Polydimethylsiloxane (PDMS) sponge with porous structure and preparation method thereof

Abstract

The invention relates to the technical field of radiation refrigeration materials, and particularly discloses a porous structure PDMS sponge preparation method, which comprises: laying ammonium bicarbonate powder in a mold, and constructing an ammonium bicarbonate sacrificial template; the preparation method comprises the following steps: weighing a PDMS main agent and a curing agent, uniformly stirring, and degassing to obtain a PDMS prepolymer; pouring the PDMS prepolymer into the ammonium bicarbonate sacrificial template, and standing under the condition of constant temperature and humidity; and sequentially carrying out three gradient heat treatments of low-temperature pre-curing, high-temperature heating and high-temperature curing on the product after standing to obtain the PDMS sponge with the porous structure. The PDMS sponge prepared by the method is of a white uniform and stable porous structure, is low in light transmittance and high in haze, and can efficiently reflect light of various wavelengths and reduce absorption of solar radiation. High reflectivity can be realized in a visible light wave band, and heat entering the material is effectively reduced; in the infrared band, rich pores provide efficient transmission channels for thermal radiation, and the radiation rate is high, so that the radiation refrigeration performance is excellent.

Description

Technical Field

[0001] The present invention relates to the technical field of radiative cooling materials, and particularly to a porous PDMS sponge and a preparation method thereof. Background Art

[0002] In the current situation where global climate problems continue to deteriorate and the energy crisis is intensifying, the development of new refrigeration technologies has become an urgent task. Reports from the International Institute of Refrigeration show that the electricity consumed by global refrigeration operation systems accounts for approximately 20% of the total global electricity consumption. The "Global Cooling Observatory" report released by COP28 predicts that by 2050, carbon dioxide emissions in the refrigeration sector will climb to 4.4 billion to 6.1 billion tons of carbon dioxide equivalent, accounting for more than 10% of the global emissions of that year.

[0003] Facing such severe dual challenges of climate and energy, it is urgent to explore efficient and sustainable refrigeration technology paths. Traditional refrigeration technologies are deeply troubled by energy consumption and emissions, while radiative cooling technology, as an emerging field, is gradually emerging. The core of this technology lies in the ingenious use of the optical properties of special materials to effectively dissipate heat without additional energy input, bringing new hope for addressing energy loss and global warming problems.

[0004] Among many materials, polydimethylsiloxane (PDMS) has been widely used in the field of radiative cooling due to its extremely low absorption rate in the visible and near-infrared bands, extremely high emissivity in the atmospheric window band, and other excellent optical properties, which has strongly promoted the development of this field. PDMS belongs to a high molecular polymer, and its appearance is colorless, transparent, and has a very high viscosity of silica gel. Common commercial products such as Sylgard 184 silicone rubber elastomer kits are composed of a main agent and a curing agent. Its preparation process requires mixing and degassing the compounds to prevent the formation of microbubbles, and then pouring the PDMS solution onto the main mold and curing it in an oven. The curing time is affected by the oven temperature and the size of the PDMS sample, usually requiring 60 minutes at 80°C. The low absorption rate of PDMS in the visible and near-infrared bands and the high emissivity in the atmospheric window band endow it with broad application prospects in the field of radiative cooling. In addition, PDMS has a low thermal conductivity and good hydrophobicity. This unique combination of radiative cooling characteristics and heat insulation performance enables it to effectively suppress heat exchange with solar-heated roofs or the external environment, showing good application potential in the construction field.

[0005] Porosity is a key factor affecting the performance of radiative cooling materials, and its precise regulation is crucial for improving material performance. Different porosities can have a significant impact on the optical, thermal, and surface properties of materials. An increase in porosity can improve the visible light reflectivity and infrared emissivity, but excessive porosity may affect the structural strength and hydrophobic properties of the material; appropriate porosity helps to reduce the thermal conductivity, but improper porosity may damage the heat insulation effect. At present, in the preparation of radiative cooling materials, precisely controlling the porosity still faces great challenges. Existing technologies are difficult to achieve precise regulation of porosity while ensuring the comprehensive performance of the material, which limits the further optimization and large-scale application of the performance of radiative cooling materials.

[0006] Due to the high reflectivity in the visible light band and large infrared emissivity of porous polymer films, the diffuse reflection of their pores can significantly inhibit solar absorption. Therefore, PDMS sponges with a porous structure have a high infrared emissivity in the atmospheric window. However, most current radiative cooling materials face many problems during large-scale production, such as environmental pollution, high raw material costs, and complex preparation processes. To obtain a suitable porosity, some key processes involve harmful chemical substances that are not required in large-scale production, emitting toxic gases and causing pollution. Therefore, it is urgent to develop a pollution-free, high-performance radiative cooling material with precise porosity regulation. Summary of the Invention

[0007] Aiming at the above deficiencies, the present invention provides a porous structure PDMS sponge and its preparation method. Based on the ammonium bicarbonate sacrificial template, the porosity is precisely regulated. The prepared PDMS sponge has a unique porous structure, can efficiently reflect sunlight in the visible light band, and can achieve strong thermal emission in the infrared band, with good radiative cooling characteristics. The specific technical solutions are as follows:

[0008] A preparation method of a porous structure PDMS sponge, comprising the following steps:

[0009] (1) Lay ammonium bicarbonate powder in a mold to construct an ammonium bicarbonate sacrificial template;

[0010] (2) Weigh the PDMS base agent and curing agent, stir evenly, and then degas to obtain a PDMS prepolymer;

[0011] (3) Pour the PDMS prepolymer obtained in step (2) into the ammonium bicarbonate sacrificial template obtained in step (1). The mass ratio of ammonium bicarbonate to the PDMS prepolymer is 0.8 - 1.2:1, and let it stand under constant temperature and humidity conditions;

[0012] (4) Perform three gradient heat treatments on the product after standing in step (3), namely low-temperature pre-curing, high-temperature heating, and high-temperature curing, to obtain a porous structure PDMS sponge.

