol; illustratively, it is 20 wt %, 25 wt %, 30 wt %, 35 wt % or 40 wt %.

[0035] According to an embodiment of the present invention, in step (3), the mixing reaction time is 0.5-12 h, illustratively 0.5, 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h or 12; the mixing reaction temperature is 20-35 ° C, such as room temperature.

[0036] According to an embodiment of the present invention, in step (3), when the non-solvent is selected from water, the vapor partial pressure of the water is controlled at a relative humidity of 60-96%, and the temperature is controlled at room temperature.

[0037] According to an embodiment of the present invention, the substrate is selected from silicon-based substrates, for example, glass substrates or silicon wafer substrates, preferably a glass substrate.

[0038] According to an embodiment of the present invention, in step (3), after the phase separation process is complete, the porous coating is prepared by standing still until the organic solvent is completely evaporated; for example, standing still in air atmosphere for at least 24 hours.

[0039] The present invention also provides applications of the polyethylene-polysiloxane-based organic-inorganic hybrid porous coating, which can be used in energy-saving buildings, photovoltaic equipment, power plants, automobiles, electronic products, clothing and other fields.

[0040] Beneficial effects of the present invention:

[0041] (1) The present invention prepares a polyethylene-polysiloxane-based organic-inorganic hybrid porous coating by mixing polyvinyldimethylethoxysilane (PVDMES) with an alkyl-modified polysiloxane sol (e.g., an octyl-modified polysiloxane sol), and casting the coating with the aid of non-solvent-induced phase separation (NIPS) under high humidity suppression. The mixed silica sol is catalyzed by acidic compounds to hydrolyze and condense the silane groups at room temperature, and a polyethylene-polysiloxane double-crosslinked hybrid molecular network can be spontaneously formed during the film formation process without the aid of any heating device or mechanical equipment.

[0042] (2) The present invention optimizes the preparation process conditions between the sol-gel process caused by the hydrolysis and condensation of silane in the mixed silica sol and the non-solvent induced phase separation. When the thickness of the porous coating is 590 μm, the average total reflectivity in the solar radiation band (0.3-2.5 μm) reaches 95%, and the average total infrared emissivity in the atmospheric window band (8-13 μm) reaches 96%. The porous coating has a three-dimensional continuous random network skeleton structure of the white-like beetle Cyphochilus oriented parallel to the surface direction (in-plane direction), and the skeleton volume filling rate is as high as 64±1%, which is close to the upper limit of the scatterer filling fraction range (40-70%) under the optimal wide-band reflectivity in the scattering structure of the white-like beetle Cyphochilus. Therefore, the coating of the present invention can maximize its own mechanical properties while meeting the optical properties. It has good mechanical properties under Taber wear (1000 cycles of wear under a load of 250 g), water jet impact (~17 m s -1 The coating demonstrated excellent robustness in tests of optical stability (long-term water flow, mortar / sand flow impact, and 6 times, with a single ~0.45kg water flow rate) and optical stability (long-term water flow, mortar / sand flow impact). The coating also demonstrated good durability in tests of long-term UV irradiation (50 days) and water immersion (21 days).

[0043] (3) Good optical properties can meet the coating's requirements for sunny days (solar radiation intensity I solar The average is 790W m -2 ), cloudy(I solar Average 200W m -2 ) and hazy days (I solar The average is 420W m -2) The sub-ambient temperature dropped by 6.2°C, 2.9°C and 5.8°C at noon and afternoon respectively. All-weather continuous outdoor testing showed that the average sub-ambient temperature drop of the coating during the day and night was 5.9°C and 7.7°C respectively.

[0044] In summary, the polyethylene-polysiloxane-based organic-inorganic hybrid porous coating prepared in the present invention can simultaneously possess significant mechanical robustness, optical stability and excellent PDRC performance, providing a powerful solution to the practical challenges of PDRC materials for low-cost, large-scale applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 The reflectivity graphs (1a and 1b) and the coating photograph (1c) of the porous coating prepared in Example 1.

[0046] Figure 2 The reflectivity graphs (2a and 2b) and the coating photograph (2c) of the porous coating prepared in Example 2.

[0047] Figure 3 The reflectivity graphs (3a and 3b) and the coating photograph (3c) of the porous coating prepared in Example 3.

[0048] Figure 4 The coating photograph (4b) and reflection spectrum diagram (4a) of the porous coating prepared in Comparative Example 1.

[0049] Figure 5 This is the reflection spectrum of the porous coating prepared in Example 4.

[0050] Figure 6 This is a reflection spectrum diagram of the porous coating sample 10 prepared in Example 4.

[0051] Figure 7 10-80° normalized angle-resolved reflectance spectrum of the coating sample 10 and the standard diffuse reflector in Example 4.

[0052] Figure 8 This is a cross-sectional scanning electron microscope image of the coating sample 10 in Example 4.

[0053] Figure 9 This is the composite spectral refractive index diagram of the coating sample 10 in Example 4.

[0054] Figure 10 This is the ATR-FTIR spectrum of the coating sample 10 in Example 4.

[0055] Figure 11 This is the thermal weight loss curve of the coating sample 10 of Example 4.

[0056] Figure 12a is the nanoindentation load-displacement curve of coating sample 10 in Example 4.

[0057] Figure 12 b is a diagram of the mechanical properties of polymers in the prior art.

[0058] Figure 13 a is the mass loss curve of sample 10 in Example 4, Figure 13 b-13e are SEM images of the coating surface (b) and cross-section (d) before wear and the coating surface (c) and cross-section (e) after 1000 wear cycles, respectively.

[0059] Figure 14 a is a photo of the water jet impact experiment in Test Example 13; Figure 14 b is the static water contact angle (θ) of the coating removed from the surface during the 0-6 water jet impact cycle test in Test Example 13. A )’s changing trend chart; Figure 14 c and d are SEM images of the coating surface before and after 6 water jet impacts in Test Example 13 with the surface skin removed.

[0060] Figure 15 This is a stability test diagram of the optical performance of the coating sample 10 of Example 4 under different environments.

[0061] Figure 16 Graphs 1 and 2 are the reflection spectrum (a) and infrared emission spectrum (b) of the coating sample 10 of Example 4 after 50 days of UV light irradiation.

[0062] Figure 17 This is a graph showing the daytime outdoor cooling test results of the coating sample 10 of Example 4 under different weather conditions.

