Hierarchical porous pdms material, its preparation method and application

Abstract

The application provides a hierarchical porous PDMS material and a preparation method and application thereof. The preparation method does not involve any complex chemical reaction, the process equipment is simple, easy to realize, the controllability of material performance is strong, and the hierarchical porous PDMS material has great application prospects in large-scale promotion. The hierarchical porous PDMS material has ordered or disordered connected pores, and is composed of large pores and small pores to form a multi-level pore structure, and has great application value in the technical fields of wearable flexible electronic devices, biomedical materials and the like.

Description

Technical Field

[0001] This invention relates to the field of porous PDMS material preparation technology, and in particular to a hierarchical porous PDMS material, its preparation method and application. Background Technology

[0002] Electronic skin (E-skin) possesses sensory functions similar to human skin, converting external stimuli into detectable electrical signals. It is characterized by its thinness, softness, and flexibility. Flexible electronic skin has attracted widespread attention due to its immense potential in health monitoring, human-computer interaction (HMI), intelligent robotics, and the Internet of Things (IoT). PDMS membrane materials, with their high transparency, biocompatibility, elasticity, and stretchability, are ideal flexible substrates for current wearable flexible electronic devices. However, the density and impermeability of PDMS can lead to skin hypoxia or allergic reactions, significantly impacting the practicality, comfort, and safety of electronic skin. Forming a porous structure can improve the water vapor permeability of PDMS; therefore, developing porous PDMS membrane materials for wearable electronics has significant practical implications and application value. Furthermore, porous PDMS, due to its unique properties, including high biocompatibility, mechanical flexibility, and tunable porosity, has various potential applications in the biomedical field. Porous PDMS can be used as a scaffold material for tissue engineering applications. The porosity of the material allows for the permeation of cells and nutrients while 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. Pore size and distribution can be customized to achieve specific release rates and distributions, resulting in more precise and efficient drug delivery. Overall, porous PDMS has the potential to drive advancements in biomedical engineering and enable new applications in biomedical fields such as tissue engineering, drug delivery, biosensors, and wound healing.

[0003] Chinese invention patent (publication number: CN113912902A) discloses a method for preparing a porous PDMS / PVA hydrogel composite cooling film. The method involves mixing and stirring NaCl microparticles with uncrosslinked PDMS raw materials, uniformly coating the resulting mixture onto a glass plate to form a coating, and then curing it in an oven. The cured coating is then peeled off from the glass plate and dissolved in room-temperature deionized water to form porous PDMS. The porous PDMS and PVA hydrogel are then adhered to obtain a bilayer cooling polymer film. This method uses sacrificial particles for direct curing to prepare porous PDMS materials. However, this results in severe particle aggregation and uneven particle dispersion within the system, leading to uncontrollable pore size. Furthermore, if the sacrificial particles are encapsulated by PDMS, they are difficult to remove and may remain in the material.

[0004] Chinese invention patent (publication number: CN112646226A) discloses a method for preparing porous PDMS and its application in flexible electronic devices. The preparation method includes the following steps: mixing PDMS prepolymer and a curing agent uniformly, then adding deionized water and stirring; after the PDMS and deionized water are thoroughly mixed, pouring the mixture into a prepared mold; after the mixture fills the mold, covering it with an aluminum plate and heating to cure. However, the method uses deionized water as a template, resulting in excessively large pore sizes, which reduces the strength of the porous PDMS.

[0005] Chinese invention patent (publication number: CN115232355A) discloses a method for preparing hierarchical porous PDMS based on a soft template and its application in sensors. The preparation includes the following steps: preparing a PVA-B hydrogel; preparing a PDMS solution; thoroughly mixing the PDMS solution and the PVA-B hydrogel; preparing a hierarchical porous PDMS molding mold; placing the PDMS / PVA-B in the prepared mold; and finally heating and curing the mixture; cleaning the cured product with hydrochloric acid and deionized water, and drying it to obtain the hierarchical porous PDMS. This method has a complex preparation process and is difficult to operate.

