Atmospheric moisture induced polyacrylate hydrogel system and method for passive cooling

Abstract

A photonic hydrogel film (300) includes a substrate (602) and a hybrid cooling layer (304) attached to the substrate (602) and including a sodium polyacrylate (PAAS) material (308) forming a continuous film structure. The PAAS material (308) is hydrated by atmospheric water molecules such that the chains of the PAAS material (308) are unfastened to maintain the continuous membrane structure. The PAAS material reflects sunlight due to the porous structure and simultaneously emits infrared radiation due to molecular vibrations of the chains of the PAAS material.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 524,948, filed July 5, 2023, entitled “For Mixing Passively Cooled Atmospheric Moisture-Induced Polyacrylate Hydrogels,” the entire disclosure of which is incorporated herein by reference. Background of the Invention Technical Field

[0004] The embodiments of the subject matter disclosed herein generally relate to systems and methods for passive cooling, and more specifically, to polyacrylate-based materials that exhibit high solar reflectance to reduce solar heating and high mid-infrared emissivity to maximize thermal emission. Background Technology

[0005] Climate change has led to prolonged periods of extreme heat in many parts of the world. Consequently, rapidly increasing energy demand, partly driven by air conditioning systems, is overloading existing power grids. The energy consumption and associated environmental problems associated with compressor-based cooling technologies have increased the need to explore energy-free passive cooling methods. The natural process known as the "water cycle"—evaporation, condensation, precipitation, and infiltration—describes the continuous movement of water between the Earth and the atmosphere in three phases. Primarily, a significant amount of energy is absorbed during water evaporation (e.g., 2430 kJ / kg at 30°C). -1 Therefore, it is possible to utilize this process for cooling, i.e., evaporating water to passively absorb heat from the environment. However, continuous evaporative cooling requires an external water supply, which limits its widespread application in areas with limited water resources. Global atmospheric vapor is estimated at approximately 12,900 km². 3 Atmospheric moisture is considered a ubiquitous water resource. Furthermore, rising ambient temperatures lead to increased atmospheric moisture, amplifying the warming effect of greenhouse gases such as water (moisture is the most important component of greenhouse gases, even more difficult to control than carbon dioxide). Therefore, effectively utilizing atmospheric moisture can create solutions to the challenge of global warming.

[0006] One approach to passive cooling is the use of desiccant materials. These materials, including silica gel, zeolite, hygroscopic hydrogels[1], metal-organic frameworks, and lithium chloride[2], have been extensively studied for their ability to absorb vapors from the humid atmosphere at night and evaporate them during the day, thus meeting water harvesting requirements[3]. Hygroscopic hydrogels have been specifically developed for a variety of applications, including atmospheric water harvesting[4], evaporative cooling[5], and interfacial solar evaporation[6, 7]. Their high affinity for water and relatively low temperature-activated desorption process (around 30 °C) make them promising materials. Furthermore, the inherent molecular vibrations of chemical bonds in the infrared wavelength range (5 µm to 25 µm) endow hygroscopic hydrogels with high thermal emissivity, enabling them to effectively dissipate heat through radiative cooling.

[0007] Recently, bilayer structures with polymer fiber networks on a hygroscopic hydrogel substrate have been evaluated to integrate radiative and evaporative cooling [8]. Currently used hygroscopic hydrogels consist of a hygroscopic matrix and a moisture absorption enhancer. Hygroscopic matrices include poly(N-isopropylacrylamide) (pNIPAM), polyvinyl alcohol (PVA), or polyacrylamide (PAM), while moisture absorption enhancers include LiCl and LiBr salts to enhance cooling performance. However, these hydrogel layers require complex synthetic methods, which increases manufacturing costs and hinders their widespread engineering implementation. Specifically, the manufacture of poly(vinyl alcohol)-CaCl2 hydrogels involves time-sensitive and labor-intensive processes such as gelation, freeze-drying, and moisture absorber loading. These processes lead to increased carbon emissions and exacerbate global warming.

[0008] Therefore, there is a need for new materials and “green” manufacturing methods for these materials that produce no carbon emissions, in order to further promote and develop passive cooling technology. Summary of the Invention

[0009] According to an embodiment, a photonic hydrogel film is provided, comprising a substrate and a hybrid cooling layer attached to the substrate and comprising a sodium polyacrylate (PAAS) material forming a continuous film structure. The PAAS material is hydrated by atmospheric water molecules, causing the chains of the PAAS material to unwind to maintain the continuous film structure. The PAAS material reflects sunlight due to its porous structure and simultaneously emits infrared radiation due to the molecular vibrations of the chains of the PAAS material.

[0010] According to another embodiment, a method for cooling a structure is provided, the method comprising placing a photonic hydrogel membrane on the structure, wherein the photonic hydrogel membrane comprises a sodium polyacrylate (PAAS) material forming a continuous membrane structure, hydrating the photonic hydrogel membrane with atmospheric water molecules at night, and exposing the photonic hydrogel membrane to sunlight during the day, such that the PAAS material is hydrated by atmospheric water molecules, causing the chains of the PAAS material to unwind to maintain the continuous membrane structure, and the PAAS material reflects sunlight due to its porous structure and simultaneously emits infrared radiation due to the molecular vibrations of the chains of the PAAS material.

[0011] According to another embodiment, a building material is provided that is attached to a structure to passively reduce the temperature of the structure. The building material includes a substrate and a hybrid cooling layer attached to the substrate and comprising a sodium polyacrylate (PAAS) material forming a continuous membrane structure. The PAAS material is hydrated by atmospheric water molecules, causing the PAAS material chains to unwind to maintain the continuous membrane structure. The PAAS material reflects sunlight due to its porous structure and simultaneously emits infrared radiation due to the molecular vibrations of the PAAS material chains. Attached Figure Description

[0012] To provide a more complete understanding of the present invention, reference is now made to the following description taken in conjunction with the accompanying drawings, wherein:

[0013] Figure 1 The relationship between atmospheric transmittance and wavelength is shown.

[0014] Figure 2A and Figure 2B A hybrid strategy for passive cooling of building envelopes is shown;

[0015] Figure 3 A sodium polyacrylate-based membrane with passive cooling properties according to an embodiment is shown;

[0016] Figure 4 It shows the method for forming Figure 3 A method based on sodium polyacrylate membranes;

[0017] Figure 5 The schematic diagram illustrates the application of sodium polyacrylate powder to... Figure 3 Conversion based on sodium polyacrylate membranes;

[0018] Figure 6 A cross-section of a sodium polyacrylate-based membrane according to an embodiment is shown;

[0019] Figure 7 and Figure 8 A variety of materials and Figure 3 Water intake based on sodium polyacrylate membranes;

[0020] Figure 9 Comparison Figure 7 and Figure 8 Water intake and water release of various materials in the process;

[0021] Figure 10 It shows Figure 7 and Figure 8 Temperature of various materials in the sample when exposed to sunlight;

[0022] Figure 11 The ambient temperature and the temperature around the sodium polyacrylate-based membrane are shown.

[0023] Figure 12 The reflectance and emissivity spectra of a sodium polyacrylate-based film compared to cooled wood, hierarchical polymer, and multilayer photonic structures are shown, with reference to standard solar irradiance spectra and transmittance spectra of atmospheric windows.