[0013] The technical solution of the present invention is based on the following technical principles: Ammonium bicarbonate has unique physical and chemical properties and can form a sacrificial template with a specific shape and pore structure under specific conditions. Under certain conditions, ammonium bicarbonate can be effectively removed, leaving the required cavity structure in the PDMS prepolymer. Through specific ratios and subsequent three-gradient heat treatments, a unique pore structure is formed to obtain a PDMS sponge with excellent performance. Specifically: The PDMS prepolymer usually consists of a main agent (basic polymer) and a curing agent (crosslinking agent). During the mixing process, complex chemical reactions occur between the main agent and the curing agent, gradually forming a crosslinked network structure. When the PDMS prepolymer is poured into the ammonium bicarbonate sacrificial template, the prepolymer will fully fill the pores of the sacrificial template by osmosis due to its good fluidity; during the heat treatment process, the chemical reaction inside the PDMS prepolymer is further intensified, and a crosslinking reaction occurs, gradually forming a stable elastomer structure. Among them, the low-temperature pre-curing stage mainly makes the PDMS prepolymer start to crosslink initially, forming a preliminary elastomer structure, providing a structural basis for subsequent treatments; the high-temperature heating stage utilizes the thermal decomposition characteristics of ammonium bicarbonate to decompose it to generate gas and escape, thereby removing the sacrificial template and forming a pore structure inside the material at the same time; the high-temperature curing stage further promotes the full crosslinking of the PDMS prepolymer to form a stable porous PDMS sponge structure, optimizing the various properties of the material. The prepared porous PDMS sponge can exhibit strong scattering ability in the visible light range, effectively reducing the absorption of sunlight, and showing strong thermal emission ability in the infrared range, meeting the standards of high-efficiency daytime passive radiative cooling materials and possessing excellent radiative cooling performance.

[0014] Preferably, in the preparation method of the above-mentioned porous-structured PDMS sponge, among the three-gradient treatments, the process parameters of the low-temperature pre-curing are: the heating rate is 1-2 °C / min, the heating temperature is 40-55 °C, and the heat preservation time is 6-8 h; during the low-temperature pre-curing stage, the PDMS prepolymer starts to undergo a slow crosslinking reaction, gradually forming a preliminary elastomer structure. This process can effectively fix the position of the prepolymer in the pores of the template, prevent excessive flow or deformation during subsequent high-temperature treatments, and at the same time lay a foundation for further crosslinking reactions. The temperature and time parameters of the low-temperature pre-curing need to be precisely controlled. Too low a temperature or too short a time will result in incomplete crosslinking of the prepolymer, affecting the structural strength of the material; too high a temperature or too long a time will cause the prepolymer to form a dense structure prematurely, hindering the escape of the decomposed gas of ammonium bicarbonate and affecting the formation of the pore structure. At the same time, when the temperature is too high, a large amount of ammonium bicarbonate will start to decompose, while the PDMS is not cured and it is difficult to form a stable porous structure.

[0015] Preferably, in the preparation method of the above-mentioned porous structure PDMS sponge, in the three gradient treatments, the process parameters of high-temperature heating are as follows: the heating rate is 2-3 °C / min, the heating temperature is 75-95 °C, and the heat preservation time is 2-4 h; during the high-temperature heating process, ammonium bicarbonate begins to decompose, generating gases such as ammonia, carbon dioxide, and water vapor. These gases form pressure inside the PDMS prepolymer and escape through the pores in the prepolymer, thereby forming a pore structure inside the material. The control of the heating temperature and time is extremely crucial. Too high a temperature will cause the gas generation rate to be too fast, resulting in an uneven pore structure or even damaging the material structure; too low a temperature or too short a time will cause incomplete decomposition of ammonium bicarbonate, affecting the formation of porosity. At the same time, the generated gas can be recycled through a specially designed high-efficiency collection system, which conforms to the concepts of environmental protection and sustainable development;

[0016] Preferably, in the preparation method of the above-mentioned porous structure PDMS sponge, in the three gradient treatments, the process parameters of high-temperature curing are as follows: the heating rate is 1-1.5 °C / min, the heating temperature is 110-130 °C, and the heat preservation time is 1-2 h; during the high-temperature curing stage, the PDMS prepolymer is further fully cross-linked to form a stable elastomer structure, significantly enhancing the mechanical properties and chemical stability of the porous PDMS sponge, and ensuring the reliability and durability of the material in practical applications. The temperature and time parameters of high-temperature curing also need to be precisely controlled to achieve the best cross-linking effect and material properties, and finally obtain a porous structure PDMS sponge with ideal properties.

[0017] Preferably, in the preparation method of the above-mentioned porous structure PDMS sponge, in step (2), the process parameters of stirring are as follows: the stirring speed is 350-500 r / min, and the stirring time is 30-45 min.

[0018] Preferably, in the preparation method of the above-mentioned porous structure PDMS sponge, in step (3), the conditions of constant temperature and humidity are as follows: the temperature is 20-30 °C, the humidity is 40-50%RH, and it is left standing for 6-8 h.

[0019] Preferably, in the preparation method of the above-mentioned porous structure PDMS sponge, the volume ratio of the PDMS main agent to the curing agent is 9-11:1.

