Hierarchical porous PDMS (polydimethylsiloxane) material as well as preparation method and application thereof

Abstract

The invention provides a graded porous PDMS (polydimethylsiloxane) material as well as a preparation method and application thereof. The preparation method does not involve any complex chemical reaction, is simple in process equipment, easy to implement and high in controllability of material performance, and has a huge prospect of large-scale popularization and application. The hierarchical porous PDMS material has ordered or disordered communicated pore channels, is of a hierarchical porous structure formed by compounding large pores and small pores, and has huge application value in the technical fields of wearable flexible electronic devices, biomedical materials and the like.

Description

Technical Field

[0001] The invention relates to the technical field of porous PDMS material preparation, and in particular to a graded porous PDMS material and a preparation method and application thereof. Background Art

[0002] Electronic skin (E-skin) has similar sensing functions to human skin, can convert external stimuli into detectable electrical signals, and has the characteristics of being thin, soft, and flexible. Flexible electronic skin has attracted widespread attention due to its great potential in health monitoring, human-machine interaction (HMI), intelligent robots, the Internet of Things, and other fields. PDMS membrane materials have high transparency, biocompatibility, elasticity, and stretchability, and are ideal flexible substrates for current wearable flexible electronic devices. However, the compactness and air impermeability of PDMS may cause skin hypoxia or allergic reactions, which greatly affects the practicality, comfort, and safety of electronic skin. The water vapor permeability of PDMS can be improved by forming a porous structure. Therefore, the development of PDMS membrane materials with porous structures for use in the field of wearable electronics has important practical significance and application value. In addition, porous PDMS has a variety of potential applications in the biomedical field due to its unique properties, including high biocompatibility, mechanical flexibility, and adjustable porosity. Porous PDMS can be used as a scaffold material for tissue engineering applications. The porosity of the material allows cells and nutrients to penetrate, while also providing a three-dimensional structure to support tissue growth. The high surface area and tunable porosity of porous PDMS make it a promising material for drug delivery applications. The pore size and distribution can be tailored to achieve a specific release rate and distribution, allowing for more precise and effective drug delivery. Overall, porous PDMS has the potential to advance the field of biomedical engineering and enable new applications in biomedical fields such as tissue engineering, drug delivery, biosensors, and wound healing.

[0003] A Chinese invention patent (Announcement No.: CN113912902A) discloses a method for preparing a porous PDMS / PVA hydrogel composite refrigeration film, wherein NaCl particles are mixed and stirred with uncrosslinked PDMS raw materials, and the resulting mixture is evenly scraped onto a glass plate to form a coating, which is then placed in an oven for curing; the cured coating is peeled off the glass plate, and placed in deionized water at room temperature to dissolve the NaCl particles to form a porous PDMS; the porous PDMS and PVA hydrogel are adhered to obtain a double-layer refrigeration polymer film. This method uses sacrificial particles to directly solidify and prepare porous PDMS materials. The particles are severely agglomerated and unevenly dispersed in the system, which can cause the size of the pores to be uncontrollable. Moreover, if the sacrificial particles are wrapped by PDMS, they are not easy to remove and will remain in the material.

[0004] A Chinese invention patent (Announcement No.: CN112646226A) discloses a method for preparing porous PDMS and its application in flexible electronic devices, the preparation method comprising the following steps: mixing PDMS prepolymer and curing agent evenly, then adding deionized water and stirring; after PDMS and deionized water are fully stirred and mixed evenly, pouring the mixture into a prepared mold, covering the mold with an aluminum plate after the mixture fills the mold, and heating and curing. In this method, the hole size formed by using deionized water as a template is too large, which will lead to a decrease in the strength of the porous PDMS.

[0005] A Chinese invention patent (Announcement No.: CN115232355A) discloses a method for preparing hierarchical porous PDMS based on a soft template and its application in sensors, wherein the preparation includes the following steps: preparing a hydrogel of PVA-B; preparing a PDMS solution; fully stirring the PDMS solution and the PVA-B hydrogel; preparing a hierarchical porous PDMS molding mold; placing PDMS / PVA-B in the prepared mold, and finally heating and curing it; cleaning the cured product with hydrochloric acid and deionized water, and drying it to obtain a hierarchical porous PDMS. The preparation process of this method is complicated and the operation is difficult.

[0006] A Chinese invention patent (Announcement No.: CN113912902A) discloses a method for preparing porous PDMS foam and its application. The preparation method includes the following steps: mixing the PDMS prepolymer with the crosslinking agent, and stirring evenly with a magnetic stirrer; mixing the PDMS solution with n-hexane, diluting and stirring evenly; mixing the PDMS / n-hexane mixture with deionized water, allowing the oil-water emulsion to stand at room temperature, absorbing the upper clear liquid and then prepolymerizing, and finally heating and polymerizing and drying, removing the translucent viscous covering layer on the surface to obtain a white porous PDMS foam. The method is complex and the distribution of pores is not easy to adjust.

[0007] In the above-mentioned commonly used preparation methods, when sacrificial particles are introduced into the solid phase mixing, it is difficult for the sacrificial particles to be completely dispersed in the unpolymerized PDMS in the form of single particles. The particles will agglomerate, and the size and distribution of the particles will be uneven, making the pore size larger and unevenly distributed. For example, when hard particles such as sugar are dissolved and washed away with liquid, if the particles are completely wrapped by PDMS, the particles cannot be removed (mostly water is used as a solvent, and since PDMS is hydrophobic, it is difficult to wet and wash away all the sacrificial particles). In addition, when water droplets are used as templates, the molecular weight and viscosity of water and PDMS are very different. The water droplets produced under mechanical stirring have poor stability and will merge with each other or even stratify before solidification. Due to the rapid vaporization of water droplets when the system is heated and solidified and the condensation of cooling, the resulting technical problems of irregular and unevenly distributed pores.

