A method for preparing film based on ice crystal extrusion

Abstract

The present invention provides a method for preparing a film based on ice crystal extrusion. Ice crystals are generated based on a cold source body, acting on assembly primitives, and serving as the film-forming driving force of the assembly primitives to drive film formation, thereby forming a high-performance film with controllable density in one step. Specifically, an assembly liquid is placed in a system comprising at least one cold source body and a barrier. Water in the assembly liquid begins to grow from the cold source body at a speed of 0.1 to 50 μm / s to form ice crystals. The ice crystals push the assembly primitives in the assembly liquid outward from the cold source body, and form the film between the cold source body and the barrier body. The assembly liquid contains assembly primitives that can be precipitated from the water, and the content of the assembly primitives in the dispersion liquid is 0.001 to 20 vol%. The present invention is a simple method for preparing a film that can achieve adjustable structural density of the film, and can also achieve the preparation of a complete self-supporting film.

Description

Technical Field

[0001] The present application relates to the technical field of membrane material preparation, and specifically to several membrane preparation methods and products. Background Art

[0002] Membranes are an important material form, composed of atoms, molecules, or polymers, typically with thicknesses ranging from nanometers to micrometers, and exhibiting planar or quasi-planar structures. Compared to bulk materials, membranes offer advantages such as lightness, flexibility, large surface area, and high transparency, and are widely used in packaging, energy catalysis, electronic devices, and separation and filtration. Ultrathin films, defined as membranes with thicknesses ranging from nanometers to submicrometers, have attracted considerable attention. Ultrathin films exhibit significant size effects on one dimension, and their physical and chemical properties may differ from those of their macroscopic bulk counterparts. Ultrathin films have a wide range of applications in electronics, optics, energy, catalysis, sensing, and biomedicine. For example, they are used in the manufacture of flexible electronic devices, thin-film transistors, and displays. In optics, they can serve as transparent electrodes, optical filters, and substrates for surface-enhanced Raman scattering. Furthermore, ultrathin films can be used as catalyst supports, sensitive layers in sensors, and in biomedical diagnostics and therapeutics.

[0003] Existing film-forming methods are mainly divided into two categories: film-forming methods based on solvent evaporation and film-forming methods based on vapor deposition. Film-forming methods based on solvent evaporation include spin coating, doctor blade coating, vacuum filtration and layer-by-layer assembly. In these methods, the assembly units are evenly dispersed in the solvent phase. When the solvent evaporates, the assembly units are affected by gravity and capillary forces to form a film on the substrate. However, these existing methods all have certain limitations. The spin coating method makes it difficult to accurately control the thickness of the film; the doctor blade coating method requires preparation on the substrate and cannot achieve self-support of the film. In practical applications, the film material needs to be transferred from the original substrate to the target substrate. This process can easily cause damage to the membrane structure, especially when preparing ultra-thin films. The vacuum filtration method takes a long time to prepare the membrane, and the size of the membrane is usually limited by the size of the filtration equipment, making it difficult to prepare large-sized membrane materials. The layer-by-layer assembly method has a slow film formation speed and is difficult to achieve self-support when preparing ultra-thin films. In general, while solvent evaporation-based membrane fabrication methods offer relatively simple, low-cost processes and widespread industrial application, they suffer from poor controllability of the driving force for assembly, resulting in an inability to adjust the density of the membrane structure. Furthermore, it is often difficult to achieve self-supporting membrane structures without damaging them during the fabrication of ultrathin films, limiting their application in preparing self-supporting, density-controllable ultrathin films.

[0004] Film preparation methods based on vapor deposition include physical vapor deposition, chemical vapor deposition, and molecular beam epitaxy. These methods deposit the desired film material on the surface of a solid substrate by causing a chemical reaction in the gas phase. By adjusting parameters such as deposition time, deposition rate, and deposition conditions, the thickness of the film can be precisely controlled. Good gas mixing and transport control can achieve uniform film deposition and avoid non-uniformity and inconsistency. However, vapor deposition equipment usually requires relatively complex equipment and control systems, and high-temperature treatment is usually required during the preparation process. The size of the prepared film is also limited by the size of the equipment. It is currently mainly used in the preparation of precision electronic device films, which limits its large-scale application. In addition, film formation usually requires a substrate, making it difficult to achieve self-supporting film materials.

[0005] Controlling membrane density is also crucial for expanding membrane applications. By manipulating membrane density, it is possible to adjust membrane permeability, mechanical properties, reactivity, energy efficiency, and surface properties. However, neither the aforementioned solvent evaporation nor vapor deposition methods allow for precise control of membrane density. Summary of the Invention

[0006] The purpose of the present invention is to address the shortcomings of existing membrane preparation methods and provide a method for preparing membranes based on ice crystal extrusion. Ice crystals are generated by a cold source and act on assembly units, which serve as the driving force for film formation of the assembly units to drive film formation, thereby forming a high-performance membrane with controllable density in one step.

[0007] Specifically, the present invention adopts the following technical solution: an assembly liquid is placed in a system comprising at least one cold source and a barrier, water in the assembly liquid begins to grow from the cold source at a speed of 0.1 to 50 μm / s to form ice crystals, the ice crystals push the assembly primitives in the assembly liquid outward from the cold source, and cause the assembly primitives to form the film between the cold source and the barrier; the assembly liquid contains assembly primitives that can be precipitated from the water, and the content of the assembly primitives in the dispersion is 0.001 to 20 vol%.

[0008] The solution of the present invention at least includes:

[0009] (1) The barrier has no cold source input, and ice crystals begin to grow from the cold source toward the barrier at a speed of 0.1 to 50 μm / s, pushing the assembly primitives in the assembly liquid toward the barrier, and causing the assembly primitives to form the film on the surface of the barrier.

[0010] (2) By inputting a cold source into the barrier, the barrier becomes a second cold source body, and the film is formed between the two cold source bodies; by freeze drying, the film that can be independently self-supporting is obtained.