[0024] Figure 13 The mechanism of forming a sodium polyacrylate-based membrane via hydrogel bond crosslinking is illustrated schematically;

[0025] Figure 14 Temperature variations were plotted for roof tiles, polydimethylsiloxane (PDMS), a sodium polyacrylate-based photonic film (wet state), and a sodium polyacrylate-based film (dry state); and

[0026] Figure 15 This is a flowchart of a method for using sodium polyacrylate-based membranes as building envelopes to reduce the internal temperature of a building without consuming electricity. Detailed Implementation

[0027] The following description of the embodiments refers to the accompanying drawings. The same reference numerals in different drawings denote the same or similar elements. The following detailed description does not limit the invention. Rather, the scope of the invention is defined by the appended claims. For simplicity, the following embodiments discuss materials based on sodium polyacrylate (PAAS), which combine radiative cooling and thermal emission, and can be manufactured at low cost through efficient and scalable methods. However, the embodiments discussed below are not limited to PAAS-based materials and can also be applied to variations of this material as discussed below.

[0028] The phrase "an embodiment" or "an embodiment" as used throughout this specification means that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter of this disclosure. Therefore, the phrases "in an embodiment" or "in an embodiment" appearing throughout this specification do not necessarily refer to the same embodiment. Furthermore, a particular feature, structure, or characteristic may be combined in any suitable manner in one or more embodiments.

[0029] According to the implementation plan, using only atmospheric moisture as a water source, PAAS powder is converted into a white and continuous photonic hydrogel film (also referred to herein as "PAAS-based material" or simply "film"), thereby creating an environmentally friendly photonic hydrogel film with a carbon-free manufacturing process. Note that the acrylate (A) in PAAS can be a salt, ester, and / or the conjugate base of acrylic acid. The acrylate ion is an anion CH2=CHCO. - 2. The term "acrylate" generally refers to esters of acrylic acid, the most common member being methyl acrylate. These acrylates contain vinyl groups. These compounds are of interest because they are bifunctional: the vinyl groups readily polymerize, while the carboxylate groups carry multiple functions.

[0030] The obtained photonic hydrogel film achieves both radiative and evaporative cooling. The porous structure of the photonic hydrogel film allows for efficient sunlight reflection, which reduces solar heating. Furthermore, the inherent molecular vibrations of the PAAS polymer chains in the photonic hydrogel film provide a high mid-infrared emissivity, which accelerates radiative heat dissipation through atmospheric windows. These two characteristics of the photonic hydrogel film are termed "hybrid passive cooling." In addition, the photonic hydrogel film can store water collected from the atmosphere at night, which can be used for evaporative cooling during the day to enhance its cooling effect. For example, at a solar intensity of 800 W / m²... -2 Under partially cloudy skies, the photonic hydrogel film achieved a temperature reduction of 5°C below ambient temperature (from 37°C to 32°C) due to a hybrid cooling mechanism. This performance is superior to traditional radiative cooling systems (i.e., under the same environmental conditions, the sample temperature of a purely radiatively cooled sample is more than 2°C higher than the ambient temperature).

[0031] In one embodiment, the photonic hydrogel membrane can be recycled at minimal cost through crushing and re-crosslinking (i.e., self-healing), as described below, which maintains its optical properties, extends its lifespan, and thus reduces lifespan costs. This hybrid passive cooling characteristic of the PAAS-based photonic membrane expands its potential applications in high-humidity weather or in urban areas with limited outdoor skies and dense high-rise buildings where radiative cooling is reduced. In one embodiment, this moisture absorption-induced PAAS-based hydrogel membrane facilitates micro-water circulation for passive cooling, representing a forward-looking utilization of atmospheric moisture. Combined with the environmental sustainability of its manufacturing process, implementing such a passively cooled membrane will achieve net harmful carbon emissions in long-term deployment.

[0032] Passive radiative cooling has recently emerged as a transformative cooling technology with the potential to provide "carbon-free" space cooling. It is considered a sustainable alternative to traditional cooling technologies because it utilizes the balance of radiative heat flow between ground-based objects and space. It achieves cooling by manipulating the balance of radiative heat flow between ground-based objects and space. Figure 1 As shown, the Earth's atmosphere has a transparent window 100 for electromagnetic waves ranging from 8µm to 13µm, which corresponds to the peak thermal radiation spectrum range of ground structures at typical ambient temperatures (e.g., approximately 20°C to 45°C in the tropics). This infrared transparent window 100 acts as a cooling channel through which hot bodies on the Earth's surface can radiate heat to the cold space.

[0033] To achieve radiative cooling during the day, the photonic hydrogel membrane meets two criteria: (1) it strongly reflects solar irradiance to minimize solar heating over the solar wavelength range (0.3 µm to 2.5 µm), and (2) it spontaneously transmits thermal radiation through the clear sky into space in the long-wave infrared range (LWIR, specifically 8 µm to 13 µm). The photonic hydrogel membrane achieves these spectrally selective characteristics, which will be discussed in this paper.

[0034] The photonic hydrogel membranes discussed in this paper are configured to achieve one or more of the following objectives: high solar reflectance and high infrared thermal emissivity for efficient radiative cooling; manufactured through a completely green process utilizing ambient water vapor; possessing super-reliability for extended service life; and exhibiting good adhesion to a variety of building surfaces.

[0035] The two passive cooling strategies discussed above, namely radiative cooling and evaporative cooling, are integrated into a single-layer system (photonic hydrogel membrane) to achieve a more powerful cooling capacity that is less dependent on weather conditions. During the day, such as... Figure 2AAs shown, the photonic hydrogel membrane 200 reflects sunlight 202 and emits thermal radiation 204, achieving powerful radiative cooling. Furthermore, the membrane 200 evaporates the water stored within it 206 for evaporative cooling, which is independent of atmospheric transparency. At night, as... Figure 2B As shown, the photonic hydrogel membrane 200 absorbs moisture 208 from the air and restores its evaporative cooling capacity for the next day's cooling operation. This dual function enables greater cooling potential, thus largely overcoming the challenges faced by radiative cooling technology.

[0036] Now we will discuss the general principles of radiative cooling. A blackbody radiator facing the sky emits power P concentrated at a wavelength of approximately 10 μm. B It also receives incident radiant power P from the atmosphere. A Due to the emissivity of the atmosphere within the transparent window. At zero emissivity, the incident radiant power is primarily located outside the atmospheric transparency window. In reality, clouds and water vapor create a very small non-zero emissivity, resulting in a small portion of the radiant energy residing within the atmospheric transparency window. Besides radiant energy, the blackbody also gains heat from the environment because its temperature is lower than the ambient temperature. This undesirable parasitic thermal gain can be described as P c = h (T a - T e ). Here T e and T a These are the radiator temperature and the ambient temperature, respectively, and h is the heat transfer coefficient, ranging from 0 W / m². -2 K -1 Up to 10W m -2 K -1 This depends on thermal insulation. Net cooling power can be expressed as P. n = P B - P A - P C Therefore, the net radiative cooling power is a function of the radiator's temperature, which has unit emissivity inside the transparent window and zero emissivity outside the window. When the radiator is at ambient temperature, it can generate approximately 100 W / m². -2 The cooling power is [not specified]. As it cools down, the net cooling power decreases, reaching equilibrium when the net cooling power reaches zero. Ideally, the radiator can reach a minimum temperature of 262.2 K when the emissivity of the transparent window is zero. While this temperature is quite impressive, in reality, the performance of the radiator declines rapidly with increasing atmospheric emissivity. However, the incident heat introduced by sunlight will significantly alter P [not specified]. A and P CThis affects daytime cooling. Therefore, achieving effective daytime cooling under intense direct sunlight in desert climates is a challenge.