[0008] In view of this, it is necessary to design an improved hierarchical porous PDMS material and a preparation method thereof to solve the above problems and realize its application in multiple fields. Summary of the invention

[0009] The purpose of the present invention is to provide a hierarchical porous PDMS material and a preparation method and application thereof.

[0010] To achieve the above-mentioned object of the invention, the present invention provides a method for preparing a hierarchical porous PDMS material, comprising the following steps:

[0011] S1, dissolving sacrificial particles in water according to a predetermined concentration ratio, and stirring to obtain a sacrificial particle homogeneous solution;

[0012] S2, adding the sacrificial particle homogeneous solution to the polydimethylsiloxane prepolymer, stirring until the mixture is uniform, to obtain a mixed solution; then adding a curing agent, stirring to obtain a polymer mixed solution; and then freezing the polymer mixed solution to convert it from a liquid state to a solid state, to obtain a solid polymer;

[0013] S3, freeze-drying the solid polymer to obtain a porous PDMS material;

[0014] S4, removing the sacrificial particles in the porous PDMS material to obtain a graded porous PDMS material.

[0015] As a further improvement of the present invention, the sacrificial particles are salt particles, sugar particles, or a mixture of the two;

[0016] The salt particles are a mixture of one or more of sodium salt particles and potassium salt particles; the sugar particles are a mixture of one or more of sucrose particles, glucose particles and stevia particles;

[0017] Before step S1, the sacrificial particles are pre-treated by grinding for 1 to 2 hours.

[0018] As a further improvement of the present invention, in the sacrificial particle homogeneous solution in step S1, the concentration of the sacrificial particles is 1% to 25%.

[0019] As a further improvement of the present invention, in the sacrificial particle homogeneous solution in step S1, the concentration of the sacrificial particles is 5% to 15%.

[0020] As a further improvement of the present invention, in the water-alcohol solvent system in step S1, the volume ratio of water to alcohol is greater than 4:1, and the alcohol is one or more combinations of ethanol, isopropanol, and tert-butanol.

[0021] As a further improvement of the present invention, in step S2, the mass ratio of the polydimethylsiloxane prepolymer to the sacrificial particle homogeneous solution is 1:(20-1).

[0022] As a further improvement of the present invention, in step S2, the mass ratio of the polydimethylsiloxane prepolymer to the sacrificial particle homogeneous solution is 1:(10-3).

[0023] As a further improvement of the present invention, in step S2, the mass ratio of the polydimethylsiloxane prepolymer to the curing agent is (7-15):1.

[0024] As a further improvement of the present invention, in step S2, the mass ratio of the polydimethylsiloxane prepolymer to the curing agent is (8-12):1.

[0025] As a further improvement of the present invention, in step S2, the specific process of the freezing treatment is: after packaging the polymer mixed solution, place it at a freezing temperature of -60 to -90°C for 18 to 36 hours; or, after packaging the polymer mixed solution, quickly flash freeze it, and then place the flash frozen polymer at a freezing temperature of -60 to -90°C for 18 to 36 hours.

[0026] As a further improvement of the present invention, in step S4, the specific process of removing the sacrificial particles is: placing the porous PDMS material in water for 6 to 8 hours to remove the remaining sacrificial particles, and performing post-drying treatment.

[0027] As a further improvement of the present invention, in step S3, the specific process of freeze drying is: placing the solid polymer in a freeze dryer with a cold trap temperature of -60 to -80°C and drying for 36 to 60 hours.

[0028] In order to achieve the above-mentioned object of the invention, the present invention also provides a hierarchical porous PDMS material, which is prepared by the above-mentioned preparation method.

[0029] As a further improvement of the present invention, the porosity of the graded porous PDMS material is 30±0.1% to 85±0.1%;

[0030] The hierarchical porous PDMS material has ordered or disordered interconnected pores, and a multi-level pore structure composed of large pores and small pores, with a pore diameter of 2 to 700 μm; the small pores are evenly distributed on the pore walls of the large pores, with a pore diameter of 50 to 700 μm; and the pore diameter of the small pores is 2 to 30 μm.

[0031] In order to achieve the above-mentioned purpose of the invention, the present invention also provides the application of the above-mentioned graded porous PDMS material in the technical fields of wearable flexible electronic devices, biomedical materials, etc.