[0063] Figure 18 These are all-weather outdoor cooling test diagrams of the coating sample 10 in Example 4 at different time periods. DETAILED DESCRIPTION

[0064] The technical solutions of the present invention will be described in further detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanations of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are encompassed within the scope of protection that the present invention is intended to protect.

[0065] Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0066] Reagents: Vinyldimethylethoxysilane (VDMES) was purchased from Adamas Reagents; tetraethyl orthosilicate (TEOS) was purchased from Acros; silane coupling agent n-octyltriethoxysilane (OCTEO) was purchased from Acros; sodium chloride (NaCl) was purchased from J&K; anhydrous potassium carbonate (K2CO3) was purchased from Innochem; ethanol (EtOH) was purchased from Concord Reagents; concentrated hydrochloric acid (HCl, about 12 mol L -1 ), purchased from Sinopharm Chemical Reagent Company. Dilute hydrochloric acid solution (0.1 mol L -1 ) was prepared by diluting concentrated hydrochloric acid solution with Milli-Q ultrapure water (resistivity: 18.2 MΩcm). Unless otherwise specified, all reagents listed above were used directly without purification.

[0067] Main characterization instruments: thermogravimetric analyzer (TGA), field emission scanning electron microscope (JSM-7500F, JEOL), UV-visible-near-infrared spectrophotometer (Lambda 950, Perkin Elmer), Fourier transform infrared spectrometer with gold integrating sphere accessory (model A562) (FTIR, Invenio S, Bruker), optical measurement system (R1, Ideaoptics, equipped with 0.32-1.7 μm fiber spectrometer), infrared spectroscopic ellipsometry (1.7-25 μm, IR-Vase II, JA Woollam), FTIR spectrometer with attenuated total reflectance (ATR) accessory (Tensor 27, Bruker), Wyatt DAWN HELEOS-II Gel chromatography-light scattering (GPC-MALS) coupled instrument, nanoindenter (G200, Agilent), Taber abrasion tester (DK-5612, Deka Precision Instruments), drop shape analyzer (DSA 100, Krüss).

[0068] Thermogravimetric analysis (TGA): obtained by thermogravimetric analyzer (Pyris 1, PerkinElmer). The test conditions are: in air atmosphere, temperature range 30-800 °C, heating rate 10 °C min -1 , gas flow rate 20 mL min -1 .

[0069] Micromorphology characterization: A field emission scanning electron microscope (JSM-7500F, JEOL) was used to observe the micromorphology of the coatings.

[0070] Macroscopic characterization: Coating thickness was measured using a digital micrometer (543-390B, Mitutoyo); porosity (%) was calculated using formula 3-1. Where ρ is the apparent density of the coating, obtained by dividing the coating mass by the coating volume; ρ s is the intrinsic density of the coating, which is equal to the apparent density of a dense coating with the same composition.

[0071] Porosity (%) = (1-ρ / ρ s )×100% (3-1)

[0072] Optical Characterization: Ultraviolet-visible-near-infrared (UV-vis-NIR) spectra of the coatings were obtained using a Lambda 950 UV-visible-NIR spectrophotometer (Perkin Elmer) with a 150 mm integrating sphere, using a standard white plate (SRS-99-020, Labsphere) as a reference. Mid-infrared (MIR) reflectance spectra of the coatings were obtained using a Fourier transform infrared spectrometer (FTIR, Invenio S, Bruker) equipped with a gold integrating sphere accessory (Model A562). Angular-resolved spectra of the coatings were obtained using a goniometer-based optical measurement system (R1, Ideaoptics, equipped with a 0.32-1.7 μm fiber spectrometer). The composite refractive index of the coatings was obtained using an infrared spectroscopic ellipsometer (1.7-25 μm, IR-Vase II, JA Woollam).

[0073] Chemical composition characterization: The samples were measured using an FTIR spectrometer (Tensor 27, Bruker) equipped with an attenuated total reflectance (ATR) accessory.

[0074] Gel permeation chromatography (GPC) characterization: The instrument model was a Wyatt DAWN HELEOS-II gel permeation chromatography coupled with light scattering (GPC-MALS) instrument. An MZ-gel SDplus linear 10 μm gel permeation chromatography column was used, the column temperature was 35°C, tetrahydrofuran (THF) was used as the mobile phase, and the flow rate was 1.0 mL min -1 , the injection volume was 100 μL.

[0075] Mechanical characterization: The mechanical properties of the coatings were measured using a nanoindenter (G200, Agilent) with a Berkovich tip based on the continuous stiffness method (CSM). The probing depth was 2 μm and the loading strain rate was 0.05 s. -1 The vibration frequency is 45 Hz and the Poisson's ratio is set to 0.3. The thickness of the bulk dense coating sample is at least 150 μm to eliminate the substrate effect.

[0076] Taber abrasion test: The test was conducted using a Taber abrasion tester (DK-5612, Deka Precision Instruments) in accordance with ASTM D4060. The test was conducted using a CS-10 wear-resistant rubber wheel as the grinding wheel and an additional weight of 250g. The sample rotation speed was 72r / min. -1 The wear resistance of the coating is evaluated by recording the weight loss of the coating after a specified number of wear cycles.

[0077] Contact angle test: static water contact angle of coating (WCA, θ A ) were measured at room temperature using a drop shape analyzer (DSA100, Krüss).

[0078] Water jet impact test: A high-pressure argon gas cylinder with a pressure reducing valve is connected to a stainless steel water tank filled with 0.5 kg of water. The water tank is then connected to a stainless steel syringe nozzle via a quick-insert polyurethane air duct, and a solenoid valve is installed between the two as a switch for the movement of water in the air duct. Before the high-pressure gas enters the tank, the solenoid valve is opened at normal pressure to remove the gas in the air duct and the bubbles in the initial water flow; after the high-pressure gas enters the tank, the solenoid valve is opened for testing after the pressure display of the cylinder pressure reducing valve stabilizes, to ensure that the system transiently changes to a stable water discharge stage after the solenoid valve is opened. During operation, argon gas with a pressure of 0.4 MPa after decompression is used as a driving source to drive water through the nozzle of a stainless steel syringe with a diameter of 2.5 mm to obtain a flow rate of 17 m s -1 The water jet is directed vertically to the sample surface until all the water in the device is exhausted.