[0006] Chinese invention patent (publication number: CN113912902A) discloses a method for preparing porous PDMS foam and its application. The preparation method includes the following steps: mixing PDMS prepolymer with a crosslinking agent and stirring thoroughly with a magnetic stirrer; diluting and stirring a PDMS solution with n-hexane; mixing the PDMS / n-hexane mixture with deionized water; allowing the oil-water emulsion to stand at room temperature; removing the supernatant; prepolymerizing; and finally heating and polymerizing to dry, removing the semi-transparent viscous coating layer to obtain white porous PDMS foam. This method is complex, and the pore distribution is difficult to adjust.

[0007] In the commonly used preparation methods mentioned above, when sacrificial particles are introduced into the solid-phase mixture, it is difficult for the sacrificial particles to be completely dispersed as single particles in the unpolymerized PDMS. The particles tend to agglomerate, and their size and distribution are uneven, resulting in larger and more unevenly distributed pores. For example, when hard particles such as sugar are dissolved and washed away with a liquid, if the particles are completely coated with PDMS, they cannot be removed (most often water is used as the solvent, but because PDMS is hydrophobic, it is difficult to wet and wash away all the sacrificial particles). Furthermore, when water droplets are used as templates, the significant difference in molecular weight and viscosity between water and PDMS leads to poor stability of the water droplets generated under mechanical stirring, causing them to merge or even separate before curing. The rapid vaporization and condensation of water droplets during heating and curing of the system further exacerbate the 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 its preparation method to solve the above problems and realize its application in multiple fields. Summary of the Invention

[0009] The purpose of this invention is to provide a hierarchical porous PDMS material, its preparation method, and its application.

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

[0011] S1, Dissolve the sacrificial particles in water according to the predetermined concentration ratio and stir to obtain a homogeneous solution of the sacrificial particles;

[0012] S2, the homogeneous solution of the sacrificial particles is added to the polydimethylsiloxane prepolymer and stirred until uniformly mixed to obtain a mixture; then a curing agent is added and stirred to obtain a polymer mixture solution; then a freezing treatment is performed to change the polymer mixture solution from liquid to solid to obtain a solid polymer;

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

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

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

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

[0017] Before step S1, the sacrificial particles were pretreated by grinding for 1 to 2 hours.

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

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

[0020] As a further improvement of the present invention, in the water-alcohol solvent system described in step S1, the volume ratio of water to alcohol is >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 polydimethylsiloxane prepolymer to sacrificial particle homogeneous solution is 1:(20-1).

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

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

[0024] As a further improvement of the present invention, in step S2, the mass ratio of polydimethylsiloxane prepolymer to 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 as follows: after the polymer mixture solution is packaged, it is placed at a freezing temperature of -60 to -90°C for 18 to 36 hours; or, after the polymer mixture solution is packaged, it is rapidly flash-frozen, and then the flash-frozen polymer is placed 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 for removing sacrificial particles is as follows: the porous PDMS material is placed in water and sonicated for 6 to 8 hours to remove residual sacrificial particles, and then dried.

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

[0028] To achieve the above-mentioned objectives, the present invention also provides a hierarchical porous PDMS material, which is prepared using the above-described preparation method.

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

[0030] The hierarchical porous PDMS material has ordered or disordered interconnected channels and is composed of macropores and micropores to form a multi-level pore structure with a pore diameter of 2 to 700 μm; micropores are uniformly distributed on the walls of macropores with a pore diameter of 50 to 700 μm; and micropores with a pore diameter of 2 to 30 μm.

[0031] To achieve the above-mentioned objectives, this invention also provides applications of the hierarchical porous PDMS material in the fields of wearable flexible electronic devices, biomedical materials, and other technical fields.

