Polyheptazinyl photochromic film and preparation method thereof

Abstract

The invention provides a polyheptylimido photochromic film and a preparation method thereof, and relates to the technical field of intelligent materials. The invention relates to a polyheptylimide photochromic film, which comprises a film substrate, a light reducing agent and a redox dye, the light reducing agent is polyheptylimide, and the redox dye is methylene blue. The polyheptylimide can be excited by 405nm visible light to generate photo-induced electrons, methylene blue is reduced and decolored, the film is changed from blue to white, when oxygen exists in the environment, the film adsorbs oxygen, the decolored methylene blue is oxidized by the oxygen to recover the color, the film is recovered from white to blue, and naked eye detection of the oxygen is realized. The oxygen concentration change from 0% to 20% can be detected, and the sensitivity is high; the film can be completely decolorized after being excited by light for 8 seconds, the color recovery time is 12 minutes in an air environment, and the response time is short; the repetition rate reaches 20 times, and the detection stability is good.

Description

Technical Field

[0001] The present invention relates to the technical field of smart materials, and in particular to a polyheptazine imide-based photochromic film and a preparation method thereof. Background Art

[0002] At present, food safety and quality assurance have become the focus of global consumers and regulators. As one of the key factors affecting the shelf life and flavor stability of food, accurate monitoring of oxygen is particularly important in the field of food packaging. Oxygen can promote the growth of aerobic microorganisms and accelerate food spoilage, so controlling the oxygen concentration in the package is crucial to extending the shelf life of food. This has led to a large number of studies on oxygen detection methods in food packaging at home and abroad, such as electrochemical, fluorescent oxygen indication technology and other gas detection methods. However, these traditional gas detection methods often require destructive sampling or rely on expensive analytical equipment, and cannot achieve instant and non-destructive monitoring, which limits the ability to continuously track oxygen levels during food circulation.

[0003] Therefore, visual oxygen indicator films and their supporting real-time monitoring technologies have emerged, providing an intuitive and efficient solution for controlling oxygen content during food storage and transportation. Visual oxygen indicator films are usually composed of oxygen-sensitive pigments or chemical indicators, which change color when exposed to oxygen. This change is visible to the naked eye, and the oxygen level in the package can be determined without the help of additional tools. Currently, the most widely used are light-driven redox oxygen indicators, such as WO synthesized by electrospinning technology. 3 / polyacrylonitrile nanofiber membrane or colorimetric oxygen indicators based on titanium dioxide composite materials. These technologies have certain application prospects in the field of oxygen detection, but they also have problems such as poor stability, long response time and low sensitivity. Summary of the invention

[0004] The problem solved by the invention is how to solve the problems of poor oxygen detection stability, long response time and low sensitivity of a visual oxygen indicating film.

[0005] In order to solve the above problems, the present invention provides a polyheptazine imide-based photochromic film and a preparation method thereof.

[0006] In a first aspect, the present invention provides a polyheptazinimide-based photochromic film, comprising a film matrix, a photoreductant and a redox dye, wherein the photoreductant is polyheptazinimide, the redox dye is methylene blue, and the film matrix is ​​a cross-linked polymer film of polyvinyl alcohol and ethylene glycol.

[0007] Optionally, the polyheptazine imide is a polyheptazine imide solution with a concentration of 1.2-1.8 g / L, the methylene blue is a methylene blue solution with a concentration of 8-12 mg / L, and the mass ratio of the polyheptazine imide solution to the methylene blue solution is 2.5:1.6-2.4.

[0008] Optionally, the polyvinyl alcohol is a polyvinyl alcohol solution with a mass fraction of 8-12%, the ethylene glycol is an ethylene glycol solution, the volume ratio of ethylene glycol to water in the ethylene glycol solution is 2:0.8-1.2, and the mass ratio of the polyvinyl alcohol solution to the ethylene glycol solution is 3.6-4.4:1.

[0009] In a second aspect, the present invention provides a method for preparing a polyheptazine imide-based photochromic film, wherein the method comprises the following steps:

[0010] Take polyvinyl alcohol solution and ethylene glycol solution, mix them evenly, heat to above 100°C, and stir for more than 10 minutes to obtain a membrane matrix solution;

[0011] Take the polyheptazine imide solution and the methylene blue solution, mix them evenly, add them to the membrane matrix solution, heat to above 85°C, stir for more than 45 minutes, and cool to room temperature;

[0012] The mixture was poured into a mold and heated at 25-35° C. for more than 6 hours to obtain a polyheptazine imide-based photochromic film.