[0079] Radiative cooling outdoor test: Preparation of an 18×18 cm area on a 0.5 mm thick glass substrate 2 The hybrid coating with a thickness of 590 μm was used as a radiative cooling outdoor test sample. The sample was placed vertically facing the sky on a 30×30×15 cm 3 The insulated polystyrene (PS) foam box was wrapped in reflective aluminum foil and was approximately 1 meter above the ground to reduce heat conduction from the ground. The top of the foam box was covered with a 20 μm thick linear low-density polyethylene (LLDPE) film to reduce heat convection from the ambient air. The insulated foam box was placed in a semi-enclosed windproof box (150 × 100 × 100 cm) made of polyurethane (PU) foam board with reflective aluminum foil. 3) to reduce interference from gusty winds and solar radiation caused by heat accumulation in the insulation foam box. The ambient temperature probe was placed in a semi-enclosed windproof box near the vents, while the sample temperature probe was placed in an insulation foam box and attached to the center of the back of the glass substrate. Both temperature probes were thermocouples (JY-DAM-PT08). A thermohygrometer (TH20R-EX, Yingste Technology) was placed in the windproof box to record real-time relative humidity and was set to automatically record data once per minute. A solar radiation power meter (TES-132, Taishi Electronics) was placed outside the windproof box and automatically measured solar radiation intensity. The outdoor test location was the central urban area of Haidian District, Beijing (116°21′E, 40°00′N, approximately 60 meters above sea level). Weather indicators such as solar radiation intensity, wind speed, and relative humidity were recorded in real time by the above equipment or provided by the local meteorological station. The Air Quality Index (AQI) and corresponding air quality rating, as well as PM 2.5 and PM 10 Provided by the websites https: / / www.qweather.com / historical / beijing-101010100.html and https: / / www.aqistudy.cn / historydata / daydata.php?city=%E5%8C%97%E4%BA%AC&month=202 1-10, respectively.

[0080] Example 1

[0081] (1) Preparation of polyvinyl dimethylethoxysilane (PVDMES)

[0082] DTBP (10 mol%) and monomer VDMES (DTBP is 10% of the molar content of VDMES) are mixed evenly in a hydrothermal reactor. Use high-purity nitrogen to purge the space above the mixed liquid, and then seal the reaction device. Place the hydrothermal reactor in a 120°C oven and heat for 24 hours to perform free radical polymerization, and then cool to room temperature to obtain PVDMES. The typical molecular weight and molecular weight distribution of the obtained polymer are confirmed by gel permeation chromatography (GPC) to be the number average molecular weight M n =3.5×10 3 , weight average molecular weight M w =1.9×10 4 , molecular weight distribution M w / M n =5.4.

[0083] (2) Preparation of alkyl-modified polysiloxane sol (i.e., modified silica sol)

[0084] 3.08 g EtOH and 1.21 g 0.1 mol L -1A dilute HCl solution (pH 1) was mixed in a sample bottle and magnetically stirred at room temperature for 5 minutes. TEOS was rapidly added dropwise to the above solution under stirring, and then a hydrolysis-condensation reaction was carried out at room temperature for 24 hours to generate a polysilicic acid sol. Subsequently, OCTEO was added to the above acid-catalyzed polysilicic acid sol and the reaction was continued for another 48 hours. OCTEO partially modified the polysilicic acid chain through a co-condensation reaction (the other part remained in the entire sol system after condensation). The amount of TEOS and OCTEO added, the mass concentration of TEOS, and the mass concentration of OCTEO are shown in Table 1 below.

[0085] (3) Preparation of polyethylene-polysiloxane-based organic-inorganic hybrid coatings

[0086] 20 wt% PVDMES (20 wt% is the mass content of PVDMES in the modified silica sol) was added to the modified silica sol and stirred at room temperature for 6 hours to prepare a mixed silica sol. The mixed silica sol was poured into a prefabricated glass substrate mold (approximately 1 ml of the modified silica sol was used to coat the glass substrate) and allowed to stand at room temperature in a high humidity environment (RH greater than 95%) controlled by ultrapure water for 24-48 hours to form a film. The sample was then removed and dried in air to constant weight (approximately 3-7 days), thereby obtaining a polyethylene-polysiloxane organic-inorganic hybrid porous coating.

[0087] The prepared porous coating is named a-SiO x -0.2-PE-c, where a represents the modified silica sol number in Table 1 below, b represents the PVDMES input amount (calculated by the mass ratio of PVDMES to modified silica sol), and c represents the mixing reaction time of the modified silica sol and PVDMES before casting into a film. The prepared porous coatings are numbered A, B, C, D, and E (as shown in Table 1), respectively.

[0088] Table 1 Input amount and concentration ratio of TEOS and OCTEO in different modified silica sols

[0089]

[0090] In Table 1, W TEOS It refers to the mass proportion of TEOS in the entire solution of TEOS, OCTEO, EtOH and HCl;

[0091] T TEOS It refers to the volume proportion of TEOS in the entire solution of TEOS, OCTEO, EtOH and HCl;

[0092] W OCTEO It refers to the mass proportion of OCTEO in the entire solution of TEOS, OCTEO, EtOH and HCl;

[0093] T OCTEO It refers to the volume proportion of OCTEO in the entire solution of TEOS, OCTEO, EtOH and HCl.

[0094] Example 2

[0095] The difference between Example 2 and Example 1 is that the 20 wt% PVDMES in Example 1 is replaced by 30 wt% PVDMES. The numbers of the modified silica sol and the porous coating are the same as those in Example 1, and the obtained porous coating is named a-SiO x -0.3-PE-c.

[0096] Example 3

[0097] The difference between Example 3 and Example 1 is that the 20 wt% PVDMES in Example 1 is replaced by 40 wt% PVDMES. The numbers of the modified silica sol and the porous coating are the same as those in Example 1, and the obtained porous coating is named a-SiO x -0.4-PE-c.

[0098] Example 4

[0099] The difference between Example 4 and Coating B in Example 2 is that after a mixing reaction time of about 6 hours, the film thicknesses of Example 4 were 97 μm, 118 μm, 164 μm, 219 μm, 293 μm, 350 μm, 590 μm, and 1108 μm, respectively. The prepared coatings were recorded as samples 4, 5, 6, 7, 8, 9, 10, and 11, respectively.

[0100] Comparative Example 1

[0101] The difference between Comparative Example 1 and Coating B in Example 2 is that: Comparative Example 1 forms a film at relative humidity of 77%, 49% and 18% after a mixing reaction time of about 6 hours, wherein the relative humidity of 77% is an atmosphere of supersaturated NaCl solution, the relative humidity of 49% is an atmosphere of supersaturated potassium carbonate solution, and the relative humidity of 18% is an air atmosphere. The prepared products are recorded as samples 1, 2 and 3, respectively.

