Method for observing microscopic formation process of porous membrane prepared by phase separation method

Abstract

Disclosed in the present invention are a method and device for observing a microscopic formation process of a porous membrane prepared by a phase separation method. Observation using the device has the advantages such as easy disassembly and cleaning, and good repeatability. The microstructural evolution and kinetic rate during the formation of porous membranes from different non-solvent induced polymer solutions can be observed. The experimental results are clear and intuitive, enabling simple, accurate, and convenient evaluation of the functions and effects of different non-solvents, which is of great significance for porous membrane preparation research and the field of interface synthesis.

Description

A method for observing the microscopic formation process of porous membranes prepared by phase separation. Technical Field

[0001] This invention relates to the field of membrane science and technology, specifically to a method and apparatus for the microscopic formation process of porous membranes prepared by phase separation. Background Technology

[0002] Ion-conducting membranes can be classified into dense ion-exchange membranes and porous ion-sieving membranes based on their structure, and are widely used in seawater desalination, electrodialysis, and flow battery technologies. The non-solvent-induced phase separation method is an important and conventional method for preparing porous membranes. It involves immersing a substrate coated with a polymer solution of a certain thickness in a non-solvent (usually water) to undergo phase transformation, thus forming a porous membrane. This method is widely adopted industrially due to its simplicity and low cost. However, the formation mechanism of the membrane pore structure during this process remains a subject of much debate. One commonly used method is to observe the membrane structure formed when the polymer solution comes into contact with the non-solvent using a microscope. Traditional testing methods simply involve superimposing two glass slides and adding non-solvent into the slits of the slides. This approach makes it difficult to accurately control the non-solvent flow field distribution, resulting in poor repeatability and a lack of consistent conclusions. Currently, the fundamental principles of phase separation membrane fabrication remain unclear, and observation methods are extremely limited and lack repeatability.

[0003] In view of this, the present invention is proposed. Summary of the Invention

[0004] The purpose of this invention is to provide a method and apparatus for observing the microscopic formation process of porous membranes prepared by phase separation method. It is applicable to in-situ / ex-situ observation of the microstructure formation process of membranes prepared by phase separation method, and is simple to operate, highly repeatable, and convenient to use.

[0005] This invention is implemented as follows:

[0006] Firstly, this device provides an apparatus for observing the microscopic formation process of porous membranes prepared by phase separation method, comprising: a cover glass, a slide, a fixing device, and a gasket. The cover glass is placed on top of the slide, such that a portion A of the upper surface of the slide is covered by the cover glass, while the upper part of another portion B is not covered by the cover glass. The overlapping cover glass and slide form an observation cell through the fixing device. A gasket is added or not added to the surface of region A between the cover glass and the slide. The gap width (or thickness) between the cover glass and the slide is adjusted by adding or not adding a gasket. If a gasket is added, the surface of region A between region A and region B is not obstructed by the gasket, that is, when a gasket is added to region A, the surface of region A facing region B has a gap without the gasket.

[0007] In some embodiments, the cover glass near the objective lens should have good light transmittance and a thickness of 0.01-10 mm.

[0008] In some embodiments, the cover glass and slide are made of glass or quartz.

[0009] In some embodiments, the aforementioned gaskets need to be evenly placed on the surface of region A of the glass slide, forming a hollow blank area, the area of ​​which must be greater than 1 cm². 2 Preferably 1-9cm 2 More preferably 4-9cm 2 .

[0010] In some embodiments, the thickness of the gasket is between 10-100 μm, with a relatively uniform overall thickness, and the material includes general polymers, metals, silicon wafers, and ceramics.

[0011] In some embodiments, the fixing force of the above-mentioned multiple fixing devices should be substantially the same, and they should be easy to disassemble.

[0012] Secondly, the present invention provides the application of the above-mentioned observation device in observing the microscopic formation process of porous membranes prepared by phase separation method.

