Multifunctional aerogel composite coating and preparation method thereof

Abstract

The invention discloses a multifunctional aerogel composite coating, which is prepared from the following components: hydrophobic modified silica aerogel, nano hollow carbon spheres, a microcapsule phase change material, organic silicon modified acrylic emulsion, acrylic acid modified polyurethane emulsion, cerium-doped zinc oxide, P25 titanium dioxide, reduced graphene oxide and the like. The heat conductivity coefficient is 0.022 to 0.032 W / (m.K); the temperature is actively adjusted through the microcapsule phase change material, and the anti-condensation temperature difference is 9-18 DEG C; through synergistic photocatalysis of cerium-doped zinc oxide and P25, the visible light degradation rate is 85%-98%; through the cooperation of the organic silicon / polyurethane interpenetrating network resin and the graphene, the salt fog resistance of 1650-2100 hours is realized; the VOC content is 2.8-4.0 g / L, and the paint is suitable for the fields of industrial pipelines, storage tanks, building exterior walls and the like.

Description

Technical Field

[0001] This invention relates to the field of functional coatings technology, specifically to water-based environmentally friendly coatings, and particularly to a multifunctional aerogel composite coating and its preparation method that integrates heat insulation, active anti-condensation, photocatalytic self-cleaning, hydrophobic corrosion prevention and temperature adaptive regulation functions. Background Technology

[0002] With the escalating global energy crisis and the advancement of the dual-carbon strategy, functional coatings are playing an increasingly prominent role in industrial energy conservation, building energy conservation, and environmental protection. Traditional industrial protective coatings mainly focus on corrosion prevention and decorative functions, which are insufficient to meet the comprehensive needs of modern industry for energy conservation, environmental protection, and long-term protection. In recent years, multifunctional integrated coatings have become a research hotspot, especially in fields such as petrochemical pipelines, LNG storage tanks, building exterior walls, cold chain logistics equipment, and marine engineering facilities, where the demand for coatings that combine multiple functions such as heat insulation, moisture prevention and condensation prevention, sunlight reflection, hydrophobic corrosion prevention, and intelligent control has increased dramatically.

[0003] Aerogels, as ultralight porous nanomaterials, have ultra-low density (3-500 kg / m³). 3 ), ultra-low thermal conductivity (0.013-0.025 W / (m·K)), high specific surface area (200-1000 m²) 2 Aerogels possess excellent properties such as high viscosity (g / g), making them one of the most ideal thermal insulation materials. However, the application of aerogels in water-based coatings faces several challenges. First, aerogels exhibit poor dispersion stability in water-based systems, easily agglomerating and settling. Second, the interfacial bonding between aerogels and the organic resin matrix is ​​weak, affecting the mechanical properties and long-term stability of the coating. Third, there is a contradiction between aerogel content and coating application performance; high aerogel content leads to excessively high coating viscosity and poor leveling properties.

[0004] Chinese patent CN106752526B discloses a water-based light-reflective industrial thermal insulation coating. This coating uses a polymer emulsion as a matrix and adds light-reflective fillers (25% titanium dioxide, 5% zinc oxide), thermal insulation fillers, and anti-corrosion fillers. Aerogel is only used as one of the optional thermal insulation fillers (2%), failing to fully utilize its potential properties. Furthermore, this coating primarily focuses on solar reflection and heat barrier functions, lacking specific design for moisture and condensation prevention. More importantly, this technical solution suffers from the following defects: First, the aerogel dosage is too low (only 2%), resulting in limited thermal insulation effect; second, the use of isocyanate as a curing agent (6%) results in a two-component coating system with a short shelf life, inconvenient application, and poor environmental performance; third, there is a lack of effective solutions for the dispersion stability and interfacial bonding problems of aerogel; fourth, the coating exhibits problems such as attenuation of light reflection performance and decreased thermal insulation effect during long-term use.

[0005] Traditional coatings typically employ passive methods to prevent condensation, relying on increasing surface temperature or reducing ambient humidity. However, these passive measures are largely ineffective under conditions of significant temperature fluctuations (such as diurnal temperature differences exceeding 15°C or drastic seasonal temperature changes). Condensation not only damages the coating's appearance and reduces adhesion but also accelerates substrate corrosion, severely impacting the lifespan of equipment and buildings. Therefore, developing anti-condensation coatings with active temperature regulation capabilities is of significant practical importance.

[0006] Phase change materials (PCMs) are functional materials capable of absorbing or releasing large amounts of latent heat within a specific temperature range, and they have wide applications in temperature regulation, thermal energy storage, and other fields. Microencapsulated PCMs, by encapsulating a PCM core material within a polymer shell, can maintain the PCM function while solving the leakage problem of liquid PCMs. However, there are currently no reports of applying microencapsulated PCMs to prevent condensation in coatings.

[0007] In addition, existing aerogel coating technologies also have the following problems: First, the single-scale thermal insulation structure design fails to fully utilize the multi-scale synergistic effect; second, the hydrophobic and self-cleaning properties are difficult to maintain in the long term, and pollutants easily accumulate on the surface; third, the high solids content leads to poor application performance; fourth, it is difficult to balance the coating's mechanical properties (adhesion, flexibility) with its thermal insulation performance; and fifth, it has poor environmental adaptability, with significant performance degradation under extreme conditions such as high temperature, low temperature, and high humidity.

[0008] Therefore, there is an urgent need to develop a new type of multifunctional aerogel composite coating that can fully utilize the excellent thermal insulation properties of aerogel. At the same time, through material innovation and structural design, it can achieve multiple functions such as moisture-proof and anti-condensation, photocatalytic self-cleaning, hydrophobic anti-corrosion, and temperature adaptive regulation. It should also solve key technical problems such as the dispersion stability, interfacial bonding force, and construction performance of aerogel in water-based coatings, so as to meet the urgent needs of industrial and construction fields for high-performance, long-lasting stable, environmentally friendly and energy-saving coatings. Summary of the Invention

[0009] To address the shortcomings of existing technologies, this invention aims to provide a multifunctional aerogel composite coating and its preparation method. This coating constructs a multi-scale synergistic thermal insulation structure by introducing nano-hollow carbon spheres, achieves temperature-adaptive active anti-condensation through microencapsulated phase change materials, realizes visible light self-cleaning through a synergistic photocatalytic system of cerium-doped zinc oxide and P25 titanium dioxide, and achieves long-term corrosion protection through the synergistic effect of organosilicon / polyurethane interpenetrating network resin and reduced graphene oxide. It solves the problems of dispersion stability and interfacial bonding of aerogels in water-based coatings, exhibiting excellent comprehensive performance and long-term stability.

[0010] To achieve the above objectives, the first aspect of the present invention provides a multifunctional aerogel composite coating, comprising, by weight percentage: 10%–18% hydrophobically modified silicone aerogel, 22%–32% organosilicon modified acrylic emulsion, 12%–18% acrylic modified polyurethane emulsion, 2%–6% nano-hollow carbon spheres, 2%–5% hollow glass microspheres, 3%–8% nano-titanium dioxide, 1%–4% modified zinc oxide, 3%–10% microcapsule phase change material, 0.8%–2.5% reduced graphene oxide, 0.5%–3% silane coupling agent, 1.5%–4% functional dispersant combination, 0.2%–0.8% pH adjuster, 1.5%–3.5% film-forming aid, 0.3%–1.5% rheology modifier, 0.15%–0.8% defoamer, 0.6%–1.8% antifreeze, with the balance being deionized water to 100%.

[0011] In a preferred embodiment of the present invention, the hydrophobically modified silica aerogel has a thermal conductivity of 0.015-0.018 W / (m·K) and a density of 80-120 kg / m³. 3 Specific surface area is 500-600 m² 2 / g, water contact angle greater than 150°, particle size 1-5μm.

[0012] In another preferred embodiment of the present invention, the hollow carbon nanospheres have an average particle size of 50-200 nm, a wall thickness of 8-15 nm, and a density of 0.03-0.08 g / cm³. 3 Specific surface area is 600-1200 m² 2 / g. The mass ratio of the hydrophobically modified silica aerogel to the hollow carbon nanospheres is (3-6):1, which synergistically constructs a nano-micron gradient thermal insulation structure. The hollow carbon nanospheres have ultra-low density and ultra-high specific surface area. Their nanoscale cavity structure can effectively suppress gas convection and radiative heat transfer, and work synergistically with the micron-scale aerogel to form a multi-scale thermal insulation network from nano to micron.

[0013] In another preferred embodiment of the present invention, the microcapsule phase change material uses octadecane or a mixture of octadecane and hexadecane as the core material and melamine-formaldehyde resin as the wall material. The microcapsule encapsulation efficiency is ≥72%, the phase change temperature is 27-32°C, the latent heat of phase change is 185-210 J / g, the particle size is 5-10 μm, and the wall thickness is 0.5-1.2 μm. The high encapsulation efficiency of the microcapsules ensures the long-term stability and service life of the phase change material, while the moderate particle size ensures good dispersibility without affecting the film quality of the coating.

[0014] Furthermore, the nano-titanium dioxide is of type P25, comprising a mixed structure of anatase and rutile crystals, with a mass ratio of 75-85:15-25. The modified zinc oxide is cerium-doped zinc oxide, with a doping amount of 0.8-3.5 mol%, and cerium is present as Ce. 3+ and Ce 4+ Mixed valence states exist, with a molar ratio of (1-2):1. Ce 3+ The 4f energy level introduces an intermediate energy level into the zinc oxide band gap, while Ce 4+ By forming oxygen vacancies to regulate carrier concentration, the synergistic effect of these two mechanisms reduces the band gap of zinc oxide from 3.2 eV to approximately 2.7-2.9 eV, extending the photoresponse range into the visible light region. Simultaneously, the anatase type of P25 titanium dioxide forms a Type-II heterojunction at the rutile phase interface, promoting the separation of photogenerated electron-hole pairs and forming a synergistic photocatalytic system with doped zinc oxide, exhibiting excellent self-cleaning properties under visible light conditions.

[0015] Preferably, the silane coupling agent is selected from one or a mixture of two of γ-aminopropyltriethoxysilane and γ-methacryloyloxypropyltrimethoxysilane, with a mixing mass ratio of (1-3):1. The amino group of γ-aminopropyltriethoxysilane can react with the carboxyl and hydroxyl groups in the resin to form chemical bonds, and the methacryloyloxy group of γ-methacryloyloxypropyltrimethoxysilane can copolymerize with acrylic monomers. The combined use of the two significantly improves the interfacial bonding force between the filler and the resin matrix, solving the problems of dispersion stability and compatibility of aerogels in water-based coatings.

[0016] Preferably, the functional dispersant combination is a mixture of polyoxyethylene-polyoxypropylene block copolymer and ethylene oxide-propylene oxide-ethylene oxide triblock polymer in a mass ratio of (1.5-2.5):1. This dispersant combination effectively prevents the agglomeration and sedimentation of functional fillers such as aerogels and nano-hollow carbon spheres through a dual mechanism of steric hindrance and electrostatic repulsion, ensuring the long-term storage stability of the coating.

[0017] Preferably, the coating has a solids content of 38%–42%, a viscosity of 8000–14000 mPa·s (25°C, Forecast cup 4), a pH value of 8.3–9.2, and a density of 0.95–1.15 g / cm³. 3 The dry film density is 0.35-0.55 g / cm³. 3 By optimizing the formula composition and adding rheology modifiers, the solid content is reduced from over 43% in traditional formulas to 38%–42%, ensuring both good workability and the heat insulation effect of the coating.

[0018] The second aspect of the present invention provides a method for preparing the above-mentioned multifunctional aerogel composite coating, comprising the following steps: (1) preparing hydrophobically modified silica aerogel; (2) preparing nano-hollow carbon spheres; (3) preparing microcapsule phase change materials; (4) performing surface treatment of functional fillers; (5) preparing functional pigment and filler dispersions; (6) preparing modified emulsion systems; and (7) synthesizing multifunctional aerogel composite coatings.

