CN113072737B - Porous polydimethylsiloxane with daytime radiation refrigeration and preparation method thereof - Google Patents

Abstract

The invention relates to a preparation method of porous polydimethylsiloxane with daytime radiation refrigeration, which comprises the steps of firstly synthesizing a micron-sized NaCl pore-forming agent, controlling the distribution and the size of pores in the synthesized porous PDMS by controlling the size and the using amount of the micron-sized NaCl pore-forming agent, and realizing the daytime radiation refrigeration of the porous PDMS without additional conditions; the pores in the porous polydimethylsiloxane improve the mid-infrared emissivity (compared with non-porous PDMS) of the PDMS and scatter light in a solar spectrum band on one hand, and the air in the pores isolates heat exchange between a heat dissipation object and the surrounding environment on the other hand. The excellent radiation refrigeration effect of the porous PDMS film is ensured by the synergistic thermo-optic effect; the method has the advantages of simple preparation process, low cost and capability of realizing batch preparation; the preparation process does not need to add an additional metal or polymer reflecting layer, and 95% of solar radiation can be reflected by utilizing the pore structure of the porous PDMS.

Description

Porous polydimethylsiloxane with daytime radiation refrigeration and preparation method thereof

technical field

The invention belongs to the technical field of radiation cooling materials, in particular to a porous polydimethylsiloxane with daytime radiation cooling and a preparation method thereof.

Background technique

Due to global warming, industrial development, population growth and improvement of people's living standards, the energy demand for refrigeration and air conditioning is increasing dramatically. According to statistics, the energy required for air conditioning to cool down is expected to increase by more than 30 times between 2000 and 2100. However, traditional air-conditioning and refrigeration methods usually consume a lot of energy, and high energy consumption will directly cause excessive emissions of greenhouse gases, which will seriously damage the climate balance. Radiation cooling technology provides a new energy-saving and environmentally friendly cooling method for solving the internal cooling of high-energy-consuming buildings. Radiation cooling can spontaneously dissipate the heat of an object to the largest cold source (outer space) through radiative heat exchange, thereby achieving the purpose of cooling and dissipating heat. For surface objects, the troposphere, which is about 50K cooler than standard room temperature (300K), can serve as a potential radiative heat sink for ground-level cooling. Therefore, different from the ordinary heat dissipation method (which only reduces the temperature to room temperature), the radiative cooling technology can reduce the temperature of objects to below the ambient temperature without consuming any energy, saving energy and low carbon, and being green and environmentally friendly, which is in line with today's sustainable development trend .

The cooling capacity of a radiant cooler is not only affected by its radiative emissivity, but also by the way heat is captured in the surrounding environment (conduction, convection or with atmospheric and solar radiation, etc.). Only if the radiative cooling capacity of the radiant cooler is greater than the heat input by other means, the net cooling effect of the whole unit can be obtained. At present, materials with high emissivity in the atmospheric window (8-13 μm) can easily achieve nighttime radiative cooling (the atmospheric window refers to the 8-13 μm band where radiation is hardly absorbed by the atmosphere and can be fully transmitted). However, there are still huge challenges to achieve a temperature difference below room temperature under sunlight. This is because the solar radiation power is large (1000W/m ² ), and the radiative cooling device will generate significant heat flux as long as a small amount of sunlight is absorbed. To overcome these challenges, daytime radiative coolers need to maintain high emissivity in the atmospheric transparent window while having minimal absorption in the solar spectral range. The rise of a large number of modern tools in optics and photonics helps people to better control the spectrum of thermal radiation, making it possible for daytime radiative cooling. However, expensive metal raw materials, complicated fabrication processes, and fragile device characteristics limit their further applications. And materials like paint or polymer films are not only easy to store and transport, but can also be easily applied to surfaces of different shapes. These materials have attracted much attention due to their attractive properties as heat sinks.