[0011] Furthermore, there is a critical ice crystal growth rate v cr , when the ice crystal growth rate is less than v cr When the ice crystal grows in a planar mode, the ice crystal growth rate is greater than or equal to v cr When the ice crystals grow in a lamellar or random pattern.

[0012]

[0013] Where Δσ0 is the interfacial free energy of the system, which can be obtained by contact angle measurement. R is the radius of the solid particle, a0 is the average distance between molecules in the liquid phase, usually the diameter of a water molecule, about 10nm, η is the viscosity of the assembly liquid, k p and k l are the thermal conductivity of the assembly unit and water respectively. Taking the graphene oxide dispersion system of Example 1 as an example, its v cr 10μm / s.

[0014] The equivalent way of radius is that for flake materials, R is half of the lateral dimension; for polymer materials, R is the mean square radius of gyration of the polymer chain; for monomer emulsions, R is the radius of the emulsion particles.

[0015] Compared with the solvent evaporation method that cannot control the density and the vapor deposition method with complex and harsh preparation conditions, the present invention can achieve the preparation of a membrane with controllable density by designing a simple barrier and a cold source body, regulating the ice crystal growth rate and the concentration of the assembly liquid, and combining freeze drying to remove ice crystals. Specifically, by simply changing the ice crystal growth rate, the micromorphology of the membrane material can be regulated so that it can be adjusted between dense and loose. When the ice crystal growth rate is low, preferably, below the critical growth rate (the precipitation rate of the assembly unit), the ice crystal growth is a planar growth mode that pushes the assembly unit toward the barrier, and realizes dense stacking of the assembly unit under an extrusion stress of up to hundreds of MPa; when the ice crystal growth rate is high, the ice crystal growth is a lamellar growth mode that pushes the assembly unit toward the barrier, and simultaneously forms lamellar ice crystals between the assembly units, thereby obtaining a membrane with a loose structure. Taking the aforementioned graphene oxide dispersion system as an example, when the ice growth rate is 0.1 to 10 μm / s, the ice crystals grow in a planar manner. When the ice growth rate is 10 to 50 μm / s, ice crystals grow in lamellar forms.

[0016] In the present invention, the cooling source is generally supplied from the bottom of the cooling source body, which creates a temperature gradient from low to high from the bottom to the top. This causes ice crystals to grow faster at the bottom and slower at the top, resulting in a curved structure with a wider bottom and narrower top. This curved growth of ice crystals can further induce the orientation of assembly units. This highly oriented assembly can further improve density.

[0017] In the present invention, the concentration of the assembly fluid used is between 0.001 and 20 vol%, primarily considering the minimum amount of assembly primitives required for thin film formation and the need for the assembly fluid to maintain a certain fluidity to ensure ice crystal growth and primitive precipitation. The minimum required amount of assembly primitives varies depending on the properties of the primitives. By adjusting the assembly fluid concentration, the thickness of the film material can be precisely controlled from the nanometer to the micrometer scale.

[0018] Achieving self-support of ultra-thin films is of great significance and value in ensuring that the performance of the films is not impaired in practical applications. However, existing film-making methods such as solvent evaporation and vapor deposition require forming a thin film on a substrate, which is then removed from the original substrate and transferred to a target substrate using complex methods. However, this process often inevitably causes structural damage to the film, thereby reducing the performance of the film. Based on the present invention, when the barrier is a second cold source, ice crystals will also form on the surface of the barrier, and eventually the film will be formed between the two ice crystals. The ice crystals are removed by freeze-drying, and an independent, self-supporting film with good integrity can be obtained without the need for peeling or secondary transfer.

[0019] In the present invention, the heat sink can be of any shape, including but not limited to regular / irregular planar sheets, regular / irregular planar columns, and regular / irregular planar cones, ultimately resulting in films of varying shapes. When the heat sink is a flat sheet, the resulting film is a flat sheet. When the heat sink is an irregular sheet, the film can adhere evenly to the irregular surface. When the heat sink is a columnar sheet, the film can be linear or planar. When the heat sink is a cone, the film is a flat membrane.

[0020] In the present invention, the barrier can be of any shape, including but not limited to the heat sink body, which can be a regular or irregular flat sheet, a regular or irregular flat column, or a regular or irregular flat cone, ultimately forming a film of varying shapes. When the barrier is a flat sheet, the resulting film is a flat sheet. When the barrier is a irregular sheet, the film can be evenly adhered to the irregular surface. When the barrier is a column, the film can be a linear or flat structure. When the barrier is a cone, the film is a flat membrane.

[0021] In the present application, the solvent is generally water, which forms ice crystals under the action of a cold source. As is common knowledge in the art, other solvents that can achieve liquid-to-solid phase transition under the action of a cold source are also applicable to the present invention.

[0022] The assembly elements in the assembly fluid can be zero-dimensional materials, including metal nanoparticles, such as gold nanoparticles, silver nanoparticles, etc.; metal oxide nanoparticles, such as ferric oxide nanoparticles, copper oxide nanoparticles, zinc oxide nanoparticles, etc.; carbon particles; organic quantum dots such as polydopamine nanoparticles; inorganic quantum dots such as silicon quantum dots, graphene quantum dots, black phosphorus quantum dots; one-dimensional materials, including metal nanowires, such as silver nanowires, gold nanorods, copper nanowires, etc.; inorganic material nanowires, such as carbon nanowires. fibers, silicon carbide nanowires, carbon nanotubes, etc.; organic material nanowires, such as nanocellulose fibers, aramid fibers, etc.; two-dimensional materials, including boron nitride nanosheets, aluminum oxide nanosheets, graphene nanosheets, clay sheets, molybdenum disulfide nanosheets, tungsten disulfide nanosheets, covalent organic framework nanosheets (COF), etc.; polymers, including polyamic acid, silk fibroin, polyvinyl alcohol, chitosan, sodium alginate, etc.; emulsions, including epoxy emulsions, polyurethane emulsions, silicone rubber emulsions, etc.