[0032] The beneficial effects of the present invention are:

[0033] 1. The preparation method of the hierarchical porous PDMS material provided by the present invention utilizes the dissolution of sacrificial particles to construct a uniform incompatible system (PDMS is incompatible with salt / sugar solution), and combines the blending-freezing-freeze drying-dissolution joint process to realize a three-step collaborative hierarchical pore-forming process. The specific process is: the process of the polymer mixed solution forming a solid phase is carried out under low temperature freezing, at which time the PDMS does not form a cross-linked structure, and the water (or water-alcohol solvent) solvent ice crystals grow in the PDMS system to form micropores (one-time pore formation, based on the volume difference between the liquid solvent and the solid solvent); then in the freeze-drying process, the PDMS forms a cross-linked structure, and the ice crystals are directly changed from the solid state to the gas state, and the path for the gas to leave the system from the inside to the outside allows the holes to be connected (this also provides a path premise for the subsequent sacrificial particles to precipitate, so that the sacrificial particles will not be wrapped in the PDMS material), leaving a large-aperture hole structure in the PDMS (secondary pore formation); finally, the sacrificial particles that have been solidified and precipitated are further removed, and a small-aperture hole structure is obtained on the wall of the large pores (three-time pore formation), and finally a hierarchical porous PDMS material is obtained. The present invention is based on the low-temperature condition setting, and the cross-linking and curing reaction process of the PDMS system and the curing, vaporization and dissolution process of the sacrificial particle homogeneous solution are differentially and asynchronously processed, so that the ice crystal growth and the precipitation of the sacrificial particles can be fully carried out. At the same time, under the premise of ensuring the effective cross-linking reaction, the present invention effectively overcomes the technical defects of irregular and unevenly distributed pores caused by the rapid vaporization and cooling condensation of water droplets when the system is heated and cured when water droplets are used as pore-forming templates in the prior art.

[0034] 2. The preparation method of the hierarchical porous PDMS material provided by the present invention adopts a sacrificial particle homogeneous solution, which can significantly increase the porosity of the system compared with the conventional single aqueous solution system; and, by utilizing the different physical and chemical properties of sacrificial particles and aqueous solvents, after the ice crystals formed by the aqueous solvent are directly vaporized to form connected large pores, the sacrificial particles will re-precipitate and return to the state of solid particles, loaded on the pore walls of the large pores, and after being removed by dissolution post-treatment, a uniformly distributed small pore structure is constructed on the pore walls of the large pores, thereby constructing a hierarchical porous composite structure on the surface and inside of the material. The present invention effectively overcomes the technical defects of the prior art that directly uses sacrificial particles for solid phase mixing (the size of the pores formed depends on the size of the particles), the particles are easy to agglomerate during mixing, resulting in a larger pore size, inconvenient size adjustment, and the particles and PDMS are easy to mix unevenly, and if the sacrificial particles are completely wrapped by PDMS, the particles cannot be removed. In addition, the molecular weight of the sacrificial particle homogeneous solution is significantly higher than that of the single aqueous solution, which can effectively overcome the technical defects of mutual fusion and even stratification with PDMS before curing.

[0035] 3. The preparation method of the hierarchical porous PDMS material provided by the present invention can effectively adjust the size and porosity of the pores in the hierarchical porous structure by adjusting parameters such as the ratio of PDMS prepolymer and curing agent, the concentration of the sacrificial particle homogeneous solution, and the mass ratio of the sacrificial particle homogeneous solution to PDMS; the arrangement and distribution of the sacrificial particle homogeneous solution in the PDMS system during solidification can also be adjusted by directional freezing and non-directional freezing process methods, thereby affecting the arrangement and distribution of the pores in the PDMS material.

[0036] 4. The preparation method of the hierarchical porous PDMS material provided by the present invention does not involve any complicated chemical reaction, has simple process equipment, is easy to implement, has strong controllability of material properties, and has great prospects for large-scale promotion and application.

[0037] 5. The hierarchical porous PDMS material provided by the present invention has ordered or disordered interconnected pores, and a multi-level pore structure composed of large pores and small pores. It has great application value in technical fields such as wearable flexible electronic devices, biomedical materials, tissue engineering, drug delivery, biosensors, wound healing and other biomedical fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 A schematic diagram of the three-step coordinated graded pore-forming process of the preparation method of the graded porous PDMS material provided by the present invention.

[0039] Figure 2 This is an electron microscope image of the hierarchical porous PDMS material provided in Example 1 of the present invention (scale: 500 μm).

[0040] Figure 3 The electron microscope image of the pore structure of the hierarchical porous PDMS material provided in Example 1 of the present invention ( Figure 3 b is Figure 3 A partial enlarged view of middle a; Figure 3 Scale bar in middle a: 100 μm; Figure 3 Scale bar in b: 10 μm).

[0041] Figure 4 This is an electron microscope image of the porous PDMS material provided for Comparative Example 1 of the present invention (scale: 100 μm).

[0042] Figure 5 This is an electron microscope image of the hierarchical porous PDMS material provided in Example 2 of the present invention (scale: 100 μm).

[0043] Figure 6 This is an electron microscope image of the macroporous structure of the graded porous PDMS material provided in Example 2 of the present invention (scale: 100 μm).

[0044] Figure 7This is an electron microscope image of the pore structure of the graded porous PDMS material provided in Example 2 of the present invention (scale: 10 μm).

[0045] Figure 8 This is a cross-sectional electron micrograph of the hierarchical porous PDMS material provided in Example 4 of the present invention (scale: 500 μm).

[0046] Fig. 9 This is a plane electron microscope image of the hierarchical porous PDMS material provided in Example 4 of the present invention (scale: 500 μm). DETAILED DESCRIPTION

[0047] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0048] It should also be noted that, in order to avoid obscuring the present invention due to unnecessary details, only structures and / or processing steps closely related to the scheme of the present invention are shown in the drawings, while other details that are not closely related to the present invention are omitted.

[0049] In addition, it should be noted that the terms "comprises", "includes" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or apparatus.