[0037] The inventors' early attempts to overcome these problems and develop radiatively cooled building envelopes were based on the need for solar wavelengths of 0.38µm to 2.5µm to suppress solar heating effects and the need for high infrared thermal emissivity of 5.0µm to 20µm to effectively project heat into space. The inventors discovered that transparent polydimethylsiloxane (PDMS) films could achieve high-performance radiative cooling within a designed architecture. A 100µm thick PDMS layer was coated onto an Al mirror, and its optical absorption and thermal emission spectra were characterized. The film is nearly transparent in the visible light range (with an average optical absorption of less than 5% in the 400nm to 700nm wavelength range). In contrast, its thermal emissivity exceeds 95% in the 8µm to 13µm range. Experimental verification showed that this film emitter could achieve a cooling effect of 11°C below ambient temperature in a controlled laboratory setting. The inventors recently improved this radiative cooling architecture and demonstrated a cooling effect of more than 12°C below ambient temperature outdoors.

[0038] Existing methods for manufacturing hybrid cooling materials involve hazardous chemicals, hindering their large-scale production. The inventors have produced the aforementioned PDMS membrane using a sustainable method employing a microsugar template. By replacing chemicals with sugar, the manufacturing process generates no toxic waste and can be infinitely recycled using methods widely used in the sugar industry. Crystalline sugar cubes with particle sizes ranging from 100µm to 600µm were used as templates. The PDMS precursor fully permeated the pores of the sugar template, which was then solidified and dissolved in water at 60°C. The resulting porous PDMS sponge exhibited strong visible light scattering to suppress solar irradiance. In the wavelength range of 0.35µm to 1.7µm, the solar absorptivity of the porous PDMS sponge was only 0.07, significantly lower than the 0.12 absorptivity of the original PDMS membrane, due to backscattering from the micropores introduced through template dissolution. The porous PDMS sample also exhibited strong, omnidirectional thermal emission in the infrared wavelength range.

[0039] In a 12-hour outdoor experimental measurement, the temperature of the pristine PDMS sample remained consistently higher than the ambient temperature due to the direct solar heating effect. In contrast, the porous PDMS sponge achieved continuous daytime radiative cooling without requiring any shading. Measurements conducted by the inventors (not shown) indicate that the porous PDMS sponge maintained a temperature 3.2 ± 1.0 °C below ambient temperature. The pristine PDMS membrane only achieved a temperature 2.0 ± 1.4 °C above ambient temperature. This experiment demonstrates that, when used as a roofing material, the porous PDMS sponge can reduce heat leakage in the space beneath the roof by approximately 90% compared to commercial asphalt shingles. This effectively inhibits heat exchange with direct sunlight or the environment, allowing for the development of new, energy-efficient building envelope materials. This sugar-template method also addresses the issue of harmful inorganic solvents encountered during the manufacturing process of other hybrid cooling materials.

[0040] However, due to the limited size of the sugar template, this method is not suitable for scalable manufacturing. Furthermore, the cost of PDMS remains higher than the requirements for large-scale deployment.

[0041] The methods and membranes currently under discussion overcome these problems. Figure 3 A membrane 300 is shown, configured to achieve the aforementioned hybrid cooling with a low-cost and simplified manufacturing method. As shown, the optional top layer 302 has high solar reflectivity 310 and mid-infrared emissivity 312 to facilitate radiative cooling. In one application, the top layer 302 can be any white membrane made of polymers, plastics, cotton, wood, and / or metal wires. The desired characteristics of this layer are a white color (or other non-reflective color) and permeability to moisture. For example, the top layer 302 can be porous PE or PTFE. Meanwhile, the bottom layer 304 (also referred to as the “hybrid cooling layer”) is used to absorb moisture at night (e.g., due to moisture-absorbing particles 306 and / or fibers 308) and release moisture during the day for evaporative cooling. In one embodiment, a monolayer (e.g., the bottom layer 304) performs the functions of both the top and bottom layers, i.e., the membrane 300 comprises a monolayer 304. In one embodiment, the bottom layer 304 comprises PAAS fibers 308 and CaCl2 particles 306. Note that in this embodiment, the CaCl2 particles 306 are optional. This combination retains a significant amount of water 309. PAAS 308, also known as a water lock, is a superabsorbent polymer composed of repeating chains of acrylate compounds, possessing many other advantageous characteristics, including mechanical durability and excellent thermal resistance.

[0042] Recently, interest in this anionic polyelectrolyte material has been rekindled due to its novel applications in dilatational microscopy for bioimaging and pressure-sensitive adhesives. It is typically commercially available as a white powder due to its ability to backscatter ambient light and is used in many everyday commercial products, such as baby diapers. These white particles strongly backscatter incident sunlight, a desirable property for radiative cooling. However, the powder form in its dry state makes PAAS inconvenient in many practical applications, such as building envelopes and personal thermal management.

[0043] like Figure 4 As shown, dry PAAS powder 410 is uniformly distributed onto a plastic film (e.g., a polypropylene substrate) 414 via a powder feeder 412 and a blade coating method (see blade 416 in the figure, which controls the thickness of the PAAS powder). In one embodiment, the height of the feeder 412 relative to the substrate 414 determines the thickness of the final film 300. The powder and substrate are placed in an open area at midnight to absorb atmospheric moisture 309. Alternatively, steam 418 can be injected via a steam heater (not shown) to turn the PAAS into a wet film 420. In one embodiment, if the film is manufactured indoors, the steam heater operates at approximately 20 g / min. -1 Up to 25g min -1 Spray moisture for 20 minutes and adjust the temperature to 65°C to 70°C. PAAS particles 308 are activated by water vapor molecules 309 (from steam 418 if the membrane is manufactured indoors; water vapor molecules are naturally absorbed from the environment if the membrane is manufactured outdoors) and form a continuous membrane of uniform density through hydrogen bonds between water molecules. A drying process is then carried out by applying heat 422 (if indoors) via heater 424 or at room temperature (if outdoors) to form a PAAS dry film 300. The final film 300 can be rolled up, as schematically shown in the figure. If carried out overnight in an open environment, the process may take approximately 6 hours under conditions of 60% or greater relative humidity.

[0044] Figure 5 The same process is illustrated schematically to show the actual membrane 300 constructed by the inventors. Figure 5 The conversion process of the PAAS photonic film is demonstrated, which begins with a raw material of white PAAS dry powder 410 with a diameter of approximately 100µm (i.e., a layer of PAAS powder 410 with a thickness of approximately 1mm). A wet film 420 is formed by spraying water onto its top surface and causing it to swell, and then it is dried to obtain a self-standing white film 300 with dimensions of 1m × 0.4m × 3mm.