[0023] In the present invention, when the assembly unit has good film-forming properties, such as graphene oxide nanosheets, nanocellulose fibers, polyvinyl alcohol, etc. with surface functional groups, only the assembly unit needs to be added to the assembly liquid; when the assembly unit has poor film-forming properties, such as boron nitride nanosheets, glass fibers, gold nanoparticles, etc. with inert surfaces, a small amount (less than 10wt% of the assembly unit content) of auxiliary adhesives, such as polyvinyl alcohol, polyurethane, nanocellulose, etc., needs to be added to the assembly liquid to assist the film in self-supporting.

[0024] Compared with the prior art, the present invention has the following beneficial effects: it is a simple film preparation method that can achieve controllable structural density of the film. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is an optical photograph of the preparation process when the barrier is a cold source body, including the nucleation of ice crystals on the surface of the cold source body, the precipitation of assembly primitives from the assembly liquid and spreading at the front of the ice crystals, the assembly primitives assembling at the front of the ice crystals, and the extrusion of the assembly primitives between the cold source body and the barrier to form a thin film.

[0026] Figure 2 It is a schematic diagram of the device.

[0027] Figure 3 An optical photograph of a film deposited on the surface of a barrier when the barrier is not a cold source.

[0028] Figure 4 This is an optical photograph of the self-supporting film when the barrier is a cold source.

[0029] Figure 5 These are the atomic force microscope optical photographs and thickness measurement results of the self-supporting dense membrane.

[0030] Figure 6is the SEM image of the free-standing dense membrane.

[0031] Figure 7 This is an optical photograph of a self-supporting loose membrane. DETAILED DESCRIPTION

[0032] The present invention will be further described below with reference to the embodiments.

[0033] In the following examples, the ice crystal growth rate was regulated by controlling the temperature of the hot and cold stages; the lower the temperature, the faster the ice crystal growth. Furthermore, the freezing process was recorded in situ using a microscope, and the ice crystal growth rate was calculated based on the change in the position of the ice crystal front in each frame.

[0034] Example 1: Preparation process of the film preparation method based on ice crystal extrusion:

[0035] (1) 0.02 g of graphene oxide nanosheets were dispersed in 19.98 g of deionized water and slowly stirred for 1 h, wherein the volume fraction of the graphene oxide nanosheets was 0.048 vol%.

[0036] (2) A temperature-averaging plate (length × width × thickness = 2 × 2 × 0.1 cm) was used as a cooling source, and a polytetrafluoroethylene plate (length × width × thickness = 2 × 2 × 0.05 cm) was used as a barrier. The barrier and cooling source were glued to both sides of a U-shaped frame (length × width × thickness = 2 × 2 × 0.2 cm) with hydrophobic sealant to form a refrigeration device (e.g. Figure 2 a).

[0037] (3) The freezing device is placed on a hot and cold stage (cold source) with a temperature controllable range of -120-200°C. Graphene oxide dispersion is added to the U-shaped frame and the temperature is adjusted so that ice crystals always grow from the cold source side to the barrier side at a rate of 1 μm / s. The freezing is completed after about 30 minutes, and the graphene oxide nanosheets in the assembly liquid are completely pushed onto the barrier by the ice crystals.

[0038] (4) The blocking polytetrafluoroethylene plate carrying the graphene oxide film is freeze-dried to obtain the graphene oxide film.

[0039] (5) In order to facilitate performance testing, the aforementioned graphene oxide film was placed in a hydroiodic acid solution (50 wt %) for 24 h, and the graphene oxide film was reduced to a reduced graphene oxide film.

[0040] (6) Film thickness characterization

[0041] The film thickness was characterized by atomic force microscopy. The sample was placed in liquid nitrogen and a cross section was created using a scalpel tip. The height difference between the substrate and the film was the thickness of the film, which was approximately 130 nm (e.g. Figure 3 shown).

[0042] (7) Characterization of structural density

[0043] By scanning within 5-70° through wide-angle XRD, the position of the characteristic peak of reduced graphene oxide was analyzed to obtain the interlayer spacing of reduced graphene oxide nanosheets in the film, which was about 0.755 nm. The smaller the interlayer spacing, the better the structural density.

[0044] (8) Electrical performance characterization:

[0045] The sheet resistance of the film was characterized using a four-probe resistance meter, which was approximately 32Ω / sq.

[0046] Comparative Example 1:

[0047] (1) 0.02 g of graphene oxide nanosheets were dispersed in 19.98 g of deionized water and stirred slowly for 1 h, wherein the volume fraction of graphene oxide nanosheets was 0.048 vol%

[0048] (2) A PMMA frame (length × width × height = 2 × 2 × 0.2 cm) with upper and lower openings was glued to the polytetrafluoroethylene plate using hydrophobic sealant.

[0049] (3) Add graphene oxide dispersion to the PMMA frame and dry it at room temperature for about 48 h until the water is completely evaporated, and attach the graphene oxide film to the polytetrafluoroethylene plate.

[0050] (4) The polytetrafluoroethylene plate carrying the graphene oxide film is placed in a hydroiodic acid solution (50 wt %) for 24 h, and the graphene oxide film is reduced to a reduced graphene oxide film.

[0051] (5) Film thickness characterization

[0052] The film thickness was characterized by atomic force microscopy. The sample was placed in liquid nitrogen and a cross-section was created using the tip of a scalpel. The height difference between the substrate and the film was the thickness of the film, which was approximately 130 nm.

[0053] (6) Characterization of structural density

[0054] By scanning within 5-70° through wide-angle XRD, the characteristic peak position of reduced graphene oxide was analyzed to obtain the interlayer spacing of reduced graphene oxide nanosheets in the membrane, which was about 0.915nm. Compared with the film prepared based on ice crystal extrusion, the membrane structure density is poor.