[0102] Test Example 1

[0103] Film forming properties and reflectivity tests were performed on the porous coating prepared in Example 1.

[0104] The present invention adopts the non-solvent induced phase separation (NIPS) method to prepare the porous coating. During the film formation process of the porous coating, different ratios of modified silica sol and PVDMES content will affect the formation of the porous skeleton structure of the coating, thereby affecting the film formation effect and the reflective properties of the coating.

[0105] At different reaction times c (c is 0.5h, 2h, 3.5h, 6h, 9h, 11h), the film-forming properties of coatings A, B, C, D, and E prepared in Example 1 were studied (corresponding to samples 219, 237, 255, 273, and 300, respectively). The test results are shown in 1c ( Figure 1 c is a photo of each porous coating), as shown in Figure 1 As shown in Figure c, when the modified silica sol lacks the silane coupling agent OCTEO (sample 300), no film can be formed in the presence of 20 wt% PVDMES. However, when 3.7 wt% OCTEO is added (sample 273), the film still cracks after formation. As the OCTEO content increases (samples 255, 237, and 219), the film-forming properties of the mixed silica sols significantly improve. This indicates that OCTEO, through the steric hindrance of the n-octyl group, reduces the degree of Si–OH condensation crosslinking in the system, reducing the rigidity of the coating and improving film-forming properties.

[0106] In the process of preparing the porous coating by the non-solvent induced phase separation method of the present invention, high humidity is used to delay the volatilization of water in the mixed silica sol. The concentration of the non-solvent water increases continuously during the volatilization of the solvent ethanol, thereby inducing the mixed silica sol to undergo phase separation to form a skeleton network. After the liquid is completely evaporated, the porous coating has a micro-nano porous structure. In the present invention, the mechanical strength of the skeleton network formed during the phase separation process depends on the condensation cross-linking of Si-OH. Under low mixing reaction time (such as 0-0.5h), the alkoxy side groups of PVDMES are hydrolyzed to generate Si-OH but have not yet condensed with the polysilicic acid chains in the modified silica sol to form a sufficient cross-linked molecular network. That is, when the degree of Si-OH condensation is low, the capillary force caused by the volatilization of the liquid during the film drying process will cause the collapse of the skeleton network, and thus it is impossible to form a sufficient micro-nano porous structure to effectively scatter the solar radiation band. On the contrary, under high mixing reaction time (such as 6-11 hours), when the degree of Si-OH condensation in the double-crosslinked network before film formation is high, the spontaneous sol-gel process caused by condensation crosslinking during the drying process will kinetically freeze (glass transition) phase separation behavior prematurely, making the resulting porous structure skeleton smaller in size and unable to produce strong scattering in the long-wavelength NIR band (0.8-2.5um).

[0107] The modified silica sol samples 219, 237, 255, and 273 in Example 1 were mixed and reacted for c hours (c was 0.5 h, 2 h, 6 h, 9 h, and 11 h, respectively), and reflectivity tests were performed. The test results are as follows: Figure 1 As shown in a-1b, Figure 1 a is a comparison of the reflectivity of the modified silica sol sample in Example 1 at a near-infrared wavelength of 0.5 μm. Figure 1b is a comparison of the reflectivity of the modified silica sol sample in Example 1 at a near-infrared wavelength of 1.5 μm. Figure 1 As can be seen in a-1b, as the mixing reaction time c increases, the coating's reflectivity in the solar radiation band first increases and then decreases, particularly in the NIR band. The reflectivity of sample 219 is less dependent on the mixing reaction time than samples 255 and 237, indicating that the higher amount of OCTEO further hinders Si–OH condensation, delaying the competitive process of sol-gel transition and phase separation, and widening the processability window. However, due to the strong hydrophobicity brought about by the high OCTEO content, the mixed silica sol in sample 219 gradually precipitates before film formation as the mixing reaction time increases, becoming a heterogeneous system. The uniformity of the coating after film formation is poor, as shown by the circle in Figure 1c.

[0108] Test Example 2

[0109] Film forming properties and reflectivity tests were performed on the porous coating prepared in Example 2.

[0110] The film forming properties of samples 219, 237, 255, 273 and 300 prepared in Example 2 were studied at different reaction times c (c was 0.5h, 2h, 3.5h and 6h, respectively). The test results are as follows: Figure 2 c shown ( Figure 2 c is a photo of each porous coating). When the PVDMES content increases to 30 wt%, it can be seen from samples 300 and 273 that the film-forming property of the mixed silica sol is improved, indicating that the increase of polyethylene chains in the sol improves the flexibility of the coating.

[0111] The modified silica sol samples 219, 237, 255, 273, and 300 in Example 2 were mixed and reacted for c hours (c was 0.5 h, 2 h, 3.5 h, and 6 h, respectively). The test results are as follows: Figure 2 As shown in a-2b, Figure 2 a is a comparison of the reflectivity of the sample in Example 2 at a near-infrared wavelength of 0.5 μm. Figure 2 b is the reflectivity comparison result of the sample in Example 2 at 1.5 μm near-infrared wavelength. Figure 2 As can be seen from a-2b, the reflective properties of the porous coating containing 30wt% PVDMES also have a significant dependence on the mixing reaction time c. The increase in PVDMES content further enhances the hydrophobicity of the resin and exacerbates the non-uniformity of coating A (e.g. Figure 2c), its optical properties also show a significant decline compared to 20wt%. Therefore, an appropriate OCTEO content (e.g., porous layer B) not only maintains the coating's hydrophobicity, enabling good film-forming properties, but also mitigates the spectral attenuation caused by the spontaneous sol-gel transition, resulting in a wide processing window.

[0112] Test Example 3

[0113] The film forming property and reflectivity test of the porous coating prepared in Example 3 were carried out

[0114] At different reaction times c (c is 0.5h, 2h, 3.5h, 6h), the film-forming properties of the coating samples A, B, C, D, and E prepared in Example 3 (corresponding to samples 219, 237, 255, 273, and 300, respectively) were studied. The test results are shown in 3c ( Figure 3 c is a photo of each porous coating). From coating E (i.e., sample 300), it can be seen that when the PVDMES content is increased to 40 wt%, the film-forming property of the coating is further improved compared with that at 30 wt% ( Figure 3 c). However, further increase in PVDMES content accelerates the kinetic freezing of the spontaneous sol-gel transition. At the same time, the increased PVDMES further enhances the flexibility of the polymer cross-linked network. The small-sized and flexible network skeleton formed by phase separation is not enough to resist the shrinkage deformation caused by capillary force during the film formation and drying process, and the porous structure cannot be effectively retained. Therefore, the number of dense transparent coatings or uneven translucent coatings in coating AE increases significantly (e.g. Figure 3 c).