[0050] See also Figure 1 As shown, the present invention provides a method for preparing a hierarchical porous PDMS material, comprising the following steps:

[0051] S1, dissolving sacrificial particles in water or a water-alcohol solvent according to a predetermined concentration ratio, and stirring to obtain a sacrificial particle homogeneous solution;

[0052] S2, adding the sacrificial particle homogeneous solution to the polydimethylsiloxane prepolymer, stirring until the mixture is uniform, to obtain a mixed solution; then adding a curing agent, stirring to obtain a polymer mixed solution; and then freezing the polymer mixed solution to convert it from a liquid state to a solid state, to obtain a solid polymer;

[0053] S3, freeze-drying the solid polymer to obtain a porous PDMS material;

[0054] S4, removing the sacrificial particles in the porous PDMS material to obtain a graded porous PDMS material.

[0055] As a further improvement of the present invention, the sacrificial particles are salt particles, sugar particles, or a mixture of the two;

[0056] The salt particles are a mixture of one or more of sodium salt particles and potassium salt particles; the sugar particles are a mixture of one or more of sucrose particles, glucose particles and stevia particles;

[0057] Before step S1, the sacrificial particles are pre-treated by grinding for 1 to 2 hours.

[0058] Preferably, in the sacrificial particle homogeneous solution in step S1, the concentration of the sacrificial particles is 1% to 25%.

[0059] Preferably, in the sacrificial particle homogeneous solution in step S1, the concentration of the sacrificial particles is 5% to 15%.

[0060] Preferably, in the water-alcohol solvent system in step S1, the volume ratio of water to alcohol is greater than 4:1, and the alcohol is one or more combinations of ethanol, isopropanol, and tert-butanol.

[0061] Preferably, in step S2, the mass ratio of the polydimethylsiloxane prepolymer to the sacrificial particle homogeneous solution is 1:(20-1).

[0062] Preferably, in step S2, the mass ratio of the polydimethylsiloxane prepolymer to the sacrificial particle homogeneous solution is 1:(10-3).

[0063] Preferably, in step S2, the mass ratio of the polydimethylsiloxane prepolymer to the curing agent is (7-15):1.

[0064] Preferably, in step S2, the mass ratio of the polydimethylsiloxane prepolymer to the curing agent is (8-12):1.

[0065] Preferably, in step S2, the specific process of the freezing treatment is: packaging the polymer mixed solution and placing it at a freezing temperature of -60 to -90°C for 18 to 36 hours; or, packaging the polymer mixed solution and quickly flash freezing it, and then placing the flash frozen polymer at a freezing temperature of -60 to -90°C for 18 to 36 hours.

[0066] Preferably, in step S4, the specific process of removing the sacrificial particles is: placing the porous PDMS material in water for 6 to 8 hours for ultrasonic treatment to remove the residual sacrificial particles, and performing post-drying treatment.

[0067] Preferably, in step S3, the specific process of freeze drying is: placing the solid polymer in a freeze dryer with a cold trap temperature of -60 to -80°C for drying for 36 to 60 hours.

[0068] Example 1

[0069] This embodiment 1 provides a method for preparing a hierarchical porous PDMS material, and the specific preparation process is as follows:

[0070] S1, preparation of sacrificial particle homogeneous solution: first grind sodium chloride particles for 1 to 2 hours, then dissolve the sodium chloride particles in deionized water at a concentration of 5% by mass, and stir magnetically for 24 hours to finally form a clear sodium chloride solution.

[0071] S2, preparation of polymer solution: take an appropriate amount of polydimethylsiloxane (PDMS) prepolymer (without adding curing agent first) in a beaker, and then add an appropriate amount of the prepared sodium chloride solution, and use magnetic stirring for 24 hours to mix the two evenly (wherein, the mass ratio of PDMS prepolymer to sodium chloride solution is 1:10); then, add PDMS curing agent and use magnetic stirring for 2 hours (wherein, the mass ratio of PDMS prepolymer to curing agent is 10:1); finally, wrap the polymer mixed solution with plastic wrap and place it in a -80℃ low-temperature refrigerator for 24 hours to allow the polymer system to change from liquid to solid.

[0072] S3, freeze drying: the frozen solution is then taken out and placed in a freeze dryer with a cold trap temperature of -80°C for 48 hours to finally obtain a solidified porous PDMS material.

[0073] S4, sacrificial particle dissolution: the above-mentioned freeze-dried porous PDMS material is taken out and placed in deionized water for ultrasonic treatment for 6 to 8 hours to remove residual sodium chloride particles; finally, it is taken out and dried to finally obtain a slightly transparent hierarchical porous PDMS material.

[0074] See also Figures 1 to 3 As shown, the hierarchical porous PDMS material has interconnected three-dimensional channels, and a multi-level pore structure composed of large pores and small pores. The pore diameter is distributed in the size range of 2 to 700 μm, which makes it have an excellent fluid (gas and liquid) transmission path, and the air permeability can be significantly improved; among them, the small pores are evenly distributed on the pore walls of the large pores, and the pore size range of the large pores is 50 to 700 μm; the pore size range of the small pores is 2 to 30 μm. Specifically, the average diameter of the large pores is about 400 μm, the average diameter of the small pores is about 10 μm, and the porosity is 70.8 ± 0.1%. After testing, the thickness of the hierarchical pore PDMS material is 0.52 cm, the breaking strength is 1.51 Mpa, and it has excellent mechanical properties.

