A microfluidic chip and method for directly observing phase separation behavior of polymer droplets

Abstract

The application discloses a microfluidic chip and method for directly observing phase separation behavior of polymer droplets, and belongs to the technical field of microfluidics. The microfluidic chip comprises a chip substrate, a cover glass and a metal wire for carrying polymer droplets; a plurality of uniformly arranged grooves are arranged on the chip substrate; the cover glass is arranged on the chip substrate; and the metal wire is arranged between the chip substrate and the cover glass and located in the grooves. The method comprises the steps of dip coating of the metal wire in a polymer solution, embryo preparation in the microfluidic chip, introduction of a non-solvent into the microfluidic chip, observation and recording of phase separation behavior by a biological microscope and the like. The microfluidic chip is simple in structure, can uniformly, stably and controllably prepare polymer droplets in size and shape, and effectively eliminates the influence of air bubbles on the phase separation behavior of the polymer droplets. The method is simple in steps and easy to operate, and can directly observe the phase separation dynamic process of polymer droplets in any shape.

Description

Technical Field

[0001] This invention relates to the field of microfluidics, specifically to a microfluidic chip and method for directly observing the phase separation behavior of polymer droplets. Background Technology

[0002] Wet spinning is one of the industrial techniques for preparing various membrane materials. During wet spinning, a polymer solution formed by dissolving a solid polymer in a solvent comes into contact with water. Rapid exchange of solvent and water occurs at the interface, causing complex phase separation within the polymer solution. After phase separation, a complex pore structure forms within the polymer solution. Different membrane applications require membrane materials with different pore structures. While process experiments are typically used to determine the formation rules of these pores, the preparation process for these experiments is very time-consuming and results in significant raw material waste. Therefore, a method is needed to rapidly observe the phase separation behavior of membrane liquid droplets.

[0003] Early literature disclosed methods for studying macropore formation in membranes using polymer droplets. Specifically, polymer droplets were placed between two glass slides spaced at a certain distance, and a non-solvent was added to the droplets to study the pore formation process. However, this method has the following problems: 1. The polymer liquid preform can only be circular, which means the observed liquid phase separation behavior cannot be correlated with the actual membrane preform phase separation behavior during the spinning process. This is because the cross-sectional shape of the polymer liquid preform in actual hollow fiber spinning is annular, with the width of the annulus approximately equal to the thickness of the hollow fiber; 2. Air bubbles are inevitably introduced during the droplet introduction process. The presence of these bubbles affects the growth of pores within the droplet, rendering the observation results unreliable; 3. During the observation process, the liquid preform is easily affected by air humidity, causing premature phase separation and making the observation process incomplete and not very meaningful for reference regarding the droplet phase separation behavior in actual hollow fiber spinning.

[0004] Given the shortcomings of existing research methods, it is essential to develop a microfluidic chip and method that can control ambient air humidity and polymer liquid embryos, and avoid introducing air bubbles, to directly observe the phase separation behavior of polymer droplets. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, one of the objectives of this invention is to provide a microfluidic chip for directly observing the phase separation behavior of polymer droplets with arbitrary shapes. This microfluidic chip has a simple structure, can prepare polymer droplets uniformly, stably, and with controllable size and shape, and effectively eliminates the influence of air bubbles on the phase separation behavior of polymer droplets.

[0006] To solve the above problems, the technical solution adopted by the present invention is as follows:

[0007] A microfluidic chip for directly observing the phase separation behavior of polymer droplets includes a chip substrate, a cover glass, and an inducing metal wire for carrying polymer droplets; the chip substrate has a plurality of uniformly distributed channels, the cover glass covers the chip substrate, and the metal wire is disposed between the chip substrate and the cover glass and located within the channels.

[0008] In a preferred embodiment of the present invention, the inducing wire is a titanium alloy wire.

[0009] In a preferred embodiment of the present invention, the depth of the channel is equal to the diameter of the inducing wire.

[0010] In a preferred embodiment of the present invention, the volume of the channel is 20 to 30 times the volume of the polymer droplets carried by the inducing metal wire.

[0011] In a preferred embodiment of the present invention, the channel includes a main channel and a secondary channel communicating with the main channel. The main channel is a square channel with a length and width ≥ 40 mm and a depth of 50 to 100 μm. One end of the secondary channel communicating with the main channel is a constriction throat channel, and the other end is a circular channel.

[0012] In a preferred embodiment of the present invention, the chip substrate is a thin glass sheet with grooves formed by precision etching.

[0013] The second objective of this invention is to provide a method for directly observing the phase separation behavior of polymer droplets, which uses a microfluidic chip as described above to observe the phase separation behavior of polymer droplets, specifically including the following steps:

[0014] S1. Immerse the shaped induction wire in the polymer solution to be tested inside the glove box;

[0015] S2. Take out the induction wire carrying the polymer droplets from the glove box and place it in the channel of the chip substrate, then quickly cover it with a coverslip.