[0115] The modified silica sol samples 219, 237, 255, 273, and 300 in Example 3 were mixed and reacted for c hours (c was 0.5 h, 2 h, 3.5 h, and 6 h, respectively). The test results are as follows: Figure 3 As shown in a-3b, Figure 3 a is a comparison of the reflectivity of the sample in Example 3 at a near-infrared wavelength of 0.5 μm. Figure 3 b is the reflectivity comparison result of the sample in Example 3 at 1.5 μm near-infrared wavelength. Figure 3 As can be seen from a-3b, the reflectivity of the porous coating of Example 3 shows a significant downward trend compared to that under the condition of 30 wt% PVDMES ( Figure 3 a-3b), the processable window for obtaining high reflective coatings is significantly narrowed.

[0116] Test Example 4: Impact of Environmental Humidity

[0117] The photos of coating samples 1, 2 and 3 in Comparative Example 1 (the reaction time c of samples 1, 2 and 3 is 6h) are as follows: Figure 4 As shown in b (where Figure 4 b, the relative humidity of the left image is 18%, the relative humidity of the middle image is 49%; the relative humidity of the right image is 77%). Samples 1, 2, and 3 prepared in Comparative Example 1 were tested for reflectance spectra. The test results are shown in FIG. Figure 4 As shown in a, Figure 4 It can be seen that no matter under low relative humidity (air atmosphere, RH 18%) or high relative humidity (supersaturated NaCl solution atmosphere, RH 77%), the obtained coating does not have the ability to reflect the 0.3-2.5μm band. Compared with the high reflective spectrum performance after film formation under the highest relative humidity (ultrapure water atmosphere, RH greater than 95%, i.e., Example 2 Sample 237) Figure 2 a-2b), indicating that the preparation of the porous coating of the present application requires a higher water vapor concentration environment to suppress the volatilization rate of water in the mixed silica sol, provide sufficient time for the formation and growth of the polymer skeleton network during the phase separation process, and at the same time delay the contraction effect of the capillary force during the volatilization of water, so that the porous network structure formed by phase separation is retained.

[0118] Test Example 5: Thickness Impact

[0119] When preparing thick coatings, the volume of mixed silica sol required increases exponentially, significantly increasing the solvent evaporation time. For a prolonged period after coating (or casting), the slower diffusion gradient of the solvent concentration causes the lower layer of the liquid film to continue condensing and crosslinking, undergoing spontaneous sol-gelation, without initiating phase separation. Therefore, to predict the optical properties of thick coatings, it is necessary to examine the optical properties of thin coatings with the same sol ratio but a longer mixing reaction time before coating (or casting).

[0120] The reflection spectra of the coating samples 4-11 prepared in Example 4 were tested respectively. The test results are as follows: Figure 5 As shown, from Figure 5 It can be seen that when the coating thickness is less than 590 μm, the reflectivity gradually increases with the thickness of the coating; after the thickness is higher than 590 μm, the reflectivity gradually stabilizes and reaches a maximum value of 95%.

[0121] In summary, taking into account high reflectivity, a wide processing window (spectral attenuation caused by weak mixing reaction time) and material flexibility, the coating sample 10 prepared in Example 4 was selected, and the coating thickness was 590 μm (named 237-SPE-590) for subsequent research on actual radiative cooling performance and related cooling mechanisms.

[0122] Test Example 6

[0123] The coating sample 10 in Example 4 was tested for reflectance spectrum, and the test results are as follows: Figure 6As shown, from Figure 6 As can be seen from the figure, in the visible light and part of the near-infrared light region (i.e., wavelength 0.4-1.1μm), the reflectivity of coating sample 10 is higher than 95%. Among them, at a wavelength of 0.5μm, the reflectivity can reach 99%, greatly reducing the heat gain from solar radiation. In the near-infrared light band (0.8-2.5μm), the reflection spectrum is attenuated due to the frequency-harmonic vibration absorption of silanol and (methylene) groups in the coating. The average total solar reflectivity of the coating in the 0.3-2.5μm band ( Calculated by the formula) can still reach 95%. Among them, Calculated using the following formula 3-2 or formula 3-3.

[0124] Figure 7 is a 10-80° normalized angle-resolved reflectance spectrum of the coating sample 10 and the standard diffuse reflector (i.e., a reference white plate) in Example 4, wherein: Figure 7 The left is the 10-80° normalized angle-resolved reflectance spectrum tested at a wavelength of 0.5μm. Figure 7 The right side shows the 10-80° normalized angle-resolved reflectance spectrum measured at a wavelength of 1.5 μm. Figure 7 It can be seen that the coating of the present invention has almost the same angle-dependent reflection characteristics as a standard diffuse reflector (reference white board), indicating that the coating is a Lambertian-like body and can effectively scatter sunlight incident over a wide angle range.

[0125]

[0126] in, is the average total reflectance of sunlight; λ is the wavelength, I solar (λ) is the normalized ASTM G173 total solar radiation intensity spectrum, R solar (λ, θ) is the coating reflectivity related to the incident angle and wavelength. Since coating sample 10 exhibits Lambertian-like properties, the angle has little effect on its reflectivity. Formula 3-2 can be simplified to Formula 3-3:

[0127]

[0128] Test Example 7

[0129] Figure 8The scanning electron microscope images of the coating sample 10 in Example 4 are 1 μm in scale, wherein Figure a is a cross-sectional SEM, i.e., the out-of-plane direction; Figure b is a SEM image of the internal skeleton structure exposed after the skin layer is polished off, i.e., the surface in the in-plane direction; Figure c is an average size image in the out-of-plane direction; Figure d is an average size image in the in-plane direction; Figure e is an average size image of the total size of Figures c and d; Figure f is a size image of the slit-shaped pores along the out-of-plane direction; Figure g is a size image of the circular pores in the in-plane direction; Figure 8 It can be seen that the average size of the porous network skeleton inside the coating is 0.28±0.07μm, which is also consistent with the theoretical prediction of the ideal visible light scatterer characteristic size of 0.2-0.3μm, indicating that the skeleton structure of the coating of the present invention can effectively reflect the visible light wavelength region with the strongest solar radiation. Figure 8 It can be seen from a that the network skeleton structure of the coating is not a fluffy honeycomb pore structure, but rather a fibrous or long rod-like morphology perpendicular to the film thickness direction (out-of-plane direction); the average size of the slit-like pores along the out-of-plane direction is 0.19±0.09um, and the average size of the circular pores in the in-plane direction is 0.34±0.13um. It can be seen that the pores along the out-of-plane direction are smaller (flatter) and the skeleton packing density is higher (see Figure 8 f and g). This indicates that the shrinkage of the coating along the thickness direction during the film formation and drying process affects the phase separation process, squeezing the growing network skeleton, and ultimately forming a three-dimensional random network structure with an orientation parallel to the horizontal direction.