[0075] Comparative Example 1

[0076] The difference from Example 1 is that water is used as the homogeneous solution, and the process is as follows:

[0077] Take an appropriate amount of polydimethylsiloxane (PDMS) prepolymer (without adding curing agent first) in a beaker, then add an appropriate amount of water, and use magnetic stirring for 24 hours to mix the two evenly (wherein, the mass ratio of PDMS prepolymer to water is 1:10); then, add PDMS curing agent, and use magnetic stirring for 2 hours (wherein, the mass ratio of PDMS prepolymer to curing agent is 10:1); finally, wrap the polymer mixed solution with plastic wrap and place it in a -80°C low-temperature refrigerator for 24 hours to allow the polymer system to change from liquid to solid.

[0078] The frozen solution was then taken out and placed in a freeze dryer with a cold trap temperature of -80°C for 48 hours to finally obtain a solidified porous PDMS material.

[0079] After testing, the thickness of the porous PDMS material prepared in Comparative Example 1 is 0.31 cm. Figure 4 As shown, the porosity of the porous PDMS material is 25.1±0.1%, which is much lower than the porosity of the graded pore PDMS material of the present application. In addition, it does not have a graded pore structure, the pore size distribution is in the size range of 20-50μm, and it does not have a connected pore structure, which will significantly affect the air permeability of the porous material.

[0080] Compared with Comparative Example 1, the porosity and pore size of the hierarchical porous PDMS material prepared by the present invention are significantly improved, and it has excellent hierarchical porous structure and fluid transmission performance, as well as excellent mechanical properties. It has great application value in technical fields such as wearable flexible electronic devices, biomedical materials, tissue engineering, drug delivery, biosensors, wound healing and other biomedical fields.

[0081] Example 2

[0082] This embodiment 2 provides a method for preparing a hierarchical porous PDMS material, and the specific preparation process is as follows:

[0083] S1, preparation of sacrificial particle homogeneous solution: first grind sodium chloride particles for 1 to 2 hours, then dissolve the sodium chloride particles in deionized water at a mass concentration of 10%, and stir magnetically for 24 hours to finally form a clear sodium chloride solution.

[0084] S2, preparation of polymer solution: take an appropriate amount of polydimethylsiloxane (PDMS) prepolymer (without adding curing agent first) in a beaker, and then add an appropriate amount of the prepared sodium chloride solution, and use magnetic stirring for 24 hours to mix the two evenly (wherein, the mass ratio of PDMS prepolymer to sodium chloride solution is 1:5); then, add PDMS curing agent and use magnetic stirring for 2 hours (wherein, the mass ratio of PDMS prepolymer to curing agent is 8:1); finally, wrap the polymer mixed solution with plastic wrap and place it in a -80°C low-temperature refrigerator for 24 hours to allow the polymer system to change from liquid to solid.

[0085] S3, freeze drying: the frozen solution is then taken out and placed in a freeze dryer with a cold trap temperature of -80°C for 48 hours to finally obtain a solidified porous PDMS material.

[0086] S4, sacrificial particle dissolution: the freeze-dried porous PDMS material is taken out and placed in deionized water for ultrasonic treatment for 6 to 8 hours to remove residual sodium chloride particles; finally, it is taken out and dried to obtain a slightly transparent hierarchical porous PDMS material with a thickness of 0.47 cm.

[0087] See also Figures 5 to 7 As shown, the diameter of the macropores is about 200-400 μm, the diameter of the micropores is about 10-15 μm, and the porosity is 65.5±0.1%.

[0088] Example 3

[0089] This embodiment 3 provides a method for preparing a hierarchical porous PDMS material, and the specific preparation process is as follows:

[0090] S1, preparation of sacrificial particle homogeneous solution: first grind sodium chloride particles for 1 to 2 hours, then dissolve the sodium chloride particles in deionized water at a concentration of 5% by mass, and stir magnetically for 24 hours to finally form a clear sodium chloride solution.

[0091] S2, preparation of polymer solution: take an appropriate amount of polydimethylsiloxane (PDMS) prepolymer (without adding curing agent first) in a beaker, and then add an appropriate amount of the prepared sodium chloride solution, and use magnetic stirring for 24 hours to mix the two evenly (wherein, the mass ratio of PDMS prepolymer to sodium chloride solution is 1:1); then, add PDMS curing agent and use magnetic stirring for 2 hours (wherein, the mass ratio of PDMS prepolymer to curing agent is 9:1); finally, wrap the polymer mixed solution with plastic wrap and place it in a -70°C low-temperature refrigerator for 24 hours to allow the polymer system to change from liquid to solid.

[0092] S3, freeze drying: the frozen solution is then taken out and placed in a freeze dryer with a cold trap temperature of -80°C for 48 hours to finally obtain a solidified porous PDMS material.

[0093] S4, sacrificial particle dissolution: the above-mentioned freeze-dried porous PDMS material is taken out and placed in deionized water for ultrasonic treatment for 6 to 8 hours to remove residual sodium chloride particles; finally, it is taken out and dried to finally obtain a slightly transparent hierarchical pore PDMS material. The porous PDMS material is 0.35 cm thick, the diameter of its large pores is about 200 to 300 μm, the diameter of its small pores is about 10 to 15 μm, and the porosity is 32.2±0.1%.