[0045] This atmospheric moisture-induced process can even manufacture the PAAS photonic film 300 without artificial water spraying. It involves spreading dry PAAS powder 410 (approximately 2 mm thick) onto a flat substrate in an outdoor environment with a nighttime relative humidity of 65% to 90%. A continuous film 300 can be formed within 6 hours overnight. Based on experiments at an ambient temperature of approximately 22°C, the minimum relative humidity for the dry PAAS powder 410 to form a continuous film 300 is approximately 60%. This "natural" and "green" method further simplifies manufacturing, minimizing the labor and energy requirements for large-scale deployment. Furthermore, pigments can be introduced into the structure of layer 308 to form a colored PAAS photonic film 300 without affecting the formation of a continuous film, increasing the versatility of the PAAS photonic film for aesthetic purposes. In addition, the PAAS photonic film can also be applied to various substrates with different textures, such as plastics, wood, and metals, broadening its application scenarios, such as roofing, outdoor electronics, automotive, and industrial applications.

[0046] It is worth noting that membrane 300 has sufficient strength to suspend from its ends without a substrate. An optional top layer 302 can be added to membrane 300 before it is rolled up. Due to their surface chemical characteristics, the two membranes can be easily pressed and adhered to each other. They can be pressed together using an industrial mechanical roll press. In another embodiment, PAAS or PAM powder can be added directly to layer 302 during the manufacturing process. They can adhere together naturally. Furthermore, considering that natural rainfall may degrade PAAS-based layers, layer 302 can introduce hydrophobicity, making it impossible for liquid water to pass through, allowing only moisture to permeate.

[0047] A corrugated cover with holes on the sides (not shown) can be used to protect the membrane from wind or rain while allowing regular airflow through those holes. Although Figure 4 The method shown uses steam 418 and heat 422 generated by heater 424, but in one embodiment, steam 418 is replaced by natural moisture in the air, and heat 422 is replaced by solar heat. Thus, the method is completely green, meaning it does not use any electricity or other resources and does not produce any harmful chemicals. The initial PAAS dry powder 410 can be applied to various substrates, such as plastics, wood, or metal 602, as... Figure 6The diagram is shown schematically. It illustrates the entire membrane 300 and its substrate 602, which are placed / attached to a structure 603, such as a building. The membrane 300 and its substrate 602 (which constitute building material 600) can be used as roofing material or the walls of structure 603. After absorbing moisture, these PAAS dry powders 410 become a continuous membrane 304 and bond with the underlying substrate 602. In one embodiment, an adhesive 604 is first applied to the substrate 602. The PAAS dry powder is then processed to form the membrane 300, which is adhered to the substrate 602 by the adhesive 604 to enhance the adhesion of the PAAS-based layer 300 to the substrate 602. Therefore, the final membrane 300 and its substrate 602 can be used in a variety of applications, such as wooden roofs of buildings, metal casings for outdoor electronics, plastics in automobiles and other industries, etc.

[0048] In one embodiment, a functional layer is added to the photonic hydrogel membrane 300. Figure 6 A cross-section of a photonic hydrogel membrane 300 is shown, comprising an optional substrate 602, an optional adhesive 604, a bottom layer 304, an optional top layer 302, and an optional functional layer 610 situated above the top layer 302 (if present), or otherwise directly above the bottom layer 304. The functional layer 610 may be a melamine layer coated with PDMS. This type of layer protects the bottom layer 304 and top layer 302 from rainwater (e.g., excessive water intake) while maintaining high solar reflectivity and thermal emissivity. Other types of functional layers may be used if the bottom layer 304 is attached to the substrate 602, such as wood, plastic, metal, or other building materials. This modified membrane 300 (i.e., comprising a substrate 602 and a PAAS-based or PAAS-AN-based layer 304, and an optional reflective layer 302 and / or functional layer 610) can be used in construction to provide an envelope for buildings. The membrane 300 can also be used in other industrial applications.

[0049] In another implementation, functional layer 610 is selected to extend the durability of membrane 300 in harsh environments, achieving long-term spectral selectivity. In this regard, real-world aging of cold roofing materials primarily comprises contamination and weathering. Contamination mainly originates from airborne deposits of carbon black, dust, particulate organic matter, and microbial growth. Weathering primarily results from UV exposure to natural sunlight, accompanied by diurnal humidity and temperature variations. To achieve self-cleaning functionality, a superhydrophobic surface can be used. Therefore, functional layers are selected to achieve both superhydrophobicity and UV resistance, enhancing the membrane's performance in terms of contamination resistance and the durability of passively cooled buildings.

[0050] In one embodiment, the PAAS-based material 410 is mixed with one or more other materials before forming the membrane 300. Various thin films were prepared from pure PAAS, pure LiCl, pure CaCl2, pure AN, and mixtures of PAAS+LiCl, PAAS+CaCl2, and PAAS+AN. In one application, the ratio of PAAS particles to AN particles was approximately 1:1. Other ratios may also be used. These membranes were investigated in dry powder form, in a wet state, and in a dry state. Only the PAAS membrane and the PAAS+AN membrane maintained a stable solid membrane structure in all states. The other membranes formed a solution in the wet state. Therefore, the bottom layer 304 of the membrane 300 can be made of PAAS or PAAS+AN, but not of other materials. Figure 7 and Figure 8 The diagram illustrates the water intake of the aforementioned membrane (i.e., the amount of water absorbed by membrane 300 through bottom layer 304 at night if top layer 302 were absent). Notably, the PAAS+AN membrane exhibits superior water intake compared to the pure PAAS membrane. Since water absorption in AN is an endothermic process, this results in improved cooling. The cooling effect lowers the temperature of the mixture, which promotes water absorption.

[0051] Furthermore, the inventors observed that the addition of AN increased the water release of the PAAS-based membrane. Notably, AN powder can be mixed with PAAS powder at the initial stage of the manufacturing process and then uniformly blended. In one application, AN can also be added after PAAS foam formation. The addition of AN enhances water uptake capacity, thereby increasing the water release rate. Figure 9 The water absorption and release capacities of the membranes under consideration are shown. It is worth noting that while desiccant materials such as LiCl and CaCl2 have higher water absorption capacities, they become liquid during manufacturing and therefore cannot be used to create building envelopes. Since moisture absorption by PAAS is an exothermic process that generates heat, while moisture absorption by AN is an endothermic process, mixing PAAS and AN can lower the solution temperature, which is desirable. Figure 10 Temperature curves for various materials during moisture absorption at 80% relative humidity (RH) are shown. Furthermore, compared to PAAS-based membranes, the PAAS+AN membrane exhibits better evaporative cooling performance, such as… Figure 11 As shown.

[0052] In one embodiment, for a thickness of 2 mm to 3 mm, the amount of water required to form a stable substrate 304 (PAAS or PAAS+AN) is 0.5 g / g to 0.8 g / g. The thickness of the substrate 304 (i.e., PAAS or PAAS+AN) can be approximately 2 mm to 3 mm. The temperature for manufacturing the membrane 300 can be 5°C to 65°C, the relative humidity for manufacturing the membrane 300 can be 60% to 99%, and the time required for manufacturing the membrane 300 is 0.5 hours to 6 hours.

[0053] As described above, membrane 300 (primarily due to the bottom layer 304) collects water at night, and the collected water evaporates during the day, carrying heat away from the membrane when heated, for example, during daytime sunlight. In this case, the porous structure of membrane 300 (due to the bottom layer 304 or the top layer 302, or the functional layer 610) backscatters sunlight to reduce the solar heating effect. Simultaneously, thermal radiation is absorbed through atmospheric windows (as above). Figure 1 The membrane 300 dissipates heat into space. Therefore, the membrane 300 can achieve hybrid passive radiative cooling, thanks to its high scattering characteristics and high thermal emissivity derived from the molecular vibrations of the PAAS polymer chains.