[0130] The coating of the present invention has a skeleton volume filling rate of up to 64±1% (i.e., the porosity of the coating is 36±1%). This skeleton volume filling rate is close to the upper limit of the scatterer filling fraction range (40-70%) under the optimal broadband reflectivity in the scattering structure of the white beetle Cyphochilus, indicating that the high skeleton volume fraction of the 237-SPE-590 coating allows the maximum increase in the number of scatterers to improve the scattering ability of the incident light without optical crowding. At the same time, the E / E S ∝(ρ / ρ S ) m or σ / σ S ∝(ρ / ρ S ) m It can be seen that a high skeleton filling rate makes the coating as dense as possible without causing optical crowding to maximize its own mechanical properties.

[0131] Test Example 8

[0132] like Figure 6 As shown in b, the average total infrared emissivity of the coating sample 10 in Example 4 in the atmospheric infrared transmission window band (8-13 μm) is Able to reach 96% average total infrared emissivity It is calculated by the following formula 3-4. It can be seen that the coating prepared by the present invention has excellent infrared emission capability.

[0133]

[0134] Among them, I BB (T, λ) is the intensity of the blackbody thermal emission spectrum at temperature T ( k B is the Boltzmann constant, h is the Planck constant, c is the speed of light; the temperature is 298K (25℃), ∈ LWIR (T,λ) is the hemispherical infrared emissivity of the coating in the range of 8-13 μm (i.e. Figure 6 emissivity in b).

[0135] Test Example 9

[0136] The coating's high infrared emissivity effectively transfers its own heat into space through the atmospheric window via radiation, dissipating heat and creating a cooling effect. This excellent thermal radiation performance stems from the ideal intrinsic electromagnetic properties of the polyethylene-polysiloxane organic-inorganic hybrid coating.

[0137] Figure 9 is the composite spectral refractive index of sample 10 in Example 4 (n+iκ, n is the spectral refractive index, κ is the extinction coefficient, and i is the square root of -1), where Figure 9 a is the spectral refractive index (i.e. n), Figure 9 b is the extinction coefficient (i.e. κ), and the shaded area in the figure refers to the atmospheric window band. Figure 9 It can be seen that near the wavelength of 7.5-10μm, the spectral refractive index of the coating fluctuates significantly and its extinction coefficient increases significantly, indicating that there is strong infrared absorption (emission) caused by molecular vibration in this band.

[0138] Figure 10 The ATR-FTIR spectrum of the coating sample 10 of Example 4 is shown in FIG. The shaded portion in the figure refers to the atmospheric transmission window band. Figure 9 and Figure 10 It can be seen that the high infrared emissivity of the coating comes from the polysiloxane network (SiO x ), the vibration absorption of the silyl bond (Si–O–Si) of the PVDMES main chain methine (–Si–CH–), the side chain silyl methyl (–Si–CH3) and the silane coupling agent OCTEO silyl methylene (–Si–CH2–).

[0139] Test Example 10

[0140] Figure 11The thermal weight loss curve of the coating sample 10 of Example 4 is shown in FIG. Figure 11 It can be seen that the coating of the present invention can not decompose at 250°C and has good thermal stability. Figure 11 It can also be seen that the organic content and the inorganic content in the coating of the present invention each account for 50 wt%.

[0141] Test Example 11

[0142] In the present invention, a large amount of PVDMES is added when preparing the coating sample 10 of Example 10. By increasing the content of polyethylene chains, the mixed silica sol resin is given sufficient flexibility to improve the film-forming ability. However, after the PVDMES side chain silanol is hydrolyzed to form silanol, the polyethylene-polysiloxane double cross-linked molecular network formed by condensation with the modified silica sol has a high degree of cross-linking, which can give the coating good mechanical properties.

[0143] Figure 12 a is the nanoindentation load-displacement curve of the coating sample 10 of Example 4, Figure 12 b is a diagram of the mechanical properties of polymers in the prior art. Figure 12 It can be seen that the intrinsic elastic modulus E of the coating of the present invention is 1.4 GPa, and the hardness H ave The rigid inorganic polysiloxane in the double-crosslinked hybrid network of the coating of the present invention makes the mechanical properties of the coating close to those of ultra-high molecular weight polyethylene (UHMWPE) (UHMWPE hardness is 0.073 GPa). It can be seen that the coating of the present invention has similar properties to ultra-high molecular weight polyethylene, and also has high mechanical strength, high wear resistance, low friction coefficient, excellent chemical stability and biocompatibility, and can be used as a biomedical load-bearing material.

[0144] Test Example 12: Taber Abrasion Test

[0145] The Taber wear test is a test that involves rotating a standard double grinding wheel on a coating surface under a certain load, pressure, and abrasion. During the wear process, the sample rotates and the grinding wheels rotate. The two grinding wheels generate outward and inward friction on the sample under load, forming a friction of about 30 cm. 2 annular wear area.

[0146] The Taber abrasion test according to ASTM D4060 was used to characterize the wear resistance, i.e. the mechanical robustness, of the coatings.

[0147] Figure 13 a is the mass loss curve of sample 10 in Example 4 under 250g Taber abrasion cycle, Figure 13b-13e are SEM images of the coating surface (b) and cross section (d) before wear and the coating surface (c) and cross section (e) after 1000 wear cycles (scale is 1 μm), respectively. Figure 13 As shown in a, the porous coating of the present invention exhibits significant mechanical robustness, with a mass loss of only 0.04 g (5 wt% of the total coating weight) after 1000 Taber abrasion cycles. Figure 13 The SEM images of b-13e show that the wear-resistant Figure 13 b and Figure 13 d), after 1000 cycles, the original dense cortex of the coating surface has been worn away, and the surface of the internal network skeleton exposed subsequently undergoes a certain degree of aggregation and deformation under the action of the grinding wheel (Figure 13c, 13e). In the thickness direction, despite the application of load pressure, Taber wear does not cause invasive damage to the network skeleton below the abrasion exposure surface ( Figure 13 d, Figure 13 e), the internal microstructure can still be well preserved.