[0032] The beneficial effects of this invention are:

[0033] 1. The method for preparing hierarchical porous PDMS material provided by this invention utilizes the dissolution of sacrificial particles to construct a uniform incompatible system (PDMS is incompatible with salt / sugar solutions). Combined with a blending-freezing-freeze-dissolution process, a three-stage synergistic hierarchical pore-forming process is achieved. Specifically, the process of forming a solid phase from the polymer mixture solution is carried out at low temperature. At this time, PDMS has not formed a cross-linked structure, and water (or water-alcohol solvent) solvent ice crystals grow in the PDMS system to form micropores (primary pore-forming, based on the volume difference between liquid and solid solvents). Then, during freeze-drying, PDMS forms a cross-linked structure, and the ice crystals change directly from a solid to a gaseous state. The path of the gas leaving the system from the inside out allows the pores to connect (this also provides a path for the subsequent precipitation of sacrificial particles, preventing them from being encapsulated in the PDMS material), leaving large-diameter pore structures in the PDMS (secondary pore-forming). Finally, the solidified sacrificial particles are further removed, resulting in small-diameter pore structures on the walls of the large pores (tertiary pore-forming), ultimately yielding a hierarchical porous PDMS material. This invention, based on low-temperature conditions, differentiates and asynchronously processes the cross-linking and curing reaction of the PDMS system and the curing, vaporization, and dissolution processes of the homogeneous solution of sacrificial particles. This allows for sufficient ice crystal growth and sacrificial particle precipitation. At the same time, while ensuring effective cross-linking reaction, it effectively overcomes the technical defects of existing technologies that use water droplets as pore-forming templates, where the rapid vaporization and condensation of water droplets during system heating and curing results in irregular and unevenly distributed pores.

[0034] 2. The method for preparing hierarchical porous PDMS material provided by this invention uses a homogeneous solution of sacrificial particles, which significantly increases the porosity of the system compared to conventional single aqueous solutions. Furthermore, by utilizing the different physicochemical properties of the sacrificial particles and the aqueous solvent, after the ice crystals formed by the aqueous solvent directly vaporize to form interconnected large pores, the sacrificial particles re-precipitate and revert to a solid particle state, loading onto the pore walls of the large pores. After removal through dissolution and post-treatment, a uniformly distributed micropore structure is constructed on the pore walls, thereby creating a hierarchical porous composite structure both on the surface and inside the material. This invention effectively overcomes the technical defects of existing technologies that directly mix sacrificial particles in a solid phase (the size of the formed pores depends on the particle size), which leads to particle agglomeration during mixing, resulting in large pore sizes, inconvenient size adjustment, uneven mixing of particles and PDMS, and the inability to remove particles if they are completely encapsulated by PDMS. Moreover, the molecular weight of the homogeneous solution of sacrificial particles is significantly higher than that of a single aqueous solution, effectively overcoming the technical defects of mutual fusion or even stratification between the sacrificial particles and PDMS before curing.

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

[0036] 4. The method for preparing hierarchical porous PDMS material provided by the present invention does not involve any complex chemical reactions, the process equipment is simple and easy to implement, the material properties are highly controllable, and it has great potential for large-scale application.

[0037] 5. The hierarchical porous PDMS material provided by the present invention has ordered or disordered interconnected channels and is composed of macropores and micropores to form a multi-level pore structure. It has great application value in the fields of wearable flexible electronic devices, biomedical materials, tissue engineering, drug delivery, biosensors and wound healing. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the three-stage synergistic pore-forming process in the preparation method of the hierarchical porous PDMS material provided by the present invention.

[0039] Figure 2 Electron micrograph of the hierarchical porous PDMS material provided in Embodiment 1 of the present invention (scale bar: 500 μm).

[0040] Figure 3 Electron microscopy image of the micropore structure of the hierarchical porous PDMS material provided in Embodiment 1 of the present invention ( Figure 3 b is Figure 3 Enlarged view of part 'a' in the middle; Figure 3 The scale bar for 'a' is 100 μm. Figure 3 The scale bar for b in the middle is 10 μm.

[0041] Figure 4 Electron micrograph of the porous PDMS material provided in Comparative Example 1 of this invention (scale bar: 100 μm).