[0055] (7) Electrical performance characterization:

[0056] The sheet resistance of the film was characterized using a four-probe resistance meter, which was approximately 267Ω / sq.

[0057] Example 2: Same as Example 1, except that a copper sheet is used to replace the temperature equalizing plate in Example 1.

[0058] (1) Film thickness characterization

[0059] The film thickness was characterized by atomic force microscopy. The sample was placed in liquid nitrogen and a cross-section was created using the tip of a scalpel. The height difference between the substrate and the film was the thickness of the film, which was approximately 130 nm.

[0060] (2) Characterization of structural density

[0061] By scanning within 5-70° through wide-angle XRD, the position of the characteristic peak of reduced graphene oxide was analyzed to obtain the interlayer spacing of reduced graphene oxide nanosheets in the film, which was about 0.728nm. The interlayer spacing was smaller and the film density was better.

[0062] (3) Electrical performance characterization:

[0063] The sheet resistance of the film was characterized using a four-probe resistance meter, which was approximately 23Ω / sq.

[0064] Example 3:

[0065] (1) 0.02 g of graphene oxide nanosheets were dispersed in 19.98 g of deionized water and slowly stirred for 1 h, wherein the volume fraction of the graphene oxide nanosheets was 0.048 vol%.

[0066] (2) A copper sheet (length × width × thickness = 2 × 2 × 0.1 cm) is used as a cooling source, and a copper sheet (length × width × thickness = 2 × 2 × 0.1 cm) is used as a barrier. The barrier and cooling source are respectively glued to both sides of a U-shaped frame (length × width × thickness = 2 × 2 × 0.2 cm) with a hydrophobic sealant to form a refrigeration device (such as Figure 2 b).

[0067] (3) The freezing device is placed on a hot and cold stage (cold source) with a temperature controllable range of -120-200°C. Graphene oxide dispersion is added to the U-shaped frame and the temperature is adjusted so that ice crystals always grow from the cold source side to the barrier side at a rate of 1 μm / s. The freezing is completed after about 15 minutes, and the graphene oxide in the assembly liquid is fixed in the ice crystals between the barrier and the cold source.

[0068] (4) The ice crystals were removed from the freezing device and placed on a polytetrafluoroethylene plate. The ice crystals were removed by freeze drying in situ for about 4 h. The film was then placed on a polytetrafluoroethylene plate in a self-supporting state (e.g. Figure 4 shown).

[0069] (5) The self-supporting graphene oxide film is reduced to a graphene oxide film by high-temperature hydrogen. The graphene oxide film is placed in a tubular furnace, passed through a mixed gas (5% H2+95% Ar), and thermally reduced at 800°C.

[0070] (6) Film thickness characterization

[0071] The membrane was placed in anhydrous ethanol, picked up with a silicon wafer and transferred to the surface of the silicon wafer. The sample was placed in liquid nitrogen and a cross section was created using the tip of a scalpel. The height difference between the substrate and the membrane was the thickness of the membrane, which was approximately 130 nm.

[0072] (7) Characterization of structural density

[0073] The membrane was placed in anhydrous ethanol, picked up with a silicon wafer and transferred to the silicon wafer surface. Wide-angle XRD was performed to scan within 5-70° to analyze the position of the characteristic peak of reduced graphene oxide to obtain the interlayer spacing of the reduced graphene oxide nanosheets in the membrane, which was approximately 0.76 nm.

[0074] (8) Characterization of film structural integrity

[0075] The integrity of the film structure was characterized under an optical microscope, and the film had good integrity.

[0076] (9) Electrical performance characterization:

[0077] The sheet resistance of the film was characterized using a four-probe resistance meter and was found to be approximately 38Ω / sq.

[0078] Comparative Example 2:

[0079] (1) 0.02 g of graphene oxide nanosheets were dispersed in 19.98 g of deionized water and slowly stirred for 1 h, wherein the volume fraction of the graphene oxide nanosheets was 0.048 vol%.

[0080] (2) Using a cellulose membrane as a filter, pour the graphene oxide dispersion into a funnel and vacuum filter for about 1 hour. A graphene oxide film is deposited on the surface of the cellulose membrane and placed in a 40°C oven to dry for 24 hours.

[0081] (3) The cellulose membrane was immersed in DMF for 24 h to completely dissolve the cellulose membrane. The graphene oxide membrane floated in the DMF. The membrane was fixed with a copper ring and dried to obtain a self-supporting graphene oxide membrane.

[0082] (4) The self-supporting graphene oxide film is reduced to a graphene oxide film by high-temperature hydrogen. The graphene oxide film is placed in a tubular furnace, passed through a mixed gas (5% H2+95% Ar), and thermally reduced at 800°C.

[0083] (5) Film thickness characterization

[0084] The film was placed in anhydrous ethanol, picked up with a silicon wafer and transferred to the surface of the silicon wafer. The sample was placed in liquid nitrogen and a cross section was created using the tip of a scalpel. The height difference between the substrate and the film was the thickness of the film, which was approximately 130 nm.

[0085] (6) Characterization of structural density

[0086] The film was placed in anhydrous ethanol, picked up with a silicon wafer and transferred to the silicon wafer surface. Wide-angle XRD was used to scan within 5-70° to analyze the position of the characteristic peak of reduced graphene oxide to obtain the interlayer spacing of the reduced graphene oxide nanosheets in the film, which was about 0.83nm. Compared with the film prepared by cold source extrusion, the density was insufficient.

[0087] (7) Characterization of film structural integrity

[0088] When the film is placed under an optical microscope for observation, holes and cracks are generated during the transfer of the film from the cellulose membrane surface.

[0089] (8) Electrical performance characterization:

[0090] The sheet resistance of the film was characterized using a four-probe resistance meter, which was approximately 573Ω / sq.

[0091] Example 4:

[0092] (1) 0.02 g of graphene oxide nanosheets were dispersed in 19.98 g of deionized water and slowly stirred for 1 h, wherein the volume fraction of the graphene oxide nanosheets was 0.048 vol%.