Among the many polymers for radiative cooling, polydimethylsiloxane (PDMS) is an excellent material for radiative cooling due to its high transparency in the visible range and high selective emission in the mid-infrared range. Despite the excellent emissivity of PDMS in the infrared range, absorption in the solar spectral range hinders its further application in daytime radiative cooling. In recent years, there are PDMS-based radiative coolers that coat the backside of the PDMS film with a highly reflective film (aluminum or silver). This can result in significant cooling performance but also adds cost and difficulty to the manufacturing process. Later, inspired by the coordinated photothermal effects of polar bear fur in nature, researchers developed a flexible, superhydrophobic cooling by stacking PDMS films with highly scattering polyethylene aerogel (PE) layer by layer.” skin". The double-film structure not only increases the thickness of the cooler but also increases the fabrication cost. Other researchers added deionized water to the PDMS prepolymer to form an opaque emulsion, and rapidly evaporated the water during the curing process to form a PDMS film. It was coated on carbon black particles to obtain a bifunctional film. Under the application of external force, the PDMS film appeared porous and reflected about 93% of the solar radiation. None of the existing preparation schemes can directly obtain PDMS-based daytime radiative coolers that maintain high emissivity in the atmospheric transparent window and have minimal absorption in the solar spectral range.

SUMMARY OF THE INVENTION

In order to solve the above problems existing in the prior art, the present invention provides a porous polydimethylsiloxane with daytime radiation refrigeration and a preparation method thereof. The PDMS-based daytime radiation cooler of the present invention not only maintains a high emissivity in the atmospheric transparent window, but also has minimal absorption in the solar spectrum range, thereby effectively improving the daytime radiation capability of the material. Further, the preparation method of the PDMS-based daytime radiant cooler of the present invention is simple in operation and low in cost.

The technical scheme adopted in the present invention is:

A preparation method of porous polydimethylsiloxane with daytime radiation refrigeration, comprising the following steps:

(1) Synthesis of micron-scale NaCl porogen:

The NaCl solution was added dropwise to absolute ethanol under stirring conditions, reacted for a period of time, stopped stirring, after standing, poured out the supernatant, centrifuged, and collected the precipitate; the precipitate was washed with absolute ethanol and then centrifuged, The precipitate is collected, dried and pulverized to obtain micron-scale NaCl porogen;

(2) Take the PDMS prepolymer and the curing agent and mix them thoroughly to obtain a PDMS mixed solution; add the micron-scale NaCl porogen in step (1) to the PDMS mixed solution, and after fully mixing, A mixture of PDMS and micron-sized NaCl porogen is prepared;

(3) curing the mixture of PDMS and micron-scale NaCl porogen in step (2) first, then immersing in deionized water for soaking and etching, and drying to obtain porous polydimethylsilicon with daytime radiation refrigeration oxane.

In step (1), the concentration of the NaCl solution is 0.5-5M, the volume ratio of the NaCl solution to absolute ethanol is 1:100-20:100, and the solvent of the NaCl solution is water and/or glycerol.

In step (1), the time of reaction is 1-10min;

The drying temperature is 40-100° C., and the drying time is 3-24 h.

In step (1), the particle size of the micron-scale NaCl porogen is 5-10 μm.

In step (2), the molecular weight of the PDMS ranges from 50,000 to 200,000. As an optional embodiment, commercially available PDMS with molecular weights ranging from 50,000 to 200,000 can be used. Preferably, Dow Corning 184A is used in the present invention.

In step (2), the mass ratio of the PDMS prepolymer to the curing agent is 10:1-10:2.

In step (2), the mass ratio of the micron-scale NaCl porogen to the PDMS mixed solution is 1:2-10:1.

In step (3), the curing temperature is 60-200° C., and the curing time is 3-24 h.

In step (3), the soaking time in deionized water is 1-5 days;

The drying is vacuum drying or freeze drying.

The porous polydimethylsiloxane with daytime radiation refrigeration prepared by the method.

The beneficial effects of the present invention are:

(1) The preparation method of the porous polydimethylsiloxane with daytime radiation refrigeration according to the present invention, by first synthesizing a micron-scale NaCl porogen, and further by controlling the size and dosage of the micron-scale NaCl porogen By controlling the distribution and size of pores in the synthesized porous PDMS, the daytime radiation refrigeration of the porous PDMS is realized for the first time without additional conditions; the pores in the porous polydimethylsiloxane of the present invention can improve the PDMS on the one hand. Its own mid-infrared emissivity (compared to non-porous PDMS), scatters light in the solar spectrum band, and on the other hand, the air in the pores can isolate the heat exchange between the heat-dissipating object and the surrounding environment. The synergistic thermo-optic effect ensures the excellent radiation cooling effect of the porous PDMS film;

(2) The method of the present invention has the advantages of simple preparation process, low cost, and can realize batch preparation; no additional metal or polymer reflective layer needs to be added in the whole preparation process, and the pore structure of the porous PDMS itself can reflect 95% of the solar radiation ; The synergistic thermo-optic effect caused by the pore structure prepared by the invention improves the excellent radiation cooling effect of the porous PDMS film.