[0094] Example 4

[0095] This embodiment 4 provides a method for preparing a hierarchical porous PDMS material, and the specific preparation process is as follows:

[0096] S1, preparation of sacrificial particle homogeneous solution: first grind sodium chloride particles for 1 to 2 hours, then dissolve the sodium chloride particles in deionized water at a concentration of 5% by mass, and stir magnetically for 24 hours to finally form a clear sodium chloride solution.

[0097] S2, preparation of polymer solution: take an appropriate amount of polydimethylsiloxane (PDMS) prepolymer (without adding curing agent first) in a beaker, then add an appropriate amount of the prepared sodium chloride solution, and use magnetic stirring for 24 hours to mix the two evenly (wherein, the mass ratio of PDMS prepolymer to sodium chloride solution is 10:1); then, add PDMS curing agent, and use magnetic stirring for 2 hours (wherein, the mass ratio of PDMS prepolymer to curing agent is 8:1); finally, wrap the mixed solution with plastic wrap, place it in a liquid nitrogen insulation tank, quickly add liquid nitrogen until it covers the bottom of the container, so that the solution is quickly flash-frozen and quickly changes from liquid to solid, and cover the insulation tank to keep warm for 2 minutes. The above liquid nitrogen addition process is repeated 2 to 3 times until the solution is completely frozen. Place the flash-frozen polymer system together with the container in a -80℃ low-temperature refrigerator for 24 hours to change the polymer system from liquid to solid.

[0098] S3, freeze drying: the frozen solution is then taken out and placed in a freeze dryer with a cold trap temperature of -80°C for 48 hours to finally obtain a solidified porous PDMS material.

[0099] S4, sacrificial particle dissolution: the above-mentioned freeze-dried porous PDMS material is taken out and placed in deionized water for ultrasonic treatment for 6 to 8 hours to remove residual sodium chloride particles; finally, it is taken out and dried to obtain a slightly transparent hierarchical pore PDMS material. The porous PDMS material is 0.51 cm thick and has an ordered interconnected pore structure. The average diameter of the large pores is about 400 μm, the average diameter of the small pores is about 10 μm, and the porosity is 81.9±0.1%.

[0100] See also Figures 8 to 9 As shown in the figure, the hierarchical porous PDMS material prepared in this embodiment has more orderly three-dimensional interconnected channels, and a multi-level pore structure composed of large pores and small pores, wherein the large pores are evenly distributed, and the small pores are also evenly distributed on the pore walls of the large pores, the pore size range of the large pores is 100-700μm; the pore size range of the small pores is 5-25μm. It has an excellent fluid (gas and liquid) transmission path, and the air permeability can be significantly improved.

[0101] The present invention uses two different process methods, directional freezing and non-directional freezing, to adjust the arrangement and distribution of the sacrificial particle homogeneous solution in the PDMS system when solidifying, thereby affecting the arrangement and distribution of the holes in the PDMS material. Figure 8 It can be seen that in the porous PDMS material prepared in Example 4, the pore size shows a distribution trend from large to small along the freezing gradient direction. The present invention realizes the orderly regulation of the three-dimensional porous structure through the directional freezing process.

[0102] Example 5

[0103] This embodiment 5 provides a method for preparing a hierarchical porous PDMS material, and the specific preparation process is as follows:

[0104] S1, preparation of sacrificial particle homogeneous solution: first grind sodium chloride particles for 1 to 2 hours, then dissolve the sodium chloride particles in deionized water at a mass concentration of 10%, and stir magnetically for 24 hours to finally form a clear sodium chloride solution.

[0105] S2, preparation of polymer solution: take an appropriate amount of polydimethylsiloxane (PDMS) prepolymer (without adding curing agent first) in a beaker, then add an appropriate amount of the prepared sodium chloride solution, and use magnetic stirring for 24 hours to mix the two evenly (wherein the mass ratio of PDMS prepolymer to sodium chloride solution is 1:9); then, add PDMS curing agent, and use magnetic stirring for 2 hours (wherein the mass ratio of PDMS prepolymer to curing agent is 12:1); finally, wrap the mixed solution with plastic wrap, place it in a liquid nitrogen insulation tank, quickly add liquid nitrogen until it covers the bottom of the container, so that the solution is quickly flash-frozen and quickly changes from liquid to solid, and cover the insulation tank to keep warm for 2 minutes. Repeat the above liquid nitrogen addition process 2 to 3 times until the solution is completely frozen. Place the flash-frozen polymer system together with the container in a -80℃ low-temperature refrigerator for 24 hours to change the polymer system from liquid to solid.

[0106] S3, freeze drying: the frozen solution is then taken out and placed in a freeze dryer with a cold trap temperature of -80°C for 48 hours to finally obtain a solidified porous PDMS material.

[0107] S4, sacrificial particle dissolution: the above-mentioned freeze-dried porous PDMS material is taken out and placed in deionized water for ultrasonic treatment for 6 to 8 hours to remove residual sodium chloride particles; finally, it is taken out and dried to obtain a slightly transparent hierarchical pore PDMS material. The porous PDMS material is 0.66 cm thick and has an ordered interconnected pore structure. The average diameter of the large pores is about 400 μm, the average diameter of the small pores is about 10 μm, and the porosity is 73.7±0.1%.

[0108] Example 6

[0109] This embodiment 6 provides a method for preparing a hierarchical porous PDMS material, and the specific preparation process is as follows:

[0110] S1, preparation of sacrificial particle homogeneous solution: first grind sugar particles (sucrose particles) for 1 to 2 hours, then dissolve the sugar particles in deionized water at a mass concentration of 10%, and stir magnetically for 24 hours to finally form a clear sugar solution.