[0093] (2) The freezing device is placed on a hot / cold stage with a temperature adjustable between -120°C and 200°C. A graphene oxide dispersion is added between the polytetrafluoroethylene column and the copper ring. The temperature is adjusted so that ice crystals always grow from the cold source side to the barrier side at a rate of 1 μm / s. After about 30 minutes, the freezing is completed. The graphene oxide in the assembly liquid is fixed in the ice crystals between the barrier and the cold source, and a cylindrical graphene oxide film is obtained on the outer surface of the polytetrafluoroethylene column. The barrier polytetrafluoroethylene plate carrying the graphene oxide film is freeze-dried to obtain a cylindrical graphene oxide film.

[0094] (3) In order to facilitate performance testing, the polytetrafluoroethylene column with the attached graphene oxide film was placed in a hydroiodic acid solution (50 wt%) for 24 h, and the graphene oxide film was reduced to a reduced graphene oxide film.

[0095] (4) Film thickness characterization

[0096] The thickness of the membrane was characterized by atomic force microscopy. The sample was placed in liquid nitrogen and a cross section was created using a scalpel tip. The height difference between the substrate and the membrane was the membrane thickness, which was approximately 120 nm (e.g. Figure 3 shown).

[0097] (5) Characterization of structural density

[0098] By scanning within 5-70° through wide-angle XRD, the position of the characteristic peak of reduced graphene oxide was analyzed to obtain the interlayer spacing of reduced graphene oxide nanosheets in the film, which was about 0.755 nm. The smaller the interlayer spacing, the better the structural density.

[0099] (6) Electrical performance characterization:

[0100] The sheet resistance of the film was characterized using a four-probe resistance meter and was found to be approximately 36 Ω / sq.

[0101] Example 5:

[0102] (1) 0.02 g of graphene oxide nanosheets were dispersed in 19.98 g of deionized water and slowly stirred for 1 h, wherein the volume fraction of the graphene oxide nanosheets was 0.048 vol%.

[0103] (2) Two copper sheets (length × width × thickness = 2 × 2 × 0.1 cm) are placed on the left and right sides of a polytetrafluoroethylene plate barrier (length × width × thickness = 2 × 0.4 × 0.05 cm) as cold sources, and a U-shaped frame is placed in the middle. The U-shaped frame, the cold source, and the barrier are bonded with hydrophobic sealant to form a freezing device (such as Figure 2 d).

[0104] (3) The freezing device is placed on a hot / cold stage with a temperature adjustable within the range of -120-200°C. The temperature is adjusted so that ice crystals always grow from the cold source side to the barrier side at a rate of 1 μm / s. After about 30 minutes, the freezing is completed and the graphene oxide sheets in the assembly liquid are deposited on the surface of the barrier to form a graphene oxide film.

[0105] (4) After the blocking polytetrafluoroethylene plate carrying the graphene oxide film is freeze-dried, the graphene oxide film is carried on both the left and right sides of the polytetrafluoroethylene plate.

[0106] (5) In order to facilitate performance testing, the aforementioned graphene oxide film was placed in a hydroiodic acid solution (50 wt %) for 24 h, and the graphene oxide film was reduced to a reduced graphene oxide film.

[0107] (6) Film thickness characterization

[0108] The membrane was placed in anhydrous ethanol, picked up with a silicon wafer and transferred to the surface of the silicon wafer. The sample was placed in liquid nitrogen and a cross section was created using the tip of a scalpel. The height difference between the substrate and the membrane was the thickness of the membrane, which was approximately 120 nm.

[0109] (8) Characterization of structural density

[0110] The membrane was placed in anhydrous ethanol, picked up with a silicon wafer and transferred to the silicon wafer surface. Wide-angle XRD was used to scan within 5-70° to analyze the position of the characteristic peak of reduced graphene oxide to obtain the interlayer spacing of the reduced graphene oxide nanosheets in the membrane, which was about 0.74 nm. Compared with the membrane prepared by cold source extrusion, the density was insufficient.

[0111] (9) Electrical performance characterization: The sheet resistance of the film was characterized using a four-probe resistance tester, which was approximately 39Ω / sq

[0112] Example 6:

[0113] (1) 0.02 g of graphene oxide nanosheets were dispersed in 19.9 g of deionized water and slowly stirred for 1 h, wherein the volume fraction of the graphene oxide nanosheets was 0.048 vol%.

[0114] (2) A copper sheet (length × width × thickness = 2 × 2 × 0.1 cm) is used as a cold source, and a copper sheet body (length × width × thickness = 2 × 2 × 0.1 cm) is used as a barrier. The barrier and the cold source are glued to both sides of a U-shaped frame (length × width × thickness = 2 × 2 × 0.2 cm) with hydrophobic sealant to form a refrigeration device.

[0115] (3) The freezing device is placed on a hot and cold table with a temperature adjustable within the range of -120-200 °C, and graphene oxide dispersion is added to the U-shaped frame. The temperature of the cold table is controlled and maintained at -90 °C, -20 °C, and -0.1 °C, respectively. The ice crystals are controlled to grow at speeds of 50 μm / s, 10 μm / s, and 0.1 μm / s, respectively. After the freezing is completed, when the ice crystal growth rate is less than 10 μm / s, the graphene oxide nanosheets are squeezed by the planar ice crystals to form dense pore walls. When the ice crystal growth rate is greater than or equal to 10 μm / s, the graphene oxide nanosheets are fixed between the layered ice crystals.

[0116] (4) The ice crystals were taken out of the freezing device and placed on a polytetrafluoroethylene plate. The ice crystals were removed by freeze drying in situ for about 4 h. The graphene oxide film was placed on the surface of the polytetrafluoroethylene plate in a self-supporting state (e.g. Figure 7 shown).