[0148] The wear-resistant properties of the coating of the present invention can be attributed to three reasons: 1. The high cross-linking density of the polysiloxane component in the polyethylene-polysiloxane hybrid double cross-linked molecular network gives the coating a porous skeleton firmness and provides a good mechanical basis; 2. The continuity of the three-dimensional porous network skeleton enables it to effectively disperse the local stress generated by external pressure and friction, avoiding local stress concentration and causing the skeleton structure to be destroyed prematurely. 3. The continuous network skeleton oriented parallel to the surface direction (in-plane) minimizes the force it receives when it is worn, and at the same time, the high skeleton volume filling rate makes the structure denser and gives it better wear resistance. In addition, in the first 100 wear cycles, the coating exhibits stronger wear resistance. This is because the cortex formed on the surface of the coating during the phase separation process is denser than the porous structure inside ( Figure 13 b and Figure 13 d), can provide better protection for the overall structure of the coating.

[0149] Test Example 13

[0150] The coating sample 10 of Example 4 was subjected to a water jet impact test. The specific test process was as follows: the surface cortex of the coating was first polished off with 200-grit sandpaper to expose the skeleton structure formed by phase separation inside the coating; argon gas with a pressure of 0.4 MPa was used to drive water flow through the nozzle of a stainless steel syringe with a diameter of 2.5 mm to obtain a flow rate of 17 m s -1 The water jet impact removes the skin coating. The total mass of the water jet in a single impact test is 0.45kg. Figure 14 a is a photo of the water jet impact experiment. Figure 14b is the static water contact angle (θ) of the coating removed from the surface during the 0-6 water jet impact cycle test. A )’s changing trend chart, from Figure 14 b It can be seen that the static water contact angle of the coating (θ A ) is 157.1±2.15°, and when the number of cycles is 0, it exhibits super-hydrophobic properties. This shows that the coating of the present invention has good hydrophobicity, which is beneficial for its operation and maintenance under complex and harsh outdoor conditions.

[0151] After 6 high-speed water jet impacts (i.e., 6 cycles, 6 times with a total of 2.7 kg), the coating still exhibits superhydrophobic properties, θ A All remained at around 150° without significant changes. Figure 14 c and 14d are SEM images of the coating surface before and after 6 water jet impacts to remove the surface skin layer, respectively. Figure 14 c and 14d, it can be seen that the six water jet impacts did not damage the coating skeleton structure, indicating that the coating has good mechanical robustness.

[0152] Test Example 14

[0153] Figure 15 This is a stability test diagram of the optical performance of the coating sample 10 in Example 4 under different environments; wherein, Figure 15 a is a water flushing test with a water flow rate of 42g s -1 , the flushing time is 10 minutes (i.e. 25kg water flow for flushing); Figure 15 b is the mortar impact test, the mortar was obtained by mixing 0.2 kg of sand and 3 kg of tap water; Figure 16 c is a sand flow impact test, using 0.25 kg of sand to impact the coating; Figure 15 de are the reflection spectrum and infrared emission spectrum of the coating after stability test under different environments. Figure 15 As shown in a, the coating was subjected to a 42 g s -1 After water flushing, there is no macroscopic water infiltration, penetration or coating swelling phenomenon. The average total solar reflectance of the coating is Maintain an average total infrared emissivity of 95% Maintained at 96%, almost the same as the performance before the test (such as Figure 6 and Figure 15 de). In mortar impact ( Figure 15 b) and sand flow impact ( Figure 15 c) After the test, the coating can be easily cleaned by simply washing with tap water. At the same time, the coating is not significantly contaminated or damaged by the impact of mortar and sand flow. Still maintained at 94%, Still maintained at 96%, consistent with the performance before the test ( Figure 6 , Figure 15 In addition, the coating had been placed in an indoor environment for about 7 months before the stability test in Test Example 14, indicating that the coating of the present invention can be stored in an air atmosphere for a long time without obvious aging leading to optical performance degradation.

[0154] Figure 16 The coating sample 10 of Example 4 was exposed to UV light (wavelength of 365 nm, power of 2 W m -2 ) after 50 days of irradiation, the reflection spectrum (a) and infrared emission spectrum (b) are shown in Figure 2. Figure 16 As shown, at a wavelength of 365 nm and an irradiation intensity of 2 W m -2 The coating will be irradiated with UV light for up to 50 days. and It can be maintained at 94% and 96%, and the optical properties have not been significantly attenuated. In addition, after the coating was immersed in water for 23 days, there was no obvious swelling on the macro scale and the optical properties did not decay significantly. and The test results show that the surface coating has high resistance to UV, indicating that the coating of the present invention has excellent stability.

[0155] Test Example 15

[0156] Figure 17 17a-c are graphs showing the daytime outdoor cooling test results of the coating sample 10 of Example 4 under different weather conditions, wherein FIG17a-c are sunny, cloudy and foggy weather, respectively. Figure 17 In a, the average solar radiation intensity at noon is I solar 790W m -2 , the average wind speed is 0.3ms -1 , the average relative humidity RH is 27%, AQI is 25 (air quality is good), Figure 17 It can be seen from a that the average sub-ambient temperature drop ΔT of the coating at noon can reach 6.2°C. Figure 17 In b, the average solar radiation intensity at noon is I solar 200W m -2 , the average wind speed is 0.9ms -1 The average relative humidity is 53%, and the AQI is 40 (excellent air quality). Figure 17b It can be seen that the average sub-ambient temperature drop ΔT of the coating at noon can reach 2.9°C. In clear weather, the infrared transmittance of the atmosphere is high, and the coating transfers heat directly to the outer space through thermal radiation (about -270°C (3K), basically no thermal radiation), resulting in significant heat loss and achieving a high cooling effect. On the contrary, under cloudy conditions, even if the solar radiation intensity is greatly reduced, the average temperature drop of the coating is still reduced by nearly half. This shows that cloudy weather and high humidity environments absorb part of the thermal radiation from the coating, while its downward thermal radiation causes the coating to generate heat. These two reasons offset part of the cooling effect. Figure 17 c, the average afternoon solar radiation intensity I solar 420W m -2 , the average wind speed is 0.6ms -1 The average relative humidity was 36%, the AQI was 152 (the air quality was moderately polluted), and the PM 2.5 (117 μg m -3 ) / PM 10 (109 μg m -3 ) conditions, the average midday sub-ambient temperature drop ΔT of the coating can still reach 5.8°C. Compared with sunny and cloudy days, the radiative cooling effect under haze weather is between clear and cloudy days.