[0019] In step (1), the hydrophobic modified silica aerogel is prepared using a sol-gel method combined with supercritical drying and surface hydrophobic modification techniques. Tetramethyl tetraethyl orthosilicate and methyltrimethoxysilane are mixed at a molar ratio of (6.5-7.5):(2.5-3.5), and silica sol is prepared by a two-step acid-base catalytic method. After aging, solvent exchange, and supercritical CO2 drying, the aerogel powder with a particle size of 1-5 μm is obtained by gas-phase hydrophobic modification with hexamethyldisilazane and high-energy ball milling. Compared with the prior art, this invention optimizes the number of solvent exchange cycles and supercritical drying parameters, and adds a nitrogen atmosphere heat treatment step, which significantly improves the hydrophobic stability and particle size uniformity of the aerogel.

[0020] Step (2) involves the preparation of hollow carbon nanospheres using a combination of hydrothermal carbonization and high-temperature carbonization techniques. Glucose is used as the carbon source, and polyvinylpyrrolidone (PVP) is used as a soft template. A carbon nanosphere precursor is formed through a hydrothermal reaction, followed by high-temperature carbonization to obtain hollow carbon nanospheres. The carbon nanospheres prepared by this method possess a uniform hollow structure, ultra-thin wall thickness, and ultra-low density, making them one of the innovative components of this invention. Compared to traditional hollow glass microspheres (density 0.15-0.25 g / cm³), these nanospheres exhibit superior performance. 3 The density of the hollow carbon nanospheres is only 0.03-0.08 g / cm³. 3 It also has a higher specific surface area and stronger wave absorption capacity, giving it significant advantages in heat insulation and corrosion protection.

[0021] Step (3) The microcapsule phase change material was prepared using in-situ polymerization. Melamine and formaldehyde were prepolymerized to form a prepolymer, which was then interfacially polymerized in the phase change material emulsion to form the microcapsule wall material. By optimizing the pH value to 4.0-4.5 (current technology typically uses 4.5-5.0), the density and encapsulation efficiency of the wall material were significantly improved, with the microcapsule encapsulation efficiency reaching over 72%, ensuring the long-term stability of the phase change function.

[0022] Step (4) involves surface treatment of the functional fillers, using silane coupling agents to modify the surfaces of titanium dioxide, zinc oxide, and reduced graphene oxide. By introducing resin-compatible functional groups onto the filler surface, the dispersion stability and interfacial bonding force between the filler and the resin matrix are significantly improved.

[0023] In step (5), an innovative hierarchical dispersion strategy was adopted when preparing the functional pigment and filler dispersion. First, reduced graphene oxide was dispersed, then a mixture of titanium dioxide and zinc oxide was dispersed, followed by the sequential addition of nano-hollow carbon spheres, aerogel, and hollow glass microspheres, and finally, microcapsule phase change material was added. This hierarchical dispersion strategy fully considers the differences in density, particle size, and surface properties of different fillers, effectively preventing agglomeration and sedimentation, and ensuring the uniform distribution of each component in the coating.

[0024] In step (6), when preparing the modified emulsion system, the silicone-modified acrylic emulsion and the acrylic-modified polyurethane emulsion are compounded at a mass ratio of (2.8-3.2):(1.8-2.2) to form an interpenetrating network structure. The silicone provides hydrophobicity and weather resistance, while the polyurethane provides adhesion and flexibility. The synergistic effect of the two achieves a balance between hydrophobic properties and mechanical properties.

[0025] The multifunctional aerogel composite coating of the present invention has the following beneficial effects.

[0026] First, superior thermal insulation performance. Through the synergistic effect of multi-scale components—hydrophobically modified silica aerogel (10%–18%), hollow carbon nanospheres (2%–6%), and hollow glass microspheres (2%–5%)—a gradient thermal insulation structure from nanometers (50–200 nm) to micrometers (1–60 μm) is constructed, reducing the coating's thermal conductivity to 0.022–0.032 W / (m·K), a reduction of 45%–65% compared to traditional thermal insulation coatings. The introduction of hollow carbon nanospheres is a key innovation, with their ultra-low density (0.03–0.08 g / cm³). 3 The nanoscale hollow structure effectively suppresses gas convection and radiative heat transfer, and works synergistically with the micron-sized aerogel to achieve a synergistic effect in thermal insulation. Experiments show that, with the same amount of aerogel, adding 3% nano-hollow carbon spheres can further reduce the thermal conductivity by 18% to 25%.

[0027] Second, the active temperature-adaptive anti-condensation capability. The microencapsulated phase change material (3%–10%) achieves active temperature regulation through phase change heat absorption and release during temperature fluctuations, which is one of the core innovations of this invention. When the ambient temperature drops, the phase change material changes from a liquid to a solid state, releasing latent heat of phase change (185-210 J / g), maintaining the coating surface temperature above the dew point temperature and effectively preventing condensation. Thermodynamic calculations show that, based on a 5% phase change material content, the phase change process can release approximately 9.25-10.5 kJ / kg of coating heat, corresponding to a temperature maintenance capability of 4-6°C. Combined with the coating's own thermal insulation properties, the anti-condensation temperature difference can reach 10-15°C. Compared to traditional passive hydrophobic coatings (which can only prevent condensation with a temperature difference of 3-5°C), this invention achieves a synergistic effect of active temperature regulation and passive hydrophobicity. Experimental verification shows that even under extreme conditions of a sudden 15°C drop in ambient temperature, the coating surface remains condense-free, while the control sample shows significant condensation at a temperature difference of only 10°C.

[0028] Third, the system exhibits durable self-cleaning properties under visible light response. The synergistic photocatalytic system constructed from cerium-doped zinc oxide (0.8-3.5 mol%) and P25 titanium dioxide demonstrates excellent self-cleaning performance under visible light conditions. 3+ The 4f level is used as an intermediate level, Ce 4+ The formed oxygen vacancies act as charge carriers, synergistically reducing the band gap of zinc oxide from 3.2 eV to 2.7-2.9 eV, enabling it to respond to visible light. Simultaneously, the anatase / rutile phase interface of P25 forms a bi-heterogeneous structure with the doped zinc oxide, further promoting photogenerated charge separation. Under natural light irradiation, reactive oxygen species (·OH, ·OH, ·OH) are continuously generated on the coating surface. It decomposes organic pollutants (such as H2O2). Methylene blue degradation tests show that the degradation rate reaches 88%–95% within 4 hours, significantly higher than the 65%–75% of the undoped system. After long-term exposure testing (500 hours), the coating still retains more than 85% of the photocatalytic activity, proving the durability of the self-cleaning function.

[0029] Fourth, highly efficient thermo-optical synergistic management capability. Nano-titanium dioxide (3%–8%) and modified zinc oxide (1%–4%) provide solar light reflection (reflectivity 0.82–0.88), while reduced graphene oxide (0.8%–2.5%) regulates infrared emission (emissivity 0.85–0.90), achieving thermo-optical synergistic management of short-wave reflection and long-wave radiation. By precisely controlling the content of reduced graphene oxide between 0.8% and 2.5%, the contradiction between visible light reflection and infrared emission is balanced. High visible light reflectivity is maintained at low content, while the sheet structure of reduced graphene oxide provides high infrared emissivity. Thermal imaging tests show that under direct sunlight (irradiance 800 W / m²), [the system achieves high infrared emissivity]. 2The surface temperature of the coating is 12-18°C lower than that of the substrate and 6-10°C lower than that of traditional white paint.

[0030] Fifth, the multi-layered synergistic long-term corrosion protection. The synergistic effect of organosilicon / polyurethane interpenetrating network resin (34%–50% total content), reduced graphene oxide (0.8%–2.5%), and hollow carbon nanospheres (2%–6%) constructs a triple corrosion protection mechanism of hydrophobic barrier, physical barrier, and chemical passivation. Organosilicon provides surface hydrophobicity (water contact angle 138–145°), blocking the penetration of moisture and corrosive ions; the layered / hollow structure of reduced graphene oxide and hollow carbon nanospheres extends the diffusion path of corrosive media, forming a labyrinth effect; the oxygen-containing functional groups on the surface of reduced graphene oxide can adsorb metal ions, forming a passivation layer on the substrate surface and inhibiting the anodic dissolution process. After salt spray resistance test (5% NaCl, 1800 hours) and weather resistance test (UV 8h / condensation 4h, 2000 hours), the coating showed no obvious blistering, cracking or peeling, and the adhesion remained within level 1, far exceeding traditional anti-corrosion coatings (usually 500-1000 hours).

[0031] Sixth, excellent long-term stability. Surface modification of various fillers using silane coupling agents (0.5%–3%) forms chemical bonds between the fillers and the resin matrix, significantly improving interfacial adhesion. After thermal cycling stability testing (-20°C to 60°C, 500 cycles), the coating's thermal conductivity increased by less than 8%, solar reflectivity decreased by less than 5%, adhesion remained unchanged, and performance retention exceeded 92%. Storage stability testing (6 months at room temperature) showed no delamination, no sedimentation, and viscosity change of less than 15%. These data demonstrate the success of this invention in solving the problems of aerogel dispersion stability and interfacial adhesion.

[0032] Seventh, environmentally friendly with low VOC and excellent workability. Utilizing a fully water-based system, the VOC content is below 4g / L, meeting the strictest environmental standards (GB 18582-2020, VOC≤80g / L). By optimizing the solids content (38%~42%) and adding rheology modifiers (0.3%~1.5%), the coating viscosity is controlled at 8000-14000mPa·s (25°C), exhibiting good leveling and workability. The coating can be applied via spraying, brushing, roller coating, and other methods, suitable for various substrates such as steel, concrete, wood, and aluminum alloys. It has a wide application temperature range (5-40°C) and a large humidity tolerance range (relative humidity 20%~85%), offering high convenience in practical applications.

[0033] Eighth, multifunctional synergistic effect. The core innovation of this invention lies in the synergistic design of multifunctional components. Aerogel, hollow carbon nanospheres, and microcapsule phase change materials synergistically enhance the thermal insulation function; cerium-doped zinc oxide and P25 titanium dioxide synergistically enhance the photocatalytic function; organosilicon / polyurethane resin, reduced graphene oxide, and hollow carbon nanospheres synergistically enhance the anti-corrosion function; the active temperature regulation of microcapsule phase change materials and the passive protection of the coating's hydrophobicity synergistically enhance the anti-condensation function. This multi-dimensional and multi-level synergistic design makes the comprehensive performance of the coating of this invention far exceed the effect of simply adding the components together, truly realizing a synergistic effect. Detailed Implementation

[0034] The technical solution of the present invention will be described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto. Content not described in detail in the specification is common knowledge to those skilled in the art.

[0035] The main raw materials used in the examples are as follows: Tetramethyltetraethyl orthosilicate (TMOS), analytical grade, purity ≥98%, Aladdin Reagent Company; Methyltrimethoxysilane (MTMS), analytical grade, purity ≥97%, Aladdin Reagent Company; Anhydrous methanol, analytical grade, purity ≥99.5%, Sinopharm Chemical Reagent Co., Ltd.; Hexamethyldisilazane (HMDS), analytical grade, purity ≥98%, Aladdin Reagent Company; D-(+)-glucose, analytical grade, purity ≥99.5%, Sinopharm Chemical Reagent Co., Ltd.; Polyvinylpyrrolidone (PVP) K30), average molecular weight approximately 40,000, Aladdin Reagent Company; melamine, industrial grade, purity ≥99%, Jinan Chuangshi Chemical Co., Ltd.; formaldehyde solution (37wt%), analytical grade, Sinopharm Chemical Reagent Co., Ltd.; octadecane, industrial grade, purity ≥96%, phase transition temperature 28°C, Shanghai Maclean Biochemical Technology Co., Ltd.; hexadecane, industrial grade, purity ≥95%, phase transition temperature 18°C, Shanghai Maclean Biochemical Technology Co., Ltd.; sodium dodecyl sulfate (SDS), analytical grade, purity ≥99%, Sinopharm Chemical Reagent Co., Ltd.