[0111] S2, preparation of polymer solution: take an appropriate amount of polydimethylsiloxane (PDMS) prepolymer (without adding curing agent first) in a beaker, and then add an appropriate amount of the prepared sugar solution, and use magnetic stirring for 24 hours to mix the two evenly (wherein, the mass ratio of PDMS prepolymer to sugar solution is 1:10); then, add PDMS curing agent and use magnetic stirring for 2 hours (wherein, the mass ratio of PDMS prepolymer to curing agent is 10:1); finally, wrap the polymer mixed solution with plastic wrap and place it in a -70°C low-temperature refrigerator for 24 hours to allow the polymer system to change from liquid to solid.

[0112] S3, freeze drying: the frozen solution is then taken out and placed in a freeze dryer with a cold trap temperature of -80°C for 48 hours to finally obtain a solidified porous PDMS material.

[0113] S4, sacrificial particle dissolution: the freeze-dried porous PDMS material is taken out and placed in deionized water for ultrasonic treatment for 6 to 8 hours to remove residual sugar particles; finally, it is taken out and dried to obtain a slightly transparent hierarchical pore PDMS material. The porous PDMS material is 0.52 cm thick, with a large pore diameter of about 400 μm, a small pore diameter of about 10 μm, and a porosity of 63.4±0.1%.

[0114] Example 7

[0115] This embodiment 7 provides a method for preparing a hierarchical porous PDMS material, and the specific preparation process is as follows:

[0116] S1, preparation of sacrificial particle homogeneous solution: first grind sugar particles (glucose particles) for 1 to 2 hours, then dissolve the sugar particles in deionized water at a concentration of 5% by mass, and stir magnetically for 24 hours to finally form a clear sugar solution.

[0117] S2, preparation of polymer solution: take an appropriate amount of polydimethylsiloxane (PDMS) prepolymer (without adding curing agent first) in a beaker, then add an appropriate amount of the prepared sugar solution, and use magnetic stirring for 24 hours to mix the two evenly (wherein the mass ratio of PDMS prepolymer to sugar solution is 3:10); then, add PDMS curing agent, and use magnetic stirring for 2 hours (wherein the mass ratio of PDMS prepolymer to curing agent is 8:1); finally, wrap the mixed solution with plastic wrap, place it in a liquid nitrogen insulation tank, quickly add liquid nitrogen until it covers the bottom of the container, so that the solution is quickly flash-frozen and quickly changes from liquid to solid, and cover the insulation tank to keep warm for 2 minutes. Repeat the above liquid nitrogen addition process 2 to 3 times until the solution is completely frozen. Place the flash-frozen polymer system together with the container in a -80℃ low-temperature refrigerator for 24 hours to change the polymer system from liquid to solid.

[0118] S3, freeze drying: the frozen solution is then taken out and placed in a freeze dryer with a cold trap temperature of -80°C for 48 hours to finally obtain a solidified porous PDMS material.

[0119] S4, sacrificial particle dissolution: the above-mentioned freeze-dried porous PDMS material is taken out and placed in deionized water for ultrasonic treatment for 6 to 8 hours to remove residual sugar particles; finally, it is taken out and dried to finally obtain a slightly transparent hierarchical pore PDMS material. The porous PDMS material is 0.42 cm thick, the diameter of its large pores is about 400 μm, the diameter of its small pores is about 10 μm, and the porosity is 52.6±0.1%.

[0120] Example 8

[0121] The difference from Example 1 is that the sacrificial particles are a mixture of sodium chloride and glucose particles.

[0122] This embodiment 8 provides a method for preparing a hierarchical porous PDMS material, and the specific preparation process is as follows:

[0123] S1, preparation of sacrificial particle homogeneous solution: first grind sodium chloride particles and sucrose particles for 1 to 2 hours, then dissolve the sodium chloride particles and sucrose particles (mass ratio 1:1) in deionized water at a mass concentration of 5%, and use magnetic stirring for 24 hours to finally form a clear salt-sugar mixed solution.

[0124] S2, preparation of polymer solution: take an appropriate amount of polydimethylsiloxane (PDMS) prepolymer (without adding curing agent first) in a beaker, and then add an appropriate amount of the above-prepared salt-sugar mixed solution, and use magnetic stirring for 24 hours to mix the two evenly (wherein, the mass ratio of PDMS prepolymer to salt-sugar mixed solution is 1:10); then, add PDMS curing agent and use magnetic stirring for 2 hours (wherein, the mass ratio of PDMS prepolymer to curing agent is 10:1); finally, wrap the polymer mixed solution with plastic wrap and place it in a -80℃ low-temperature refrigerator for 24 hours to allow the polymer system to change from liquid to solid.

[0125] S3, freeze drying: the frozen solution is then taken out and placed in a freeze dryer with a cold trap temperature of -80°C for 48 hours to finally obtain a solidified porous PDMS material.

[0126] S4, sacrificial particle dissolution: the above-mentioned freeze-dried porous PDMS material is taken out and placed in deionized water for ultrasonic treatment for 6 to 8 hours to remove residual salt and sugar particles; finally, it is taken out and dried to finally obtain a slightly transparent hierarchical porous PDMS material. The porous PDMS material is 0.58 cm thick, the average diameter of its large pores is about 400 μm, the average diameter of its small pores is about 10 μm, and the porosity is 68.8±0.1%.