[0117] (5) To facilitate subsequent characterization, the graphene oxide film was reduced to a reduced graphene oxide film by high-temperature hydrogen. The graphene oxide film was placed in a tubular furnace and passed through a mixed gas (5% H2 + 95% Ar) and thermally reduced at 800°C.

[0118] (6) Film thickness characterization

[0119] The thickness of the cross sections of the film (-90), film (-20), and film (-0.1) were measured under a scanning electron microscope, and the thickness of the films were approximately 20 μm, 5 μm, and 130 nm, respectively.

[0120] (7) Characterization of structural density

[0121] The density of the membrane structure was observed under a scanning electron microscope. The membrane (-90) was a completely loose layered membrane, the membrane (-20) was a semi-dense layered membrane, and the membrane (-0.1) was a completely dense membrane.

[0122] (8) Electrical performance characterization:

[0123] The sheet resistance of the film was characterized using a four-probe resistance tester. The sheet resistances of the film (-90), film (-20), and film (-0.1) were 2300Ω / sq, 980Ω / sq, and 28Ω / sq, respectively.

[0124] Example 7:

[0125] (1) 0.01 g, 0.04 g, and 0.08 g of graphene oxide nanosheets were dispersed in 19.98 g of deionized water, and the mixture was slowly stirred for 1 h to obtain graphene oxide nanosheets with volume fractions of 0.024 vol%, 0.095 vol%, and 0.19 vol%, respectively.

[0126] (2) A copper sheet (length × width × thickness = 2 × 2 × 0.1 cm) is used as a cold source, and a copper sheet (length × width × thickness = 2 × 2 × 0.1 cm) is used as a barrier. The barrier and the cold source are glued to both sides of the U-shaped frame (length × width × thickness = 2 × 2 × 0.2 cm) with hydrophobic sealant to form a refrigeration device.

[0127] (3) The freezing device is placed on a hot and cold table with a temperature adjustable within the range of -120-200°C. Graphene oxide dispersion is added to the U-shaped frame. The temperature is adjusted so that ice crystals always grow from the cold source side to the barrier side at a rate of 1 μm / s. The freezing is completed after about 30 minutes, and the graphene oxide in the assembly liquid is fixed in the ice crystals between the barrier and the cold source.

[0128] (4) The ice crystals were removed from the freezing device and placed on a polytetrafluoroethylene plate. The ice crystals were removed in situ by freeze drying for about 4 h. The membrane was then placed on the polytetrafluoroethylene plate surface in a self-supporting state.

[0129] (5) The self-supporting graphene oxide film is reduced to a graphene oxide film by high-temperature hydrogen. The graphene oxide film is placed in a tubular furnace and passed through a mixed gas (5% H2+95% Ar) and thermally reduced at 800°C.

[0130] (6) Film thickness characterization

[0131] The membrane was placed in anhydrous ethanol, picked up with a silicon wafer and transferred to the surface of the silicon wafer. The sample was placed in liquid nitrogen and a cross section was created using the tip of a scalpel. The height difference between the substrate and the membrane was the thickness of the membrane. The thicknesses of the membrane (0.024), membrane (0.095), and membrane (0.19) were 62nm, 372nm, and 894nm, respectively.

[0132] (7) Characterization of structural density

[0133] The film was placed in anhydrous ethanol and picked up with a silicon wafer to transfer the film to the silicon wafer surface. Wide-angle XRD was performed to scan within 5-70° to analyze the position of the characteristic peak of reduced graphene oxide to obtain the interlayer spacing of reduced graphene oxide nanosheets in the film. The interlayer spacing of film (0.024), film (0.095), and film (0.19) were 0.750nm, 0.741nm, and 0.743nm, respectively.

[0134] (8) Electrical performance characterization

[0135] The sheet resistance of the film was characterized using a four-probe resistance tester. The sheet resistances of the film (0.024), film (0.095), and film (0.19) were 741nm, 0.743nm, and were approximately 34Ω / sq, 39Ω / sq, and 33Ω / sq, respectively.

[0136] Example 8:

[0137] (1) 0.1 g of carbon nanoparticles (diameter of about 50 nm), 0.01 g of polyvinyl alcohol, and 0.005 g of sodium dodecylbenzenesulfonate were dispersed in 19.885 g of deionized water and slowly stirred for 1 h, wherein the volume fraction of the carbon nanoparticles was 0.22 vol%.

[0138] (2) A copper sheet (length × width × thickness = 2 × 2 × 0.1 cm) is used as a cold source, and a copper sheet (length × width × thickness = 2 × 2 × 0.1 cm) is used as a barrier. The barrier and the cold source are glued to both sides of the U-shaped frame (length × width × thickness = 2 × 2 × 0.2 cm) with hydrophobic sealant to form a refrigeration device.

[0139] (3) The freezing device is placed on a hot and cold table with a temperature adjustable within the range of -120-200°C. A carbon nanoparticle dispersion is added to the U-shaped frame. The temperature is adjusted so that ice crystals always grow from the cold source side to the barrier side at a rate of 1 μm / s. The freezing is completed after about 30 minutes, and the carbon nanoparticles in the assembly liquid are fixed in the ice crystals between the barrier and the cold source.

[0140] (4) The ice crystals were removed from the freezing device and placed on a polytetrafluoroethylene plate. The ice crystals were removed in situ by freeze drying for about 4 h. The membrane was then placed on the polytetrafluoroethylene plate surface in a self-supporting state.

[0141] (5) Film thickness characterization

[0142] The membrane was placed in anhydrous ethanol, picked up with a silicon wafer and transferred to the surface of the silicon wafer. The sample was placed in liquid nitrogen and a cross section was created using the tip of a scalpel. The height difference between the substrate and the membrane was the thickness of the membrane, which was approximately 1 μm.

[0143] (6) Electrical performance characterization

[0144] The sheet resistance of the film was characterized using a four-probe resistance meter and was found to be approximately 53Ω / sq.