[0042] Figure 5 Electron micrograph of the hierarchical porous PDMS material provided in Embodiment 2 of the present invention (scale bar: 100 μm).

[0043] Figure 6 Electron micrograph of the macroporous structure of the hierarchical porous PDMS material provided in Embodiment 2 of the present invention (scale bar: 100 μm).

[0044] Figure 7Electron microscopy image of the pore structure of the hierarchical porous PDMS material provided in Embodiment 2 of the present invention (scale bar: 10 μm).

[0045] Figure 8 A cross-sectional electron microscope image (scale bar: 500 μm) of the hierarchical porous PDMS material provided in Embodiment 4 of the present invention.

[0046] Figure 9 A planar electron microscope image (scale bar: 500 μm) of the hierarchical porous PDMS material provided in Embodiment 4 of the present invention. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be 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 with unnecessary details, only the structures and / or processing steps closely related to the present invention are shown in the accompanying drawings, while other details that are not closely related to the present invention are omitted.

[0049] Additionally, it should be noted that the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

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

[0051] S1, Dissolve the sacrificial particles in water or water-alcohol solvent according to the predetermined concentration ratio, and stir to obtain a homogeneous solution of sacrificial particles;

[0052] S2, the homogeneous solution of the sacrificial particles is added to the polydimethylsiloxane prepolymer and stirred until uniformly mixed to obtain a mixture; then a curing agent is added and stirred to obtain a polymer mixture solution; then a freezing treatment is performed to change the polymer mixture solution from liquid to solid to obtain a solid polymer;

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

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

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

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

[0057] Before step S1, the sacrificial particles were pretreated by grinding for 1 to 2 hours.

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

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

[0060] Preferably, in the water-alcohol solvent system described in step S1, the volume ratio of water to alcohol is >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 homogeneous solution of sacrificial particles is 1:(20-1).

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

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

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

[0065] Preferably, in step S2, the specific process of the freezing treatment is as follows: after encapsulating the polymer mixture solution, it is placed at a freezing temperature of -60 to -90°C for 18 to 36 hours; or, after encapsulating the polymer mixture solution, it is rapidly flash-frozen, and then the flash-frozen polymer is placed at a freezing temperature of -60 to -90°C for 18 to 36 hours.

[0066] Preferably, in step S4, the specific process for removing sacrificial particles is as follows: the porous PDMS material is placed in water and sonicated for 6 to 8 hours to remove residual sacrificial particles, and then dried.

[0067] Preferably, in step S3, the specific process of freeze drying is as follows: the solid polymer is placed in a freeze dryer with a cold trap temperature of -60 to -80°C and dried 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 homogeneous solution of sacrificial particles: First, grind sodium chloride particles for 1-2 hours, then dissolve sodium chloride particles in deionized water at a mass concentration of 5%, 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) into a beaker, then add an appropriate amount of the prepared sodium chloride solution, and mix the two evenly by magnetic stirring for 24 hours (wherein, the mass ratio of PDMS prepolymer to sodium chloride solution is 1:10); then, add PDMS curing agent, and stir magnetically for 2 hours (wherein, the mass ratio of PDMS prepolymer to curing agent is 10:1); finally, seal the polymer mixture solution with plastic wrap and place it in a -80℃ low temperature freezer for 24 hours to allow the polymer system to change from liquid to solid state.

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

[0073] S4, Sacrificial Particle Dissolution: The above freeze-dried porous PDMS material is taken out and placed in deionized water for ultrasonication for 6-8 hours to remove residual sodium chloride particles; finally, it is taken out and dried to obtain a micro-transparent hierarchical porous PDMS material.