[0013] Optionally, the concentration of the polyheptazinimide solution is 1.2-1.8 g / L.

[0014] Optionally, the concentration of the methylene blue solution is 8-12 mg / L.

[0015] Optionally, the mass ratio of the polyheptazine imide solution to the methylene blue solution is 2.5:1.6-2.4.

[0016] Optionally, the mass fraction of the polyvinyl alcohol solution is 8-12%.

[0017] Optionally, the volume ratio of ethylene glycol to water in the ethylene glycol solution is 2:0.8-1.2.

[0018] Optionally, the mass ratio of the polyvinyl alcohol solution to the ethylene glycol solution is 3.6-4.4:1.

[0019] The beneficial effects of the polyheptazine imide-based photochromic film and the preparation method thereof of the present invention are as follows: polyheptazine imide (PHI) is a highly crystalline carbon nitride (CN) prepared by a eutectic molten salt method. Compared with ordinary CN, PHI has higher carrier mobility, improves the utilization rate of photogenerated carriers, solves the problem of high electron-hole recombination rate of CN, enhances photoreduction activity, and broadens the light absorption range to 280nm-460nm. The photoreduction agent polyheptazine imide can be excited by 405nm visible light to generate photogenerated electrons, thereby reducing and decolorizing the redox dye methylene blue, so that the photochromic film changes from blue to white. When there is oxygen in the environment, the film adsorbs oxygen, and oxygen diffuses in the film. The decolorized film is then decolorized by oxygen. The oxidation of methylene blue restores its color, so that the photochromic film returns from white to blue, realizing the naked eye detection of oxygen. This visual change in the color of the film is used to detect oxygen, which can ensure food safety. Within the specified time, different oxygen concentrations correspond to different film colors. As the oxygen concentration increases, the film color becomes darker and darker. It can detect concentration changes from 0% to 20%. At an oxygen concentration of 5%, obvious color change can be seen, with high sensitivity. The film can be completely decolorized in 8 seconds after being excited by 405nm light. In an air environment (oxygen content is about 20%), the color recovery time is 12 minutes, and the response time is short. The repetition rate of the polyheptazine imide-based photochromic film can reach 20 times, and it can ensure good color change performance and good oxygen detection stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the design and mechanism of the polyheptazine imide-based photochromic film according to an embodiment of the present invention;

[0021] Figure 2 This is a schematic diagram of the color change of the polyheptazine imide-based photochromic film of Example 1 of the present invention;

[0022] Figure 3 This is a schematic diagram of the color change time of the polyheptazine imide-based photochromic film of Example 1 of the present invention under visible light irradiation;

[0023] Figure 4 It is a schematic diagram of the time it takes for the polyheptazine imide-based photochromic film of Example 1 of the present invention to recover blue in an air environment;

[0024] Figure 5 Schematic diagram of the number of color change cycles of the polyheptazine imide-based photochromic film of Example 1 of the present invention.

[0025] Figure 6 A digital photograph showing the colorimetric response time of the polyheptazine imide-based photochromic film of Example 1 of the present invention to oxygen;

[0026] Figure 7 is a fitting curve diagram of the B value and oxygen concentration corresponding to the polyheptazine imide-based photochromic film of Example 1 of the present invention at a certain time;

[0027] Figure 8 This is a schematic diagram of the oxygen concentration of the film at 9 minutes calculated by the equation in Example 1 of the present invention. DETAILED DESCRIPTION

[0028] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. Although certain embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be interpreted as being limited to the embodiments described herein. On the contrary, these embodiments are provided to provide a more thorough and complete understanding of the present invention. It should be understood that the drawings and embodiments of the present invention are only for exemplary purposes and are not intended to limit the scope of protection of the present invention.

[0029] Unless otherwise defined, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention;

[0030] The term "including" and its variations used herein are open inclusions, i.e., "including but not limited to"; the term "based on" means "based at least in part on"; the term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one other embodiment"; the term "some embodiments" means "at least some embodiments"; the term "optionally" means "optional embodiments". The relevant definitions of other terms will be given in the following description.

[0031] In the related technology, the selection of semiconductor photoreducing agents should not only have a suitable preparation cost, good chemical stability and resistance to light corrosion, and be able to be used efficiently for a long time, but also have high solar energy utilization and photoreduction activity. 2 The wide band gap (3.0eV-3.2eV) leads to low solar energy utilization, limited light absorption range (280nm-400nm), and inability to respond to visible light.