[0013] Thirdly, this invention also provides a method for observing the microscopic formation process of porous membranes prepared by phase separation. This method employs the aforementioned observation device and includes: adding a small drop of polymer solution to the center of a glass slide; assembling a coverslip and the glass slide together using a fixing device to form the observation device; adjusting the microscope to reveal the boundary of the polymer solution spot in the field of view; adding a small amount of non-solvent at the mating edge of the coverslip and the glass slide; and initiating the observation of the porous membrane formation process when the non-solvent is drawn into the slit between the two slides and encounters the polymer solution spot. The thickness of the shim can be adjusted to control the flow rate of the non-solvent.

[0014] In some embodiments, the droplet volume of the polymer solution described above is 0.1-10 μL.

[0015] In some embodiments, the volume of the non-solvent added is 0.1-10 mL.

[0016] In some embodiments, the temperature of the above-mentioned observation environment is 15-35°C and the relative humidity is <40%.

[0017] The present invention has the following beneficial effects:

[0018] This invention presents a method and apparatus for observing the microscopic formation process of porous membranes prepared by phase separation. The apparatus offers the advantage of high repeatability in detection. Furthermore, observing the microstructure of the phase separation at the polymer solution-non-solvent interface using a microscope outside the apparatus allows for a better understanding of the phase separation mechanism. This is of significant importance for the preparation and industrial application of polymer membranes. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments are briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 is a schematic diagram of the observation device of the present invention;

[0021] Figure 2 is a schematic diagram of the method of using the observation device of the present invention for observation with a microscope.

[0022] Figure 3 is an optical microscope image of the phase separation structure formed in the observation device when the number of gasket layers is different in Example 1;

[0023] Figure 4 is an optical microscope image of the phase separation structure formed in the observation device when the number of gasket layers is different in Example 2;

[0024] Figure 5 is a fluorescence microscope image of the phase separation structure formed in the observation device in Example 3;

[0025] Figure 6 is an optical microscope image of the phase separation structure formed in the observation device under different conditions with gaskets in Example 4;

[0026] Figure 7 is an optical microscope image of the phase separation structure in Comparative Example 1 without the fixing device and gasket. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. All reagents or instruments without specified manufacturers are conventional products that can be purchased commercially.

[0028] The apparatus structure for observing the microscopic formation process of porous membranes using the phase separation method provided by this invention is shown in Figure 1. It consists of a coverslip, a glass slide, a gasket, and a fixing device, forming a whole. The coverslip, glass slide, and gasket are connected by the fixing device to form an observation cell. The gasket can be added between the coverslip and glass slide to adjust the gap width between them. A coverslip is placed on top of a slide, covering a portion A of the slide's upper surface while leaving another portion B uncovered. The overlapping coverslip and slide form an observation cell via a fixing device. A spacer is placed on the surface of region A between the coverslip and slide. The width (or thickness) of the gap between the coverslip and slide is adjusted by adding or removing the spacer. If a spacer is added, the surface of region A between region A and region B will not be obstructed by the spacer; that is, when a spacer is added to region A, the surface of region A facing region B will have an unobstructed gap. The spacers need to be evenly placed on the surface of region A on the slide, forming a hollow blank area with an area ≥ 1 cm². 2 Preferably 1-9cm 2 More preferably 4-9cm 2 .

[0029] The coverslip, located near the objective lens, should have good light transmittance and a thickness between 0.01 and 10 mm, enabling optical magnification of 5-40 times for the objective lens. The coverslip and slide can be made of glass or quartz; the transparency of the slide depends on whether the microscope uses a transmission or reflection optical path.

[0030] The thickness of the aforementioned gaskets is between 10-100μm, with a relatively uniform overall thickness. The materials include polymers, metals, silicon wafers, and ceramics that are generally easy to process into film.

[0031] The fixing force of the above-mentioned fixing devices should be basically the same, and they should be easy to disassemble.

[0032] The materials used in the above preparation process are not limited to the listed materials, but can also be other materials with the same or similar properties in this field.