Description of drawings

In order to explain the embodiments of the present invention or the technical solutions in the prior art more clearly, the following briefly introduces the accompanying drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained according to these drawings without creative efforts.

1 is a scanning electron microscope image of the porous polydimethylsiloxane film described in Example 1 of the present invention;

2 is a scanning electron microscope image of the porous polydimethylsiloxane film described in Example 3 of the present invention;

3 is a scanning electron microscope image of the porous polydimethylsiloxane film described in Comparative Example 1 of the present invention;

Fig. 4 is the ultraviolet spectrum comparison diagram of the porous polydimethylsiloxane film described in Example 3 of the present invention and non-porous PDMS;

5 is a comparison diagram of the cooling effect of the porous polydimethylsiloxane film described in Example 3 of the present invention in the radiation refrigeration experiment with the environment and the existing reported non-porous PDMS backside Al film (Al-PDMS).

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be described in detail below. Obviously, the described embodiments are only some, but not all, embodiments of the present invention. Based on the embodiments of the present invention, all other implementations obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present invention.

Example 1

The present embodiment provides a method for preparing a porous polydimethylsiloxane with daytime radiation refrigeration, comprising the following steps:

(1) Synthesis of micron-scale NaCl porogen:

5ml, 3M NaCl solution (solvent is water) was added dropwise to 100ml of absolute ethanol under stirring conditions, stirred for 10min, stopped stirring, after standing for 1min, poured out the supernatant, centrifuged with a centrifuge , collect the white precipitate; after washing the white precipitate with absolute ethanol, centrifuge it with a centrifuge to collect the precipitate, place the precipitate in a vacuum drying box at 100 ° C to dry for 12 hours, take it out, use agate smoke wave to grind to powder, That is to obtain a micron-scale NaCl porogen with a particle size of 7.5 μm;

(2) Weigh 10g of Dow Corning PDMS (Dow Corning 184A) and 2g of Dow Corning curing agent (Dow Corning 184B), and after thorough mixing, obtain a PDMS mixture; take 5g of the PDMS mixture and 5g of the micron described in step (1) After fully mixing the micron-scale NaCl porogen, a mixture of PDMS and micron-scale NaCl porogen was prepared;

(3) Evenly spread the mixture of PDMS and micron-scale NaCl porogen in step (2) in a flat rectangular groove of 5cm×5cm×0.5mm, and cure it on a glue baking machine at 120°C for 12h; then immerse it in deionized water After soaking in water for 3 days for etching to remove NaCl, and drying in a freeze dryer for 2 days, a porous polydimethylsiloxane membrane with daytime radiation refrigeration was obtained.

The scanning electron microscope picture of the porous polydimethylsiloxane film described in this example is shown in Fig. 1. It can be seen from Fig. 1 that there are only micron-sized NaCl in the prepared porous PDMS film. The pore size remains uniform, with pores having an average size of 7.5 μm.

Example 2

The present embodiment provides a method for preparing a porous polydimethylsiloxane with daytime radiation refrigeration, comprising the following steps:

(1) Synthesis of micron-scale NaCl porogen:

5ml, 3M NaCl solution (solvent is water) was added dropwise to 100ml of absolute ethanol under stirring conditions, stirred for 10min, stopped stirring, after standing for 1min, poured out the supernatant, centrifuged with a centrifuge , collect the white precipitate; after washing the white precipitate with absolute ethanol, centrifuge it with a centrifuge to collect the precipitate, place the precipitate in a vacuum drying box at 100 ° C to dry for 12 hours, take it out, use agate smoke wave to grind to powder, That is to obtain a micron-scale NaCl porogen with a particle size of 7.5 μm;

(2) Weigh 10g of Dow Corning PDMS (Dow Corning 184A) and 2g of Dow Corning curing agent (Dow Corning 184B), and after thorough mixing, obtain a PDMS mixture; take 1g of the PDMS mixture and 6g of the micron described in step (1). After fully mixing the micron-scale NaCl porogen, a mixture of PDMS and micron-scale NaCl porogen was prepared;

(3) Put the mixture of PDMS and NaCl into a rectangular vessel and compact it hard and put it into an oven at 80° C. to cure for 1 hour. The solidified PDMS block was immersed in hot water at 80 °C for 48 h, and the aqueous solution was changed every 10 h to remove the NaCl in the middle. The template-removed PDMS was dried in an oven at 80 °C for 12 h to obtain a porous polydimethylsiloxane membrane with daytime radiation refrigeration.