[0074] Please see Figures 1 to 3 As shown, this hierarchical porous PDMS material possesses interconnected three-dimensional channels and a multi-level porous structure composed of macropores and micropores. The pore diameters range from 2 to 700 μm, providing excellent fluid (gas and liquid) transport pathways and significantly improving air permeability. Specifically, the micropores are uniformly distributed on the walls of the macropores, with macropore diameters ranging from 50 to 700 μm and micropore diameters ranging from 2 to 30 μm. The average diameter of the macropores is approximately 400 μm, the average diameter of the micropores is approximately 10 μm, and the porosity is 70.8 ± 0.1%. Testing revealed that this hierarchical porous PDMS material has a thickness of 0.52 cm and a tensile strength of 1.51 MPa, exhibiting 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) into a beaker, add an appropriate amount of water, and mix the two evenly with magnetic stirring for 24 hours (wherein, the mass ratio of PDMS prepolymer to water is 1:10); then, add PDMS curing agent and stir magnetically for 2 hours (wherein, the mass ratio of PDMS prepolymer to curing agent is 10:1); finally, seal the polymer mixture solution with plastic wrap and place it in a -80℃ low temperature freezer for 24 hours to allow the polymer system to change from liquid to solid state.

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

[0079] After testing, the thickness of the porous PDMS material prepared in Comparative Example 1 was found to be 0.31 cm. Please refer to [link / reference needed]. Figure 4 As shown, the porosity of the porous PDMS material is 25.1±0.1%, which is much lower than that of the hierarchical pore PDMS material of this application. Furthermore, it does not have a hierarchical pore structure, and the pore size is distributed in the range of 20-50μm. 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 this invention are significantly improved, and it also has excellent hierarchical porous structure and fluid transport performance, as well as excellent mechanical properties. It has great application value in the fields of wearable flexible electronic devices, biomedical materials, tissue engineering, drug delivery, biosensors and wound healing.

[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 homogeneous solution of sacrificial particles: First, grind sodium chloride particles for 1-2 hours, then dissolve sodium chloride particles in deionized water at a mass concentration ratio 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) into a beaker, then add an appropriate amount of the prepared sodium chloride solution, and mix the two evenly by magnetic stirring for 24 hours (wherein, the mass ratio of PDMS prepolymer to sodium chloride solution is 1:5); then, add PDMS curing agent, and stir magnetically for 2 hours (wherein, the mass ratio of PDMS prepolymer to curing agent is 8:1); finally, seal the polymer mixture solution with plastic wrap and place it in a -80℃ low temperature freezer for 24 hours to allow the polymer system to change from liquid to solid state.

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

[0086] S4, Sacrificial Particle Dissolution: The above freeze-dried porous PDMS material is taken out and placed in deionized water for ultrasonication for 6-8 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] Please see Figures 5 to 7 As shown, the diameter of its macropores is about 200-400 μm, the diameter of its 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 homogeneous solution of sacrificial particles: First, grind sodium chloride particles for 1-2 hours, then dissolve sodium chloride particles in deionized water at a mass concentration of 5%, 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) into a beaker, then add an appropriate amount of the prepared sodium chloride solution, and mix the two evenly by magnetic stirring for 24 hours (wherein, the mass ratio of PDMS prepolymer to sodium chloride solution is 1:1); then, add PDMS curing agent, and stir magnetically for 2 hours (wherein, the mass ratio of PDMS prepolymer to curing agent is 9:1); finally, seal the polymer mixture solution with plastic wrap and place it in a -70℃ low temperature freezer for 24 hours to allow the polymer system to change from liquid to solid state.

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

[0093] S4, Sacrificial Particle Dissolution: The freeze-dried porous PDMS material is taken out and placed in deionized water for sonication for 6-8 hours to remove residual sodium chloride particles; finally, it is taken out and dried to obtain a micro-transparent hierarchical porous PDMS material with a thickness of 0.35 cm, a macropore diameter of about 200-300 μm, a micropore diameter of about 10-15 μm, and a porosity of 32.2±0.1%.