[0036] P25 type titanium dioxide (TiO2), average particle size 25 nm, specific surface area 50 ± 15 m² 2 / g, anatase:rutile phase mass ratio approximately 80:20; cerium-doped zinc oxide (Ce-ZnO), nanoscale, doping amount 1.5 mol% (Ce 3+ :Ce 4+ ≈1.5:1), average particle size 35 nm, self-made (preparation method described below); hollow glass microspheres (K series), average particle size 45 μm, density 0.20 g / cm³ 3Compressive strength 28 MPa; Reduced graphene oxide (rGO), average number of layers 6, transverse size 2-4 μm, oxygen content 10 wt%; Organosilicon modified acrylic emulsion, solid content 45±2%, pH value 7.8-8.2, viscosity 650 mPa·s (25°C), Dow Corning; Acrylic modified polyurethane emulsion, solid content 40±2%, pH value 7.2-7.8, viscosity 950 mPa·s (25°C), BASF.

[0037] γ-Aminopropyltriethoxysilane (KH550), industrial grade, purity ≥98%; γ-methacryloyloxypropyltrimethoxysilane (KH570), industrial grade, purity ≥97%; Polyoxyethylene-polyoxypropylene block copolymer (Pluronic F127), average molecular weight approximately 12600, HLB value 18-23, BASF; Ethylene oxide-propylene oxide-ethylene oxide triblock polymer (PEO-PPO-PEO), average molecular weight approximately 14000, HLB value 24-29, Dow Chemical Company; Hydroxyethyl cellulose (HEC), medium viscosity type, 2% aqueous solution viscosity 500 mPa·s (25°C), Dow Chemical Company; Ethylene glycol butyl ether (BC), analytical grade, purity ≥99%, boiling point 171°C, Sinopharm Chemical Reagent Co., Ltd.; Dipropylene glycol Dimethyl ether (DPM), analytical grade, purity ≥99%, boiling point 188°C, Dow Chemical Company; Polydimethylsiloxane defoamer, 10% aqueous dispersion, BYK-011, BYK Chemical Company; Ammonia (NH3·H2O), analytical grade, concentration 25%–28%, Sinopharm Chemical Reagent Co., Ltd.; Hydrochloric acid (HCl), analytical grade, concentration 36%–38%, Sinopharm Chemical Reagent Co., Ltd.; Propylene glycol, industrial grade, purity ≥99.5%, Sinopec Group; Sodium polyacrylate (PAAS), average molecular weight 5000, 30% solid content aqueous solution, Shandong Taihe Chemical Co., Ltd.; Liquid carbon dioxide (CO2), industrial grade, purity ≥99.5%, Hangzhou Fuqiduo Gas Co., Ltd.; High-purity nitrogen (N2), purity ≥99.999%, Hangzhou Fuqiduo Gas Co., Ltd.

[0038] The preparation method of cerium-doped zinc oxide is as follows: Zinc nitrate (Zn(NO3)2·6H2O) and cerium nitrate (Ce(NO3)3·6H2O) were dissolved in deionized water at a Zn:Ce molar ratio of 98.5:1.5 to prepare a mixed solution with a total concentration of 0.1M. Under vigorous stirring, 2M sodium hydroxide solution was added dropwise to adjust the pH to 10-11, resulting in a white precipitate. Stirring was continued for 30 minutes, and the mixture was aged for 2 hours. The precipitate was collected by centrifugation, washed three times alternately with deionized water and anhydrous ethanol, and then vacuum dried at 80°C for 12 hours. The dried precursor was calcined in a muffle furnace under air atmosphere at a rate of 5°C / min to 550°C, held at that temperature for 3 hours, and then naturally cooled to room temperature. The resulting powder was then ground to obtain light yellow cerium-doped zinc oxide nanoparticles.

[0039] Example 1

[0040] The multifunctional aerogel composite coating of this embodiment is composed of the following components by weight percentage: 12% hydrophobic modified silica aerogel, 28% organosilicon modified acrylic emulsion, 15% acrylic modified polyurethane emulsion, 3% nano hollow carbon spheres, 4% hollow glass microspheres, 5% nano titanium dioxide, 2.5% cerium-doped zinc oxide, 5% microcapsule phase change material, 1.2% reduced graphene oxide, 1.5% silane coupling agent (KH550:KH570 mass ratio of 2:1), 2.5% functional dispersant combination, 0.4% pH adjuster, 2.5% film-forming aid, 0.8% rheology modifier, 0.3% defoamer, 1.0% antifreeze, and the balance being deionized water to 100%.

[0041] The specific preparation method is as follows. First, hydrophobically modified silica aerogel is prepared. In a 500 mL three-necked flask, 26.4 g of tetramethyl orthosilicate (TMOS) and 10.2 g of methyltrimethoxysilane (MTMS) are mixed in a molar ratio of 7:3, and 120 mL of anhydrous methanol is added as a co-solvent. The flask is placed in an ice-water bath, and 6.5 g of deionized water is slowly added dropwise (over approximately 15 minutes) with mechanical stirring (700 rpm) to achieve a water / methanol / silanol ester molar ratio of 4:12:1. Subsequently, 1.5 mL of 0.01 M hydrochloric acid solution is added as a catalyst, and stirring is continued at room temperature for 30 minutes. The solution gradually changes from clear to a transparent sol.

[0042] Next, while continuously stirring, dilute ammonia (0.5M) was added dropwise to adjust the pH to 9.2, and the sol began to gel. A uniform gel formed after approximately 60 minutes. The gel was sealed in a container and aged in a 60°C incubator for 24 hours. The aged gel was translucent white and possessed a certain degree of mechanical strength.

[0043] Then, cut the aged gel into small pieces (about 1cm). 3The gel was placed in a high-pressure reactor, and excess anhydrous ethanol was added. The mixture was then soaked at room temperature for 12 hours for the first solvent exchange. The process was repeated three times, each time for 12 hours, to ensure that the water in the gel pores was completely replaced by ethanol.

[0044] After solvent exchange, the gel was transferred to a supercritical drying apparatus. Liquid CO2 was first introduced to replace the ethanol, with the temperature controlled at 10°C, pressure at 6 MPa, and flow rate at 50 mL / min for 24 hours, until no ethanol was detected in the effluent. Then, the temperature was raised to 40°C, and the pressure was simultaneously increased to 10.5 MPa, bringing the CO2 into a supercritical state (the critical point of CO2 is 31.1°C and 7.38 MPa). This supercritical state was maintained for 2 hours, followed by a slow release of CO2 at a rate of 10 mL / min over approximately 4 hours to reduce the pressure to atmospheric pressure, completing the drying process. The resulting aerogel was milky white with a density of approximately 90 kg / m³. 3 .

[0045] Finally, the dried aerogel was placed in a tube furnace and treated with hexamethyldisilazane (HMDS) vapor (generated by evaporation of liquid HMDS at 100°C) at 120°C for 2 hours. This allowed the silanol groups (Si-OH) on the aerogel surface to react with HMDS to form hydrophobic silanyl groups (Si-CH3). After hydrophobic modification, the aerogel was heat-treated at 250°C in a nitrogen atmosphere (flow rate 80 mL / min) for 1 hour to remove unreacted HMDS and byproducts. After cooling to room temperature, the aerogel was dry-milled for 30 minutes using a high-energy ball mill at 2200 rpm and a ball-to-particle ratio of 10:1 to obtain hydrophobic aerogel powder with an average particle size of 3 μm.

[0046] Characterization results showed that the prepared hydrophobic aerogel had a thermal conductivity of 0.017 W / (m·K) (Hot Disk method) and a density of 90 kg / m³. 3 (Volume mass method), specific surface area is 560 m² 2 / g (BET method), water contact angle is 157° (contact angle measuring instrument), D measured by laser particle size analyzer 50 It is 3.2μm, D 90 It is 4.8μm.

[0047] Next, hollow carbon nanospheres were prepared. 9.0 g of D-(+)-glucose and 1.8 g of polyvinylpyrrolidone (PVP K30) were dissolved in 180 mL of deionized water to prepare a 5% glucose solution (containing 1% PVP). The solution was magnetically stirred at room temperature for 30 minutes until completely dissolved. Then, while continuing to stir, concentrated ammonia was added dropwise to adjust the pH to 10.0. Stirring was continued for 40 minutes until the solution became a pale yellow and homogeneous state.

[0048] The above solution was transferred to a 250 mL hydrothermal reactor lined with polytetrafluoroethylene (PTFE) (75% filling), the lid was tightened, and the reactor was placed in a constant temperature oven at 180°C for 8 hours. During the reaction, glucose underwent hydrothermal carbonization, forming carbon sphere precursors under the soft template of PVP. After the reaction was completed, the reactor was allowed to cool naturally to room temperature.

[0049] Upon opening the reaction vessel, the solution was dark brown with a black solid precipitate. The solid product was collected by centrifugation (8000 rpm, 10 minutes), washed three times with deionized water, and then twice with anhydrous ethanol to remove residual glucose, PVP, and soluble carbonized products. The washed solid was then dried in a vacuum oven at 90°C for 12 hours.

[0050] The dried carbon sphere precursor (approximately 3.5 g) was placed in a corundum boat and pushed into the isothermal zone of a tube furnace (OTF-1200X). High-purity nitrogen gas (flow rate 200 mL / min) was introduced and purged for 30 minutes to remove air from the tube. Under nitrogen protection, the temperature was increased to 850°C at a rate of 6°C / min and held at that temperature for 2.5 hours for high-temperature carbonization. During carbonization, the precursor underwent further dehydration and deoxygenation, forming a stable carbon sphere structure. The PVP template completely decomposed and volatilized, leaving a hollow structure. After carbonization, the precursor was naturally cooled to room temperature to obtain black nano-hollow carbon sphere powder (approximately 1.8 g, yield approximately 20%).

[0051] The carbon spheres exhibit a uniform hollow structure with an average outer diameter of approximately 120 nm and a wall thickness of approximately 12 nm. The hollow structure is clearly visible, indicating good dispersion and uniform particle size distribution. The BET specific surface area is 850 m². 2 / g, pore volume 1.2cm 3 / g.

[0052] Microcapsule phase change materials were prepared again. The first step was the prepolymerization of melamine-formaldehyde prepolymer. In a 500 mL three-necked flask, 12.6 g of melamine and 38.5 g of formaldehyde solution (37 wt%, equivalent to 14.2 g of pure formaldehyde) were added, with a molar ratio of melamine to formaldehyde of 1:3. 100 mL of deionized water was added, and under mechanical stirring, dilute sodium hydroxide solution was added dropwise to adjust the pH to 8.5. The flask was placed in a constant temperature water bath and heated to 80°C, where the mixture was stirred for 2 hours. During the reaction, melamine and formaldehyde underwent an addition reaction to form hydroxymethyl melamine prepolymer, and the solution gradually changed from turbid to clear. After the reaction was complete, the solution was cooled to 60°C for later use.

[0053] The second step is to prepare the octadecane emulsion. In another 500 mL flask, add 28.0 g of octadecane and 0.3 g of sodium dodecyl sulfate (SDS), and then add 200 mL of deionized water. Heat in a 60°C water bath until the octadecane is completely melted (octadecane melting point 28°C), and then emulsify using a high-shear homogenizer at 12000 rpm for 5 minutes to form a milky white octadecane emulsion. The emulsion droplet diameter is approximately 3-5 μm (measured by a laser particle size analyzer).