[0032] The organic semiconductor material carbon nitride (CN) has attracted widespread attention due to its good chemical stability, thermal stability, suitable conduction band and valence band positions, suitable band gap width (2.7 eV), and visible light response.

[0033] Polyheptazine imide (PHI) is a highly crystalline CN prepared by the eutectic molten salt method. Compared with ordinary CN, PHI has higher carrier mobility, improves the utilization rate of photogenerated carriers, solves the problem of high electron-hole recombination rate of CN, enhances photoreduction activity, and broadens the light absorption range (280nm-460nm).

[0034] In view of the problems existing in the above-mentioned related technologies, this embodiment provides a polyheptazine imide-based photochromic film and a preparation method thereof.

[0035] A polyheptazine imide-based photochromic film provided in an embodiment of the present invention comprises a film matrix, a photoreductant and a redox dye, wherein the photoreductant is polyheptazine imide, the redox dye is methylene blue, and the film matrix is ​​a cross-linked polymer film of polyvinyl alcohol and ethylene glycol.

[0036] In this embodiment, polyheptazine imide (PHI) is a highly crystalline carbon nitride (CN) prepared by a eutectic molten salt method. Compared with ordinary CN, PHI has higher carrier mobility, improves the utilization rate of photogenerated carriers, solves the problem of high electron-hole recombination rate of CN, enhances photoreduction activity, and broadens the light absorption range to 280nm-460nm; Figure 1 As shown, the photoreducing agent polyheptazine imide can be excited by 405nm visible light to generate photogenerated electrons, thereby reducing and decolorizing the redox dye methylene blue, so that the photochromic film changes from blue to white. When there is oxygen in the environment, the film adsorbs oxygen, and oxygen diffuses in the film. The decolorized methylene blue is oxidized by oxygen to restore the color, so that the photochromic film is restored from white to blue, and the naked eye detection of oxygen is realized. This visual film color change is used to detect oxygen, which can ensure food safety. Within a specified time, different oxygen concentrations correspond to different film colors. As the oxygen concentration increases, the film color becomes darker and darker. The concentration change from 0% to 20% can be detected. At an oxygen concentration of 5%, obvious color change can be seen, and the sensitivity is high. The film can be completely decolorized 8s after being excited by 405nm light. In an air environment (oxygen content is about 20%), the color recovery time is 12min, and the response time is short. The repetition rate of the polyheptazine imide-based photochromic film can reach 20 times, and it can ensure good color change performance and good oxygen detection stability.

[0037] Specifically, Figure 1In the design and mechanism of the polyheptazine imide-based photochromic film of this embodiment, the photoreducing agent polyheptazine imide (PHI) can be excited by 405nm visible light to generate photogenerated electrons, thereby reducing and decolorizing the redox dye methylene blue, and the film changes from blue to white; for the film to restore from white to blue, the key is the diffusion of oxygen in the film, that is, the adsorption of oxygen by the film. The film restores the color of the decolorized methylene blue through oxygen oxidation, so the oxygen in the package can be detected by this visual change in film color, and the naked eye detection of oxygen is realized.

[0038] Optionally, the polyheptazine imide is a polyheptazine imide solution with a concentration of 1.2-1.8 g / L, the methylene blue is a methylene blue solution with a concentration of 8-12 mg / L, and the mass ratio of the polyheptazine imide solution to the methylene blue solution is 2.5:1.6-2.4.

[0039] In this optional embodiment, the mass ratio of polyheptazine imide and methylene blue, the photoreducing agent polyheptazine imide is excited by 405nm visible light to produce photogenerated electrons, which can just completely reduce and decolorize the redox dye methylene blue, so that the photochromic film changes from blue to white, and when there is oxygen in the environment, the film adsorbs oxygen, and the oxygen oxidizes the decolorized methylene blue to restore the color, so that the photochromic film is restored from white to blue, realizing the naked eye detection of oxygen.

[0040] Optionally, the polyvinyl alcohol is a polyvinyl alcohol solution with a mass fraction of 8-12%, the ethylene glycol is an ethylene glycol solution, the volume ratio of ethylene glycol to water in the ethylene glycol solution is 2:0.8-1.2, and the mass ratio of the polyvinyl alcohol solution to the ethylene glycol solution is 3.6-4.4:1.