[0157] In summary, the coating of the present invention can tolerate weather pollution and has a sub-ambient cooling effect of 6°C on sunny and hazy days; while cloud cover on cloudy days has the greatest impact on the cooling performance of the coating.

[0158] Figure 18 This is a graph showing all-weather outdoor cooling test results for the coating sample 10 in Example 4 at different time periods, where: Figure 18 a is the solar radiation intensity, Figure 18 b is humidity, Figure 18 c is the temperature. Figure 18 It can be seen that compared with the ambient temperature, the average temperature drop of the coating (237-SPE-590) during the day is 5.9°C, and the average temperature drop at night is 7.7°C. The higher temperature drop at night is mainly because there is no solar radiation energy input, which makes the net cooling power of the coating higher than that during the day and can achieve a stronger cooling effect. In the noon time period (12:00-14:00 noon) when the solar radiation is the strongest, the average sub-ambient temperature drop of the coating for three consecutive days was 4.3°C. In addition, in the first test (12:00-13:00), although the solar radiation intensity was close to 900W m -2Even at relative humidity near 50%, the coating still achieved an average sub-ambient cooling effect of 2.8°C. The results demonstrate that even in high-heat and high-humidity environments, the coating, in synergistic effect with average total solar reflectance and average total infrared emissivity, can still provide excellent sub-ambient temperature radiative cooling capabilities.

[0159] The above describes exemplary embodiments of the present invention. However, the scope of protection of the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the spirit and principles of the present invention are intended to be included within the scope of protection of the present invention.

Claims

1. A method for preparing a polyethylene-polysiloxane-based organic-inorganic hybrid porous coating, characterized in that: The porous coating has a three-dimensional random network skeleton structure oriented parallel to the surface direction; In the porous coating, the skeleton packing density along the out-of-plane direction is higher than the skeleton packing density along the surface direction; The method for preparing the porous coating comprises the following steps: (1) Preparation of polyvinyl dimethylethoxysilane (PVDMES); (2) mixing an organic solvent, an acidic compound, and a silicon-containing compound to react to obtain a polysilicic acid sol, and then adding a silane coupling agent to react to prepare an alkyl-modified polysiloxane sol; (3) mixing the PVDMES in step (1) with the alkyl-modified polysiloxane sol in step (2) to prepare a mixed silica sol, coating the mixed silica sol on the surface of the substrate, and inducing phase separation by a non-solvent to prepare the polyethylene-polysiloxane-based organic-inorganic hybrid porous coating; The skeleton volume filling rate of the porous coating layer is 40-70%.

2. The method according to claim 1, characterized in that The thickness of the porous coating layer is 80-1400 μm.

3. The method according to claim 1, characterized in that When the wavelength is 0.3-2.5 μm, the reflectivity of the porous coating is 80-99%; when the wavelength is 0.4-1.1 μm, the reflectivity of the porous coating is 90-99%.

4. The method according to claim 1, wherein When the porous coating has a thickness of 590 μm, the average total sunlight reflectivity in the solar radiation band reaches a maximum of 95%, and the average total infrared emissivity in the atmospheric window band reaches a maximum of 96%.

5. The method according to claim 1, characterized in that The pore size of the three-dimensional random network skeleton structure is 0.1-0.5 μm.

6. The method according to claim 1, wherein The porosity of the porous coating layer is 30-60%.

7. The method according to claim 1, characterized in that The refractive index of the porous coating layer is 1.2-1.

7.

8. The method according to claim 1, characterized in that The porous coating layer is hydrophobic.

9. The method according to claim 1, characterized in that The number average molecular weight of the polyvinyl dimethylethoxysilane is 2×10 3 -5×10 3 g / mol, and the weight average molecular weight is 1×10 4 -5×10 4 g / mol, and the molecular weight distribution is 2-25.

10. The method according to claim 1, characterized in that In step (2), the organic solvent is selected from at least one of ethanol, methanol, acetone, isopropanol, pentanol, N,N-dimethylformamide, dimethyl sulfoxide, and dioxane; The acidic compound is selected from at least one of sulfuric acid, nitric acid, oxalic acid, citric acid, acetic acid, and aluminum chloride; The silicon-containing compound is selected from at least one of tetraethyl silicate, tetramethyl silicate, tetraisopropyl silicate, tetrabutyl silicate, methyltrimethoxysilane, methyltriethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, trimethylmethoxysilane, and trimethylethoxysilane.

11. The method according to claim 1, wherein In step (2), the mass volume ratio of the organic solvent, the acidic compound and the silicon-containing compound is (1-6) g:1 g:(0.5-5) mL.

12. The method according to claim 1, characterized in that In step (2), the silane coupling agent is selected from at least one of n-octyltriethoxysilane, hexadecyltriethoxysilane, n-hexyltriethoxysilane, n-butyltriethoxysilane, n-octyltrimethoxysilane, dodecyltriethoxysilane, and phenyltriethoxysilane.

13. The method according to claim 1, wherein In step (2), the volume ratio of the silicon-containing compound to the silane coupling agent is 1-10:

1.

14. The method according to claim 1, wherein In step (2), after adding the silane coupling agent, the reaction temperature is 15-35° C.; and the reaction time is 12-72 h.

15. The method according to claim 1, wherein In step (3), the mass of the PVDMES is 15-45 wt % of the alkyl-modified polysiloxane sol.

16. The method according to claim 1, wherein In step (3), the mixing reaction time is 0.5-12h; the mixing reaction temperature is 20-35°C.

17. The method according to claim 1, wherein In step (3), when the non-solvent is selected from water, the vapor partial pressure of the water is controlled at a relative humidity of 60-96%, and the temperature is controlled at room temperature.

18. Use of a polyethylene-polysiloxane-based organic-inorganic hybrid porous coating prepared by the method according to any one of claims 1 to 17, characterized in that: Used in energy-saving buildings, photovoltaic equipment, power plants, automobiles, electronics or clothing.

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