[0033] As shown in Figure 2, the microscopic process of preparing porous membranes by phase separation was observed using the above-mentioned observation device. The observation method is as follows:

[0034] A small drop of polymer solution is added to the center of a glass slide. The coverslip and slide are then symmetrically assembled using multiple fixing devices to form an observation setup. Under pressure, a polymer solution spot will form. The microscope is then quickly adjusted so that the boundary of the polymer solution spot appears in the field of view. A small amount of non-solvent is added to the channel on the slide that does not fit with the coverslip. Due to capillary action, the non-solvent is drawn into the slit between the two slides. When the non-solvent encounters the polymer solution spot, a phase separation process occurs, forming a porous structure, which allows for phase separation observation. The flow rate of the non-solvent can be controlled by adjusting the thickness of the shims. The flow behavior of the non-solvent within the slit between the two slides can be described using the Lucas-Washburn model formula:

[0035] In the formula, h is the height to which the non-solvent rises within the slit of the glass plate, L is the width of the slit, μ is the kinematic viscosity of the non-solvent, θ is the contact angle between the non-solvent and the glass plate wall, and t is the flow time of the non-solvent within the slit of the glass plate.

[0036] More preferably, the drop volume of the polymer solution is 0.1-10 μL.

[0037] More preferably, the volume of the non-solvent added is 0.1-10 mL.

[0038] Preferably, the temperature of the above-mentioned observation environment is between 15-35℃ and the relative humidity is <40%, to prevent interference caused by vapor-induced phase transformation or solvent evaporation.

[0039] In the observation method of the present invention, the image magnification device can be an optical microscope, a fluorescence microscope, or a microscope or magnifying glass of other different wavelengths, and the present invention does not limit it.

[0040] The above observation method is a simple, accurate, and efficient way to study the microscopic formation process of porous membranes prepared by phase separation. This method can meet the requirements for specificity, accuracy, and repeatability in the process of method validation. This method is of great significance for all studies involving two-phase synthesis.

[0041] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0042] Example 1

[0043] This embodiment provides a method for adjusting the phase separation microstructure, as detailed below:

[0044] S1: Cleaning of the observation equipment and control of the experimental environment

[0045] Soda-lime glass rectangular slides (76mm×25mm×1mm), soda-lime glass rectangular coverslips (76mm×25mm×1mm), and three identical polybenzimidazole rectangular gaskets (30mm×5mm×25μm) were sequentially immersed in ultrapure water and anhydrous ethanol for ultrasonication, wiped clean with lint-free paper, and then air-dried. The operating environment was controlled at a temperature of 25±5℃ and a relative humidity of 15±5%.

[0046] S2: Dropping of polymer solution

[0047] Using a micro-injector, 0.5 μL of a 15% polybenzimidazole N,N-dimethylacetamide (DMAC) solution was drawn and dropped onto the center of a glass slide.

[0048] S3: Device Assembly and Microscope Field of View Selection

[0049] On the front of the slide, draw a straight line to define rectangular areas A (50mm × 25mm × 1mm) and B (26mm × 25mm × 1mm). Area A needs to be covered by a coverslip, while area B is not covered by a coverslip. A and B are connected by a slit between the coverslip and the slide. Place three polybenzimidazole rectangular spacers around area A of the slide, as shown in Figure 1, leaving approximately 4cm of space within area A. 2 Region C (spacer layer 1), and the channel connecting region C and region B, are not covered by the polybenzimidazole film (i.e., a portion of region A between region C and region B remains uncovered). The coverslip is then assembled as described above, and four dovetail clips are evenly distributed around the slide (around region A) and the coverslip to form the observation device. After completing these steps, the microscope is focused, and the boundary of the polymer solution spot closest to the non-solvent channel is selected as the center of the field of view. Video recording begins in advance. The same operation can be performed with two layers of polybenzimidazole film (spacer layer 2) or without polybenzimidazole film (spacer layer 0).

[0050] S4: Non-solvent addition and microscopic observation

[0051] 0.5 mL of ultrapure water (non-solvent) was rapidly added to the channel openings in the reserved areas A and B. After the ultrapure water was drawn into the slits of the slide and coverslip and encountered the polymer solution spot, phase separation occurred, and a porous polymer structure was precipitated. The process was observed from the moment the water encountered the polymer solution spot until the porous polymer was completely precipitated, for a total of 5 minutes.