[0041] In this optional embodiment, polyvinyl alcohol and ethylene glycol in this mass ratio are used as film matrix materials, and film-forming properties are good, and the prepared film can meet the requirements of food packaging.

[0042] An embodiment of the present invention provides a method for preparing a polyheptazine imide-based photochromic film, and the method comprises the following steps:

[0043] Take polyvinyl alcohol solution and ethylene glycol solution, mix them evenly, heat to above 100°C, and stir for more than 10 minutes to obtain a membrane matrix solution;

[0044] Take the polyheptazine imide solution and the methylene blue solution, mix them evenly, add them to the membrane matrix solution, heat to above 85°C, stir for more than 45 minutes, and cool to room temperature;

[0045] The mixture was poured into a mold and heated at 25-35° C. for more than 6 hours to obtain a polyheptazine imide-based photochromic film.

[0046] In this embodiment, polyvinyl alcohol and ethylene glycol are prepared into solutions in advance and then mixed, so that the mixing is more uniform and the quality of the obtained membrane matrix solution is uniform; polyheptazinimide and methylene blue are prepared into solutions in advance and then mixed, and during the mixing process, polyheptazinimide and methylene blue can be mixed more quickly and uniformly, the photoreducing agent polyheptazinimide is excited by 405nm visible light to generate photogenerated electrons, and the redox dye methylene blue is quickly decolorized with a short response time.

[0047] Optionally, the concentration of the polyheptazinimide solution is 1.2-1.8 g / L.

[0048] Optionally, the concentration of the methylene blue solution is 8-12 mg / L.

[0049] Optionally, the mass ratio of the polyheptazine imide solution to the methylene blue solution is 2.5:1.6-2.4.

[0050] In this optional embodiment, the volume ratio of polyheptazine imide solution and methylene blue solution, the photoreducing agent polyheptazine imide is excited by 405nm visible light to produce photogenerated electrons, which can completely reduce and decolorize the redox dye methylene blue, so that the photochromic film changes from blue to white, and when there is oxygen in the environment, the film adsorbs oxygen, and the oxygen oxidizes the decolorized methylene blue to restore the color, so that the photochromic film is restored from white to blue, thereby realizing the naked eye detection of oxygen.

[0051] Optionally, the mass fraction of the polyvinyl alcohol solution is 8-12%.

[0052] In this optional embodiment, the concentration of the polyvinyl alcohol solution is moderate, the film forming speed is fast, and the film forming quality is good. If the concentration is too low, the film forming process will be slow, and if the concentration is too high, the film forming quality will decrease due to the increase in solution viscosity.

[0053] Optionally, the volume ratio of ethylene glycol to water in the ethylene glycol solution is 2:0.8-1.2.

[0054] In this optional embodiment, the concentration of the ethylene glycol solution is moderate, which can improve the durability and stability of the membrane and prevent aging and damage of the membrane; at the same time, ethylene glycol can also reduce the plasticizing effect of the membrane and prevent deformation and loss of stability of the membrane.

[0055] Optionally, the mass ratio of the polyvinyl alcohol solution to the ethylene glycol solution is 3.6-4.4:1.

[0056] In this optional embodiment, the polyvinyl alcohol solution and the ethylene glycol solution in this mass ratio are used as film matrix materials, and the film-forming property is good, and the prepared film can meet the requirements of food packaging.

[0057] The present invention is further described below in conjunction with specific embodiments.

[0058] Example 1, a method for preparing a polyheptazine imide-based photochromic film.

[0059] (1) Weigh 8 g of polyvinyl alcohol particles and dissolve them in 72 g of pure water. Heat and stir at 85° C. for 45 min until they are completely dissolved. Cool and the mass fraction of the polyvinyl alcohol solution is 10%.

[0060] (2) At the same time, 20 ml of ethylene glycol (ethylene glycol is used as a cross-linking agent for polyvinyl alcohol) is dissolved in 10 ml of pure water and stirred at room temperature until completely mixed. The volume ratio of ethylene glycol to water in the ethylene glycol solution is 2:1;

[0061] (3) Weigh 12 g of polyvinyl alcohol solution and 3 g of ethylene glycol solution, mix them evenly, heat and stir at 100° C. for 10 min to obtain a membrane matrix solution, wherein the mass ratio of the polyvinyl alcohol solution to the ethylene glycol solution is 4:1;

[0062] (4) Weigh 30 mg of polyheptazine imide powder and mix it with 20 ml of pure water, and ultrasonically vibrate for 5 h. The concentration of the polyheptazine imide solution is 1.5 g / L;

[0063] (5) At the same time, weigh 5 mg of methylene blue powder and dissolve it in 500 ml of pure water. Stir at room temperature until it is completely dissolved. The concentration of the methylene blue solution is 10 mg / L.