[0094] Example 4

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

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

[0097] S2, Preparation of the polymer solution: Take an appropriate amount of polydimethylsiloxane (PDMS) prepolymer (without adding the curing agent initially) in a beaker, then add an appropriate amount of the prepared sodium chloride solution. Stir magnetically for 24 hours to mix the two evenly (the mass ratio of PDMS prepolymer to sodium chloride solution is 10:1). Then, add the PDMS curing agent and stir magnetically for 2 hours (the mass ratio of PDMS prepolymer to curing agent is 8:1). Finally, seal the mixed solution with plastic wrap and place it in a liquid nitrogen insulated container. Quickly add liquid nitrogen until it covers the bottom of the container, causing the solution to flash-freeze rapidly from a liquid to a solid state. Cover the container and insulate for 2 minutes. Repeat the above liquid nitrogen addition process 2-3 times until the solution is completely frozen. Place the flash-frozen polymer system and container in a -80°C freezer for 24 hours to allow the polymer system to change from a liquid to a solid state.

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

[0099] S4, Sacrificial Particle Dissolution: The freeze-dried porous PDMS material is taken out and placed in deionized water for sonication for 6-8 hours to remove residual sodium chloride particles; finally, it is taken out and dried to obtain a micro-transparent hierarchical porous PDMS material with a thickness of 0.51 cm and an ordered interconnected pore structure. The average diameter of the macropores is about 400 μm, the average diameter of the micropores is about 10 μm, and the porosity is 81.9 ± 0.1%.

[0100] Please see Figures 8 to 9 As shown, the hierarchical porous PDMS material prepared in this embodiment possesses more ordered three-dimensional interconnected channels and a multi-level pore structure composed of macropores and micropores. The macropores are relatively uniformly distributed, and the micropores are also uniformly distributed on the pore walls of the macropores. The macropore diameter ranges from 100 to 700 μm, and the micropore diameter ranges from 5 to 25 μm. It exhibits excellent fluid (gas and liquid) transport pathways, and its air permeability is significantly improved.

[0101] This invention utilizes two different processes—directional freezing and non-directional freezing—to adjust the arrangement and distribution of sacrificial particles in a homogeneous solution during solidification within a PDMS system, thereby influencing the arrangement and distribution of pores in the PDMS material. Figure 8 As can be seen from the above, in the porous PDMS material prepared in Example 4, the pore size shows a distribution trend from large to small along the direction of the freezing gradient. The present invention achieves the orderly control of the three-dimensional porous structure through 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 homogeneous solution of sacrificial particles: First, grind sodium chloride particles for 1-2 hours, then dissolve sodium chloride particles in deionized water at a mass concentration ratio of 10%, and stir magnetically for 24 hours to finally form a clear sodium chloride solution.

[0105] S2, Preparation of the polymer solution: Take an appropriate amount of polydimethylsiloxane (PDMS) prepolymer (without adding the curing agent initially) in a beaker, then add an appropriate amount of the prepared sodium chloride solution, and mix them evenly using magnetic stirring for 24 hours (wherein, the mass ratio of PDMS prepolymer to sodium chloride solution is 1:9); then, add the PDMS curing agent, and stir magnetically for 2 hours (wherein, the mass ratio of PDMS prepolymer to curing agent is 12:1); finally, seal the mixed solution with plastic wrap, place it in a liquid nitrogen insulated container, and quickly add liquid nitrogen until it covers the bottom of the container, so that the solution is rapidly flash-frozen, changing from a liquid state to a solid state. Cover the insulated container and keep it at that temperature for 2 minutes. Repeat the above liquid nitrogen addition process 2-3 times until the solution is completely frozen. Place the flash-frozen polymer system and container in a -80℃ low-temperature freezer for 24 hours to allow the polymer system to change from a liquid state to a solid state.