[0052] S5: Results Analysis

[0053] The detection results are shown in Figure 3. Figure 3 is a frame image taken 3 minutes after phase separation using the optical microscope with the apparatus in Experiment Example 1. The image position corresponds to the number of gasket layers and the non-solvent flow rate: upper left - 0 layers / 40μm s -1 Top right -1 layer / 1460μm s -1 , lower -2 layers / 2270μm s -1 Therefore, this device can change the slit width between the slide and coverslip by simply adjusting the number of shims, thereby altering the velocity at which the non-solvent and polymer solution spots meet. Ultimately, it can obtain a phase-separated structure that progresses from no finger-like pores to small finger-like pores and then to large finger-like pores. This device design represents the first time that artificially controlled phase-separated microstructures have been achieved, which is of great significance for studying phase separation mechanisms.

[0054] Example 2

[0055] This embodiment provides a method for adjusting the phase separation microstructure, as detailed below:

[0056] S1: Cleaning of the observation equipment and control of the experimental environment

[0057] Soda-lime glass rectangular slides (76mm×25mm×1mm), soda-lime glass rectangular coverslips (76mm×25mm×1mm), and three identical polybenzimidazole rectangular gaskets (30mm×5mm×25μm) were sequentially immersed in ultrapure water and anhydrous ethanol for ultrasonication, wiped clean with lint-free paper, and then air-dried. The operating environment was controlled at a temperature of 25±5℃ and a relative humidity of 15±5%.

[0058] S2: Dropping of polymer solution

[0059] Using a micro-injector, 0.5 μL of a 20% polyethersulfone DMAC solution was drawn and dropped onto the center of a glass slide.

[0060] S3: Device Assembly and Microscope Field of View Selection

[0061] On the front of the slide, draw a straight line to define rectangular areas A (50mm × 25mm × 1mm) and B (26mm × 25mm × 1mm). Area A needs to be covered by a coverslip, while area B is not covered by a coverslip. A and B are connected by a slit between the coverslip and the slide. Place three polybenzimidazole rectangular spacers around area A of the slide, as shown in Figure 1, leaving approximately 4cm of space within area A. 2Region C (spacer layer 1), and the channel connecting region C and region B, are not covered by the polybenzimidazole film (i.e., a portion of region A between region C and region B remains uncovered). The coverslip is then assembled as described above, and four dovetail clips are evenly distributed around the slide (around region A) and the coverslip to form the observation device. After completing these steps, the microscope is focused, and the boundary of the polymer solution spot closest to the non-solvent channel is selected as the center of the field of view. Video recording begins in advance. The same operation can be performed with two layers of polybenzimidazole film (spacer layer 2) or without polybenzimidazole film (spacer layer 0).

[0062] S4: Non-solvent addition and microscopic observation

[0063] 0.5 mL of ultrapure water (non-solvent) is rapidly added to the channel openings in the reserved areas A and B. After the ultrapure water is drawn into the slits of the slide and coverslip and encounters the polymer solution spot in area C, phase separation occurs, and a porous polymer structure is precipitated.

[0064] S5: Results Analysis

[0065] The detection results are shown in Figure 4. Figure 4 is a frame image taken 3 minutes after phase separation using the optical microscope with the device described in Example 2. The image position corresponds to the number of gasket layers and the non-solvent flow rate: top left - 0 layers / 36 μm s -1 Top right -1 layer / 1550μm s -1 , lower -2 layers / 2300μm s -1 Comparing Examples 1 and 2, different polymer solutions were selected, and the device was used to achieve artificially controlled phase separation microstructures, which can be mutually verified to study the phase separation mechanism.

[0066] Example 3

[0067] This embodiment provides a method for observing the evolution of phase separation over time, as detailed below:

[0068] S1: Cleaning of the observation equipment and control of the experimental environment

[0069] Soda-lime glass rectangular slides (76mm×25mm×1mm), soda-lime glass rectangular coverslips (76mm×25mm×1mm), and three identical polybenzimidazole rectangular gaskets (30mm×5mm×25μm) were sequentially immersed in ultrapure water and anhydrous ethanol for ultrasonication, wiped clean with lint-free paper, and then air-dried. The operating environment was controlled at a temperature of 25±5℃ and a relative humidity of 15±5%.