Example 3

The present embodiment provides a method for preparing a porous polydimethylsiloxane with daytime radiation refrigeration, comprising the following steps:

(1) Synthesis of micron-scale NaCl porogen:

Add 5ml, 3M NaCl solution (solvent is water) dropwise to 100ml absolute ethanol under stirring conditions, stir for 10min, stop stirring, after standing for 1min, pour off the supernatant, use a centrifuge to centrifuge, Collect the white precipitate; after washing the white precipitate with absolute ethanol, centrifuge it with a centrifuge to collect the precipitate, place the precipitate in a vacuum drying box at 100°C for 12 hours, and then take it out. A micron-scale NaCl porogen with a particle size of 7.1 μm was obtained;

(2) Weigh 10 g of Dow Corning PDMS (Dow Corning 184A) and 2 g of Dow Corning curing agent (Dow Corning 184B), and after thorough mixing, obtain a PDMS mixed solution; take 2 g of the PDMS mixed solution and 10 g of the micron described in step (1) After fully mixing the micron-scale NaCl porogen, a mixture of PDMS and micron-scale NaCl porogen was prepared;

(3) Evenly spread the mixture of PDMS and micron NaCl porogen in step (2) in a flat rectangular groove of 5cm×5cm×0.5mm, and cure it on a glue baking machine at 150°C for 12h; then immerse it in deionized water After soaking in water for 5 days for etching to remove NaCl, and drying in a 60°C vacuum oven for 12 hours, a porous polydimethylsiloxane membrane with daytime radiation refrigeration was obtained.

The scanning electron microscope picture of the porous polydimethylsiloxane film described in this example is shown in FIG. 2 . Comparing the structures of Fig. 1 and Fig. 2, it can be seen that the porous PDMS membrane prepared in Fig. 2 is not only filled with pores of 7.1 μm with the size of the micron-sized NaCl porogen, but also a part of the pore size is much larger than that of the porogen. The size of the macropore (25.7 μm), the whole sample presents a three-dimensional network interweaving structure. This is due to the increase in the amount of micron-sized NaCl porogen incorporated (the mass ratio of micron-sized NaCl porogen to the PDMS mixture is 5:1), so that NaCl cannot be uniformly distributed in the PDMS mixture, resulting in some reunion. After this part of the agglomerated NaCl was cured and etched, a slightly larger hole of 25.7 μm was left. Increasing the feed ratio of NaCl would exacerbate this type of agglomeration, resulting in a larger pore structure. Therefore, the amount of micron-sized NaCl porogen can affect the distribution and size of pores within the synthesized porous PDMS.

FIG. 4 is a comparison diagram of the ultraviolet spectra of the porous polydimethylsiloxane film of the present embodiment and the non-porous PDMS. It can be seen from the figure that compared with the non-porous PDMS, the porous PDMS has superior Reflectivity. Non-porous PDMS is prepared by the following method: Weigh 10g of Dow Corning PDMS (Dow Corning 184A) and 2g of Dow Corning curing agent (Dow Corning 184B), and after thorough mixing, the PDMS mixture is prepared, and after curing on a glue machine at 150 ° C for 12h , that is, non-porous PDMS.

In order to quantitatively evaluate the reflection performance, the solar reflectance was calculated using the formula (1).

Among them, I _sun (λ) represents the radiation intensity of sunlight at a wavelength of λ nm. Here, the standard spectrum I _AM1.5 (λ) of ASTM G173 reference solar spectral irradiance is used for simplification. R _sun (λ) is the spectral reflectance of the sample surface.

Substituting the data in Fig. 4 into formula (1), the solar reflectance of PDMS with holes (95%) and PDMS without holes (6%) can be calculated respectively. This is caused by the scattering of light by the porous structure within the porous PDMS that matches the wavelength of sunlight.

FIG. 5 is a comparison diagram of the cooling effect of the porous polydimethylsiloxane film described in this example in the radiation refrigeration experiment with the environment and the existing reported PDMS backside Al film with a high reflection layer (Al-PDMS). It can be seen that in the radiation refrigeration experiment, the porous PDMS prepared by the method of this embodiment can reduce the temperature of the space to be measured to 8°C below room temperature under the condition of sunlight. The good radiative cooling effect of the porous PDMS film is caused by the synergistic thermo-optic effect of the porous structure. On the one hand, the porosity fabricated by the NaCl template enhances the reflectivity of sunlight and avoids the self-heating phenomenon caused by the absorption of sunlight by the material. On the other hand, the existence of a large number of pores can effectively suppress the thermal convection between the external hot air and the cooled space. , so as to ensure the cooling effect. Compared with the reported non-porous PDMS films of the same thickness prepared on commercial aluminum foils, the cooling effect of porous PDMS is better. This is because the porous structure can also promote the increase of the electromagnetic wave emissivity by increasing the radiation area and causing multiple diffuse reflections of the electromagnetic wave on the rough surface.