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

[0107] S4, Sacrificial Particle Dissolution: The freeze-dried porous PDMS material is taken out and placed in deionized water for sonication for 6-8 hours to remove residual sodium chloride particles; finally, it is taken out and dried to obtain a micro-transparent hierarchical porous PDMS material with a thickness of 0.66 cm and an ordered interconnected pore structure. The average diameter of the macropores is about 400 μm, the average diameter of the micropores 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 homogeneous solution of sacrificial particles: first grind sugar particles (sucrose particles) for 1-2 hours, then dissolve 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) into a beaker, then add an appropriate amount of the sugar solution prepared above, and mix the two evenly by magnetic stirring for 24 hours (wherein, the mass ratio of PDMS prepolymer to sugar solution is 1:10); then, add PDMS curing agent, and stir magnetically for 2 hours (wherein, the mass ratio of PDMS prepolymer to curing agent is 10:1); finally, seal the polymer mixture solution with plastic wrap and place it in a -70℃ low temperature freezer for 24 hours to allow the polymer system to change from liquid to solid state.

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

[0113] S4, Sacrificial Particle Dissolution: The freeze-dried porous PDMS material was taken out and placed in deionized water for sonication for 6-8 hours to remove residual sugar particles; finally, it was taken out and dried to obtain a micro-transparent hierarchical porous PDMS material with a thickness of 0.52 cm, a macropore diameter of about 400 μm, a micropore 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. The specific preparation process is as follows:

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

[0117] S2, Preparation of the polymer solution: Take an appropriate amount of polydimethylsiloxane (PDMS) prepolymer (without adding the curing agent initially) in a beaker, then add an appropriate amount of the prepared sugar solution. Stir magnetically for 24 hours to mix the two evenly (the mass ratio of PDMS prepolymer to sugar solution is 3:10). Then, add the PDMS curing agent and stir magnetically for 2 hours (the mass ratio of PDMS prepolymer to curing agent is 8:1). Finally, seal the mixed solution with plastic wrap and place it in a liquid nitrogen insulated container. Quickly add liquid nitrogen until it covers the bottom of the container, causing the solution to flash-freeze rapidly from a liquid to a solid state. Cover the container and insulate for 2 minutes. Repeat the above liquid nitrogen addition process 2-3 times until the solution is completely frozen. Place the flash-frozen polymer system and container in a -80°C freezer for 24 hours to allow the polymer system to change from a liquid to a solid state.

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

[0119] S4, Sacrificial Particle Dissolution: The freeze-dried porous PDMS material was taken out and placed in deionized water for sonication for 6-8 hours to remove residual sugar particles; finally, it was taken out and dried to obtain a micro-transparent hierarchical porous PDMS material with a thickness of 0.42 cm, a macropore diameter of about 400 μm, a micropore diameter of about 10 μm, and a porosity of 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. The specific preparation process is as follows:

[0123] S1, preparation of homogeneous solution of sacrificial particles: First, grind sodium chloride particles and sucrose particles for 1-2 hours, then dissolve sodium chloride particles and sucrose particles (mass ratio 1:1) in deionized water at a mass concentration of 5%, and stir magnetically 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) into a beaker, then add an appropriate amount of the prepared salt-sugar mixed solution, and stir magnetically for 24 hours to mix them evenly (wherein, the mass ratio of PDMS prepolymer to salt-sugar mixed solution is 1:10); then, add PDMS curing agent, and stir magnetically for 2 hours (wherein, the mass ratio of PDMS prepolymer to curing agent is 10:1); finally, seal the polymer mixed solution with plastic wrap and place it in a -80℃ low temperature freezer for 24 hours to allow the polymer system to change from liquid to solid state.

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

[0126] S4, Sacrificial Particle Dissolution: The freeze-dried porous PDMS material was taken out and placed in deionized water for sonication for 6-8 hours to remove residual salt and sugar particles; finally, it was taken out and dried to obtain a micro-transparent hierarchical porous PDMS material with a thickness of 0.58 cm, an average diameter of macropores of about 400 μm, an average diameter of micropores of about 10 μm, and a porosity of 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] Due to the different physicochemical properties and freezing points of water and ethanol, mixing them will lower the freezing point of the solvent to some extent. Furthermore, the sublimation of ethanol and water occurs asynchronously, thus affecting the construction of three-dimensional interconnected channels. The volume ratio of water to alcohol in the water-ethanol solvent system can be used to 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 will understand that, depending on the actual application requirements, in other specific embodiments, the alcohol in the water-alcohol solvent system may be one or more combinations of isopropanol and tert-butanol; the sacrificial particles may also be one or more mixtures 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 be set in other proportions to control the size of pores, porosity, and crosslinking strength.