[0064] (6) Weigh 12 g of the supernatant of the polyheptazine imide solution and 9.6 g of the methylene blue solution, mix them, add them to the membrane matrix solution of step (3), heat and stir at 85° C. for 45 min, cool, and the mass ratio of the polyheptazine imide solution to the methylene blue solution is 2.5:2;

[0065] (7) 3 ml of the mixed solution obtained in step (6) was poured into a 4 cm×4 cm×1 mm mold, placed in an oven, and heated at 30° C. for 6 hours to obtain a polyheptazine imide-based photochromic film.

[0066] Example 2, a method for preparing a polyheptazine imide-based photochromic film.

[0067] (1) Weigh 8 g of polyvinyl alcohol granules and dissolve them in 92 g of pure water. Heat and stir at 85°C for 45 min until completely dissolved, and cool.

[0068] (2) At the same time, take another 20 ml of ethylene glycol (ethylene glycol is used as a cross-linking agent for polyvinyl alcohol) and dissolve it in 12 ml of pure water. Stir at room temperature until completely mixed.

[0069] (3) Weigh 10.8 g of polyvinyl alcohol solution and 3 g of ethylene glycol solution, mix them evenly, and heat and stir at 100 °C for 10 min to obtain a membrane matrix solution;

[0070] (4) Weigh 24 mg of polyheptazine imide powder and mix with 20 ml of pure water, and shake with ultrasound for 5 h;

[0071] (5) At the same time, weigh 4 mg of methylene blue powder and dissolve it in 500 ml of pure water. Stir at room temperature until it is completely dissolved.

[0072] (6) Weigh 12 g of the supernatant of polyheptazine imide and 7.68 g of methylene blue solution, mix them, add them to the membrane matrix solution of step (3), heat and stir at 85° C. for 45 min, and cool;

[0073] (7) 3 ml of the mixed solution obtained in step (6) was poured into a 4 cm×4 cm×1 mm mold, placed in an oven, and heated at 25° C. for 6 hours to obtain a polyheptazine imide-based photochromic film.

[0074] Example 3, a method for preparing a polyheptazine imide-based photochromic film.

[0075] (1) Weigh 8 g of polyvinyl alcohol granules and dissolve them in 60 g of pure water. Heat and stir at 85°C for 45 min until completely dissolved, and cool.

[0076] (2) At the same time, take another 20 ml of ethylene glycol (ethylene glycol is used as a cross-linking agent for polyvinyl alcohol) and dissolve it in 8 ml of pure water. Stir at room temperature until completely mixed.

[0077] (3) Weigh 13.2 g of polyvinyl alcohol solution and 3 g of ethylene glycol solution, mix them evenly, and heat and stir at 100 °C for 10 min to obtain a membrane matrix solution;

[0078] (4) Weigh 36 mg of polyheptazine imide powder and mix with 20 ml of pure water, and shake with ultrasound for 5 h;

[0079] (5) At the same time, weigh 6 mg of methylene blue powder and dissolve it in 500 ml of pure water. Stir at room temperature until it is completely dissolved.

[0080] (6) Weigh 12 g of the polyheptazine imide supernatant and 11.5 g of the methylene blue solution, mix them, add them to the membrane matrix solution of step (3), heat and stir at 85° C. for 45 min, and cool;

[0081] (7) 3 ml of the mixed solution obtained in step (6) was poured into a 4 cm×4 cm×1 mm mold, placed in an oven, and heated at 35° C. for 6 hours to obtain a polyheptazine imide-based photochromic film.

[0082] Effect Example

[0083] The color changing performance of the polyheptazine imide-based photochromic film prepared in Example 1 was tested. The test results are as follows: Figures 2 to 5As shown, Figure 2 The discoloration of the film can be seen in Figure 3 As can be seen in the figure, the film is irradiated with 405nm visible light and can be completely colorless after 8s of light excitation. Figure 4 It can be seen that in an air environment (oxygen content is about 20%), the film can completely return to blue in about 12 minutes. Figure 5 It can be seen that the repetition rate of this film can reach 20 times and still ensure good color-changing performance.