[0054] Advantageously, the PAAS-based hydrogel membrane 300 can self-regenerate by absorbing moisture when ambient humidity increases (e.g., at night). The evaporation and self-absorption processes create a perfect daily water cycle, simultaneously promoting heat absorption and release. Furthermore, the entire manufacturing process is suitable for industrial roll-to-roll processes (including PAAS dry powder feeding, moisture-induced crosslinking, and natural air drying, such as…). Figure 4 (As shown).

[0055] In addition to its scalable and simple manufacturing technology, the self-standing PAAS-based photonic film 300 also exhibits excellent whiteness in its dry state, with a solar reflectance of 0.93. Figure 12 As shown (solid curve 1200). The strong solar reflectance is due to the efficient backscattering characteristics of the porous structure. The PAAS-based photonic film 300 is within the atmospheric window (see...). Figure 12 Curve 1200 in the 8µm to 13µm region shows a thermal emissivity of 0.99, which is higher than that of the multilayer photonic structure 1202 and the cooled wood 1204, and comparable to that of the hierarchical polymer 1206. All these results are presented in contrast to the standard solar irradiance spectrum 1210 and the transmittance spectrum of the atmospheric window 1212. Figure 12 middle.

[0056] It should be noted that typical photonic structures require sophisticated nanofabrication equipment. For example, cooling wood relies on a bleaching process to remove lignin from the raw wood and a hot-pressing process to form a densified microstructure. The bleaching process requires the use of chemicals such as sodium hydroxide, sodium sulfite, or hydrogen peroxide. Simultaneously, the subsequent overnight hot-pressing process also requires additional energy consumption and extended processing time (e.g., overnight). Furthermore, phase inversion processes for obtaining layered polymer films involve the use of many volatile and harmful organic solvents (e.g., acetone).

[0057] In comparison, such as Figure 4 The environmentally friendly manufacturing method shown for producing PAAS-based photonic membranes utilizes atmospheric moisture and cost-effective raw materials, demonstrating the advantages of an industrial-grade "green" manufacturing approach. The 2mm thick PAAS (or PAAS-AN) photonic membrane 300 manufactured using this "green" method exhibits excellent flexibility, demonstrated by its ability to recover after severe folding, rapid curling, or stretching. Furthermore, the PAAS (or PAAS-AN) photonic membrane 300 can be stretched to approximately 1.8 times its original length before tearing. Advantageously, after such a tear, the PAAS photonic membrane 300 can be reconnected by simply applying 90% to 95% relative humidity for 6 hours (overnight). The "repaired" PAAS-based photonic membrane 300 can be stretched to 1.5 times its original length without mechanical failure. The mechanical flexibility and self-healing capabilities of the PAAS (or PAAS-AN) photonic membrane 300 potentially reduce maintenance costs for numerous outdoor applications, particularly in radiative or evaporative cooling systems.

[0058] In addition to its mechanical and self-healing advantages, the PAAS-based photonic film 300 can be easily recycled using the following conventional steps: freezing the used film with liquid nitrogen, pulverizing it into powder, and forming a recycled film by humidifying a mixture of the pulverized powder and the original PAAS powder. The recycled PAAS photonic film exhibits a 0.02 reduction in solar reflectance while maintaining its original mid-infrared thermal emissivity, extending its lifespan without significantly sacrificing optical performance. Overall, the PAAS photonic film is a cost-effective material (approximately $1.2m). -2 Its high-volume manufacturing methods, mechanical robustness, and self-healing capabilities make it a promising candidate for large-scale passive cooling applications.

[0059] The physical mechanism of the unique photothermal properties of PAAS photonic films will be discussed next. Figure 13This illustrates the mechanism behind the formation of a mechanically robust, continuous film from loose PAAS powder. The long chains of the PAAS polymer are initially coiled in the dry powder. When the dry chains absorb water, they stretch due to the negative charge present in each repeating unit of the PAAS, i.e., when water is added to the polymer. These regions form negatively charged ions that repel each other and cause the polymer to stretch. Observation under an optical microscope reveals that, in the presence of moisture, the PAAS powder 410 swells, becomes contact with each other, and eventually forms a continuous film 300. As adjacent powders connect during the swelling process, hydrogel bonds form between the different PAAS molecules, creating a cross-linked network.

[0060] Raman spectroscopy explained the formation of hydrogen bonds between adjacent PAAS powders with different water contents. 868 cm⁻¹ -1 and 898cm -1 The peaks at 868 cm⁻¹ (not shown) are attributed to the stretching vibration of C-COO⁻ and the out-of-plane bending of the -OH group in C-COOH, respectively. With increasing water content, the peak at 868 cm⁻¹... -1 The peak weakens at 898cm, while at 898cm -1 The peak enhancement at 3520 cm⁻¹ is due to the increased ionization of PAAS. Fourier transform infrared spectroscopy (FTIR) (not shown) elucidates the overlap between the corresponding molecular vibrations of the chemical bonds in wet PAAS and the atmospheric window. -1 The absorption peak at 1410 cm⁻¹ indicates the stretching vibration of the HOH bonds in the interlayer water molecules of the PAAS after water absorption. -1 The peak at that location is attributed to -(CH2). n - Planar rocking vibrations and carbonates. 1560cm -1 The peak at that location corresponds to the carboxylate group (COO). - The -OH group of PAAS imparts a unique moisture absorption characteristic under high humidity conditions, which is crucial for evaporative cooling, while the -(CH2) group... n - The (COO-) chemical groups provide a high thermal emissivity within the atmospheric window.

[0061] To investigate the water absorption capacity of the PAAS-based photonic membrane 300, a PAAS sample was placed in a humidity- and temperature-controlled chamber, and its mass change with relative humidity was recorded. The humidity within the chamber was regulated by intermittent operation of a humidifier and dehumidifier controlled by a proportional-integral-derivative (PID) controller. The water absorption rate of the PAAS photonic membrane ranged from 0.05 g / cm³. -1 (Relative humidity, 50%) to 0.27 gg -1(Relative humidity, 90%). Thermogravimetric analysis (TGA) characterization showed that evaporated water accounts for approximately 41% of the total mass of the PAAS-based photonic membrane 300, enabling its use for evaporative cooling. Heating the PAAS-based photonic membrane 300 to above 200°C resulted in a significant color change, followed by combustion into char, demonstrating its excellent light and heat resistance. Differential scanning calorimetry (DSC) (not shown) explained the enthalpy of evaporation of water in the PAAS hydrogel network. The DSC thermal spectrum showed a sharp peak at 100°C, followed by a rapid decrease in heat flux, indicating rapid water evaporation. Notably, the heat flux signal peak of the PAAS-based photonic membrane is lower than that of pure water, indicating that the membrane provides a larger surface area for water evaporation, thereby enhancing its evaporative cooling capability.