[0020] Preferably, in the preparation method of the above-mentioned porous structure PDMS sponge, the process parameters of low-temperature pre-curing are as follows: the heating rate is 1.5 °C / min, the heating temperature is 40-55 °C, and the heat preservation time is 6-8 h; the process parameters of high-temperature heating are as follows: the heating rate is 2.5 °C / min, the heating temperature is 80-90 °C, and the heat preservation time is 2-4 h; the process parameters of high-temperature curing are as follows: the heating rate is 1 °C / min, the heating temperature is 110-120 °C, and the heat preservation time is 1-2 h.

[0021] Preferably, in the method for preparing the porous structure PDMS sponge described above, the degassing is carried out in a vacuum degassing device with a vacuum degree of 15-30 mmHg for 10-20 minutes.

[0022] On the other hand, the present invention also provides a porous structure PDMS sponge, and the PDMS sponge is prepared by the preparation method described above.

[0023] On the other hand, the present invention also provides the application of the above-mentioned porous structure PDMS sponge in the preparation of radiative cooling materials.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] 1. In the preparation method of the porous structure PDMS sponge of the present invention, the prepared PDMS sponge has a white, uniform and stable porous structure, high haze and low light transmittance, can efficiently reflect light of various wavelengths, and reduce the absorption of solar radiation. It can achieve a high reflectivity and low absorption in the visible light band, effectively reducing the heat entering the material interior; in the infrared band, the abundant pores provide an efficient transmission channel for thermal radiation, with a large emissivity, and can quickly dissipate the heat inside the material to the external environment, thus showing excellent radiative cooling performance.

[0026] 2. In the preparation method of the porous structure PDMS sponge of the present invention, the prepared PDMS sponge has a uniform and stable porous structure. This structural design enables the air in the pores to achieve good synergistic effects with the material. Compared with the traditional transparent PDMS colloid, the porous structure PDMS sponge of the present invention has significant advantages in radiative cooling performance. Its stable pore structure ensures that good cooling effects can be maintained under different environmental conditions, which makes the porous structure PDMS sponge of the present invention have broad application prospects in the field of radiative cooling and can be widely applied to many fields such as building energy conservation, industrial refrigeration, aerospace, etc., effectively contributing to energy conservation and environmental improvement.

[0027] 3. In the preparation method of the porous structure PDMS sponge of the present invention, by optimizing the raw material ratio and heat treatment process, a stable and uniform pore structure is constructed, and the comprehensive properties such as radiative cooling and heat insulation performance of the porous structure PDMS sponge are improved.

[0028] 4. The microscopic design of the porous structure of the PDMS sponge of the present invention significantly improves the hydrophobicity of the material surface. When a water droplet touches the surface of the PDMS sponge, the water droplet will immediately form a water bead and quickly slide off, leaving no residue on the material surface, having a self-cleaning function. This self-cleaning function benefits from the stable pore structure, enabling the material to maintain a clean surface in practical applications for a long time, reducing the attachment of dust and dirt, facilitating the long-term stable performance of its radiative cooling performance, while reducing maintenance costs, increasing the service life and usability of the material, and enhancing the reliability and practicality of the material in practical applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0030] Figure 1 A physical photo of the PDMS sponge prepared for Example 1;

[0031] Figure 2 A schematic structural diagram of the PDMS sponge prepared for Example 1: (a) cross-sectional schematic diagram; (a) top view schematic diagram;

[0032] Figure 3 A structural simulation diagram of the PDMS sponge prepared for Example 1;

[0033] Figure 4 SEM diagrams of the PDMS sponges prepared for Examples 1 and 2: The diagram for Example 1 is the longitudinal cross-sectional SEM diagram of the sponge sample of Example 1, and the diagram for Example 2 is the surface SEM diagram of the sponge sample of Example 2;

[0034] Figure 5 Metallurgical microscope diagrams of the surfaces of the PDMS sponges prepared for Examples 1 and 2;

[0035] Figure 6 Absorption spectra of the PDMS sponges prepared for Examples 1 to 4;

[0036] Figure 7 Haze spectra of the PDMS sponge prepared for Example 1;

[0037] Figure 8 Hydrophobicity display diagram of the PDMS sponge prepared for Example 1;

[0038] Figure 9 Comparison spectra of the thermal conductivity of the PDMS sponge prepared for Example 1 with similar materials on the market;

[0039] Figure 10 Actual cooling effect diagram of the PDMS sponge prepared in Example 1;

[0040] Figure 11 Physical photo of the PDMS sponge prepared in Comparative Example 1;

[0041] Figure 12 Physical photo of the PDMS sponge prepared in Comparative Example 2;

[0042] Figure 13 Physical photo of the PDMS sponge prepared in Comparative Example 3;

[0043] Figure 14 Physical photo of the PDMS sponge prepared in Comparative Example 4. Detailed Description of the Invention

[0044] The following is a detailed description of the specific embodiments of the present invention. It should be understood that the protection scope of the present invention is not limited by the specific embodiments. Unless otherwise defined, all professional terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention. Unless otherwise specifically stated, various raw materials, reagents, instruments, and equipment used in the present invention can be obtained through market purchases or can be prepared by existing methods.