Example 4

The present embodiment provides a method for preparing a porous polydimethylsiloxane with daytime radiation refrigeration, comprising the following steps:

(1) Synthesis of micron-scale NaCl porogen:

Add 20ml, 0.5M NaCl solution (the solvent is glycerol) dropwise to 100ml absolute ethanol under vigorous stirring conditions, stir for 1min, stop stirring, after standing for 1min, pour off the supernatant, and use centrifugation. Centrifuge with a machine to collect the white precipitate; after washing the white precipitate with anhydrous ethanol, centrifuge with a centrifuge to collect the precipitate, put the precipitate in a vacuum drying box at 40 ° C to dry for 24 hours, take out, and grind it to powder with agate smoke wave Then, a micron-scale NaCl porogen with a particle size of 5 μm was obtained;

(2) Weigh 10g of Dow Corning PDMS (Dow Corning 184A) and 1g of Dow Corning curing agent (Dow Corning 184B), stir by hand until a lot of air bubbles appear, and after fully mixing, obtain a PDMS mixture; take 1g of the PDMS mixture and 10g In step (1), after the micron-scale NaCl porogen is fully mixed, a mixture of PDMS and micron-scale NaCl porogen is prepared;

(3) The mixture of PDMS and micron-sized NaCl porogen described in step (2) is evenly and directly coated on the surface of the sample to be cooled, and cured on a glue baking machine at 60°C for 24 hours; and then immersed in deionized water for 3 days. After etching and removing the NaCl template, the porous polydimethylsiloxane membrane with daytime radiation refrigeration was obtained after drying in a vacuum drying oven at 30° C. for 24 hours.

Example 5

The present embodiment provides a method for preparing a porous polydimethylsiloxane with daytime radiation refrigeration, comprising the following steps:

(1) Synthesis of micron-scale NaCl porogen:

20ml, 5M NaCl solution (solvent is water) was added dropwise to 100ml absolute ethanol under vigorous stirring conditions, stirred for 10min, stopped stirring, after standing for 1min, poured out the supernatant, and used a centrifuge. Centrifuge to collect the white precipitate; after washing the white precipitate with anhydrous ethanol, centrifuge with a centrifuge to collect the precipitate, place the precipitate in a vacuum drying box at 100°C for 3 hours, take out, and grind it to powder with agate smoke wave , that is, the micron-scale NaCl porogen with a particle size of 10 μm is obtained;

(2) Weigh 10g of Dow Corning PDMS (Dow Corning 184A) and 1-2g of Dow Corning curing agent (Dow Corning 184B), stir by hand until a lot of air bubbles appear, and after fully mixing, the PDMS mixture is prepared; take 20g of the PDMS mixture After fully mixing with 10 g of the micron-level NaCl porogen in step (1), a mixture of PDMS and micron-level NaCl porogen was prepared;

(3) Evenly spread the mixture of PDMS and micron-scale NaCl porogen in step (2) in a flat rectangular groove of 5cm×5cm×0.5mm, and cure it on a glue baking machine at 200°C for 3h; then immerse it in deionized water After soaking in water for 3 days for etching to remove the NaCl template, and drying in a vacuum drying oven at 100°C for 3 hours, a porous polydimethylsiloxane membrane with daytime radiation refrigeration was obtained.