[0062] In addition to its enormous potential for heat dissipation, the developed PAAS-based photonic membrane 300 also exhibits favorable mechanical properties during the diurnal cycle. In this cycle of continuous variation in solar intensity and relative humidity, the mechanical properties of the PAAS-based membrane are affected by changes in water content. Heating and cooling cycles were simulated in the PAAS photonic membrane to mimic the aforementioned process. The heating step was performed using 1000 W / m². -2 The solar intensity was set at 31.4°C and 17% relative humidity. The nighttime cooling step was achieved by maintaining the PAAS-based photonic membrane in a dark room (zero solar intensity) at 23.2°C and 86% relative humidity. The hardness of the photonic membrane at each stage was then measured using an A-scale hardness meter. It was found that the hardness of the PAAS-based photonic membrane increased and peaked after 6 hours of heating, indicating that water evaporates from the membrane relatively slowly. Upon cooling, the hardness of the PAAS-based photonic membrane decreased as it absorbed water from the environment, indicating that the membrane has the ability to recover its flexibility.

[0063] Furthermore, to quantitatively characterize the flexibility and self-healing ability of membrane 300, the inventors conducted tensile tests on “original” and “cut-and-repair” PAAS samples. Here, “original” means the sample was subjected to 90% to 95% relative humidity at 25°C, while “cut-and-repair” means the sample was cut into two pieces, rejoined, and subjected to 90% to 95% relative humidity at 25°C for 6 hours. The obtained stress-strain curves (not shown) indicate that the “original” PAAS photonic membrane exhibited a strength of 25 kPa and 72% failure strain. A re-repair process using ambient temperature and 90% to 95% relative humidity fully restored the strength and most of the ductility of the PAAS photonic membrane (failure strain of 48%). It is expected that longer re-repair of the cut sample (>24 hours) may be able to fully restore its tensile properties. Nevertheless, this demonstrates the great potential for self-repair of the hydrogel membrane 300 after being completely cut or diced. The effect of "drying" on the mechanical response of PAAS photonic films was investigated by placing them at an ambient temperature of 25°C and a relative humidity of 55% for 60 days. It was found that the drying process can increase strength and ductility by up to 2 times. Furthermore, the compressibility of PAAS hydrogels revealed their potential as materials for shape and volume changes.

[0064] Next, the photothermal characteristics of the PAAS-based photonic film 300 were investigated to further reveal its potential for radiative cooling. The PAAS photonic film appears diffuse white to the naked eye. Its solar reflectance exceeds 0.93, resulting in minimized solar heating under direct sunlight. This high solar reflectance, compared to mirror-like radiatively cooled surfaces, is primarily attributed to its hierarchical structural design. As observed in scanning electron microscopy (SEM) images (not shown), micrometer-scale PAAS structures coexist with a surface texture of a hierarchically constructed porous nanostructure. With increasing water content in the PAAS-based photonic film, the visible light reflectance decreases due to the reduced refractive index difference between PAAS and ambient air. Simultaneously, the higher water content leads to significant differences in the infrared wavelength range. Most microstructures range from 10 µm to 50 µm and from 100 nm to 600 nm, respectively. As described by the refractive index extracted by fitting the transmittance spectrum (not shown), the PAAS-based film exhibits a negligible extinction coefficient k. Therefore, its micron and nanostructures effectively backscatter sunlight of longer (>500 nm) and shorter (300 nm to 500 nm) wavelengths, respectively, as verified by scattering efficiency analysis. Abundant micron or nanostructures can effectively backscatter sunlight of various wavelengths, with nanostructures reflecting visible light wavelengths and micron structures reflecting both visible and near-infrared wavelengths.

[0065] To further elucidate the photon scattering phenomenon, finite-difference time-domain (FDTD) simulations were performed on four characteristic wavelengths (300 nm, 500 nm, 1000 nm, and 1700 nm) within the solar spectrum. It was observed that longer wavelengths (i.e., λ = 1000 nm and 1700 nm) penetrate deeper into the surface compared to shorter wavelengths (i.e., λ = 300 nm and 500 nm). Therefore, the PAAS porous structure is more efficient at scattering shorter wavelength photons, which is also consistent with... Figure 12 The reduction in solar reflectance is related (see Reduction in Solar Reflectance in the Near-Infrared Wavelength Range from 1.0 µm to 2.5 µm). When the PAAS photonic film is wet, it exhibits a weakened scattering effect. This can be attributed to the smaller difference in refractive index between wet PAAS and air compared to that between dry PAAS and air. Specifically, water absorption through the PAAS photonic film leads to a decrease in its refractive index, as the refractive indices of PAAS, water, and air are 1.49, 1.33, and 1.0, respectively, at 500 nm. The weakened scattering is also illustrated by the reduced solar reflectance of the wet PAAS photonic film, which exhibits a reduced solar reflectance of 0.89. Compared to the dry PAAS surface, the OH stretching vibrations of absorbed water in the wet PAAS photonic film induce a higher thermal emissivity for more efficient radiative heat dissipation.

[0066] Quantifying the water evaporation behavior of wet PAAS photonic membranes under different solar intensities and humidity levels helps to understand their cooling potential. The evaporation rate of the wet PAAS photonic membrane as a function of solar intensity and humidity was measured. Indoor simulated evaporation tests showed that water evaporation was promoted when solar irradiance and wind speed increased, or when ambient humidity decreased. The evaporation rate was measured at 23±0.5℃, relative humidity of 20±2%, and wind speed of 1 m / s. -1 Under these conditions, it reaches 1.75 kg m -2 h -1 Under windy conditions, convection is the primary factor in water evaporation, because the evaporation rate increases with solar irradiance intensity from 0 kW / m². -2 Change to 1.0kWm -2 And it increases slowly. However, when there is no wind and the relative humidity is high (e.g., relative humidity of 60% and wind speed of 0 m / s),... -1 Evaporation, enhanced by solar heating, dominates, as the evaporation rate increases with solar intensity from 0 kW / m². -2 Increased to 1.0kW m -2 And rapidly from 0.12kg m -2 h -1 Increased to 0.43 kg m -2 h -1 .

[0067] To further elucidate the physical mechanisms underlying the evaporative cooling potential under various convection scenarios, the inventors simulated the temperature reduction of the PAAS-based photonic film under various heat transfer coefficients and evaporation rates. Due to the high solar reflectance of the PAAS-based photonic film, even with a non-radiative thermal coefficient exceeding 20 W / m², the temperature reduction was achieved. -2 K -1 The simulated temperature decreases (ΔT = T) 膜 - T 环境 The effect remains significant, thanks to its high evaporative cooling potential. The efficient solar scattering effect enables PAAS-based photonic films to reflect sunlight, thereby reducing the heating effect. Furthermore, its evaporative capacity promotes evaporative cooling, thus enhancing the hybrid cooling performance. The unique combination of scattering and evaporative characteristics introduces an additional cooling pathway beyond radiative cooling. This results in hybrid passive cooling performance that is less dependent on weather conditions.

[0068] The radiative and evaporative cooling performance of membrane 300 was also investigated. The spectral selectivity of the PAAS-based photonic membrane in the range of solar and thermal wavelengths enables it to achieve a hybrid cooling effect below ambient temperature (i.e., radiative and evaporative cooling). To decouple the combined effect of these two cooling mechanisms, the inventors measured the temperature reduction of the PAAS-based photonic membrane separately by controlling the experimental setup.