[0045] Example 1

[0046] A preparation method of a porous structure PDMS sponge, comprising the following steps:

[0047] (1) Weigh 10 g of ammonium bicarbonate analytical pure powder, lay the ammonium bicarbonate powder on a clean and dry polytetrafluoroethylene mold, and evenly spread the ammonium bicarbonate powder to construct an ammonium bicarbonate sacrificial template with a specific pore structure prototype;

[0048] (2) Mix the PDMS base and the curing agent (Dow Corning 184) at a volume ratio of 10:1, stir evenly, the stirring speed is 400 r / min, the stirring duration is 35 min, and then place it in a vacuum degassing device (under a vacuum of 20 mmHg) for 10 min to remove the bubbles in the mixed solution and form a uniform PDMS prepolymer;

[0049] (3) Weigh 10 g of the PDMS prepolymer obtained in step (2), slowly and uniformly pour it into the ammonium bicarbonate sacrificial template obtained in step (1), the mass ratio of ammonium bicarbonate to the PDMS prepolymer is 1:1, and then place it in a constant temperature and humidity chamber at 25°C and 45% RH for 6 h to allow the prepolymer to further fully penetrate into the template pores;

[0050] (4) Place the product after standing in step (3) in a high-precision temperature-controlled heater, heat it up to 50 °C at a rate of 1.5 °C / min, and carry out low-temperature pre-curing treatment at this temperature for a holding time of 8 h;

[0051] After pre-curing is completed, heat it up to 80 °C at a rate of 2.5 °C / min and carry out high-temperature heating treatment for a holding time of 4 h;

[0052] After removing the sacrificial template by high-temperature heating treatment, heat the sample to 110 °C at a heating rate of 1 °C / min and carry out high-temperature curing treatment for a holding time of 1 h, and then cool it naturally to obtain a porous PDMS sponge.

[0053] The physical photo of the porous PDMS sponge sample prepared in this example is as Figure 1 shown, and its sectional view and top view structure schematic diagram are as Figure 2 shown, Figure 3 It is the simulation structure diagram of the PDMS sponge (simulated and drawn by C4D software), which has an obvious porous structure. Figure 4 and Figure 5 are the micrographs of the PDMS sponge sample. The sponge sample shows rich and diverse pores evenly distributed. These pores are of moderate size and interconnected, forming a complex and orderly pore network system. The pores are evenly and stably distributed inside the material. The boundaries between different phases are intertwined with the pores, presenting a unique microstructural organization.

[0054] It can be seen from Figure 6 that the prepared PDMS sponges all have low absorption rates in the visible light range, show strong scattering, and show strong thermal emission in the infrared range, meeting the standards of high-efficiency daytime passive radiative cooling materials.

[0055] PDMS colloid naturally appears colorless and transparent and has the characteristic of high light transmittance. However, in the specific context of radiative cooling applications, this high light transmittance conflicts with the requirement of strong visible light scattering, making it difficult to meet the needs of all-weather radiative cooling. The porous PDMS sponge obtained by the preparation method of the present invention presents an opaque white appearance. It can be seen from Figure 7 that the porous PDMS sponge of this example has a high haze value and a low light transmittance, showing significant advantages in optical property regulation.

[0056] Figure 8This is the result diagram of the hydrophobic test of the PDMS sponge in this embodiment. Water droplets can slide off its surface at an extremely fast speed, and the entire sliding process takes within 0.5 s. The results show that the PDMS sponge has significant hydrophobic characteristics. Due to its unique pore structure, the air filled inside the pores and the pore walls jointly construct a special microscopic hydrophobic environment. When a water droplet touches the surface of the PDMS sponge, the pore structure effectively reduces the actual contact area between the water droplet and the material surface. At the same time, the pressure difference generated by the air in the pores prompts the water droplet to quickly form a spherical water bead, which quickly slides off under the action of gravity without leaving any trace, successfully realizing the self-cleaning function. This self-cleaning function can not only keep the material surface clean, but also reduce the performance degradation that may be caused by dirt accumulation, thereby greatly extending the service life and reliability of the material in practical applications.

[0057] It can be seen from Figure 9 that the PDMS sponge prepared in this embodiment has a low thermal conductivity. The pore structure is filled with air, and air, as an excellent heat insulation medium, effectively hinders the heat conduction process and has a significant effect of heat insulation and temperature reduction.

[0058] In order to deeply study the cooling ability of the PDMS sponge based on the ammonium bicarbonate sacrificial template, the prepared porous PDMS sponge was placed on a wooden house model to carry out the actual cooling performance test. The results are as Figure 10 shown. The temperature of the area covered with the PDMS sponge is lower, and it is 5 °C lower than that of the uncovered area. Relatively speaking, the porous PDMS sponge can achieve continuous daytime radiative cooling effect, proving its refrigeration potential and advantages in practical application scenarios.

[0059] Example 2

[0060] A preparation method of a porous structure PDMS sponge includes the following steps:

[0061] (1) Weigh 10 g of ammonium bicarbonate analytical pure powder, lay the ammonium bicarbonate powder on a clean and dry polytetrafluoroethylene mold, and evenly spread the ammonium bicarbonate powder to construct an ammonium bicarbonate sacrificial template with a specific pore structure prototype;

[0062] (2) Mix the PDMS base agent and the curing agent according to a volume ratio of 10:1, stir evenly, the stirring speed is 400 r / min, the stirring duration is 35 min, and then place it in a vacuum degassing device (under a vacuum degree of 20 mmHg) for degassing for 10 min to remove the bubbles in the mixed solution and form a uniform PDMS prepolymer;

[0063] (3) Weigh 10 g of the PDMS prepolymer obtained in step (2), and slowly and uniformly pour it into the ammonium bicarbonate sacrificial template obtained in step (1). The mass ratio of ammonium bicarbonate to the PDMS prepolymer is 1:1. Then place it in a constant temperature and humidity chamber at 25 °C and 45% RH and let it stand for 6 h to allow the prepolymer to further fully penetrate into the pores of the template;

[0064] (4) Place the product after standing in step (3) in a high-precision temperature-controlled heater, heat it to 55 °C at a rate of 1.5 °C / min, and perform a low-temperature pre-curing treatment at this temperature for a continuous holding time of 6 h;

[0065] After the pre-curing is completed, heat it to 90 °C at a rate of 2.5 °C / min and perform a high-temperature heating treatment for a continuous holding time of 3 h;

[0066] After removing the sacrificial template by high-temperature heating treatment, heat the sample to 110 °C at a heating rate of 1 °C / min and perform a high-temperature curing treatment for a continuous holding time of 1 h, and then let it cool naturally to obtain a porous-structured PDMS sponge. The micrographs of the PDMS sponge samples prepared by the present invention are as shown in Figure 4 and Figure 5 shown. It has a porous structure, a low absorption rate in the visible light range, shows strong scattering, shows strong thermal emission in the infrared range, meets the standards of an efficient daytime passive radiative cooling material, has a high haze and a low light transmittance, hydrophobicity, a low thermal conductivity, and a good heat insulation and cooling effect.