[0054] The third step is the microencapsulation reaction. Under vigorous stirring (500 rpm), the prepolymer solution prepared in step one is slowly added dropwise to the octadecane emulsion from step two at a rate of 2 mL / min. During the addition, dilute hydrochloric acid solution is added dropwise to adjust the pH to 4.2. Under this pH condition, hydroxymethyl melamine undergoes a condensation reaction, gradually forming a melamine-formaldehyde resin shell on the surface of the octadecane droplets. The temperature is raised to 70°C, and the reaction continues for 4 hours. The stirring speed is kept constant throughout the reaction to avoid microcapsule breakage.

[0055] After the reaction was complete, the mixture was cooled to room temperature. The microcapsules were collected by filtration through a 200-mesh sieve (the sieve can retain particles larger than 74 μm, retaining microcapsules of 5-10 μm), and washed three times with 500 mL of deionized water each time to remove unreacted monomers and surfactants. The collected microcapsules were dried in a vacuum oven at 40°C for 24 hours to obtain a white powdery microcapsule phase change material (approximately 23 g, yield approximately 82%). The microcapsules were regularly spherical with a smooth and dense surface, an average particle size of 7.5 μm, and a particle size distribution D. 10 It is 5.2 μm, D 50 It is 7.5μm, D 90 The microcapsule has a diameter of 9.8 μm and a wall thickness of approximately 0.8 μm. Differential scanning calorimetry (DSC) testing showed that the microcapsule exhibited a significant endothermic peak at 29.8°C, with a peak value of 188 J / g. Theoretically, the phase transition enthalpy of pure octadecane is 243 J / g, resulting in a calculated encapsulation efficiency of (188 / 243) × 100% = 77.4%. Thermogravimetric analysis (TGA) showed that the microcapsule experienced a weight loss of less than 2% below 250°C, indicating that the shell material effectively encapsulates and protects the core material.

[0056] Next, the surface treatment of the functional filler is carried out. The first step is the surface modification of titanium dioxide / zinc oxide. In a 250mL beaker, 50.0g of P25 type titanium dioxide and 12.5g of cerium-doped zinc oxide (mass ratio 4:1) are weighed, 150mL of deionized water is added, and 0.3g of sodium polyacrylate (0.48% of the powder mass) is added as a dispersing agent. The mixture is ultrasonically dispersed for 30 minutes at 300W using an ultrasonic cleaner (KQ-500DE, Kunshan Shumei Ultrasonic Instrument Co., Ltd.) to obtain a uniform suspension.

[0057] Add 1.25 g of γ-methacryloxypropyltrimethoxysilane (KH570) (2% of the powder mass) to the above suspension and mechanically stir (500 rpm) in a 60°C water bath for 2 hours. The methoxy group of KH570 undergoes a hydrolytic condensation reaction with the hydroxyl group on the powder surface to form a silane coupling layer on the powder surface. The methacryloxy group extends outward, providing compatibility with acrylic resin.

[0058] After the reaction was complete, the solid product was collected by centrifugation (6000 rpm, 10 min), washed twice with anhydrous ethanol to remove unreacted silane and sodium polyacrylate. The product was then dried in a vacuum oven at 60°C for 12 hours to obtain a surface-modified titanium dioxide / zinc oxide mixed powder (approximately 61.5 g, considering silane coating).

[0059] The second step is the surface functionalization of reduced graphene oxide. 3.0 g of reduced graphene oxide (rGO) was weighed into a 100 mL beaker and dispersed in a mixed solution of 70 mL isopropanol and 30 mL deionized water (volume ratio 7:3). The solution was ultrasonically treated for 30 minutes at 400 W in intermittent mode (8 seconds on, 3 seconds off) to ensure complete exfoliation and dispersion of the rGO, resulting in a uniformly black solution.

[0060] Add 0.15 g of γ-aminopropyltriethoxysilane (KH550) (5% of the mass of rGO) to the above rGO dispersion, and mechanically stir (300 rpm) in a 50°C water bath for 4 hours. The ethoxy group of KH550 undergoes a condensation reaction with the residual hydroxyl and carboxyl groups on the surface of rGO, and the amino group extends outward, providing compatibility and reactivity with the resin.

[0061] After the reaction was complete, the solid product was collected by centrifugation (5000 rpm, 10 min) and washed twice with anhydrous ethanol. It was then dried in a vacuum oven at 60°C for 12 hours to obtain functionalized reduced graphene oxide (approximately 3.1 g).

[0062] Contact angle tests showed that the water contact angle of the unmodified titanium dioxide powder was less than 10° (superhydrophilic), while the water contact angle increased to 65° after modification, proving that the silane grafting was successful and improved the hydrophobicity. Thermogravimetric analysis showed that the modified powder exhibited decomposition weight loss of organosilane (approximately 2.5 wt%) at 450-600°C, which is consistent with the theoretical grafting amount.

[0063] Then, the functional pigment and filler dispersion was prepared. The first step was to prepare the dispersant solution. In a 2L stainless steel high-speed dispersion tank, 550g of deionized water, 8g of ammonia (to adjust pH), 30g of propylene glycol (cosolvent and antifreeze), 16.7g of Pluronic F127 (polyoxyethylene-polyoxypropylene block copolymer), and 8.3g of PEO-PPO-PEO triblock polymer (the two dispersants had a mass ratio of 2:1, and the total amount accounted for 2.5% of the formulation) were added. The mixture was stirred at 800rpm for 10 minutes in a high-speed disperser (FSJ-400, Shanghai Modern Environmental Engineering Technology Co., Ltd.) to form a uniform, light yellow dispersant solution.

[0064] The second step is the hierarchical dispersion of the functional filler. The dispersant solution is heated to 30°C and the speed is increased to 1500 rpm. First, 12g of functionalized reduced graphene oxide is slowly added (completely over about 5 minutes), and dispersed at 1500 rpm for 20 minutes. The layered structure of rGO is prone to aggregation, requiring preferential dispersion and thorough exfoliation under high shear.

[0065] Then, 61.5g of surface-modified titanium dioxide / zinc oxide mixed powder was added in batches (3 times, 10 minutes apart each time), while the rotation speed was increased to 2500 rpm, and the mixture was dispersed for 30 minutes under these conditions. The high rotation speed and high shear force can break down the agglomerates and allow the nanoparticles to be fully dispersed.

[0066] Next, reduce the rotation speed to 1200 rpm, add 30g of hollow carbon nanospheres, and disperse for 25 minutes. Since the hollow carbon nanospheres have extremely low density, they need to be added slowly at a moderate rotation speed to avoid incorporating too many air bubbles.

[0067] Then, after thoroughly mixing 120g of hydrophobic aerogel powder and 40g of hollow glass microspheres, slowly add the mixture in batches (5 times, 5 minutes apart each time), dispersing at 1200 rpm for 25 minutes. Since both the aerogel and microspheres have low densities, rapid addition will cause them to float on the liquid surface; therefore, they must be added slowly and thoroughly stirred.

[0068] Finally, reduce the speed to 800 rpm and slowly add 50g of microcapsule phase change material (in 3 portions, 5 minutes apart each time), and gently disperse under these conditions for 15 minutes. Microcapsules are brittle particles and are easily damaged by high-speed stirring; therefore, a low-speed, gentle dispersion is used.

[0069] After all components were added, an ultrasonic disperser (with a 20mm diameter probe) was used at 300W in intermittent mode (6 seconds on, 2 seconds off) for 10 minutes to further break up the agglomerates and improve the dispersion uniformity. After ultrasonication, a grayish-white functional pigment and filler dispersion (approximately 930g) was obtained, and no obvious stratification or sedimentation was observed upon standing.

[0070] The third step is dispersion quality testing. The dispersion fineness is tested using a scraper fineness meter and is confirmed to be 18 μm (target ≤20 μm). The particle size distribution is determined using a laser particle size analyzer. 50 It is 3.8μm, D 90 The particle size was 12.5 μm. Microscopic observation (400x) showed that various fillers such as aerogels, carbon spheres, and microcapsules were uniformly dispersed, with no obvious large particle agglomerates.

[0071] Next, the modified emulsion system was prepared. In another 1L beaker, 280g of silicone-modified acrylic emulsion and 150g of acrylic-modified polyurethane emulsion (mass ratio approximately 1.87:1, within the formulation range of 2.8-3.2:1.8-2.2) were weighed and mixed evenly under mechanical stirring (500rpm).

[0072] Add 8g of hydroxyethyl cellulose (HEC) as a rheology modifier (0.8% of the total formulation). HEC swells in the aqueous phase to form a network structure, significantly improving the viscosity and thixotropy of the system. Stir for 30 minutes to allow the HEC to fully swell.

[0073] A mixture of 18.8 g of ethylene glycol butyl ether and 6.2 g of dipropylene glycol methyl ether was added as a film-forming aid (mass ratio of 3:1, total amount 2.5% of the formulation). The film-forming aid can lower the minimum film-forming temperature (MFFT) of the emulsion and improve the film-forming properties and leveling of the coating.

[0074] Stir at 1000 rpm for 15 minutes to obtain a homogeneous modified emulsion system (approximately 463 g). Let the beaker stand for 30 minutes to remove air bubbles entrained during stirring.

[0075] Finally, a multifunctional aerogel composite coating was synthesized. The modified emulsion system (463g) prepared above was transferred into a dispersion tank in a high-speed disperser, and stirring was started (1200rpm).

[0076] The prepared functional pigment and filler dispersion (930 g) was added dropwise to the emulsion system at a slow rate of 5 mL / min. The stirring speed was kept constant during the addition process to avoid excessively high local concentrations that could lead to flocculation. The addition time was approximately 3 hours (actual addition time was approximately 186 minutes).

[0077] After adding all of the pigments and fillers, continue stirring at 1200 rpm for 30 minutes to ensure that the pigments and fillers are evenly dispersed in the emulsion.

[0078] Add 3g of polydimethylsiloxane defoamer (10% aqueous dispersion, 0.3% active ingredient), and stir at 800rpm for 5 minutes to remove bubbles generated during mixing.

[0079] Adjust the pH to 8.6 using dilute ammonia (target range 8.3-9.2). Test the viscosity using a Ford Cup No. 4; the result should be 95 seconds (approximately 11500 mPa·s, 25°C), within the target viscosity range (8000-14000 mPa·s corresponds to a Ford Cup outflow time of approximately 70-120 seconds). If the viscosity is too high, add a small amount of deionized water to adjust; if the viscosity is too low, add HEC solution to thicken.

[0080] Filtering through a 200-mesh stainless steel filter (74μm pore size) removes any undispersed particles and impurities that may be present.

[0081] Approximately 1400g of the finished multifunctional aerogel composite coating was obtained (considering preparation losses and sampling). The coating is a uniform grayish-white color, without stratification or sedimentation, and exhibits good flowability.

[0082] The basic physicochemical properties of the coating were tested as follows: Solid content: 39.8% (GB / T 1725-2007, dried at 105°C for 1 hour); Viscosity: 11500 mPa·s, 25°C (French cup flow time 95 seconds); pH value: 8.6 (GB / T 1717-1986, pH meter method); Density: 1.05 g / cm³ (GB / T 6750-2007, specific gravity cup method, 25°C); VOC content is 3.2 g / L (GB / T23986-2009, gas chromatography).

[0083] The storage stability test results are as follows. After 6 months of storage at room temperature (25°C), there was no stratification, no sedimentation, no flocculation, and the viscosity change was less than 12%, maintaining good performance. After accelerated aging (50°C, 14 days), the viscosity change was less than 15%, and the solid content change was less than 1%. After freeze-thaw cycles (-5°C to 25°C, 5 times), there was no change in appearance, the viscosity change was less than 10%, and there was no demulsification.

[0084] The coating application and coating performance testing are as follows. For substrate treatment, Q235 steel plate (150mm×100mm×2mm) was selected. It was degreased with acetone, sanded with 180-grit sandpaper until the roughness Ra was 1.5-2.0μm, blown away the floating dust with compressed air, and wiped clean with anhydrous ethanol.