Example 6

The present embodiment provides a method for preparing a porous polydimethylsiloxane with daytime radiation refrigeration, comprising the following steps:

(1) Synthesis of micron-scale NaCl porogen:

10ml, 5M NaCl solution (solvent is water) was added dropwise to 100ml of absolute ethanol under vigorous stirring conditions, stirred for 5min, stopped stirring, left standing for 1min, poured out the supernatant, and used a centrifuge. Centrifuge to collect the white precipitate; after washing the white precipitate with absolute ethanol, centrifuge it with a centrifuge to collect the precipitate, place the precipitate in a vacuum drying box at 70°C for 12 hours and take it out, and grind it to a powder with agate smoke wave , that is, the micron-scale NaCl porogen with a particle size of 7.5 μm is obtained;

(2) Weigh 10g of Dow Corning PDMS (Dow Corning 184A) and 2g of Dow Corning curing agent (Dow Corning 184B), stir by hand until a large number of bubbles appear, and after fully mixing, obtain a PDMS mixed solution; take 10 g of the PDMS mixed solution and 10 g In step (1), after the micron-scale NaCl porogen is fully mixed, a mixture of PDMS and micron-scale NaCl porogen is prepared;

(3) Evenly spread the mixture of PDMS and micron-scale NaCl porogen in step (2) in a flat rectangular groove of 5cm×5cm×0.5mm, and cure it on a glue baking machine at 120°C for 12h; then immerse it in deionized water After soaking in water for 3 days to perform etching to remove the NaCl template, and drying in a freeze dryer for 5 days, a porous polydimethylsiloxane membrane with daytime radiation refrigeration was obtained.

Comparative Example 1

This comparative example provides a preparation method of porous polydimethylsiloxane, and the difference from Example 2 is only:

In step (2), the "micron-scale NaCl porogen" is replaced with "NaCl directly purchased without recrystallization", that is, the mixed solution of NaCl and PDMS purchased directly without recrystallization is used to fully mix to obtain A mixture of PDMS and micron-sized NaCl porogen; other raw materials and operations were the same as in Example 2.

The scanning electron microscope picture of the porous polydimethylsiloxane membrane described in this comparative example is shown in Fig. 3. It can be seen from Fig. 3 that the pore size distribution inside the prepared porous PDMS membrane is wider and is similar to that of the porous PDMS membrane. The added NaCl size maintains a consistent pore size. Compared with the pore structure of the porous PDMS membrane in Figure 1, it can be seen that the size of the NaCl template can affect the distribution and size of the pores in the porous PDMS.

The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention. should be included within the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims (7)

1. a preparation method of the porous polydimethylsiloxane with daytime radiation refrigeration, is characterized in that, comprises the steps: (1) Synthesis of micron-scale NaCl porogen: The NaCl solution was added dropwise to absolute ethanol under stirring conditions, reacted for a period of time, stopped stirring, after standing, poured out the supernatant, centrifuged, and collected the precipitate; the precipitate was washed with absolute ethanol and then centrifuged, The precipitate is collected, dried and pulverized to obtain micron-scale NaCl porogen; The volume ratio of the NaCl solution to absolute ethanol is 1:100-20:100; the particle size of the micron-level NaCl porogen is 5-10 μm; (2) Take the PDMS prepolymer and the curing agent and mix them thoroughly to obtain a PDMS mixed solution; add the micron-scale NaCl porogen in step (1) to the PDMS mixed solution, and after fully mixing, A mixture of PDMS and micron-sized NaCl porogen is prepared; The molecular weight range of the PDMS is 50,000-200,000; (3) curing the mixture of PDMS and micron-scale NaCl porogen in step (2) first, then immersing in deionized water for soaking and etching, and drying to obtain porous polydimethylsilicon with daytime radiation refrigeration oxane; In step (1), the concentration of the NaCl solution is 0.5-5M, and the solvent of the NaCl solution is water and/or glycerol. 2. the preparation method of the porous polydimethylsiloxane with daytime radiation refrigeration according to claim 1, is characterized in that, in step (1), the time of reaction is 1-10min; The drying temperature is 40-100° C., and the drying time is 3-24 h. 3. the preparation method of the porous polydimethylsiloxane with daytime radiation refrigeration according to claim 1, is characterized in that, in step (2), the mass ratio of described PDMS prepolymer and curing agent 10:1-10:2. 4. The preparation method of porous polydimethylsiloxane with daytime radiation refrigeration according to claim 1, wherein in step (2), the micron-scale NaCl porogen is mixed with the PDMS The mass ratio of the liquid is 1:2-10:1. 5 . The preparation method of porous polydimethylsiloxane with daytime radiation refrigeration according to claim 1 , wherein in step (3), the curing temperature is 60-200° C., and the The curing time is 3-24h. 6. The preparation method of the porous polydimethylsiloxane with daytime radiation refrigeration according to claim 1, wherein in step (3), the soaking time in deionized water is 1-5 days; The drying is vacuum drying or freeze drying. 7. The porous polydimethylsiloxane with daytime radiation refrigeration prepared by the method of any one of claims 1-6.

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