[0067] Example 3

[0068] A preparation method of a porous-structured PDMS sponge, comprising the following steps:

[0069] (1) Weigh 10 g of ammonium bicarbonate analytical pure powder, spread the ammonium bicarbonate powder on a clean and dry polytetrafluoroethylene mold, and evenly flatten the ammonium bicarbonate powder to construct an ammonium bicarbonate sacrificial template with a specific pore structure prototype;

[0070] (2) Mix the PDMS base agent and the curing agent in a volume ratio of 10:1, stir evenly at a stirring speed of 400 r / min for a stirring duration of 35 min, and then place it in a vacuum degassing device (under a vacuum of 20 mmHg) for 10 min to remove the bubbles in the mixed solution and form a uniform PDMS prepolymer;

[0071] (3) Weigh 10 g of the PDMS prepolymer obtained in step (2), and slowly and uniformly pour it into the ammonium bicarbonate sacrificial template obtained in step (1). The mass ratio of ammonium bicarbonate to the PDMS prepolymer is 1:1. Then place it in a constant temperature and humidity chamber at 25 °C and 45% RH and let it stand for 6 h to allow the prepolymer to further fully penetrate into the pores of the template;

[0072] (4) Place the product after standing in step (3) in a high-precision temperature-controlled heater, heat it up to 45°C at a rate of 1.5°C / min, and carry out low-temperature pre-curing treatment at this temperature for a holding time of 6 h;

[0073] After the pre-curing is completed, heat it up to 85°C at a rate of 2.5°C / min and carry out high-temperature heating treatment for a holding time of 4 h;

[0074] After removing the sacrificial template by high-temperature heating treatment, heat the sample to 120°C at a heating rate of 1°C / min and carry out high-temperature curing treatment for a holding time of 1 h, and then cool it naturally to obtain a porous PDMS sponge. The porous PDMS sponge prepared in this example is an opaque white porous sponge, with a low absorption rate in the visible light range, showing strong scattering, showing strong thermal emission in the infrared range, having a high haze and a low light transmittance, hydrophobicity, a low thermal conductivity, and a good heat insulation and cooling effect.

[0075] Example 4

[0076] A preparation method of a porous PDMS sponge, comprising the following steps:

[0077] (1) Weigh 12 g of analytical pure ammonium bicarbonate powder, lay the ammonium bicarbonate powder on a clean and dry polytetrafluoroethylene mold, and evenly spread the ammonium bicarbonate powder to construct an ammonium bicarbonate sacrificial template with a prototype of a specific pore structure;

[0078] (2) Mix the PDMS main agent and the curing agent according to a volume ratio of 10:1, stir evenly at a stirring speed of 400 r / min for a stirring time of 35 min, and then place it in a vacuum degassing device (under a vacuum of 20 mmHg) for degassing for 10 min to remove the bubbles in the mixed solution and form a uniform PDMS prepolymer;

[0079] (3) Weigh 10 g of the PDMS prepolymer obtained in step (2), slowly and uniformly pour it into the ammonium bicarbonate sacrificial template obtained in step (1), the mass ratio of ammonium bicarbonate to the PDMS prepolymer is 1.2:1, and then place it in a constant temperature and humidity chamber at 25°C and 45% RH and stand for 6 h to allow the prepolymer to further fully penetrate into the template pores;

[0080] (4) Place the product after standing in step (3) in a high-precision temperature-controlled heater, heat it up to 55°C at a rate of 1.5°C / min, and carry out low-temperature pre-curing treatment at this temperature for a holding time of 8 h;

[0081] After the pre-curing is completed, heat it up to 85°C at a rate of 2.5°C / min and carry out high-temperature heating treatment for a holding time of 4 h;

[0082] After removing the sacrificial template by high-temperature heat treatment, the sample was heated to 120 °C at a heating rate of 1 °C / min for high-temperature curing treatment. The holding time was 1 h, and then it was naturally cooled to obtain a porous PDMS sponge. The porous PDMS sponge prepared in this example is an opaque white porous sponge with high haze, low light transmittance, hydrophobicity, low thermal conductivity, and good heat insulation and cooling effects.

[0083] Example 5

[0084] A preparation method of a porous PDMS sponge includes the following steps:

[0085] (1) Weigh 10 g of analytical pure ammonium bicarbonate powder, lay the ammonium bicarbonate powder on a clean and dry polytetrafluoroethylene mold, and evenly spread the ammonium bicarbonate powder to construct an ammonium bicarbonate sacrificial template with a specific pore structure prototype;

[0086] (2) Mix the PDMS main agent and the curing agent in a volume ratio of 10:1, stir evenly at a stirring speed of 400 r / min for 35 min, and then place it in a vacuum degassing device (under a vacuum of 20 mmHg) for 10 min to remove the bubbles in the mixed solution and form a uniform PDMS prepolymer;

[0087] (3) Weigh 10 g of the PDMS prepolymer obtained in step (2), slowly and evenly pour it into the ammonium bicarbonate sacrificial template obtained in step (1). The mass ratio of ammonium bicarbonate to the PDMS prepolymer is 1:1, and then it is placed in a constant temperature and humidity chamber at 25 °C and 45% RH and left standing for 6 h to allow the prepolymer to further fully penetrate into the template pores;

[0088] (4) Place the product after standing in step (3) in a high-precision temperature-controlled heater, heat it to 40 °C at a rate of 1.5 °C / min, and perform low-temperature pre-curing treatment at this temperature for a holding time of 8 h;

[0089] After pre-curing, heat it to 95 °C at a rate of 2.5 °C / min for high-temperature heat treatment, and the holding time is 2 h;

[0090] After removing the sacrificial template by high-temperature heat treatment, the sample was heated to 120 °C at a heating rate of 1 °C / min for high-temperature curing treatment. The holding time was 1.5 h, and then it was naturally cooled to obtain a porous PDMS sponge.