[0127] Example 9

[0128] The difference from Example 1 is that in step S1, the solvent is a water-ethanol solvent system, wherein the volume ratio of water to alcohol is 6:1.

[0129] Based on the different physical and chemical properties and freezing points of water and ethanol, mixing the two will lower the freezing point of the solvent to a certain extent, and the sublimation of ethanol and water is not synchronous, which will have a certain impact on the construction of three-dimensional interconnected pores. The volume ratio of water and alcohol in the water-ethanol solvent system can regulate the three-dimensional interconnected structure with hierarchical pores and the porosity of the system to a certain extent.

[0130] Those skilled in the art know that, according to actual application requirements, in other specific embodiments, the alcohol in the water-alcohol solvent system can also be one or more combinations of isopropanol and tert-butanol; the sacrificial particles can also be a mixture of one or more of other sodium salt particles, potassium salt particles, and other sugar particles; in addition, the ratio of PDMS prepolymer to curing agent, the concentration of sacrificial particle solution, and the mass ratio of solution to PDMS can also be set in other proportions, thereby regulating the size of the pores, porosity, and cross-linking strength.

[0131] In summary, the present invention provides a hierarchical porous PDMS material and a preparation method and application thereof. The preparation method does not involve any complex chemical reactions, the process equipment is simple, easy to implement, the material properties are highly controllable, and it has great prospects for large-scale promotion and application. The hierarchical porous PDMS material has ordered or disordered interconnected channels, and a multi-level pore structure composed of large pores and small pores, which has great application value in technical fields such as wearable flexible electronic devices and biomedical materials.

[0132] The above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for preparing a hierarchical porous PDMS material, characterized in that: The steps include: S1, dissolving sacrificial particles in water or a water-alcohol solvent system according to a predetermined concentration ratio to obtain a sacrificial particle homogeneous solution; S2, adding the sacrificial particle homogeneous solution to the polydimethylsiloxane prepolymer and mixing them evenly to obtain a mixed solution; then adding a curing agent and stirring to obtain a polymer mixed solution; and then freezing the polymer mixed solution to change it from a liquid state to a solid state to obtain a solid polymer; S3, freeze-drying the solid polymer to obtain a porous PDMS material; S4, removing the sacrificial particles in the porous PDMS material to obtain a graded porous PDMS material.

2. The method for preparing a hierarchical porous PDMS material according to claim 1, characterized in that: The sacrificial particles are salt particles, sugar particles, or a mixture of the two; The salt particles are a mixture of one or more of sodium salt particles and potassium salt particles; the sugar particles are a mixture of one or more of sucrose particles, glucose particles and stevia particles; Before step S1, the sacrificial particles are pre-treated by grinding for 1 to 2 hours.

3. The method for preparing a hierarchical porous PDMS material according to claim 1, characterized in that: In the sacrificial particle homogeneous solution in step S1, the concentration of the sacrificial particles is 1% to 25%; In the water-alcohol solvent system, the volume ratio of water to alcohol is greater than 4:1; and the alcohol is one or more combinations of ethanol, isopropanol, and tert-butanol.

4. The method for preparing a hierarchical porous PDMS material according to claim 1, characterized in that: In step S2, the mass ratio of the polydimethylsiloxane prepolymer to the sacrificial particle homogeneous solution is 1:(20-1).

5. The method for preparing a hierarchical porous PDMS material according to claim 1, characterized in that: In step S2, the mass ratio of the polydimethylsiloxane prepolymer to the curing agent is (7-15):

1.

6. The method for preparing a hierarchical porous PDMS material according to claim 1, characterized in that: In step S2, the specific process of the freezing treatment is: The polymer mixed solution is packaged by a non-directional freezing process and placed at a freezing temperature of -60 to -90°C for 18 to 36 hours; Alternatively, a directional freezing process is used to package the polymer mixed solution and then quickly flash freeze it. Then, the flash frozen polymer is placed at a freezing temperature of -60 to -90°C for 18 to 36 hours.

7. The method for preparing a hierarchical porous PDMS material according to claim 1, characterized in that: In step S4, the specific process of removing the sacrificial particles is: placing the porous PDMS material in water for 6 to 8 hours for ultrasonic treatment to remove the remaining sacrificial particles, and performing post-drying treatment.

8. The method for preparing a hierarchical porous PDMS material according to claim 1, characterized in that: In step S3, the specific process of freeze drying is: placing the solid polymer in a freeze dryer with a cold trap temperature of -60 to -80°C for drying for 36 to 60 hours.

9. A hierarchical porous PDMS material, characterized in that: The hierarchical porous PDMS material is prepared by a method for preparing a hierarchical porous PDMS material according to any one of claims 1 to 8; the porosity of the hierarchical porous PDMS material is 30±0.1% to 85±0.1%; The hierarchical porous PDMS material has ordered or disordered three-dimensional interconnected pores, and a multi-level pore structure composed of large pores and small pores, the pore diameter is 2 to 700 μm, and has a connected fluid transmission path; wherein the small pores are evenly distributed on the pore walls of the large pores, the pore diameter of the large pores is 50 to 700 μm; the pore diameter of the small pores is 2 to 30 μm.

10. The use of a hierarchical porous PDMS material according to claim 9, characterized in that: The hierarchical porous PDMS material is used in the technical fields of wearable flexible electronic devices and biomedical materials.

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