[0016] S3. Transfer the microfluidic chip obtained in step S2 to the stage of the biological microscope in the glove box. Drop non-solvent into the open channel of the microfluidic chip. Under the action of capillary force, the non-solvent is drawn into the small gap between the coverslip and the chip substrate and comes into contact with the polymer liquid embryo on the induction wire, and phase separation occurs. The pore formation process in the polymer liquid embryo at different time points is observed and recorded by the high-speed camera on the biological microscope.

[0017] In a preferred embodiment of the present invention, the humidity inside the glove box is controlled to be below 30%.

[0018] In a preferred embodiment of the present invention, the glove box controls humidity using a solid desiccant.

[0019] In a preferred embodiment of the present invention, the biological microscope is a microscope with transmission effect.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] The microfluidic chip of this invention forms an open-type fluidic chip that can be visualized by setting channels on a chip substrate and placing an inducing metal wire carrying polymer droplets in the channels, combined with a coverslip. The structure is simple and the design is reasonable. After covering with a coverslip, the polymer droplets on the inducing metal wire will extend to form a polymer liquid film with a certain thickness. The metal wire can control the shape and size of the polymer liquid embryo, making the polymer liquid embryo more uniform and stable, and can also serve as a size reference for the polymer liquid embryo. At the same time, the presence of the inducing metal wire can completely eliminate the influence of entrained air bubbles. Therefore, the microfluidic chip of this invention can realize the observation of the phase separation dynamics of polymer droplets of arbitrary shapes under a biological microscope. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the microfluidic chip described in this invention;

[0023] Figure 2 This is a schematic diagram illustrating the operation of the method described in this invention;

[0024] Figure 3 This is a schematic diagram of the structure of polymer droplets of different shapes obtained by changing the shape of the inducing metal wire in this invention;

[0025] Figure 4 This is a microscopic image of the irregular arc-shaped membrane embryo obtained in Example 1 of the present invention;

[0026] Figure 5 This is a microscopic image of the tadpole-shaped membrane embryo obtained in Example 2 of the present invention;

[0027] Figure 6 This is a microscopic image of a sharp membrane embryo undergoing phase separation, obtained in Example 3 of the present invention.

[0028] The following are the symbols in the attached diagram: 1. Chip substrate; 2. Cover glass; 3. Inducing metal wire; 4. Channel; 5. Non-solvent introduction hole; 6. Limiting metal sheet. Detailed Implementation

[0029] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0030] like Figure 1As shown, the microfluidic chip for directly observing the phase separation behavior of polymer droplets according to the present invention includes a chip substrate 1, a cover glass 2, and an inducing metal wire 3 for carrying polymer droplets; the chip substrate 1 is provided with a plurality of uniformly arranged channels 4, the cover glass 2 is placed on the chip substrate 1, and the inducing metal wire 3 is disposed between the chip substrate 1 and the cover glass 2 and located in the channels 4. In practical use, the inducing metal wire 3 is first immersed in a polymer solution to coat the surface of the inducing metal wire 3 with a thin film of polymer liquid. After covering with a coverslip 2, the polymer liquid film on the inducing metal wire 3 will extend, thereby obtaining a polymer liquid embryo that matches the shape of the inducing metal wire 3. The phase separation behavior of the polymer liquid embryo in the microfluidic chip can be observed under a biological microscope by introducing a non-solvent. Compared with the existing method of directly adding a non-solvent to the polymer droplets to simulate the phase separation behavior of polymer droplets in the actual hollow fiber spinning process, the microfluidic chip of the present invention has a simple structure and reasonable design. Using this microfluidic chip to directly observe the phase separation behavior of polymer droplets is more in line with actual production and has higher reference value.