[0084] The colorimetric response time of the polyheptazine imide-based photochromic film prepared in Example 1 to oxygen was tested. The test results are as follows: Figure 6 As shown, after the film is decolorized by light excitation, it always remains white in a completely Ar environment. As the oxygen concentration increases, the time it takes for the film to completely restore its color becomes shorter and shorter.

[0085] The fitting curve of the B value corresponding to the color of the polyheptazine imide-based photochromic film prepared in Example 1 and the oxygen concentration was tested. The test results are as follows: Figure 7 As shown, at different oxygen concentrations at every three oxygen concentration points, the B value in the RGB value corresponding to the film color is obtained through a smart device (such as a smart phone) (RGB color space, R represents the red component, G represents the green component, B represents the blue component, and the three components together synthesize the color of a pixel), and a linear fit is performed to obtain the relationship between the B value and the oxygen concentration.

[0086] According to the fitting curve of the B value corresponding to the color of the film and the oxygen concentration, the equation is obtained, and the oxygen concentration of the film at 9 minutes is calculated by the equation, as follows: Figure 8 As shown, by substituting the B value of the film color under different oxygen concentrations at 9 minutes into the fitting equation, the oxygen concentration of the film's environment at that time can be calculated, and the oxygen content in the package can be evaluated through a smart device (such as a smart phone).

[0087] Although the present invention is disclosed as above, the protection scope of the present invention is not limited thereto. Those skilled in the art may make various changes and modifications without departing from the spirit and scope of the present invention, and these changes and modifications will fall within the protection scope of the present invention.

Claims

1. A polyheptazine imide-based photochromic film, characterized in that: The invention comprises a film matrix, a photoreductant and a redox dye, wherein the photoreductant is polyheptazine imide, the redox dye is methylene blue, and the film matrix is ​​a cross-linked polymer film of polyvinyl alcohol and ethylene glycol.

2. The polyheptazine imide-based photochromic film according to claim 1, characterized in that: The polyheptazine imide is a polyheptazine imide solution with a concentration of 1.2-1.8 g / L, the methylene blue is a methylene blue solution with a concentration of 8-12 mg / L, and the mass ratio of the polyheptazine imide solution to the methylene blue solution is 2.5:1.6-2.

4.

3. The polyheptazine imide-based photochromic film according to claim 1, characterized in that: The polyvinyl alcohol is a polyvinyl alcohol solution with a mass fraction of 8-12%, the ethylene glycol is an ethylene glycol solution, the volume ratio of ethylene glycol to water in the ethylene glycol solution is 2:0.8-1.2, and the mass ratio of the polyvinyl alcohol solution to the ethylene glycol solution is 3.6-4.4:

1.

4. A method for preparing a polyheptazine imide-based photochromic film, characterized in that: The preparation of the polyheptazine imide-based photochromic film according to any one of claims 1 to 3 comprises the following steps: Take polyvinyl alcohol solution and ethylene glycol solution, mix them evenly, heat to above 100°C, and stir for more than 10 minutes to obtain a membrane matrix solution; Take a polyheptazine imide solution and a methylene blue solution, mix them evenly, add them to the membrane matrix solution, heat to above 85° C., stir for more than 45 minutes, and cool to room temperature; The mixture was poured into a mold and heated at 25-35° C. for more than 6 hours to obtain a polyheptazine imide-based photochromic film.

5. The method for preparing the polyheptazine imide-based photochromic film according to claim 4, characterized in that: The concentration of the polyheptazine imide solution is 1.2-1.8 g / L.

6. The method for preparing the polyheptazine imide-based photochromic film according to claim 5, characterized in that: The concentration of the methylene blue solution is 8-12 mg / L.

7. The method for preparing the polyheptazine imide-based photochromic film according to claim 6, characterized in that: The mass ratio of the polyheptazine imide solution to the methylene blue solution is 2.5:1.6-2.

4.

8. The method for preparing the polyheptazine imide-based photochromic film according to claim 4, characterized in that: The mass fraction of the polyvinyl alcohol solution is 8-12%.

9. The method for preparing the polyheptazine imide-based photochromic film according to claim 8, characterized in that: The volume ratio of ethylene glycol to water in the ethylene glycol solution is 2:0.8-1.

2.

10. The method for preparing the polyheptazine imide-based photochromic film according to claim 9, characterized in that: The mass ratio of the polyvinyl alcohol solution to the ethylene glycol solution is 3.6-4.4:1.

Images