[0091] The porous PDMS sponge prepared in this example is an opaque white porous sponge with high haze, low light transmittance, hydrophobicity, low thermal conductivity, and good heat insulation and cooling effects.

[0092] Example 6

[0093] A preparation method of a porous structure PDMS sponge, comprising the following steps:

[0094] (1) Weigh 8 g of ammonium bicarbonate analytical pure powder, lay the ammonium bicarbonate powder on a clean and dry polytetrafluoroethylene mold, and evenly spread the ammonium bicarbonate powder to construct an ammonium bicarbonate sacrificial template with a prototype of a specific pore structure;

[0095] (2) Mix the PDMS base agent and the curing agent according to a volume ratio of 10:1, stir evenly, with a stirring speed of 400 r / min and a stirring duration of 35 min, and then place it in a vacuum degassing device (under a vacuum of 20 mmHg) for 10 min to remove the bubbles in the mixed solution and form a uniform PDMS prepolymer;

[0096] (3) Weigh 10 g of the PDMS prepolymer obtained in step (2), slowly and uniformly pour it into the ammonium bicarbonate sacrificial template obtained in step (1), with a mass ratio of ammonium bicarbonate to PDMS prepolymer of 0.8:1, and then place it in a constant temperature and humidity chamber at 25°C and 45% RH and let it stand for 6 h to allow the prepolymer to further fully penetrate into the pores of the template;

[0097] (4) Place the product after standing in step (3) in a high-precision temperature-controlled heater, heat it to 45°C at a rate of 1.5°C / min, and perform a low-temperature pre-curing treatment at this temperature for a continuous holding time of 6 h;

[0098] After the pre-curing is completed, heat it to 80°C at a rate of 2.5°C / min and perform a high-temperature heating treatment for a continuous holding time of 3.5 h;

[0099] After removing the sacrificial template by high-temperature heating treatment, heat the sample to 130°C at a heating rate of 1°C / min and perform a high-temperature curing treatment for a continuous holding time of 1.5 h, and then let it cool naturally to obtain a porous structure PDMS sponge.

[0100] Example 7

[0101] A preparation method of a porous structure PDMS sponge, comprising the following steps:

[0102] (1) Weigh 15 g of ammonium bicarbonate analytical pure powder, lay the ammonium bicarbonate powder on a clean and dry polytetrafluoroethylene mold, and evenly spread the ammonium bicarbonate powder to construct an ammonium bicarbonate sacrificial template with a prototype of a specific pore structure;

[0103] (2) Mix the PDMS base and the curing agent at a volume ratio of 10:1, stir evenly at a stirring speed of 400 r / min for 35 min, and then place it in a vacuum degassing device (under a vacuum of 20 mmHg) for 10 min to remove the bubbles in the mixed solution and form a uniform PDMS prepolymer;

[0104] (3) Weigh 15 g of the PDMS prepolymer obtained in step (2), slowly and uniformly pour it into the ammonium bicarbonate sacrificial template obtained in step (1), and the mass ratio of ammonium bicarbonate to the PDMS prepolymer is 1:1. Then place it in a constant temperature and humidity chamber at 25 °C and 45% RH and let it stand for 6 h to allow the prepolymer to further fully penetrate into the pores of the template;

[0105] (4) Place the product after standing in step (3) in a high-precision temperature-controlled heater, heat it up to 45 °C at a rate of 1.5 °C / min, and perform a low-temperature pre-curing treatment at this temperature for a continuous holding time of 6 h;

[0106] After the pre-curing is completed, heat it up to 80 °C at a rate of 2.5 °C / min for a high-temperature heating treatment with a continuous holding time of 3.5 h;

[0107] After removing the sacrificial template by high-temperature heating treatment, heat the sample to 130 °C at a heating rate of 1 °C / min for a high-temperature curing treatment with a continuous holding time of 1.5 h, and then let it cool naturally to obtain a porous-structured PDMS sponge.

[0108] Comparative Example 1

[0109] A method for preparing a porous-structured PDMS sponge, comprising the following steps:

[0110] (1) Weigh 5 g of ammonium bicarbonate analytical pure powder, spread the ammonium bicarbonate powder on a clean and dry polytetrafluoroethylene mold, and evenly flatten the ammonium bicarbonate powder to construct an ammonium bicarbonate sacrificial template with a prototype of a specific pore structure;

[0111] (2) Mix the PDMS base and the curing agent at a volume ratio of 10:1, stir evenly at a stirring speed of 400 r / min for 35 min, and then place it in a vacuum degassing device (under a vacuum of 20 mmHg) for 10 min to remove the bubbles in the mixed solution and form a uniform PDMS prepolymer;

[0112] (3) Weigh 10 g of the PDMS prepolymer obtained in step (2), slowly and uniformly pour it into the ammonium bicarbonate sacrificial template obtained in step (1), and the mass ratio of ammonium bicarbonate to the PDMS prepolymer is 0.5:1. Then place it in a constant temperature and humidity chamber at 25 °C and 45% RH and let it stand for 6 h to allow the prepolymer to further fully penetrate into the pores of the template;

[0113] (4) Place the product after standing in step (3) in a high-precision temperature-controlled heater, heat it up to 50 °C at a rate of 1.5 °C / min, and carry out low-temperature pre-curing treatment at this temperature for a holding time of 8 h;

[0114] After the pre-curing is completed, heat it up to 80 °C at a rate of 2.5 °C / min and carry out high-temperature heating treatment for a holding time of 4 h;

[0115] After removing the sacrificial template by high-temperature heating treatment, heat the sample to 110 °C at a heating rate of 1 °C / min, carry out high-temperature curing treatment for a holding time of 1 h, and then cool it naturally to obtain a porous structure PDMS sponge.