[0070] S2: Dropping of polymer solution

[0071] Using a micro-injector, 0.5 μL of a 15% polybenzimidazole DMAC solution was drawn and dropped onto the center of a glass slide.

[0072] S3: Device Assembly and Microscope Field of View Selection

[0073] On the front of the slide, draw a straight line to define rectangular areas A (50mm × 25mm × 1mm) and B (26mm × 25mm × 1mm). Area A needs to be covered by a coverslip, while area B is not covered by a coverslip. A and B are connected by a slit between the coverslip and the slide. Place three polybenzimidazole rectangular spacers around area A of the slide, as shown in Figure 1, leaving approximately 4cm of space within area A. 2 Region C (with one pad layer) and the channel connecting regions C and B are not covered by the polybenzimidazole film (i.e., a portion of region A between regions C and B remains uncovered by the pad). The coverslip is then assembled as described above, and four dovetail clips are evenly distributed around the slide (around region A) and the coverslip to form the observation device. After completing these steps, the microscope is focused, and the boundary of the polymer solution spot closest to the non-solvent channel is selected as the center of the field of view. Video recording begins in advance.

[0074] S4: Non-solvent addition and fluorescence microscopy observation

[0075] 0.5 mL of ultrapure water (non-solvent) is rapidly added to the channel openings in the reserved areas A and B. After the ultrapure water is drawn into the slits of the slide and coverslip and encounters the polymer solution spot in area C, phase separation occurs, and a porous polymer structure is precipitated.

[0076] S5: Results Analysis

[0077] Images of the finger pores taken at 0.1 s, 0.2 s, and 0.3 s after phase separation (Figure 5). The images show almost no fluorescence signal inside the finger pores, indicating the absence of fluorescent polybenzimidazole within the pores. This device enables in-situ monitoring of the process from the formation to the growth of finger pores, which is helpful for studying the pore formation mechanism during phase separation.

[0078] Example 4

[0079] This embodiment provides a method for verifying the repeatability of a designed device, as follows:

[0080] S1: Cleaning of the observation equipment and control of the experimental environment

[0081] Soda-lime glass rectangular slides (76mm×25mm×1mm), soda-lime glass rectangular coverslips (76mm×25mm×1mm), and three identical polybenzimidazole rectangular gaskets (30mm×5mm×25μm) were sequentially immersed in ultrapure water and anhydrous ethanol for ultrasonication, wiped clean with lint-free paper, and then air-dried. The operating environment was controlled at a temperature of 25±5℃ and a relative humidity of 15±5%.

[0082] S2: Dropping of polymer solution

[0083] Using a micro-injector, 0.5 μL of a 15% polybenzimidazole DMAC solution was drawn and dropped onto the center of a glass slide.

[0084] S3: Device Assembly and Microscope Field of View Selection

[0085] On the front of the slide, draw a straight line to divide it into rectangular areas A (50mm × 25mm × 1mm) and B (26mm × 25mm × 1mm). Area A needs to be covered by a coverslip, while area B is not covered. Areas A and B are connected by a slit between the coverslip and the slide. Fit the coverslip as described above, and then evenly distribute four dovetail clips around the perimeter of the slide (area A) and the coverslip to secure them together to form the observation device. After completing the above steps, start focusing the microscope and select the side of the polymer solution spot closest to the non-solvent channel boundary as the center of the field of view. Start recording video in advance.

[0086] S4: Non-solvent addition and fluorescence microscopy observation

[0087] 0.5 mL of ultrapure water (non-solvent) is rapidly added to the channel openings in the reserved areas A and B. After the ultrapure water is drawn into the slits of the slide and coverslip and encounters the polymer solution spot, phase separation occurs, and a porous polymer structure is precipitated.

[0088] S5: Results Analysis

[0089] The S1-S4 experiments were repeated three times, and the results are shown in Figure 6. Without the gasket, the phase separation structures obtained in the three repeated experiments were consistent (none contained finger pores). Therefore, the design of this device achieves high reproducibility of the phase separation microstructure, which will greatly improve the stability and reliability of the experimental results.