[0069] For radiative cooling measurements under clear skies, a polyethylene (PE) film (not shown) was placed 1 cm above the experimental chamber at a distance of 300 W from the PAAS-based photonic membrane. This PE film has broad transparency across the solar and infrared wavelength range (0.3 µm to 25 µm), and it does not block sunlight or infrared heat dissipation. The PE film also prevents the absorption of water by the dry PAAS-based photonic membrane. Therefore, the temperature drop is primarily due to the radiative cooling effect. During the experiment, from 3:00 PM to 4:30 PM, at approximately 400 W / m... -2 Outdoor experiments were conducted under solar intensity and ambient temperatures ranging from 16°C to 20°C. The temperature reduction of the PAAS-based photonic film stabilized at approximately 3.7°C below ambient temperature. Theoretical thermal balance analysis indicated that, under these relatively cool weather conditions, the net radiative cooling power was 76 W / m². -2 .

[0070] To evaluate the evaporative cooling performance, the inventors first monitored the temperature drop and evaporative cooling power in a temperature and humidity controlled chamber (not shown). In this chamber, the PAAS-based sample was adhered to a copper (Cu) plate (which acted as a heat diffuser and supported the membrane), while a Kapton thin-film heater was attached to the back of the copper plate to provide heating power. The sides of the PAAS-based sample were covered with foam to specifically characterize evaporative cooling from the top surface. A maximum temperature drop of approximately 6 °C was recorded 20 minutes after the start of the experiment, and the temperature stabilized at approximately 2.5 °C below ambient temperature after about 130 minutes. As evaporation continued from the top surface of the PAAS-based photonic membrane, the mass change continuously increased, while its weight loss rate gradually decreased. This is because the increased time required for water to diffuse from the bottom to the top surface leads to a decrease in the weight loss rate. When water absorbed at the top surface of the membrane evaporates, the longer the migration time from the bottom to the top surface lengthens the diffusion path to the top evaporative cooling surface. Therefore, the temperature drop caused by evaporative cooling gradually decreases.

[0071] To characterize the evaporative cooling power, a sample was attached to a copper (Cu) plate above a heater controlled by a PID controller to ensure the surface temperature of the PAAS-based sample reached equilibrium with the ambient temperature. The heating power can be considered as the cooling power because the back of the heater is adiabatic. After the thin-film heater and PID controller were activated, the temperature of the PAAS-based sample adjusted to match the ambient temperature after 43 minutes. Subsequently, the evaporative cooling power was measured at 190 W / m². -2 It fluctuates left and right, and gradually decreases due to water loss during the continuous evaporation process, which can be observed from the decreasing slope of the fitted curve (not shown).

[0072] The inventors also tested the PAAS-based photonic membrane in both dry and wet states, along with two other samples—roof tiles, a common building material used for roofing, and transparent PDMS(T) coated on a polished aluminum plate—under the same outdoor conditions to demonstrate the overall hybrid cooling performance of the wet PAAS-based photonic membrane. Based on experimental data, the thickness of the PAAS-based photonic membrane 300 was optimized to 2 mm. This thickness balances enhanced mechanical robustness with increased moisture absorption, contributing to prolonged and continuous evaporative cooling.

[0073] During the experiment, the average solar intensity was 800 W / m². -2 The average relative humidity is 60%. At midday, such as... Figure 14 As shown, the temperature of commercial tiles without PE covering film reached 40°C above ambient temperature, further verifying the need for energy-saving photonic cooling materials. The dry PAAS sample reached 2°C above ambient temperature without evaporative cooling enhancement, while the PDMS(T) sample, due to direct solar irradiation, reached 4°C above ambient temperature (peak solar intensity of 920 W / m²).-2 In contrast, the PAAS-based photonic membrane 300 exhibited a cooling rate 5°C below ambient temperature, demonstrating superior hybrid cooling performance under partially cloudy conditions. At night, both the PDMS(T) and tile samples had lower temperatures than the wet PAAS-based sample, despite having similar infrared emissivity spectra. The higher temperatures were attributed to the PAAS-based membrane's absorption of moisture at night, generating heat during the regeneration process.

[0074] As day and night alternate, the wet PAAS-based photonic membrane evaporates moisture and absorbs moisture from the air, achieving hybrid cooling performance. The cooling performance of the wet PAAS-based photonic membrane 300 surpasses that of dry PAAS and PDMS(T) with only radiative cooling capabilities, as well as commercial tiles with high solar absorption. Furthermore, under clear skies, the temperature of the wet PAAS-based photonic membrane (with hybrid passive cooling) is 7.2°C lower than that of the dry PAAS sample (with only radiative cooling), confirming the advantage of hybrid passive cooling over radiative cooling under clear sky conditions.

[0075] An additional three-day experiment involved wet PAAS-based photonic membrane 300 under various weather conditions, including sunny days with smoky air, partially cloudy and warm days, and predominantly cloudy days, highlighting the superior efficiency of the hybrid mechanism compared to pure radiative cooling. Continuous evaporation of moisture from the PAAS-based photonic membrane was found to remain feasible for an impressive period exceeding nine hours. This persistence further confirms the ability of hybrid cooling to operate effectively for most of the daytime. The cooling performance of the PAAS photonic membrane 300 was also investigated under a steady-state heat source in a confined space similar to real-life conditions. The results demonstrate that hybrid cooling of the PAAS photonic membrane outperforms pure radiative cooling, elucidating its significant advantage in heat dissipation compared to conventional pure radiative cooling samples.

[0076] The aforementioned implementation scheme discloses a scalable, hybrid passively cooled spectrally selective membrane achieved by utilizing atmospheric moisture-induced polyacrylamide (PAAS) hydrogels. Moisture absorption facilitates the transformation of the PAAS hydrogel from a loose powder into a continuous and flexible membrane. Nighttime moisture absorption and daytime evaporative cooling create a dynamic water cycle. Strong hydrogel bonds between adjacent PAAS particles ensure mechanical robustness for long-term engineering applications. Furthermore, the dry PAAS photonic membrane exhibits a high reflectance of 0.93 over a broadband solar wavelength range, attributed to efficient backscattering from these randomized photonic pores. It also exhibits a high infrared thermal emissivity of 0.99 within the atmospheric transparency window due to its inherent molecular vibrations. This spectral selectivity enables efficient passive cooling, characterized by conditions under partially cloudy skies and solar intensities of 800 W / m². -2Achieving a 5°C reduction under ideal conditions. This PAAS-based photonic membrane (optionally modified with AN, or enhanced with a top reflective layer and / or functional layers) simultaneously delivers evaporative cooling independent of clear skies, thanks to its hygroscopic properties. Compared to current electrically driven air conditioning systems, this hybrid passive cooling strategy promises to reduce global carbon emissions. Scalable and economical hygroscopic hydrogels have the potential to drive further development of passive cooling applications, including infrastructure cooling for electronic devices and vehicles, as well as outdoor personal thermal management. Furthermore, the passive cooling properties of the novel PAAS-based photonic membrane can benefit tankers, refrigerated ships, and trucks that require maintaining relatively low temperatures to preserve food and temperature-sensitive cargo. Importantly, the entire atmospheric moisture treatment process does not use additional chemicals, making it a completely environmentally friendly and high-volume production process with zero carbon emissions, and even zero harmful emissions through energy savings in cooling.