[0116] Comparative Example 2

[0117] A method for preparing a porous structure PDMS sponge, comprising the following steps:

[0118] (1) Weigh 15 g of ammonium bicarbonate analytical pure powder, lay the ammonium bicarbonate powder on a clean and dry polytetrafluoroethylene mold, and evenly spread the ammonium bicarbonate powder to construct an ammonium bicarbonate sacrificial template with a specific pore structure prototype;

[0119] (2) Mix the PDMS main agent and the curing agent in a volume ratio of 10:1, stir evenly at a stirring speed of 400 r / min for a stirring time of 35 min, and then place it in a vacuum degassing device (under a vacuum of 20 mmHg) for degassing for 10 min to remove the bubbles in the mixed solution and form a uniform PDMS prepolymer;

[0120] (3) Weigh 10 g of the PDMS prepolymer obtained in step (2), slowly and uniformly pour it into the ammonium bicarbonate sacrificial template obtained in step (1), the mass ratio of ammonium bicarbonate to the PDMS prepolymer is 1.5:1, and then place it in a constant temperature and humidity chamber at 25 °C and 45% RH for standing for 6 h to allow the prepolymer to further fully penetrate into the template pores;

[0121] (4) Place the product after standing in step (3) in a high-precision temperature-controlled heater, heat it up to 50 °C at a rate of 1.5 °C / min, and carry out low-temperature pre-curing treatment at this temperature for a holding time of 8 h;

[0122] After the pre-curing is completed, heat it up to 80 °C at a rate of 2.5 °C / min and carry out high-temperature heating treatment for a holding time of 4 h;

[0123] After removing the sacrificial template by high-temperature heating treatment, heat the sample to 110 °C at a heating rate of 1 °C / min, carry out high-temperature curing treatment for a holding time of 1 h, and then cool it naturally to obtain a porous structure PDMS sponge.

[0124] Comparative Example 3

[0125] A method for preparing a porous structure PDMS sponge, comprising the following steps:

[0126] (1) Weigh 10 g of ammonium bicarbonate analytical pure powder, spread the ammonium bicarbonate powder on a clean and dry polytetrafluoroethylene mold, and evenly flatten the ammonium bicarbonate powder to construct an ammonium bicarbonate sacrificial template with a prototype of a specific pore structure;

[0127] (2) Mix the PDMS main agent and the curing agent at a volume ratio of 10:1, stir evenly, with a stirring speed of 400 r / min and a stirring duration of 35 min, and then place it in a vacuum degassing device (under a vacuum degree of 20 mmHg) for degassing for 10 min to remove the bubbles in the mixed solution and form a uniform PDMS prepolymer;

[0128] (3) Weigh 10 g of the PDMS prepolymer obtained in step (2), slowly and uniformly pour it into the ammonium bicarbonate sacrificial template obtained in step (1), with a mass ratio of ammonium bicarbonate to PDMS prepolymer of 1:1, and then place it in a constant temperature and humidity chamber at 25 °C and 45% RH and let it stand for 6 h to allow the prepolymer to further fully penetrate into the template pores;

[0129] (4) Place the product after standing in step (3) in a high-precision temperature control heater, heat it up to 55 °C at a rate of 1.5 °C / min, and perform a low-temperature pre-curing treatment at this temperature for a continuous holding time of 6 h;

[0130] After the pre-curing is completed, heat it up to 65 °C at a rate of 2.5 °C / min and perform a high-temperature heating treatment for a continuous holding time of 6 h;

[0131] After removing the sacrificial template by high-temperature heating treatment, heat the sample to 110 °C at a heating rate of 1 °C / min and perform a high-temperature curing treatment for a continuous holding time of 2 h, and then let it cool naturally to obtain a porous structure PDMS sponge.

[0132] Comparative Example 4

[0133] A method for preparing a porous structure PDMS sponge, comprising the following steps:

[0134] (1) Weigh 10 g of ammonium bicarbonate analytical pure powder, spread the ammonium bicarbonate powder on a clean and dry polytetrafluoroethylene mold, and evenly flatten the ammonium bicarbonate powder to construct an ammonium bicarbonate sacrificial template with a prototype of a specific pore structure;

[0135] (2) Mix the PDMS base agent and the curing agent at a volume ratio of 10:1, stir evenly at a stirring speed of 400 r / min for 35 min, and then place it in a vacuum degassing device (under a vacuum of 20 mmHg) for 10 min to remove the bubbles in the mixed solution and form a uniform PDMS prepolymer;

[0136] (3) Weigh 10 g of the PDMS prepolymer obtained in step (2), slowly and uniformly pour it into the ammonium bicarbonate sacrificial template obtained in step (1). The mass ratio of ammonium bicarbonate to the PDMS prepolymer is 1:1. Then place it in a constant temperature and humidity chamber at 25°C and 45% RH and let it stand for 6 h to allow the prepolymer to further fully penetrate into the pores of the template;

[0137] (4) Place the product after standing in step (3) in a high-precision temperature-controlled heater, heat it to 55°C at a rate of 1.5°C / min, and perform a low-temperature pre-curing treatment at this temperature for a continuous holding time of 6 h;

[0138] After the pre-curing is completed, heat it to 105°C at a rate of 2.5°C / min and perform a high-temperature heating treatment for a continuous holding time of 2 h;

[0139] After removing the sacrificial template by high-temperature heating treatment, heat the sample to 110°C at a heating rate of 1°C / min and perform a high-temperature curing treatment for a continuous holding time of 1 h, and then cool it naturally to obtain a porous structure PDMS sponge.