[0090] Comparative Example 1

[0091] The difference from Embodiment 1 is that there is no dovetail clip (fixing device) and no gasket.

[0092] This experimental example provides a comparative experiment with the apparatus in Experimental Example 1, as follows:

[0093] S1: Cleaning of the observation equipment and control of the experimental environment

[0094] Soda-lime glass rectangular slides (76mm×25mm×1mm), soda-lime glass rectangular coverslips (76mm×25mm×1mm), and three identical polybenzimidazole rectangular gaskets (30mm×5mm×25μm) were sequentially immersed in ultrapure water and anhydrous ethanol for ultrasonication, wiped clean with lint-free paper, and then air-dried. The operating environment was controlled at a temperature of 25±5℃ and a relative humidity of 15±5%.

[0095] S2: Dropping of polymer solution

[0096] Using a micro-injector, 0.5 μL of a 15% polybenzimidazole DMAC solution was drawn and dropped onto the center of a glass slide.

[0097] S3: Device Assembly and Microscope Field of View Selection

[0098] On the front of the slide, draw a straight line to divide it into rectangular areas A (50mm × 25mm × 1mm) and B (26mm × 25mm × 1mm). Area A needs to be covered by a coverslip, while area B is not covered. Areas A and B are connected by a slit between the coverslip and the slide. Fit the coverslip as described above. After completing the above steps, start focusing the microscope and select the side of the polymer solution spot closest to the non-solvent channel boundary as the center of the field of view. Start recording video in advance.

[0099] S4: Non-solvent addition and microscopic observation

[0100] 0.5 mL of ultrapure water (non-solvent) is rapidly added to the channel openings in the reserved areas A and B. After the ultrapure water is drawn into the slits of the slide and coverslip and encounters the polymer solution spot, phase separation occurs, and a porous polymer structure is precipitated.

[0101] S5: Results Analysis

[0102] Repeating S1-S4 three times yielded the results shown in Figure 7. Only the phase-separated structure with finger-like pores was obtained. The image positions correspond to the number of gasket layers and the non-solvent flow rate: top left - 0 layers / 2700 μm s -1 Top right -1 layer / 3580μm s -1 , lower -2 layers / 4010μm s -1 The apparatus in Example 1 allows for tuning of the non-solvent flow rate over a wider scale, especially achieving ultra-low non-solvent flow rates (<100 μm / s). -1Therefore, it can achieve a crucial phase separation structure without finger-like macropores. In contrast, Comparative Example 1 lacks a fixing device and gaskets, and the non-solvent flow rate adjustment is uncontrollable and has a narrow scope, only producing a high non-solvent flow rate (>1500 μm / s). -1 This corresponds to obtaining only phase-separated structures containing finger-like macropores. In summary, the design in Experimental Example 1 allows for precise artificial control of the formation of different phase-separated microstructures, which is of great significance for studying the pore formation mechanism of phase separation.

Claims

1. A method of observing the microformation process of a porous membrane prepared by a phase separation method, characterized by, The apparatus includes a cover glass and a slide. The cover glass is placed on top of the slide, so that a portion A of the upper surface of the slide is covered by the cover glass, while another portion B is not covered by the cover glass. The overlapping cover glass and slide are fixed in relative position by a fixing device to form an observation cell. A spacer is placed between region A of the slide and the cover glass above it, with or without a spacer. The width (or thickness) of the gap between the cover glass and the slide is adjusted by placing or not placing a spacer. If a spacer is placed, the surface of region A facing or close to region B is not covered by the spacer. That is, when a spacer is placed in region A, the surface of region A facing region B has a gap without the spacer. The detection process is as follows: The polymer solution to be formed is dropped onto the surface of region A in the middle of a glass slide. A gasket is placed around the droplet (the part of region A facing or near region B is not covered by a gasket, leaving a gap for non-solvent to pass through on the side near region B) or no gasket is placed. Then, a coverslip is placed over the upper part of region A of the glass slide or over the gasket on region A of the glass slide. The coverslip and the glass slide are fixed and positioned using a fixing device to assemble an observation device. The observation device is placed on a microscope for observation. The microscope is adjusted so that the boundary of the polymer solution spot appears in the field of view. Non-solvent is dropped onto region B on the upper surface of the glass slide, near the edge of the coverslip where the polymer solution is in region A. When the non-solvent is drawn into the slit between the coverslip and the glass slide and meets the polymer solution spot, the formation process of the porous membrane can be observed.