[0145] Example 9:

[0146] (1) 0.1 g of silicon carbide nanowires (diameter of about 20 nm, length of about 10 μm), 0.01 g of polyvinyl alcohol, and 0.005 g of sodium dodecylbenzenesulfonate were dispersed in 19.885 g of deionized water and slowly stirred for 1 h. The volume fraction of the silicon carbide nanowire particles was 0.156 vol%.

[0147] (2) A copper sheet (length × width × thickness = 2 × 2 × 0.1 cm) is used as a cold source, and a copper sheet (length × width × thickness = 2 × 2 × 0.1 cm) is used as a barrier. The barrier and the cold source are glued to both sides of the U-shaped frame (length × width × thickness = 2 × 2 × 0.2 cm) with hydrophobic sealant to form a refrigeration device.

[0148] (3) The freezing device was placed on a hot / cold stage with a temperature adjustable between -120°C and 200°C. A SiC nanowire dispersion was added to the U-shaped frame and the temperature was adjusted so that ice crystals always grew from the cold source side to the barrier side at a rate of 1 μm / s. After about 30 minutes, the freezing was completed and the SiC nanowires in the assembly solution were fixed in the ice crystals between the barrier and the cold source. (4) The ice crystals were removed from the freezing device and placed on a polytetrafluoroethylene plate. The ice crystals were removed in situ by freeze drying for about 4 hours. The membrane was then placed on the surface of the polytetrafluoroethylene plate in a self-supporting state.

[0149] (5) Film thickness characterization

[0150] The membrane was placed in anhydrous ethanol, picked up with a silicon wafer and transferred to the surface of the silicon wafer. The sample was placed in liquid nitrogen and a cross section was created using the tip of a scalpel. The height difference between the substrate and the membrane was the thickness of the membrane, which was approximately 1 μm.

[0151] (6) Characterization of thermal conductivity

[0152] The in-plane thermal conductivity of the silicon carbide nanowire film was measured using the laser flash method and was approximately 10 W / mK.

[0153] Example 10:

[0154] (1) 0.1 g of boron nitride nanosheets (lateral size of about 2 μm, thickness of about 20 nm), 0.01 g of polyvinyl alcohol,

[0155] 0.005 g of sodium dodecylbenzenesulfonate was dispersed in 19.885 g of deionized water and slowly stirred for 1 hour, wherein the volume fraction of the boron nitride nanosheets was 0.22 vol%.

[0156] (2) A copper sheet (length × width × thickness = 2 × 2 × 0.1 cm) is used as a cold source, and a copper sheet (length × width × thickness = 2 × 2 × 0.1 cm) is used as a barrier. The barrier and the cold source are glued to both sides of the U-shaped frame (length × width × thickness = 2 × 2 × 0.2 cm) with hydrophobic sealant to form a refrigeration device.

[0157] (3) The freezing device is placed on a hot / cold table with a temperature adjustable between -120°C and 200°C. Boron nitride nanosheet dispersion is added to the U-shaped frame and the temperature is adjusted so that ice crystals always grow from the cold source side to the barrier side at a rate of 1 μm / s. The freezing is completed after about 30 minutes, and the boron nitride nanosheets in the assembly liquid are fixed in the ice crystals between the barrier and the cold source.

[0158] (4) The ice crystals were removed from the freezing device and placed on a polytetrafluoroethylene plate. The ice crystals were removed in situ by freeze drying for about 4 h. The membrane was then placed on the polytetrafluoroethylene plate surface in a self-supporting state.

[0159] (5) Film thickness characterization

[0160] The membrane was placed in anhydrous ethanol, picked up with a silicon wafer and transferred to the surface of the silicon wafer. The sample was placed in liquid nitrogen and a cross section was created using the tip of a scalpel. The height difference between the substrate and the membrane was the thickness of the membrane, which was approximately 1 μm.

[0161] (6) Characterization of thermal conductivity

[0162] The in-plane thermal conductivity of the boron nitride film was measured using the laser flash method and was approximately 12 W / mK.

[0163] Example 11:

[0164] (1) Dissolve 0.1 g of polyvinyl alcohol in 19.90 g of deionized water and stir slowly in a 90°C oil bath for 8 h until the solution is completely dissolved. The volume fraction of the polyvinyl alcohol is 0.42 vol%.

[0165] (2) A copper sheet (length × width × thickness = 2 × 2 × 0.1 cm) is used as a cold source, and a copper sheet (length × width × thickness = 2 × 2 × 0.1 cm) is used as a barrier. The barrier and the cold source are glued to both sides of the U-shaped frame (length × width × thickness = 2 × 2 × 0.2 cm) with hydrophobic sealant to form a refrigeration device.

[0166] (3) Place the freezing device on a hot or cold table with a temperature adjustable between -120 and 200°C, add polyvinyl alcohol solution into the U-shaped frame, and adjust the temperature so that ice crystals always grow from the cold source side to the barrier side at a rate of 1 μm / s. The freezing is completed after about 30 minutes, and the polyvinyl alcohol in the assembly solution is fixed in the ice crystals between the barrier and the cold source.

[0167] (4) The ice crystals were removed from the freezing device and placed on a polytetrafluoroethylene plate. The ice crystals were removed in situ by freeze drying for about 4 h. The membrane was then placed on the polytetrafluoroethylene plate surface in a self-supporting state.

[0168] (5) Film thickness characterization

[0169] The membrane was placed in anhydrous ethanol, picked up with a silicon wafer and transferred to the surface of the silicon wafer. The sample was placed in liquid nitrogen and a cross section was created using the tip of a scalpel. The height difference between the substrate and the membrane was the thickness of the membrane, which was approximately 930 nm.

[0170] Example 12:

[0171] (1) 0.1 g of methyl methacrylate monomer, 0.1 g of butyl acrylate monomer, 0.05 g of functional crosslinking monomer trimethylolpropane triacrylate, 0.01 g of reactive emulsifier ER-10, and 0.03 g of co-emulsifier octadecyl acrylate were dispersed in 19.71 g of deionized water and ultrasonically dispersed for 5 min to obtain a methyl methacrylate monomer emulsion with a concentration of 0.5 wt%.