[0085] The coating method used was spraying (HVLP spray gun, spraying pressure 0.25MPa, nozzle diameter 1.5mm). The room temperature was 25°C, and the relative humidity was 55%.

[0086] The coating system includes a base coat (anti-corrosion layer) with a high rGO content formulation (2.0% rGO content, 10% aerogel content), a wet film thickness of approximately 85 μm, and a dry film thickness of approximately 60 μm; a middle coat (heat insulation layer) with a standard formulation (Example 1), a wet film thickness of approximately 120 μm, and a dry film thickness of approximately 90 μm; and a top coat (reflective self-cleaning layer) with a high TiO2 content formulation (8% TiO2 content, 14% aerogel content), a wet film thickness of approximately 60 μm, and a dry film thickness of approximately 45 μm. The total wet film thickness is approximately 265 μm, and the total dry film thickness is approximately 195 μm (measured at 192 μm using a PosiTector 6000 coating thickness gauge).

[0087] Curing conditions are natural drying at room temperature (25°C), with a surface drying time of approximately 1 hour and a complete drying time of approximately 6 hours (GB / T1728-1979, finger pressure method). Complete curing requires 7 days (at room temperature) or can be accelerated by baking at 60°C for 2 hours.

[0088] Coating performance tests were conducted after 7 days of curing at room temperature. The dry film thickness was 192 μm (GB / T 1764, target 170-220 μm); the dry film density was 0.48 g / cm³. 3(Weighing / Volume Method); Thermal conductivity: 0.027 W / (m·K) (ASTM C518, HotDisk TPS 2500S, 25°C test); Solar reflectance: 0.85 (ASTM C1549, Lambda 950 UV-Vis-NIR spectrophotometer, 300-2500nm integration); Infrared emissivity: 0.88 (ASTM C1371, emissivity meter, ET-200, 8-14μm); Water contact angle: 141° (ASTM D7334, contact angle meter, JC2000D1, static contact angle); Adhesion: Grade 1 (GB / T 9286, cross-cut test, 2mm×2mm, 100 divisions); Flexibility: 1mm pass (GB / T 6742, shaft bending test, no cracking or peeling); Pencil hardness: 2H (GB / T 6739); Impact resistance: 50 kg·cm (GB / T 1732, Impact tester, front view, no cracking); Abrasion resistance loss of 0.8g (GB / T 1768, Falling sand method, 1kg sand, 1m height); Salt spray resistance test 1800 hours (ASTM B117, Salt spray chamber, 5% NaCl, 35°C, no blistering or rusting); Acid resistance test after immersion in 5% H2SO4 for 48 hours showed no change (GB / T 9274, room temperature); Alkali resistance test after immersion in 5% NaOH for 48 hours showed no change (GB / T 9274, room temperature); Weather resistance test 2000 hours (ASTM G154, UV aging chamber, UV...) 8h (60°C) / 4h (50°C) condensation, no obvious powdering or peeling); photocatalytic activity test showed 92% degradation of methylene blue after 4 hours (methylene blue degradation method, UV-Vis spectrophotometer, visible light irradiation, 5mg / L methylene blue solution); anti-condensation performance test showed ΔT of 12.5°C (temperature difference test method, artificial climate chamber, sudden drop of 15°C, no condensation on the surface); thermal cycling stability test showed performance retention of more than 95% after 500 cycles (custom test, cold and hot cycling chamber, -20°C↔60°C, 2 hours / cycle).

[0089] The coating forms a dense and uniform porous network structure, with functional fillers such as aerogel particles, hollow carbon nanospheres, hollow glass microspheres, and microcapsule phase change materials uniformly distributed within the resin matrix. Aerogel particles (1-5 μm) and hollow carbon nanospheres (0.05-0.2 μm) form a multi-scale thermal insulation network, with the gaps between aerogel particles filled by the carbon nanospheres, further reducing the thermal conductivity. The microcapsule phase change materials (5-10 μm) maintain a complete spherical morphology, with a dense and smooth shell, showing no damage, demonstrating that the mild dispersion and mixing process effectively protects the microcapsule structure. The resin forms a good coating and wetting effect on the filler surface, demonstrating the significant effect of silane coupling agent modification. The filler and resin interface are tightly bonded, with no obvious interface cracks or voids observed. The sheet structure of reduced graphene oxide is randomly oriented in the matrix, forming a labyrinthine shielding layer that effectively blocks the penetration and diffusion of corrosive media.

[0090] The coating mechanism is analyzed as follows. Regarding the multi-scale synergistic thermal insulation mechanism, the thermal insulation performance of the coating in this invention stems from the synergistic effect of the multi-scale pore structure. The nanopores (pore size 10-50 nm) inside the aerogel are close to the mean free path of air molecules (approximately 68 nm at room temperature and pressure), located in the Knudsen diffusion region. Gas convection is significantly suppressed, and heat transfer mainly relies on molecular diffusion, resulting in extremely low thermal conductivity. The cavity size of the nano-hollow carbon spheres (outer diameter 50-200 nm, inner diameter 25-175 nm) synergizes with the aerogel pores, further refining the pore network and forming a nanoscale air interlayer. Hollow glass microspheres provide micron-scale gas cavities (inner diameter approximately 30-50 μm), enhancing the thermal insulation effect on a macroscopic scale. This multi-scale synergy from nano to micro effectively suppresses convection, conduction, and radiative heat transfer of gas molecules, achieving an extremely low thermal conductivity.

[0091] Theoretical calculations show that the effective thermal conductivity of the coating can be estimated by the Maxwell-Eucken model as λ. eff =λ matrix × [(2λ matrix + λ filler - 2φ(λ matrix - λ filler )) / (2λ matrix + λ filler + φ(λ matrix - λ filler ))], where λ matrix The thermal conductivity of the resin matrix is ​​approximately 0.20 W / (m·K), λ fillerThe thermal conductivity of the fillers is a weighted average of approximately 0.025 W / (m·K) for aerogel (0.017 W / (m·K), nano-hollow carbon spheres (approximately 0.01 W / (m·K), and hollow glass microspheres (approximately 0.05 W / (m·K)). φ represents the volume fraction of the filler (approximately 30 vol%). The calculated λ... eff The value is approximately 0.030 W / (m·K), which is basically consistent with the measured value of 0.027 W / (m·K). The value is slightly lower than the calculated value, which may be related to the thermal resistance of the filler interface.

[0092] Regarding the active temperature-adaptive anti-condensation mechanism, when the temperature of the microcapsule phase change material approaches the phase change temperature (27-32°C), a liquid-solid or solid-liquid phase change occurs, absorbing or releasing a large amount of latent heat to maintain a relatively stable coating surface temperature. When the ambient temperature drops sharply (such as at night or when cold air arrives), the coating surface temperature decreases, and the octadecane inside the microcapsules gradually solidifies from a liquid state to a solid state, releasing approximately 185-210 J / g of latent heat of phase change.

[0093] Taking Example 1 as an example, with a microcapsule content of 5% (50g / kg coating), the heat released during the phase change process is Q = m × ΔH = 50g × 188J / g = 9400J = 9.4kJ. Assuming the coating mass is 1kg and the specific heat capacity is approximately 1.8kJ / (kg·K) (weighted average of resin and filler), the heat released during the phase change can maintain a temperature ΔT = Q / (m ×c) = 9.4kJ / (1kg × 1.8kJ / (kg·K)) = 5.2°C. In reality, due to heat exchange between the coating and the substrate and the environment, the actual temperature maintenance capability is slightly lower, but still within the range of 3-5°C. Combined with the thermal insulation protection provided by the coating's low thermal conductivity (0.027W / (m·K)) and the water vapor barrier provided by the surface hydrophobicity (water contact angle 141°), the overall anti-condensation temperature difference of the coating can reach 10-15°C.

[0094] The phase transition process is reversible. During the day, as the temperature rises, solid octadecane absorbs heat and melts into a liquid state, absorbing heat from the environment and reducing the surface temperature rise; at night, as the temperature drops, liquid octadecane releases heat and solidifies into a solid state, maintaining the surface temperature. This active temperature adaptive regulation is the core innovation of this invention, distinguishing it from traditional passive anti-condensation coatings.

[0095] Regarding the visible light-responsive photocatalytic self-cleaning mechanism, the synergistic photocatalytic mechanism of cerium-doped zinc oxide and P25 titanium dioxide is as follows. First, there is bandgap modulation. Pure zinc oxide has a bandgap of 3.2 eV and can only respond to ultraviolet light (wavelength less than 387 nm). After cerium doping, Ce... 3+ The 4f level (approximately -5.3 eV) introduces an intermediate level between the conduction band bottom (-4.19 eV) and valence band top (-7.39 eV) of zinc oxide, serving as a springboard for electronic transitions and reducing the energy required for photoexcitation. Simultaneously, Ce...4+ Replace part of Zn 2+ The formation of oxygen vacancies helps maintain charge balance, and the donor levels generated by these oxygen vacancies also contribute to reducing the band gap. The combined effect reduces the band gap of doped zinc oxide to 2.7-2.9 eV, corresponding to wavelengths of approximately 430-460 nm (blue visible light), thus expanding the photoresponse range.

[0096] Secondly, the heterojunction promotes charge separation. P25 titanium dioxide comprises anatase (band gap 3.2 eV) and rutile (band gap 3.0 eV), forming a Type-II heterojunction at the interface. The conduction band bottom of the anatase phase (-4.21 eV) is higher than that of the rutile phase (-4.05 eV), and there is also a difference in the valence band top. Electrons generated by photoexcitation transfer from the anatase conduction band to the rutile conduction band, while holes are transferred in the opposite direction, achieving charge spatial separation and extending charge lifetime. The conduction band bottom (-4.0 eV) of zinc oxide doped with P25 forms a multi-level heterojunction, further promoting charge separation.

[0097] Thirdly, there is the generation of reactive oxygen species. Electrons (e) generated by photoexcitation... ) and holes (h The electrons migrate to the catalyst surface and undergo redox reactions. The electronic reaction is O2 + e-. - → (Superoxide anion free radical); Hole reaction is H2O + h + →·OH (hydroxyl radical) + H + Further reactions include +2H + +e - → H2O2 (hydrogen peroxide). These reactive oxygen species (·OH, ... H2O It has strong oxidizing properties and can decompose organic pollutants (such as oil, air pollutants, microbial metabolites, etc.) into CO2 and H2O, thus achieving a self-cleaning function.

[0098] Methylene blue degradation experiments demonstrated that under visible light irradiation (500W xenon lamp, cutoff less than 420nm ultraviolet light), the degradation rate of methylene blue reached 92% within 4 hours, which was significantly higher than that of the undoped system (65%) and pure P25 (45%), confirming the synergistic photocatalytic effect of cerium-doped zinc oxide and P25.

[0099] Regarding the thermo-optical synergistic management mechanism, the coating's thermo-optical management strategy involves reflecting short-wavelength light and radiating long-wavelength light. The first is short-wavelength reflection. Nano-titanium dioxide and zinc oxide exhibit strong scattering and reflection of ultraviolet and visible light from sunlight. The average particle size of P25, at 25 nm, is close to 1 / 20 to 1 / 10 of the visible light wavelength, falling within the Rayleigh scattering range and exhibiting high scattering efficiency. Zinc oxide has a band gap of 2.8 eV (after doping), corresponding to a wavelength of approximately 443 nm (blue light). It strongly absorbs and reflects wavelengths below blue light (ultraviolet light, short-wavelength blue light), while transmitting or scattering longer wavelengths of visible and near-infrared light. The synergistic effect of these two components results in a coating with a high overall reflectivity (0.85) for the solar spectrum of 300-2500 nm, effectively reducing the absorption of solar radiation.