[0031] Preferably, the chip substrate is a 2mm thick glass sheet, and channels can be etched on the glass sheet using a chemical precision etching method. Specifically, the channels include a main channel and a secondary channel connected to the main channel. The main channel is a square channel with a length and width ≥ 40mm and a depth of 50-100μm. One end of the secondary channel connected to the main channel is a constriction throat channel, and the other end is a circular channel. The circular channel is a non-solvent inlet 5, and its depth is the same as that of the main channel. The width of the constriction throat channel gradually decreases from the main channel to the circular channel. The constriction throat channel serves to introduce non-solvent and limit the flow rate of non-solvent. Four limiting metal sheets 6 are glued to both sides of the channel 4 on the chip substrate 1 to limit the movement of the cover glass 2. Specifically, the depth of the channel is equal to the diameter of the inducing metal wire, and the volume of the channel is 20-30 times the volume of the polymer droplet carried by the inducing metal wire. Preferably, the inducing wire is a titanium alloy wire. Titanium alloy wire has good affinity with polymer solutions. When the titanium alloy wire is immersed in a highly viscous polymer solution, a polymer liquid film of a certain thickness can be successfully coated on the surface of the titanium alloy wire. The thickness of the polymer liquid film can be adjusted by regulating its viscosity. Simultaneously, titanium alloy wire is flexible and easy to shape, such as… Figure 3 As shown, polymer liquid preforms of arbitrary shapes can be obtained by changing the shape of the titanium alloy wire, thus enabling the observation of the phase separation behavior of polymer droplets of any shape, which is closer to the actual production of hollow fiber spinning. Furthermore, the inducing wire is displayed in the image during direct observation and can therefore serve as a size reference for the polymer droplets.

[0032] like Figure 2As shown, the method for directly observing the phase separation behavior of polymer droplets provided by this invention uses a microfluidic chip as described above to observe the phase separation behavior of polymer droplets. The entire method is operated within a glove box with humidity below 30%. By controlling the humidity in the operating environment, phase separation of the polymer droplets can be effectively prevented before observation. The method of this invention uses a biological microscope with transmission properties for direct observation, and the images and other data obtained during the observation process are recorded by external electronic equipment. Specifically, the method includes the following steps:

[0033] S1. Use tweezers to immerse the shaped induction wire into the polymer solution to be tested;

[0034] S2. Use tweezers to remove the inducing metal wire carrying the polymer droplets, place it in the channel of the chip substrate, and quickly cover it with a coverslip.

[0035] S3. Transfer the microfluidic chip obtained in step S2 to the stage of a biological microscope in the glove box. Drop non-solvents such as water into the open channels of the microfluidic chip. Under the action of capillary force, the non-solvent is drawn into the small gap between the coverslip and the chip substrate and comes into contact with the polymer liquid embryo on the inducing wire, and phase separation occurs. The pore formation process in the polymer liquid embryo at different time points is observed and recorded by a high-speed camera on the biological microscope.

[0036] The above-mentioned observation method introduces a non-solvent into a microfluidic chip carrying polymer droplets under a biological microscope, thereby observing the phase separation behavior of the polymer liquid embryo within the fabricated microfluidic chip. Compared to existing methods that directly add a non-solvent to the polymer droplets to simulate the phase separation behavior of polymer droplets in the actual hollow fiber spinning process, the method of this invention uses a microfluidic chip to directly observe the phase separation behavior of polymer droplets, which is more in line with actual production and has higher reference value. Furthermore, it does not introduce air bubbles into the polymer droplets, thus avoiding affecting the observation results. At the same time, introducing a non-solvent under a microscope to perform phase separation makes the observation process more complete and further enhances its reference value.

[0037] Example 1:

[0038] A method for directly observing the phase separation behavior of polymer droplets includes the following steps:

[0039] S1. Prepare the casting solution by mass percentage using a ratio of 15% PSU + 8% PVP + 77% DMAc; use tweezers to immerse the shaped induction wire into the casting solution to be tested.

[0040] S2. Use tweezers to remove the inducing metal wire carrying the polymer droplets, place it in the channel of the chip substrate, and quickly cover it with a coverslip.

[0041] S3. Transfer the microfluidic chip obtained in step S2 to the stage of a biological microscope inside the glove box. Drop a non-solvent, such as water, into the open channels of the microfluidic chip. Under capillary action, the non-solvent is drawn into the tiny gap between the coverslip and the chip substrate and comes into contact with the polymer liquid embryo on the inducing wire, causing phase separation. Observe and record the pore formation process within the polymer liquid embryo at different time points using a high-speed camera on the biological microscope. The results are as follows: Figure 4 As shown.

[0042] Depend on Figure 4 As can be seen, this embodiment uses inducing metal wires to prepare an irregular arc-shaped membrane embryo.

[0043] Example 2:

[0044] A method for directly observing the phase separation behavior of polymer droplets, in order to prevent premature phase separation of the membrane preform, the entire operation in this embodiment is carried out under a nitrogen protective atmosphere, and the ambient humidity is controlled below 30%. The specific steps include:

[0045] S1. Prepare the casting solution by mass percentage using a ratio of 20% PSU + 5% PVP + 75% DMAc; use tweezers to immerse the shaped induction wire into the casting solution to be tested.

[0046] S2. Use tweezers to remove the inducing metal wire carrying the polymer droplets, place it in the channel of the chip substrate, and quickly cover it with a coverslip.