[0077] Membrane 300 and / or building material 600 including membrane 300 can be used to cool structures, such as buildings, as discussed below. The method for cooling the structure includes step 1500: placing a photonic hydrogel membrane on the structure, wherein the photonic hydrogel membrane comprises sodium polyacrylate (PAAS) material forming a continuous membrane structure; step 1502: hydrating the photonic hydrogel membrane at night using atmospheric water molecules; and step 1504: exposing the photonic hydrogel membrane to sunlight during the day, such that the PAAS material is hydrated by atmospheric water molecules, causing the chains of the PAAS material to unwind to maintain the continuous membrane structure, and the PAAS material reflects sunlight due to its porous structure and simultaneously emits infrared radiation due to the molecular vibrations of the chains of the PAAS material.

[0078] This method allows a photonic hydrogel film to include a substrate and a hybrid cooling layer attached to the substrate, the hybrid cooling layer comprising a PAAS material. In one application, for a thickness of 2 mm to 3 mm, the mass ratio of atmospheric water molecules to the mass of the PAAS material is 0.5 g / g to 0.8 g / g. The hybrid cooling layer may also include AN. The mass ratio of PAAS to AN is approximately 1:1. The substrate includes wood, metal, or plastic.

[0079] As used in this application, the term “about” means a maximum of 20% variation in the parameter characterized by the term.

[0080] It should be understood that while the terms first, second, etc., may be used herein to describe various elements, these elements should not be limited by these terms. These terms are used only to distinguish one element from another. For example, a first object or step may be referred to as a second object or step, and similarly, a second object or step may be referred to as a first object or step, without departing from the scope of this disclosure. Both the first object or step and the second object or step are objects or steps, but they should not be regarded as the same object or step.

[0081] The terminology used in this specification is for the purpose of describing particular embodiments and is not intended to be limiting. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the,” as well as the absence of a quantifier before an element, are intended to include the plural forms unless the context clearly indicates otherwise. It will also be understood that the term “and / or,” as used herein, refers to and covers any possible combination of one or more of the associated listed items. It will be further understood that the terms “comprising,” “including,” “containing,” and / or “covering,” as used herein, specify the presence of the stated feature, integer, step, operation, element, and / or component, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. Furthermore, as used herein, the term “if” can be interpreted, depending on the context, as “when,” “in,” “in response to determination,” or “in response to detection.”

[0082] The disclosed embodiments provide a PAAS-based hydrogel membrane that reduces the substrate temperature without consuming electricity, thereby cooling the substrate relative to the environment. It should be understood that this description is not intended to limit the invention. Rather, the embodiments are intended to cover alternatives, modifications, and equivalents included within the spirit and scope of the appended claims. Furthermore, numerous specific details are set forth in the detailed description of the embodiments to provide a comprehensive understanding of the claimed invention. However, those skilled in the art will understand that various embodiments can be practiced without these specific details.

[0083] Although the features and elements of this embodiment are described in specific combinations in the embodiment, each feature or element may be used alone without the other features and elements of the embodiment, or may be used in various combinations with or without the other features and elements disclosed herein.

[0084] This written description uses examples of the disclosed subject matter to enable any person skilled in the art to practice the same, including making and using any device or system and performing any incorporated methods. The patentable scope of the subject matter is defined by the claims and may include other examples that would occur to a person skilled in the art. Such other examples are intended to fall within the scope of the claims.

[0085] References

[0086] The entire contents of all publications listed herein are incorporated herein by reference.

[0087]

[0088]

Claims

1. A photonic hydrogel film (300), comprising: Substrate (602); as well as A hybrid cooling layer (304) is attached to the substrate (602) and comprises sodium polyacrylate (PAAS) material (308) forming a continuous film structure. The PAAS material (308) is hydrated by atmospheric water molecules, causing the chains of the PAAS material (308) to unwind to maintain the continuous membrane structure. The PAAS material reflects sunlight due to its porous structure and emits infrared radiation due to the molecular vibrations of the chains in the PAAS material.

2. The membrane according to claim 1, wherein for a thickness of 2 mm to 3 mm, the mass ratio of atmospheric water molecules to the mass of PAAS material is 0.5 g / g to 0.8 g / g.

3. The membrane according to claim 1, wherein the hybrid cooling layer further comprises AN.

4. The membrane according to claim 3, wherein the mass ratio of PAAS to AN is about 1:

1.

5. The membrane according to claim 1, further comprising: A functional layer that covers the hybrid cooling layer. The functional layer thereunder protects the hybrid cooling layer from the effects of excessive water.

6. The membrane according to claim 5, wherein the functional layer comprises a melamine layer coated with polydimethylsiloxane (PDMS).

7. The membrane according to claim 1, wherein the substrate comprises one of wood, metal or plastic.

8. The membrane according to claim 1, further comprising: An adhesive layer is located between the substrate and the mixed cooling layer.

9. The membrane of claim 1, wherein the hybrid cooling layer is configured to reduce the temperature behind the membrane relative to the ambient temperature without power consumption.

10. A method for cooling a structure, the method comprising: A photonic hydrogel membrane (300) is placed (1500) on a structure (603), wherein the photonic hydrogel membrane (300) comprises sodium polyacrylate (PAAS) material (308) forming a continuous membrane structure; At night, the photonic hydrogel film (300) is hydrated with atmospheric water molecules (1502); and During the day, the photonic hydrogel membrane (300) is exposed (1504) to sunlight, causing the PAAS material (308) to be hydrated by atmospheric water molecules, causing the chains of the PAAS material (308) to unwind to maintain the continuous membrane structure, and the PAAS material reflects sunlight due to its porous structure and emits infrared radiation due to the molecular vibration of the chains of the PAAS material.

11. The method of claim 10, wherein the photonic hydrogel film comprises a substrate (602) and a hybrid cooling layer (304) attached to the substrate (602), the hybrid cooling layer comprising the PAAS material.

12. The method according to claim 10, wherein for a thickness of 2 mm to 3 mm, the ratio of the mass of atmospheric water molecules to the mass of the PAAS material is 0.5 g / g to 0.8 g / g.

13. The method of claim 11, wherein the hybrid cooling layer further comprises AN.

14. The method of claim 13, wherein the mass ratio of PAAS to AN is approximately 1:

1.

15. The method of claim 11, wherein the substrate comprises one of wood, metal or plastic.

16. A building material (600) attached to a structure (603) to passively reduce the temperature of the structure (603), the building material (600) comprising: Substrate (602); as well as A hybrid cooling layer (304) is attached to the substrate (602) and comprises sodium polyacrylate (PAAS) material (308) forming a continuous film structure. The PAAS material (308) is hydrated by atmospheric water molecules, causing the chains of the PAAS material (308) to unwind to maintain the continuous membrane structure. The PAAS material reflects sunlight due to its porous structure and emits infrared radiation due to the molecular vibrations of the chains in the PAAS material.

17. The building material according to claim 16, wherein for a thickness of 2 mm to 3 mm, the ratio of the mass of atmospheric water molecules to the mass of PAAS material is 0.5 g / g to 0.8 g / g.

18. The building material of claim 16, wherein the hybrid cooling layer further comprises AN.

19. The building material according to claim 18, wherein the mass ratio of PAAS to AN is about 1:

1.

20. The building material according to claim 16, further comprising: A functional layer that covers the hybrid cooling layer. The functional layer thereunder protects the hybrid cooling layer from excessive water. The functional layer includes a melamine layer coated with polydimethylsiloxane (PDMS), and The substrate may be one of wood, metal or plastic.

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