[0100] Secondly, there is long-wave radiation. Reduced graphene oxide (rGO) is a black material with strong absorption and emission capabilities for infrared light. The layered structure and oxygen-containing functional groups on the surface of rGO endow it with high infrared emissivity (0.85-0.90). When the coating absorbs solar radiation or ambient heat, causing the temperature to rise, rGO acts as an emission center, radiating heat outward in the atmospheric window band of 8-14 μm (where the atmosphere absorbs less infrared radiation and has high transmittance), thus achieving passive cooling.

[0101] Thirdly, it addresses the balance between two opposing forces. rGO is a black material, and a high content reduces visible light reflectivity. This invention precisely controls the rGO content (0.8%–2.5%) to provide sufficient infrared emissivity while maintaining high visible light reflectivity. Experiments show that with an rGO content of 1.2% (Example 1), the solar reflectivity is 0.85 and the infrared emissivity is 0.88, achieving the optimal balance between reflection and emission.

[0102] Thermal imaging tests show that under direct sunlight (irradiance 800W / m²), 2 Under these conditions, the surface temperature of the coating of the present invention is 15°C lower than that of the uncoated substrate and 8°C lower than that of ordinary white paint, proving the effectiveness of thermo-photonic synergistic management.

[0103] Regarding the multi-faceted synergistic anti-corrosion mechanism, the long-lasting anti-corrosion performance of the coating stems from a triple mechanism of "hydrophobic barrier - physical barrier - chemical passivation." The first is the hydrophobic barrier. The main chain of the silicone resin has a Si-O structure, with -CH3 (methyl) side chains, giving the coating surface low surface energy and hydrophobicity. With a water contact angle of 141°, it effectively blocks moisture and water-soluble corrosive ions (Cl). - , (etc.) penetrate into the coating. Hydrophobicity also reduces the adsorption of pollutants on the coating surface, facilitating self-cleaning by rainwater.

[0104] Secondly, there is physical barrier effect. The sheet-like structure of reduced graphene oxide (2-4 μm lateral dimension, approximately 2-6 nm thickness) is randomly oriented in the coating, forming an overlapping arrangement similar to tiles. For corrosive media to penetrate the substrate surface, they must bypass these sheets, significantly extending the diffusion path and creating a labyrinth effect. The spherical shell structure of the hollow carbon nanospheres also serves as a barrier. Theoretical calculations show that 5 vol% sheet-like filler can extend the diffusion path by 3-5 times.

[0105] Thirdly, chemical passivation. This involves reducing the oxygen-containing functional groups (carboxyl-COOH, hydroxyl-OH, carbonyl C=O, etc.) remaining on the surface of reduced graphene oxide, which affect the metal ions (Fe). 2+ Fe 3+ (e.g., α-glucose) possesses chelating adsorption capabilities. When trace amounts of corrosive media penetrate to the substrate surface, rGO adsorbs metal ions, forming a passivation layer on the substrate surface, inhibiting the anodic dissolution process (Fe → Fe). 2+ +2e - This slows down the corrosion rate.

[0106] The triple mechanism works synergistically, enabling the coating to withstand 1800 hours of salt spray in a 5% NaCl environment without blistering or rusting, far exceeding the 500-1000 hours of traditional anti-corrosion coatings.

[0107] Example 2

[0108] The multifunctional aerogel composite coating of this embodiment is composed of the following components by weight percentage: 10% hydrophobic modified silica aerogel, 30% organosilicon modified acrylic emulsion, 13% acrylic modified polyurethane emulsion, 4% nano hollow carbon spheres, 3% hollow glass microspheres, 6% nano titanium dioxide, 3% cerium-doped zinc oxide (doping amount 2.5 mol%), 7% microcapsule phase change material, 1.8% reduced graphene oxide, 2% silane coupling agent (KH550:KH570 mass ratio of 1:1), 3% functional dispersant combination, 0.5% pH adjuster, 3% film-forming aid, 1.0% rheology modifier, 0.4% defoamer, 1.3% antifreeze, and the balance being deionized water to 100%.

[0109] The preparation method was basically the same as in Example 1, but with the following adjustments: When preparing the hydrophobic modified silica aerogel, the molar ratio of tetramethyl tetraethyl orthosilicate (TMOS) to methyltrimethoxysilane (MTMS) was adjusted to 6.8:3.2, the pH was adjusted to 9.4, the aging temperature was increased to 62°C, and the aging time was extended to 26 hours. The obtained hydrophobic aerogel had a thermal conductivity of 0.016 W / (m·K) and a density of 105 kg / m³. 3 Specific surface area is 580m² 2 / g, water contact angle 160°, particle size D 50 It is 2.5μm.

[0110] In preparing hollow carbon nanospheres, the mass ratio of glucose to PVP was adjusted to 1:0.20, the pH was adjusted to 10.3, the hydrothermal reaction temperature was increased to 185°C, the reaction time was extended to 8.5 hours, and the carbonization temperature was increased to 870°C. The obtained hollow carbon nanospheres had an average outer diameter of approximately 150 nm, a wall thickness of approximately 10 nm, and a specific surface area of ​​920 m². 2 / g.

[0111] In preparing the microcapsule phase change material, a mixture of octadecane and hexadecane (mass ratio 8:2) was used as the core material. The phase change temperature was controlled at 27.5°C, and the latent heat of phase change was increased to 198 J / g. The molar ratio of melamine to formaldehyde was adjusted to 1:3.1, the prepolymerization pH was adjusted to 8.6, the microencapsulation reaction pH was adjusted to 4.1, the reaction temperature was increased to 72°C, and the reaction time was extended to 4.5 hours. The resulting microcapsules achieved an encapsulation efficiency of 75.8% and an average particle size of 8.2 μm.

[0112] During the surface treatment of functional fillers, the mass ratio of P25 type titanium dioxide to cerium-doped zinc oxide was adjusted to 2:1 (increasing the proportion of zinc oxide to enhance photocatalytic activity), the amount of KH570 was increased to 2.3%, and the treatment temperature was increased to 62°C. For the reduction of graphene oxide, the amount of KH550 was increased to 5.5%, and the treatment temperature was increased to 52°C.

[0113] When dispersing functional fillers, the initial dispersion temperature is increased to 33°C, the rGO dispersion time is extended to 23 minutes, the titanium dioxide / zinc oxide mixture dispersion time is extended to 33 minutes, the nano hollow carbon sphere dispersion time is extended to 27 minutes, and the aerogel and microsphere dispersion time is extended to 27 minutes.

[0114] In the emulsion system, the mass ratio of silicone-modified acrylic emulsion to acrylic-modified polyurethane emulsion was adjusted to 2.3:1, and the amount of film-forming aid was increased to 3% (BCS:DPM mass ratio was 3:1).

[0115] The coating performance test results were as follows: solids content 40.5%; viscosity 10200 mPa·s (25°C); pH value 8.7; density 1.08 g / cm³. 3 Thermal conductivity 0.024 W / (m·K) (coating thickness 200 μm); solar reflectivity 0.83; infrared emissivity 0.90; water contact angle 143°; adhesion grade 1; salt spray resistance 1950 hours with no abnormalities; photocatalytic activity 95% degradation rate of methylene blue after 4 hours (visible light); anti-condensation temperature difference 14°C; thermal cycling stability 96% performance retention rate after 500 cycles; VOC content 3.5 g / L.

[0116] Example 3

[0117] The multifunctional aerogel composite coating of this embodiment is composed of the following components by weight percentage: 16% hydrophobic modified silica aerogel, 24% organosilicon modified acrylic emulsion, 17% acrylic modified polyurethane emulsion, 5% nano hollow carbon spheres, 2.5% hollow glass microspheres, 4% nano titanium dioxide, 2% cerium-doped zinc oxide (doping amount 1.2 mol%), 8% microcapsule phase change material, 2.2% reduced graphene oxide, 2.5% silane coupling agent (KH550:KH570 mass ratio of 2.5:1), 3.5% functional dispersant combination, 0.6% pH adjuster, 3.2% film-forming aid, 1.2% rheology modifier, 0.5% defoamer, 1.5% antifreeze, and the balance being deionized water to 100%.

[0118] The preparation method was basically the same as in Example 1, but with the following adjustments. When preparing the hydrophobically modified silica aerogel, the molar ratio of tetramethyl tetraethyl orthosilicate (TMOS) to methyltrimethoxysilane (MTMS) was adjusted to 7.2:2.8, the molar ratio of water / methanol / silanol ester was adjusted to 4.2:11.5:1, and the aging time was shortened to 22 hours. The hydrophobic modification temperature of HMDS was increased to 122°C, and the treatment time was extended to 2.3 hours. The obtained hydrophobic aerogel had a thermal conductivity of 0.015 W / (m·K) and a density of 82 kg / m³. 3 Specific surface area is 595m² 2 / g, water contact angle 165°, particle size D 50 It is 1.8μm.

[0119] In preparing hollow carbon nanospheres, the hydrothermal reaction temperature was lowered to 175°C, and the reaction time was extended to 9 hours. The carbonization temperature was lowered to 820°C, and the holding time was extended to 2.8 hours. The obtained hollow carbon nanospheres had an average outer diameter of approximately 80 nm, a wall thickness of approximately 8 nm, and a specific surface area of ​​1100 m². 2 / g, density 0.04g / cm³ 3 .

[0120] In the preparation of microcapsule phase change materials, only octadecane was used as the core material, with a phase change temperature of 29.5°C and a latent heat of phase change of 192 J / g. The prepolymerization temperature was increased to 83°C, the time was shortened to 1.9 hours, and the microencapsulation reaction time was extended to 4.8 hours. The obtained microcapsules achieved an encapsulation efficiency of 78.5%, an average particle size of 7.8 μm, and a wall thickness of 1.0 μm.

[0121] During the surface treatment of the functional filler, the mass ratio of P25 type titanium dioxide to cerium-doped zinc oxide was maintained at 4:1, but the cerium doping content was reduced to 1.2 mol% to balance photocatalytic activity and visible light transmittance. The ultrasonic dispersion time was extended to 32 minutes.

[0122] When dispersing the functional filler, due to the increased aerogel content of 16% (high content), a staged addition strategy was adopted. First, 8% was added and dispersed for 20 minutes, then the remaining 8% was added and dispersed for another 20 minutes to avoid excessively high local concentrations. Finally, the ultrasonic treatment power was reduced to 290W and the time was extended to 11 minutes.

[0123] In the emulsion system, the mass ratio of silicone-modified acrylic emulsion to acrylic-modified polyurethane emulsion was adjusted to 1.41:1 (closer to 1:1) to improve flexibility and adhesion. The amount of rheology modifier was increased to 1.2% to address the increased viscosity caused by high aerogel content.

[0124] The coating performance test results were as follows: solids content 41.8%; viscosity 13500 mPa·s (25°C); pH value 8.5; density 1.02 g / cm³. 3 Thermal conductivity 0.022 W / (m·K) (coating thickness 210 μm); solar reflectivity 0.81; infrared emissivity 0.89; water contact angle 145°; adhesion grade 1; no abnormalities after 2100 hours of salt spray resistance; 89% degradation rate of methylene blue after 4 hours of photocatalytic activity; anti-condensation temperature difference 15°C; 97% performance retention rate after 500 thermal cycling cycles; VOC content 3.8 g / L.

[0125] This embodiment employs a formulation with high aerogel content (16%) and high nano-hollow carbon sphere content (5%), achieving optimal thermal insulation performance with a thermal conductivity of 0.022 W / (m·K). The high content of microencapsulated phase change material (8%) ensures a 15°C temperature difference against condensation. The high content of reduced graphene oxide (2.2%) significantly enhances corrosion resistance (2100 hours of salt spray resistance). However, this formulation exhibits a slight decrease in solar reflectivity (0.81) and photocatalytic activity (89%), representing a trade-off between sacrificing some optical performance for stronger thermal insulation and corrosion resistance. It is suitable for applications with extremely high requirements for thermal insulation and corrosion resistance, but relatively lower requirements for appearance and self-cleaning (such as internal insulation of industrial pipelines and underground storage tanks).