[0172] (2) A copper sheet (length × width × thickness = 2 × 2 × 0.1 cm) is used as a cold source, and a copper sheet (length × width × thickness = 2 × 2 × 0.1 cm) is used as a barrier. The barrier and the cold source are glued to both sides of the U-shaped frame (length × width × thickness = 2 × 2 × 0.2 cm) with hydrophobic sealant to form a refrigeration device.

[0173] (3) The freezing device is placed on a hot and cold table with a temperature adjustable within the range of -120-200°C, and methyl methacrylate monomer emulsion is added to the U-shaped frame. The temperature is adjusted so that ice crystals always grow from the cold source side to the barrier side at a rate of 1 μm / s. The freezing is completed after about 30 minutes, and the oily monomers and cross-linking agents in the assembly liquid are completely separated from the water phase and fixed in the ice crystals between the barrier and the cold source.

[0174] (4) The ice crystals were taken out of the freezing device, placed in a refrigerator at about 23°C, and irradiated with ultraviolet light with a wavelength of 10-400 nm for photopolymerization for 24 hours.

[0175] (5) The polymerized ice crystals were placed on a polytetrafluoroethylene plate and freeze-dried to remove the ice crystals in situ for about 4 h. The membrane was then placed on the surface of the polytetrafluoroethylene plate in a self-supporting state.

[0176] (6) Film thickness characterization

[0177] The membrane was placed in anhydrous ethanol, picked up with a silicon wafer and transferred to the surface of the silicon wafer. The sample was placed in liquid nitrogen and a cross section was created using the tip of a scalpel. The height difference between the substrate and the membrane was the thickness of the membrane, which was approximately 1.2 μm.

[0178] Example 13:

[0179] (1) 14.4 g of alumina nanosheets and 0.4 g of polyvinyl alcohol were dispersed in 5.4 g of deionized water, stirred, and ball-milled for 24 h, wherein the volume fraction of the alumina nanosheets was 20 vol%.

[0180] (2) A copper sheet (length × width × thickness = 2 × 2 × 0.1 cm) is used as a cold source, and a copper sheet (length × width × thickness = 2 × 2 × 0.1 cm) is used as a barrier. The barrier and the cold source are glued to both sides of the U-shaped frame (length × width × thickness = 2 × 2 × 0.2 cm) with hydrophobic sealant to form a refrigeration device.

[0181] (3) The freezing device is placed on a hot and cold table with a temperature adjustable within the range of -120-200°C. Alumina nanosheet dispersion is added to the U-shaped frame and the temperature is adjusted so that ice crystals always grow from the cold source side to the barrier side at a rate of 1 μm / s. The freezing is completed after about 30 minutes, and the alumina nanosheets in the assembly liquid are fixed in the ice crystals between the barrier and the cold source.

[0182] (4) The ice crystals were removed from the freezing device and placed on a polytetrafluoroethylene plate. The ice crystals were removed in situ by freeze drying for about 4 h. The membrane was then placed on the polytetrafluoroethylene plate surface in a self-supporting state.

[0183] (5) Film thickness characterization

[0184] The cross-sectional dimensions of the membrane were characterized by SEM electron microscopy, and the thickness was approximately 50 μm.

Claims

1. A method for preparing a membrane based on ice crystal extrusion, wherein an assembly liquid is placed in a system comprising at least a cold source and a barrier, and water in the assembly liquid is heated at a speed within the range of 0.1-50 μm / s and less than the critical ice crystal growth rate. v cr The ice crystals begin to grow from the cold source at a speed of , and the ice crystals push the assembly primitives in the assembly liquid outward from the cold source, and form the film between the cold source and the blocking member; the assembly liquid contains assembly primitives that can be precipitated in water, and the content of the assembly primitives in the dispersion liquid is 0.001-20 vol%; in, ； in, is the interfacial free energy of the system; R is the radius of the solid particle, a0 = 10 nm, η is the viscosity of the assembly liquid, k p and k l are the thermal conductivities of the assembly unit and water, respectively; By inputting a cold source into the blocking member, the blocking member becomes a second cold source body, and the film is formed between the two cold source bodies; and by freeze drying, the film that can stand on its own is obtained.

2. The method according to claim 1, characterized in that The shape of the cooling source body is regular / irregular plane sheet, regular / irregular plane column, regular / irregular plane cone.

3. The method according to claim 1, characterized in that The blocking member has a shape of a regular / irregular plane sheet, a regular / irregular plane column, or a regular / irregular plane cone.

4. The method according to claim 1, wherein The slower the ice crystal growth rate, the denser the resulting film; the faster the ice crystal growth rate, the looser the resulting film.

5. The method according to claim 1, wherein The fewer assembly units in the assembly solution, the thinner the resulting film.

6. The method according to claim 1, characterized in that The assembly liquid is a zero-dimensional material dispersion liquid, a one-dimensional material dispersion liquid, a two-dimensional material dispersion liquid, a polymer solution, or an emulsion.

7. The method according to claim 6, characterized in that The zero-dimensional materials include metal particles, metal oxide particles, carbon particles, organic quantum dots, and inorganic quantum dots; the one-dimensional materials include organic nanowires and inorganic nanowires; the two-dimensional materials include boron nitride nanosheets, aluminum oxide nanosheets, graphene nanosheets, clay sheets, molybdenum disulfide nanosheets, tungsten disulfide nanosheets, and COF nanosheets; the polymers include polyamic acid, silk fibroin, polyvinyl alcohol, chitosan, and sodium alginate; the emulsions include epoxy emulsions, polyurethane emulsions, and silicone rubber emulsions.

8. Application of the membrane prepared by the method according to claim 1 in the fields of separation, thermal management, electronic devices, sensing, energy storage, catalysis, device packaging, and cell culture.

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