[0140] The physical photos of the porous structure PDMS sponge samples prepared in Comparative Examples 1-4 are shown in Figures 11 to 14 , as can be seen from the figure, the PDMS sponge samples prepared in Comparative Examples 1-4 did not form a stable and uniform porous structure. When the ratio of ammonium bicarbonate to the PDMS prepolymer was too low, the required "sponge" morphology could not be achieved. When the ratio was too high, the decomposition of ammonium bicarbonate would wash away the pore structure, making the material structure unstable. And if the treatment temperature was not appropriate, it was also difficult to obtain a stable porous structure. Through designing and optimizing the ratio of ammonium bicarbonate to the PDMS prepolymer and optimizing the treatment process parameters, the present invention obtained pores with uniform and appropriate sizes, enabling the material to achieve more efficient scattering in the visible light band, reducing the direct penetration of light, thereby enhancing its reflectivity, reducing the absorption of solar radiation heat, strengthening the radiative cooling effect, and more effectively regulating the temperature environment inside the building, which has great potential in building energy-saving applications.

[0141] In summary, the PDMS sponge with a hierarchical porous structure prepared by the present invention has good radiative cooling characteristics of high reflectivity in the visible light band and high infrared emissivity. Compared with transparent PDMS colloids (average visible light absorption rate of 18%, thermal conductivity of 0.27 W / m·K, etc.), the PDMS sponge with an ammonium bicarbonate sacrificial template has characteristics such as high haze, low light transmittance, hydrophobicity, low thermal conductivity, and self-cleaning function, making it have broad application potential in building envelope materials. Through actual application tests, the porous PDMS sponge has shown significant cooling capacity, verifying its effectiveness and practicality in radiative cooling technology. The porous structure PDMS sponge based on the ammonium bicarbonate sacrificial template with precisely controlled porosity of the present invention has broad application prospects in the field of radiative cooling.

[0142] The foregoing description of specific exemplary embodiments of the invention has been presented for purposes of illustration and example. These descriptions are not intended to limit the invention to the precise forms disclosed, and it is obvious that many modifications and variations are possible in light of the above teaching. The purpose of selecting and describing the exemplary embodiments is to explain the specific principles of the invention and its practical applications, so that those skilled in the art can implement and utilize various different exemplary embodiments of the invention as well as various different selections and modifications. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A method for preparing a porous PDMS sponge, characterized in that: The following steps are involved: (1) laying ammonium bicarbonate powder in a mold to construct an ammonium bicarbonate sacrificial template; (2) Weighing a PDMS main agent and a curing agent, stirring them evenly, and then degassing them to obtain a PDMS prepolymer; (3) pouring the PDMS prepolymer obtained in step (2) into the ammonium bicarbonate sacrificial template obtained in step (1), wherein the mass ratio of ammonium bicarbonate to PDMS prepolymer is 0.8 to 1.2:1, and allowing to stand under constant temperature and humidity conditions; (4) The product after standing in step (3) is subjected to three gradient heat treatments of low-temperature pre-curing, high-temperature heating, and high-temperature curing in sequence to obtain a porous PDMS sponge.

2. The method for preparing a porous PDMS sponge according to claim 1, characterized in that: In the three gradient treatments, the low-temperature pre-curing process parameters are: heating rate of 1-2°C / min, heating temperature of 40-55°C, and insulation time of 6-8h; the high-temperature heating process parameters are: heating rate of 2-3°C / min, heating temperature of 75-95°C, and insulation time of 2-4h; the high-temperature curing process parameters are: heating rate of 1-1.5°C / min, heating temperature of 110-130°C, and insulation time of 1-2h.

3. The method for preparing a porous PDMS sponge according to claim 1, characterized in that: In the step (2), the stirring process parameters are: stirring speed is 350 to 500 r / min, and stirring time is 30 to 45 min.

4. The method for preparing a porous PDMS sponge according to claim 1, characterized in that: In the step (3), the constant temperature and humidity conditions are: temperature of 20-30° C., humidity of 40-50% RH, and standing for 6-8 hours.

5. The method for preparing a porous PDMS sponge according to claim 1, characterized in that: The volume ratio of PDMS main agent and curing agent is 9-11:

1.

6. The method for preparing a porous PDMS sponge according to claim 2, characterized in that: The low-temperature pre-curing process parameters are: heating rate of 1.5°C / min, heating temperature of 40-55°C, and insulation time of 6-8h; the high-temperature heating process parameters are: heating rate of 2.5°C / min, heating temperature of 80-90°C, and insulation time of 2-4h; the high-temperature curing process parameters are: heating rate of 1°C / min, heating temperature of 110-120°C, and insulation time of 1-2h.

7. The method for preparing a porous PDMS sponge according to claim 1, characterized in that: The degassing is carried out in a vacuum degassing device with a vacuum degree of 15 to 30 mmHg for 10 to 20 minutes.

8. A porous PDMS sponge, characterized in that: The PDMS sponge is prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the porous PDMS sponge as claimed in claim 8 in preparing radiation refrigeration materials.

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