[0047] S3. Transfer the microfluidic chip obtained in step S2 to the stage of a biological microscope inside the glove box. Drop a non-solvent, such as water, into the open channels of the microfluidic chip. Under capillary action, the non-solvent is drawn into the tiny gap between the coverslip and the chip substrate and comes into contact with the polymer liquid embryo on the inducing wire, causing phase separation. Observe and record the pore formation process within the polymer liquid embryo at different time points using a high-speed camera on the biological microscope. The results are as follows: Figure 5 As shown.

[0048] Depend on Figure 5 As can be seen, this embodiment uses inducing wires to prepare irregular tadpole-shaped membrane embryos.

[0049] Example 3:

[0050] A method for directly observing the phase separation behavior of polymer droplets includes the following steps:

[0051] S1. Prepare the casting solution by mass percentage using a ratio of 28% PSU + 5% PVP; use tweezers to immerse the shaped induction wire into the casting solution to be tested.

[0052] S2. Use tweezers to remove the inducing metal wire carrying the polymer droplets, place it in the channel of the chip substrate, and quickly cover it with a coverslip.

[0053] S3. Transfer the microfluidic chip obtained in step S2 to the stage of a biological microscope inside the glove box. Drop a non-solvent, such as water, into the open channels of the microfluidic chip. Under capillary action, the non-solvent is drawn into the tiny gap between the coverslip and the chip substrate and comes into contact with the polymer liquid embryo on the inducing wire, causing phase separation. Observe and record the pore formation process within the polymer liquid embryo at different time points using a high-speed camera on the biological microscope. The results are as follows: Figure 6 As shown.

[0054] Depend on Figure 6 As can be seen, this embodiment uses inducing metal wires to prepare irregular sharp membrane embryos, and the irregular sharp membrane embryos can be observed under a microscope to be in the process of phase separation.

[0055] As can be seen from the above embodiments, the present invention, by combining a microfluidic chip with channels with an inducing metal wire, can control the shape and size of the polymer liquid embryo, making the polymer liquid embryo more uniform and stable, and can also serve as a size reference for the polymer liquid embryo. This invention enables the observation of the phase separation dynamics of polymer droplets of arbitrary shapes under a biological microscope.

[0056] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A microfluidic chip for directly observing the phase separation behavior of polymer droplets, characterized in that: The device includes a chip substrate, a cover glass, and an inducing metal wire for carrying polymer droplets. The chip substrate has several uniformly distributed channels. The cover glass covers the chip substrate, and the inducing metal wire is disposed between the chip substrate and the cover glass and located within the channels. The depth of each channel is equal to the diameter of the inducing metal wire. Each channel includes a main channel and a secondary channel communicating with the main channel. One end of the secondary channel communicating with the main channel is a constriction throat channel, and the other end is a circular channel.

2. The microfluidic chip for directly observing the phase separation behavior of polymer droplets according to claim 1, characterized in that: The inducing wire is a titanium alloy wire.

3. The microfluidic chip for directly observing the phase separation behavior of polymer droplets according to claim 1 or 2, characterized in that: The volume of the channel is 20 to 30 times the volume of the polymer droplets carried by the inducing metal wire.

4. The microfluidic chip for directly observing the phase separation behavior of polymer droplets according to claim 1 or 2, characterized in that: The main channel is a square channel with a length and width of ≥40mm and a depth of 50~100μm.

5. The microfluidic chip for directly observing the phase separation behavior of polymer droplets according to claim 4, characterized in that: The chip substrate is a thin glass sheet with grooves formed by precision etching.

6. A method for directly observing the phase separation behavior of polymer droplets, characterized in that: The observation of polymer droplet phase separation behavior using the microfluidic chip as described in any one of claims 1 to 5 specifically includes the following steps: S1. Immerse the shaped induction wire in the polymer solution to be tested inside the glove box; S2. Take out the induction wire carrying the polymer droplets from the glove box and place it in the channel of the chip substrate, then quickly cover it with a coverslip. S3. Transfer the microfluidic chip obtained in step S2 to the stage of the biological microscope in the glove box. Drop non-solvent into the open channel of the microfluidic chip. Under the action of capillary force, the non-solvent is drawn into the small gap between the coverslip and the chip substrate and comes into contact with the polymer liquid embryo on the induction wire, and phase separation occurs. The pore formation process in the polymer liquid embryo at different time points is observed and recorded by the high-speed camera on the biological microscope.

7. The method for directly observing the phase separation behavior of polymer droplets according to claim 6, characterized in that: The humidity inside the glove box is controlled below 30%.

8. The method for directly observing the phase separation behavior of polymer droplets according to claim 7, characterized in that: The glove box controls humidity using a solid desiccant.

9. The method for directly observing the phase separation behavior of polymer droplets according to claim 6, characterized in that: The biological microscope is a microscope with transmission capability.

Images