2. The method of claim 1, wherein, The coverslip is placed below the microscope objective lens on the side close to the objective lens. It should have good light transmittance and a thickness of 0.01-10 mm. Its material can be one or more of glass, quartz, and polymethyl methacrylate.

3. The method of claim 1, wherein, The gasket needs to be placed evenly on the surface of area A on the slide, and a hollow blank area with no gasket shielding gap is formed around the side close to or facing area B. The area of the hollow blank area formed around must be greater than 1 cm 2 (preferably 1-9 cm 2 , more preferably 4-9 cm 2 ); The thickness of the gasket is preferably 10-100μm, more preferably 20-60μm, and the overall thickness is relatively uniform. The material can be one or more of glass, quartz, polymethyl methacrylate, and silicon wafer. By changing the thickness of the gasket, the rate at which the non-solvent flows to the polymer solution spot can be controlled, thereby adjusting the pore structure formed by phase separation.

4. The method of claim 1, wherein, The fixing device can be one or more, preferably two to ten, and is evenly fixed around the cover glass and slide in area A. It is easy to disassemble and can be one or more of the following: rubber band (wound around the overlapping cover glass and slide), dovetail clip (clamped around the edges of the overlapping cover glass and slide), and binding rope (wound around the overlapping cover glass and slide).

5. The method of claim 1, wherein, The polymer solution is a homogeneous solution formed by dissolving one or more organic polymer resins containing polar groups in an organic solvent.

6. The method according to claim 5, characterized in that, The organic polymer resin containing polar groups is one or more of polybenzimidazole, polyethersulfone, polyetheretherketone, sulfonated polyetheretherketone, polyimide, and polyvinylpyridine. The organic solvent includes one or more of amides, furans, and sulfones; wherein the amides include one or more of N,N-dimethylacetamide (DMAC), N,N-dimethylformamide (DMF), N,N-diethylformamide (DEF), and N,N-diethylacetamide; the furans include tetrahydrofuran (THF) and one or more of furans; and the sulfones include one or more of dimethyl sulfoxide (DMSO), diethyl sulfoxide (DESO), benzylphenyl sulfoxide, dimethyl sulfone, phenylethyl sulfone, diethyl sulfone, diphenyl sulfone, sulfolane, and bisphenol S. The concentration of the organic polymer resin containing polar groups in the organic solvent is preferably 1%-30%, more preferably 5%-20%.

7. The method of claim 1, wherein, The preferred drop volume of the polymer solution is 0.1-10 μL, more preferably 0.1-1 μL.

8. The method of claim 1, wherein, The non-solvents include one or more of the following: water, alcohols, ketones, esters, and alkane solvents. The alcohol solvents are one or more of methanol, ethanol, n-propanol, isopropanol, n-butanol, n-pentanol, tert-butanol, and isobutanol; the ketone solvents are one or more of acetone, methyl ethyl ketone, cyclobutanone, methyl isopropanone, and methyl hexanone; the ester solvents are one or more of ethyl acetate, butyl acetate, and pentyl acetate; and the alkane solvents are n-pentane, cyclopentane, n-hexane, cyclohexane, n-heptane, n-octane, n-nonane, n-decane, undecane, and dodecane.

9. The method according to claim 1 or 8, characterized in that, The volume of non-solvent added should be ≥0.1 mL (preferably 0.1-10 mL, more preferably 1-5 mL).

10. The method of claim 1, wherein, The ambient temperature for observation is 15-35℃, preferably 20-30℃, and the relative humidity is 0-40%, preferably 0-20%.

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