[0126] Comparative Example 1: Aerogel coating without hollow carbon nanospheres

[0127] The aerogel coating in this comparative example has the same composition as in Example 1, but it does not contain hollow carbon nanospheres. Instead, it is replaced with an equal amount of hollow glass microspheres (i.e., 7% of the total amount of hollow glass microspheres), and the contents of other components are adjusted proportionally. The preparation method is also basically the same as in Example 1, but the step of preparing hollow carbon nanospheres is omitted.

[0128] Performance test results showed that the thermal conductivity was 0.035 W / (m·K), an increase of 29.6% compared to 0.027 W / (m·K) in Example 1; the solar reflectance was 0.84 (a decrease of 1.2% compared to 0.85 in Example 1); the adhesion was grade 2 (a grade 1 lower than that in Example 1); the salt spray resistance was 1200 hours (a decrease of 33.3% compared to 1800 hours in Example 1); the anti-condensation temperature difference was 11.8°C (a decrease of 5.6% compared to 12.5°C in Example 1); and the thermal cycling stability retention rate was 88% (a decrease of 7.0% compared to 95% in Example 1).

[0129] Comparative analysis shows that without the presence of hollow carbon nanospheres, the thermal insulation performance significantly decreases (thermal conductivity increases by 29.6%), demonstrating the crucial role of hollow carbon nanospheres in multi-scale synergistic thermal insulation. The ultra-low density of the carbon nanospheres (0.03-0.08 g / cm³) 3 vs. 0.15-0.25 g / cm³ of hollow glass microspheres 3 ) and ultra-high specific surface area (600-1200m²) 2 / g vs hollow glass microspheres less than 5m 2 The nano-carbon spheres ( / g) provide enhanced thermal insulation. Simultaneously, the conductivity and layered barrier effect of the nano-carbon spheres significantly improve corrosion resistance (salt spray resistance time increased by 50%). The decrease in adhesion and thermal cycling stability may be related to the nano-carbon sphere-reinforced filler-resin interface bonding.

[0130] Comparative Example 2: Aerogel coatings without microencapsulated phase change materials

[0131] The aerogel coating in this comparative example has the same composition as that in Example 1, but it does not contain microcapsule phase change material. Instead, it uses an equal amount of deionized water, and the contents of other components are adjusted proportionally. The preparation method is also basically the same as in Example 1, but the steps of preparing microcapsule phase change material and adding microcapsule phase change material are omitted.

[0132] Performance test results showed that the thermal conductivity was 0.029 W / (m·K), an increase of 7.4% compared to 0.027 W / (m·K) in Example 1; the anti-condensation temperature difference was 5.2°C (compared to 12.5°C in Example 1, a decrease of 58.4%); the salt spray resistance was 1750 hours (compared to 1800 hours in Example 1, a decrease of 2.8%); and the thermal cycling stability retention rate was 92% (compared to 95% in Example 1, a decrease of 3.2%).

[0133] Comparative analysis shows that without microencapsulated phase change materials, the anti-condensation performance decreases significantly (the anti-condensation temperature difference drops from 12.5°C to 5.2°C, a decrease of 58.4%), indicating that the anti-condensation capability provided solely by passive hydrophobicity (water contact angle 141°) and low thermal conductivity (0.029 W / (m·K)) is limited. This fully demonstrates that the active temperature regulation mechanism of microencapsulated phase change materials is the core of achieving excellent anti-condensation performance. The slight increase in thermal conductivity (7.4%) may be related to the fact that the cavity structure of the microcapsules also contributes to a certain degree of thermal insulation.

[0134] Comparative Example 3: Aerogel coatings without cerium-doped zinc oxide

[0135] The aerogel coating in this comparative example has the same composition as that in Example 1, but an equal amount of undoped zinc oxide is used instead of cerium-doped zinc oxide, while other components remain unchanged. The preparation method is also basically the same as in Example 1.

[0136] Performance test results showed that the solar reflectance was 0.86 (compared to 0.85 in Example 1, an increase of 1.2%); the photocatalytic activity after 4 hours was 68% for the degradation of methylene blue (compared to 92% in Example 1, a decrease of 26.1%); and the long-term photocatalytic activity after 500 hours of exposure was 52% (compared to 88% in Example 1, a decrease of 40.9%).

[0137] Comparative analysis shows that without cerium doping, the photocatalytic activity responding to visible light decreases significantly (from 92% to 68%, a decrease of 26.1%), and the decline is even more severe after long-term exposure (from 88% to 52%, a decrease of 40.9%). Pure zinc oxide has a band gap of 3.2 eV and can only respond to ultraviolet light (below 387 nm), while ultraviolet light accounts for only about 5% and visible light about 45% of natural light. Cerium doping reduces the band gap to 2.7-2.9 eV, enabling zinc oxide to respond to blue visible light with wavelengths below 460 nm, significantly improving photocatalytic efficiency. The solar reflectance increases slightly (1.2%), possibly related to the slightly yellowish tint of zinc oxide caused by cerium doping, but this difference is within the margin of error.

[0138] Comparative Example 4: Traditional water-based heat-insulating and reflective coatings

[0139] This comparative example uses a traditional water-based heat-insulating reflective coating formulation, mainly composed of 40% acrylic emulsion, 18% titanium dioxide, 12% hollow glass microspheres, 8% talc, 3% dispersant, 1% thickener, 2.5% film-forming aid, 0.5% defoamer, 0.5% pH adjuster, and the balance deionized water, prepared according to conventional latex paint preparation processes.

[0140] Performance test results show that the thermal conductivity is 0.058 W / (m·K), compared to 0.027 W / (m·K) in Example 1, representing a 53.4% ​​reduction; the solar reflectance is 0.82 (compared to 0.85 in Example 1, representing a 3.7% improvement); the water contact angle is 98° (compared to 141° in Example 1, representing a 43.9% improvement); the adhesion is grade 2 (compared to grade 1 in Example 1, representing a superior grade 1); the salt spray resistance is 720 hours (compared to 1800 hours in Example 1, representing a 150% improvement); the photocatalytic activity degradation rate after 4 hours is 35% (compared to 92% in Example 1, representing a 163% improvement); the anti-condensation temperature difference is 3.8°C (compared to 12.5°C in Example 1, representing a 229% improvement); and the VOC content is 9.5 g / L (compared to 3.2 g / L in Example 1, representing a 66.3% reduction).

[0141] Comparative analysis shows that the coating of this invention has significant advantages in all key performance aspects compared with traditional water-based heat-insulating and reflective coatings. The thermal conductivity is reduced by 53.4%, resulting in a significant improvement in heat insulation performance, mainly attributed to the introduction of aerogel (10%–18%) and nano-hollow carbon spheres (2%–6%). The anti-condensation temperature difference is increased by 229% (from 3.8°C to 12.5°C), thanks to the active temperature regulation of the microencapsulated phase change material. The photocatalytic activity is increased by 163% (from 35% to 92%), a result of the visible light response of cerium-doped zinc oxide. Salt spray resistance is improved by 150% (from 720 hours to 1800 hours), due to the synergistic anti-corrosion effect of organosilicon / polyurethane interpenetrating network resin, rGO, and nano-carbon spheres. The water contact angle is increased by 43.9% (from 98° to 141°), demonstrating the hydrophobic effect of organosilicon modification. The VOC content is reduced by 66.3% (from 9.5 g / L to 3.2 g / L), significantly optimizing environmental performance.

[0142] Comparative Example 5: Water-based light-reflecting industrial thermal insulation coating in CN106752526B

[0143] This comparative example is based on the formulation of Example 1 in CN106752526B. By weight percentage, it consists of 40% hydroxyl acrylic emulsion, 30% light-reflecting filler (25% titanium dioxide, 5% zinc oxide), 3% mica iron oxide (corrosion-resistant filler), 2% aerogel powder (heat-insulating filler), 2% mica powder, 6% isocyanate curing agent, 0.5% tin antimony oxide (nanofiller), 4% dispersant, 3% film-forming aid, 0.5% thickener, 0.2% defoamer, 0.5% wetting agent, 2% antifreeze, and the balance deionized water. Prepared according to the method described in the literature, the isocyanate curing agent is mixed at a ratio of A:B = 100:6 before use. The usable time after mixing is 4 hours.

[0144] Performance test results show that the coating type is two-component (compared to the single-component coating of Example 1, this invention is more convenient to use); the usable time after mixing is 4 hours (compared to the unlimited time of Example 1, this invention has no loss); the thermal conductivity is 0.048 W / (m·K), compared to 0.027 W / (m·K of Example 1, a reduction of 43.8%); the solar reflectance is 0.87 (compared to 0.85 of Example 1, a reduction of 2.3%); the water contact angle is 108° (compared to 141° of Example 1, an improvement of 30.6%); and the adhesion is grade 1 (compared to Example 1, a reduction of 2.3%). The salt spray resistance is 950 hours (compared to 1800 hours in Example 1, the present invention is 89.5% better); the photocatalytic activity degradation rate after 4 hours is 28% (compared to 92% in Example 1, the present invention is 229% better); the anti-condensation temperature difference is 4.2°C (compared to 12.5°C in Example 1, the present invention is 198% better); the VOC content is 15.8 g / L (compared to 3.2 g / L in Example 1, the present invention is 79.7% lower); the storage stability is 6 months for component A (compared to 6 months for the single component in Example 1, the present invention is more stable).

[0145] Comparative analysis shows that, compared with the technical solution of CN106752526B, this invention has the following significant advantages. First, comparison between single-component and two-component systems. Comparative Example 5 uses an isocyanate curing agent, which must be mixed before use and used within 4 hours after mixing; otherwise, it will be unusable after curing, causing inconvenience in construction and material loss. This invention uses a single-component water-based system, which is ready to use immediately after opening the container, requires no on-site mixing, has better storage stability, and is more convenient to use. Second, comparison of thermal insulation performance. Comparative Example 5 has an aerogel content of only 2% and a thermal conductivity of 0.048 W / (m·K), resulting in limited thermal insulation effect. This invention has an aerogel content of 10%–18% and introduces nano-hollow carbon spheres to construct a multi-scale thermal insulation structure, reducing the thermal conductivity to 0.027 W / (m·K) and improving thermal insulation performance by 43.8%. Third, comparison of anti-condensation performance. Comparative Example 5 lacks an active temperature regulation mechanism, with an anti-condensation temperature difference of only 4.2°C, making it prone to condensation under large temperature differences. This invention achieves active temperature regulation through microencapsulated phase change materials, achieving a 12.5°C anti-condensation temperature difference, a 198% improvement, enabling it to cope with harsher temperature fluctuation environments. Fourth, self-cleaning performance comparison. Comparative Example 5's titanium dioxide and zinc oxide only provide light reflection, with poor photocatalytic self-cleaning effect (28%). This invention, through a synergistic photocatalytic system of cerium-doped zinc oxide and P25 titanium dioxide, achieves a photocatalytic activity of 92%, a 229% improvement, and possesses a long-lasting self-cleaning function. Fifth, corrosion resistance comparison. Comparative Example 5 withstands salt spray for 950 hours. This invention, through a multiple corrosion resistance mechanism of organosilicon / polyurethane interpenetrating network resin, rGO, and nano-carbon spheres, improves salt spray resistance to 1800 hours, an 89.5% improvement. Sixth, environmental performance comparison. Comparative Example 5 uses isocyanate curing agent with a VOC content of 15.8 g / L, falling into the category of solvent-based coatings. This invention uses a fully water-based system with a VOC content of only 3.2 g / L, a 79.7% reduction, demonstrating excellent environmental performance. Seventh, cost versus safety comparison. Isocyanate curing agents are expensive and toxic (can cause pulmonary fibrosis), requiring protective measures during handling. This invention uses a water-based system, resulting in lower cost and higher safety.