[0131] In summary, this invention provides a hierarchical porous PDMS material, its preparation method, and its applications. The preparation method does not involve any complex chemical reactions, the process equipment is simple and easy to implement, and the material properties are highly controllable, possessing great potential for large-scale application. This hierarchical porous PDMS material possesses ordered or disordered interconnected channels, and its multi-level porous structure is composed of macropores and micropores, exhibiting significant application value in wearable flexible electronic devices, biomedical materials, and other technical fields.

[0132] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method of preparing a hierarchically porous PDMS material, characterized by: Includes the following steps: S1, Dissolve the sacrificial particles in water or a water-alcohol solvent system according to the predetermined concentration ratio to obtain a homogeneous solution of the sacrificial particles; S2, the homogeneous solution of the sacrificial particles is added to the polydimethylsiloxane prepolymer and mixed evenly to obtain a mixture; then a curing agent is added and stirred to obtain a polymer mixture solution; then a freezing treatment is performed to change the polymer mixture solution from a liquid state to a solid state to obtain a solid polymer; S3, freeze-dry the solid polymer to obtain a porous PDMS material; S4, remove the sacrificial particles from the porous PDMS material to obtain a graded porous PDMS material; The sacrificial particles are one or a mixture of salt particles, sugar particles, or both. In the homogeneous solution of sacrificial particles described in step S1, the concentration of sacrificial particles is 1% to 25%. In the water-alcohol solvent system, the volume ratio of water to alcohol is >4:1; and the alcohol is one or more combinations of ethanol, isopropanol, and tert-butanol. In step S2, the mass ratio of polydimethylsiloxane prepolymer to the homogeneous solution of sacrificial particles is 1:(20~1). In step S2, the specific process of the freezing treatment is as follows: The polymer mixture solution was encapsulated using a non-directional freezing process and then placed at a freezing temperature of -60 to -90°C for 18 to 36 hours. Alternatively, a directional freezing process can be used, in which the polymer mixture solution is encapsulated and then rapidly flash-frozen, and then the flash-frozen polymer is placed at a freezing temperature of -60 to -90°C for 18 to 36 hours.

2. The method of claim 1, wherein: The salt particles are one or more of sodium salt particles and potassium salt particles; the sugar particles are one or more of sucrose particles, glucose particles, and stevia particles. Before step S1, the sacrificial particles are pretreated 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 step S2, the mass ratio of polydimethylsiloxane prepolymer to curing agent is (7~15):

1.

4. The method for preparing a hierarchical porous PDMS material according to claim 1, characterized in that: In step S4, the specific process for removing sacrificial particles is as follows: the porous PDMS material is placed in water and sonicated for 6 to 8 hours to remove residual sacrificial particles, and then dried.

5. 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 as follows: the solid polymer is placed in a freeze dryer with a cold trap temperature of -60 to -80°C and dried for 36 to 60 hours.

6. A hierarchical porous PDMS material, characterized in that: The hierarchical porous PDMS material is prepared using the method for preparing a hierarchical porous PDMS material according to any one of claims 1 to 5; the porosity of the hierarchical porous PDMS material is 30±0.1%~85±0.1%; The hierarchical porous PDMS material has ordered or disordered three-dimensional interconnected channels and is composed of macropores and micropores to form a multi-level pore structure with a pore diameter of 2 to 700 μm, and has interconnected fluid transport paths; wherein, the micropores are uniformly distributed on the walls of the macropores, with a macropore diameter of 50 to 700 μm and a micropore diameter of 2 to 30 μm.

7. The application of the hierarchical porous PDMS material according to claim 6, characterized in that: Applications of the hierarchical porous PDMS material in the fields of wearable flexible electronic devices and biomedical materials.

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