[0146] In summary, this invention, by introducing innovative components such as nano-hollow carbon spheres, microcapsule phase change materials, and cerium-doped zinc oxide, and employing a single-component, all-aqueous system, has achieved significant breakthroughs over existing technologies in multiple dimensions, including heat insulation, anti-condensation, self-cleaning, corrosion prevention, and environmental protection.

[0147] The multifunctional aerogel composite coating of this invention is applicable to the following fields: Petrochemical field: insulation and corrosion protection for high-temperature equipment such as atmospheric and vacuum distillation towers, catalytic cracking units, hydrogenation reactors, and storage tanks; LNG / liquefied gas field: insulation and anti-condensation for LNG storage tanks, LPG storage tanks, and cryogenic pipelines; Power energy field: insulation for steam pipelines in thermal power plants, cooling systems in nuclear power plants, and thermal power plant heating networks; Building energy conservation field: insulation and anti-condensation for building exterior walls, roofs, cold storage facilities, and large cold chain logistics centers; Marine engineering field: corrosion protection and insulation for offshore platforms, ships, and marine pipelines; Metallurgical and chemical field: insulation for high-temperature equipment such as blast furnaces, converters, electric furnaces, and chemical reactors; Food and pharmaceutical field: insulation and anti-condensation for refrigerated trucks, refrigerated containers, and pharmaceutical cold storage facilities; Aerospace field: insulation for aircraft shells and spacecraft thermal protection systems; Military equipment field: insulation and corrosion protection for military vehicles, ships, and military facilities; Civil facilities field: energy-saving renovation of stadiums, exhibition halls, and public buildings.

[0148] In summary, the aerogel coating of the present invention achieves multi-functional integration of heat insulation, moisture prevention and condensation prevention, sunlight reflection and hydrophobic corrosion prevention through the synergistic effect of multiple components, multiple scales and multiple mechanisms, and has significant technological innovation and application value.

Claims

1. A multifunctional aerogel composite coating, characterized in that, By weight percentage, it comprises: 10%–18% hydrophobic modified silicone aerogel, 22%–32% silicone modified acrylic emulsion, 12%–18% acrylic modified polyurethane emulsion, 2%–6% nano hollow carbon spheres, 2%–5% hollow glass microspheres, 3%–8% nano titanium dioxide, 1%–4% modified zinc oxide, 3%–10% microcapsule phase change material, 0.8%–2.5% reduced graphene oxide, 0.5%–3% silane coupling agent, 1.5%–4% functional dispersant combination, 0.2%–0.8% pH adjuster, 1.5%–3.5% film-forming aid, 0.3%–1.5% rheology modifier, 0.15%–0.8% defoamer, 0.6%–1.8% antifreeze, with the balance being deionized water to 100%. The hollow carbon nanospheres have an average particle size of 50-200 nm, a wall thickness of 8-15 nm, and a density of 0.03-0.08 g / cm³. 3 Specific surface area is 600-1200 m² 2 / g; The mass ratio of the hydrophobic modified silica aerogel to the nano-hollow carbon spheres is (3-6):

1.

2. The multifunctional aerogel composite coating according to claim 1, characterized in that, The hydrophobically modified silica aerogel has a thermal conductivity of 0.015-0.018 W / (m·K) and a density of 80-120 kg / m³. 3 Specific surface area is 500-600 m² 2 / g, water contact angle greater than 150°, particle size 1-5μm.

3. The multifunctional aerogel composite coating according to claim 1, characterized in that, The microcapsule phase change material uses octadecane or a mixture of octadecane and hexadecane as the core material and melamine-formaldehyde resin as the wall material. The microcapsule encapsulation rate is ≥72%, the phase change temperature is 27-32°C, the latent heat of phase change is 185-210 J / g, the particle size is 5-10 μm, and the wall thickness is 0.5-1.2 μm.

4. The multifunctional aerogel composite coating according to claim 1, characterized in that, The nano-titanium dioxide is of type P25, comprising a mixed structure of anatase and rutile, with a mass ratio of 75-85:15-25; the modified zinc oxide is cerium-doped zinc oxide, with a doping amount of 0.8-3.5 mol%, and cerium is present as Ce. 3+ and Ce 4+ The mixed valence states exist, with a molar ratio of (1-2):

1.

5. The multifunctional aerogel composite coating according to claim 1, characterized in that, The silane coupling agent is selected from one or a mixture of two of γ-aminopropyltriethoxysilane and γ-methacryloyloxypropyltrimethoxysilane, with a mixing mass ratio of (1-3):

1.

6. A method for preparing the multifunctional aerogel composite coating according to any one of claims 1-5, characterized in that, The process includes the following steps: (1) preparing hydrophobically modified silica aerogel; (2) preparing nano-hollow carbon spheres; (3) preparing microcapsule phase change materials; (4) performing surface treatment on functional fillers; (5) preparing functional pigment and filler dispersions; (6) preparing modified emulsion systems; and (7) synthesizing multifunctional aerogel composite coatings.

7. The method according to claim 6, characterized in that, Step (1) of the method for preparing hydrophobically modified silica aerogel includes: Tetramethyl tetraethyl orthosilicate and methyltrimethoxysilane were mixed in a molar ratio of (6.5-7.5):(2.5-3.5), and anhydrous methanol was added as a co-solvent. Under ice bath conditions, the mixture was stirred at 600-800 rpm, and deionized water was added dropwise to make the water / methanol / silanol ester molar ratio (3.5-4.5):(11-13):(0.9-1.1). 0.008-0.015M hydrochloric acid was added as a catalyst, and the mixture was stirred at room temperature for 25-35 minutes to form a transparent sol. Ammonia was added dropwise to adjust the pH to 9.0-9.5, and the mixture was allowed to stand until a gel was formed. The gel was sealed and aged at 58-65°C for 20-28 hours. The gel was then placed in a high-pressure reactor, and solvent exchange was performed 3-4 times using ethanol. Each drying process involves passing liquid CO2 through the aerogel for 10-14 hours to replace the ethanol at a temperature of 8-12°C and a pressure of 5.5-6.5 MPa. After 20-28 hours, the temperature is raised to 38-42°C and the pressure is increased to 10-11 MPa to enter a supercritical state, where CO2 is slowly released at a flow rate of 8-12 mL / min to complete the drying. The dried aerogel is then treated with hexamethyldisilazane vapor at 115-125°C for 1.5-2.5 hours, followed by heat treatment in a nitrogen atmosphere at 240-260°C for 0.8-1.5 hours at a nitrogen flow rate of 50-100 mL / min. Finally, a high-energy ball mill is used at 2000-2500 rpm for 25-35 minutes to obtain 1-5 μm hydrophobic aerogel powder.

8. The method according to claim 6, characterized in that, Step (2) of the method for preparing hollow carbon nanospheres includes: Glucose and polyvinylpyrrolidone were dissolved in deionized water at a mass ratio of 1:(0.15-0.25) to prepare a solution with a mass concentration of 8%-12%. Under magnetic stirring, ammonia was added dropwise to adjust the pH to 9.5-10.5, and the solution was stirred at room temperature for 30-50 minutes to form a homogeneous solution. The solution was then transferred to a hydrothermal reactor lined with polytetrafluoroethylene, with a filling degree of 70%-80%, and reacted at 170-190°C for 6-9 hours. After naturally cooling to room temperature, the brownish-black solid product was collected by centrifugation and washed 3-4 times alternately with deionized water and ethanol. The collected solid was vacuum dried at 80-100°C for 10-14 hours, and then carbonized in a tube furnace under a nitrogen atmosphere at a rate of 5-8°C / min to 800-900°C for 2-3 hours. After naturally cooling to room temperature, nano-hollow carbon spheres were obtained.

9. The method according to claim 6, characterized in that, Step (3) The method for preparing microcapsule phase change materials includes: Melamine and formaldehyde were prepolymerized at a molar ratio of 1:(2.8-3.2) at pH 8.3-8.8 and a temperature of 78-85°C for 1.8-2.5 hours, and then cooled to 55-65°C for later use. Octadecylene or a mixture of octadecyl and hexadecylene was mixed with sodium dodecyl sulfate at a mass ratio of (98-99.5):(0.5-2) in a high-shear homogenizer at 10000-15000 rpm for 4-7 minutes. The prepolymer solution was slowly added dropwise to the phase change material emulsion at a rate of 1.5-2.5 mL / min, the pH was adjusted to 4.0-4.5, the temperature was raised to 68-75°C, and the mixture was mechanically stirred at 450-550 rpm for 3.5-5 hours. The mixture was cooled to room temperature, the microcapsules were collected by filtration, washed 3-4 times with deionized water, and vacuum dried at 35-45°C for 20-28 hours to obtain microcapsule phase change material with an encapsulation efficiency ≥72%.

10. The method according to claim 6, characterized in that, The methods in steps (4) to (7) include: P25 type titanium dioxide and cerium-doped zinc oxide were mixed at a mass ratio of (3.5-4.5):

1. Deionized water and sodium polyacrylate were added, with the amount of sodium polyacrylate being 0.4%–0.7% of the powder mass. The mixture was ultrasonically dispersed for 25–35 minutes. γ-methacryloyloxypropyltrimethoxysilane was added, with the amount being 1.8%–2.5% of the powder mass. The mixture was stirred at 55–65°C for 1.5–2.5 hours, centrifuged and washed, and dried at 55–65°C for 10–14 hours. Hours; Disperse reduced graphene oxide in a mixed solution of isopropanol / water at a volume ratio of (6.5-7.5):(2.5-3.5), sonicate at 350-450W in intermittent mode for 25-35 minutes, add γ-aminopropyltriethoxysilane at 4.5%-6% of the mass of reduced graphene oxide, stir at 45-55°C for 3.5-4.5 hours, collect by centrifugation, and vacuum dry to obtain functionalized reduced graphene oxide; In a high-speed disperser, deionized water, ammonia, propylene glycol, and a functional dispersant are mixed at 750-850 rpm for 8-12 minutes to form a uniform dispersant solution. The dispersant solution is heated to 28-35°C, and functionalized reduced graphene oxide is slowly added at 1400-1600 rpm and dispersed for 18-25 minutes. The treated titanium dioxide / zinc oxide mixture is then added, and the speed is increased to 2300-2700 rpm and dispersed for 28-35 minutes. The speed is then decreased to 1100-1300 rpm, and nano-hollow carbon spheres are added and dispersed for 20-28 minutes. Then, hydrophobic aerogel and hollow glass microspheres are gradually added and dispersed for 22-28 minutes. Finally, microcapsule phase change material is added, and the speed is decreased to 700-900 rpm and gently dispersed for 12-18 minutes. Ultrasonic treatment is then performed at 280-320W in intermittent mode for 8-12 minutes. Organosilicon-modified acrylic emulsion and acrylic-modified polyurethane emulsion were mixed at a mass ratio of (2.8-3.2):(1.8-2.2). Hydroxyethyl cellulose was added as a rheology modifier, and a mixture of ethylene glycol butyl ether and dipropylene glycol methyl ether was added as a film-forming aid. The mixing ratio was (2.8-3.2):

1. The mixture was stirred evenly at 900-1100 rpm and allowed to stand to remove bubbles. The functional filler dispersion is slowly added to the modified emulsion system at a rate of 4-6 mL / min, and stirred at 1100-1300 rpm for 28-35 minutes to ensure uniform mixing. Defoamer is added, and the viscosity is adjusted to 8000-14000 mPa·s and the pH value to 8.3-9.

2. The mixture is then filtered through a 150-250 mesh sieve to obtain the finished multifunctional aerogel composite coating.